MULTIFUNCTIONALAZO COMPOUNDS ANDPOLYMERS DERIVEDTHEREFROMFORNONLINEAROPTICS

This is a continuation-in-part application of U.S. Ser. No. 08/090,495, filed July 12, 1993, currently pending.

FIELD OF THE INVENTION

This invention describes new multifunctional derivatives of azo dyes, and a method of synthesis thereof, from which linear and crosslinked polymers can be synthesized. This invention also describes the incorporation of the polymers into optical devices.

BACKGROUND OF THE INVENTION

Organic optically nonlinear materials can be used in electrooptical switches and modulators. Materials which are optically nonlinear consist of nonlinear optically-active (NLO-active) molecules in a noncentrosymmetric alignment.

To be NLO-active, a molecule must possess a large molecular second- order hyperpolarizability (β). The most common way to align NLO-active materials is to expose a material in which they are incorporated to an electric field. Any ordering process based on electric field-induced alignment (i.e., poling) requires a large value for the molecular dipole moment (μ). The product μ x β is a measure of the nonlinearity acheived by the ordering process. For an organic molecule to have a large μ x β product, it will generally have a delocalized T-electron system to which both an electron donor group and an electron acceptor group are coupled. Two well-known molecules possessing this set of characteristics are Disperse Red 1 and dimethylaminonitrostilbene (DANS) .

These and similar molecules can be incorporated as side chain groups in linear polymers. A major limitation of this type of arrangement is that the noncentrosymmetric alignment necessary for optical nonlinearity (x ^a) ), induced by the application of an electric field, tends to relax over time at room or slightly elevated temperatures. This results in a lessening or loss of NLO activity.

Several recent publications have addressed the stability problem through the use of crosslinked polymers. These polymers can be divided into two broad classes. The first of these crosslink around an NLO-active unit, which is attached to the polymer chain at a single point, to restrict the free volume available for relaxation of the NLO-active moiety. Examples of this class include U.S. Patent No. 4,886,339; Park et al., Chem. Mater., 2, 229 (1990); Jin et al., Chem. Mater. , 4, 963 (1992); Chen et al., Macromolecules, 24, 5421 (1992) and 25, 4032 (1992); Miiller et al., Makromol. Chem. Rapid Comm. , 13, 289 (1992); Mandal et al., Makromol. Chem. Rapid Comm. , 12, 63-68 (1991); and Yu et al., Appl. Phys. Lett. , 14, 1655 (1992). This technique does provide materials with some enhanced second harmonic generation (SHG) stability relative to linear polymers, but the stability of the polar alignment of these materials at elevated temperatures is still poor. The polymers of the second class are crosslinked through the NLO units themselves. The NLO-active unit is covalently bound to the polymer chain at more than one point. Eich et al., J. Appl. Phys. , 66, 3241 (1992) have utilized epoxide chemistry to produce systems in which NLO units were covalently bound at more than one point and which were stable up to 85 °C (for a film corona poled at 140°C for 16 hours). In addition to this rather long curing time, the intrinsic NLO activity of the molecules incorporated in this system was not high, and the films made therefrom were not of optical quality. Additionally, the long-term dimensional stability of the polymer film of this system, especially in high humidity (since amine-cured epoxides are known to have an affinity for water), can be a problem. Hubbard et al.,

Chem. Mater. , 4, 965 (1992) have incorporated a diamino-functional azo dye into epoxy networks but did not achieve a large SHG coefficient. Hayashi et al., Macromolecules, 25, 5094 (1992) reported development of a system which is crosslinked by irradiation of azido groups, although the degree of crosslinking obtained was very low. Xu et al., Macromolecules, 25, 6714 (1992) have synthesized NLO-active polymers having sidechain NLO-active units. Crosslinking was accomplished through the NLO-active units. Although good stability was observed, chromophore density was low due to the fact that the polymers were copolymers.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a nonlinear optically-active azo compound having the general formula

wherein A is CH ₂ CHR ² R ^2' or, together with the nitrogen atom to which it is attached and R ⁵ as well as the phenyl carbon atoms to which they are attached, forms a 5- or 6- membered ring that can include a heteroatom selected from the group consisting of N, O, and S; Z is a moiety selected from the group consisting of

wherein at least one of R ⁷ through R ¹¹ is R ¹² ;

R ¹² is a group selected from the class consisting of

(1) D

wherein D is a group selected from the class consisting of NO ₂ and SO ₂ R ¹⁸ ; X, X', Y, and Y' are independently N or CR ¹⁹ ;

R ¹ and R ¹⁸ are independently selected from the class consisting of

(1) alkyl, and

(2) R ²⁰ ;

R ¹ ', R ² , R ² ', R ¹⁹ , and R ³ through R ⁶ are independently selected from the group consisting of hydrogen and the class from which R ¹ and

R ¹⁸ are chosen; R ⁷ through R ⁿ and R ¹³ through R ¹⁷ are independently selected from the group consisting of NO ₂ , SO ₂ R ¹⁸ , and the class from which R ^1' , R ² , R ^2' , R ¹⁹ , and R ³ through R ⁶ are chosen; and R ²⁰ is selected from the group consisting of

(1) epoxide, diene, substituted maleimide, isocyanate, 2-oxazolin- 5-one, aziridine, and acryloyl groups;

(2) active hydrogen-containing groups; and

(3) alkyl groups substituted with at least one active hydrogen- containing group; with the following provisos:

A. at least one of R ¹ , R ^1' , R ² , R ^2' , and R ³ through R ⁶ is R ²⁰ ;

B. at least one of R ⁷ to R" and R ¹³ to R ¹⁹ is R ²⁰ ;

C. the reactivities of R ²⁰ from proviso A and of R ²⁰ from proviso B are different; and D. where Z is the six-membered ring structure wherein R" is R ¹² with R ¹² being NO ₂ , R ²⁰ from proviso B is attached to the ring by an atom other than one from Group VIA of the Chemical Abstracts version of the periodic table of the elements. In another aspect, the present invention provides a nonlinear optically- active linear polymer comprising the above-described nonlinear optically- active azo group.

In a further aspect, the present invention provides a nonlinear optically- active crosslinked polymer prepared by subjecting the above-described linear polymer to means for crosslinking linear polymers or by reacting the above- described nonlinear optically-active linear polymer and the above-described nonlinear optically-active azo compound.

In yet another aspect, the present invention provides an optical device comprising at least one of the above-described linear and crosslinked polymers. In a still further aspect, the present invention provides a method for the synthesis of the above-described nonlinear optically-active azo compound comprising the steps: a) providing a cyclic compound selected from the group consisting of

wherein at least one of R ⁷ through R ¹¹ is R ¹² and X, Y, and R ⁷ through R ¹² are as defined previously; and

b) diazotizing, and coupling with a compound comprising a substituted or unsubstituted aniline group, said cyclic compound.

In a yet still further aspect, the present invention provides a method of preparing a nonlinear optically-active crosslinked film comprising the steps: a) providing an NLO-active compound having an electron donor end and an electron acceptor end, wherein the electron donor end comprises one functionality and the electron acceptor end comprises a second functionality, the reactivities of the two fuctionalities being different; b) reacting, under one set of reaction conditions, the more reactive functionality of the NLO-active compound with a multifunctional monomer or oligomer; c) coating a film from a solution of the reaction product of b); d) poling the film; and e) reacting, under a second set of reaction conditions (which differ from those of step b, the multifunctional monomer or oligomer with the less reactive functionality of the NLO-active compound to provide a poled crosslinked film. In a final aspect, the present invention provides a method of preparing a nonlinear optically-active crosslinked film comprising the steps: a) providing a nonlinear optically-active compound having an electron donor end and an electron acceptor end wherein the electron donor end comprises a first functionality and wherein the electron acceptor end compises a second functionality, and a monomer or oligomer having at least two functionalities, the reactivity of one of the functionalities being greater than that of the at least one other functionality; b) reacting under one set of reaction conditions

1) the more reactive of said functionalities of said coreactive monomer or oligomer, with

2) one of the functionalities of said nonlinear optically-active compound; c) coating a film from the reaction product of step b); d) poling the film; and e) reacting, under a second set of reaction conditions which differ from those in step b), the less reactive of the at least one other functionality of the coreactive monomer or oligomer with the other of the functionalities of the nonlinear optically-active compound to provide a poled crosslinked film. Unless otherwise specified, the following definitions apply in this application:

"external field" means a substantially unidirectional field (usually electrical) applied to an article containing organic molecules to pole those molecules; "poling" means orienting, in the direction of an external field, a molecule by means of interaction of its dipole with the external field;

"multifunctional" means having at least two functional groups; "alkyl" means straight or branched chain organic compounds having in the longest continuous chain thereof from 1 to 20 carbon or hetero atoms;

"acryloyl groups" means those compounds derived from acrylic acid and include, for instance, acryloyloxy, methacryloyloxy, acyryloylamide, and methacryloylamide; and

"group" or "moiety" or "compound" means a chemical species that allows for substitution by conventional substituents which do not interfere with the desired product.

The present invention teaches an NLO-active azo compound of Formula I. This NLO-active compound is polarizable and can be oriented to give a macroscopically ordered material. Functional groups can be incorporated into both the donor and acceptor ends of this compound. Where the reactivities of these functional groups

differ, they can be reacted in a stepwise fashion. Reaction of the more reactive functionality incorporates the NLO-active molecule into a material (i.e., either a polymer or an oligomer) from which a film can be formed. Reaction of the other functionality(ies) in the presence of an external field results in a cross-linked NLO-active material.

In contrast to the prior art, the present invention teaches an optically nonlinear polymeric material, having a large μ x β product and good solubility, which can operate for long periods of time at elevated temperatures (e.g., up to 60°C, preferably up to 90°C, and more preferably up to 120°C) without significant relaxation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The NLO-active azo compounds of the present invention are already functionalized to allow for incorporation into crosslinked polymers. The functionalities have differing reactivities, which allow for stepwise reaction thereof. This stepwise reaction mechanism allows the dye molecules to be attached at one end, poled, and then attached at the opposite end to form a crosslinked polymer. The general formula of these compounds is shown above (see

Compound I). The Z moiety of these compounds is selected from the group consisting of

preferably the six-membered ring structure, with the proviso that at least one of R ⁷ through R ¹¹ is R ¹² , and wherein

R ¹² is a group selected from the class consisting of (1) D

wherein D is a group selected from the class consisting of NO ₂ and SO ₂ R ¹⁸ ; X, X', Y, and Y' are independently N or CR ¹⁹ ; R ¹ and R ¹⁸ are independently selected from the class consisting of (1) alkyl, and

(2) R ²⁰ ; R ^1' , R ² , R ^2' , R ¹⁹ , and R ³ through R ⁶ are independently selected from the group consisting of hydrogen and the class from which R ¹ and R ¹⁸ are chosen; R ⁷ through R ⁿ and R ¹³ through R ¹⁷ are independently selected from the group consisting of NO ₂ , SO ₂ R ¹⁸ , and the class from which R ^1' , R ² , R ^2' , R ¹⁹ , and R ³ through R ⁶ are chosen; and R ²⁰ is selected from the group consisting of

(1) epoxide, diene, substituted maleimide, isocyanate, 2-oxazolin- 5-one, aziridine, and acryloyl groups;

(2) active hydrogen-containing groups; and

(3) alkyl groups substituted with at least one active hydrogen- containing group; with the four provisos regarding R ²⁰ discussed previously.

The two R ²⁰ groups in Compound I must have different reactivities. In other words, the R ²⁰ at the donor end of the molecule must have a reactivity that differs from that of the R ²⁰ at the acceptor end of the azo compound. This allows the azo compound to be attached at one end to a polymer, poled, and then crosslinked by reacting the other less reactive R ²⁰ group. The difference in reactivity can be as small as the difference between primary (or secondary) active hydrogen-containing groups (e.g. , OH) substituted on opposite sides of the azo linkage nearest the donor end of the azo compound. Preferred among these compounds are those where one of R ¹ and R ¹ ' is an alkyl group, most prefereably a C, to C→ alkyl group, and the other is an an active hydrogen-containing group, most preferably a hydroxy 1 group, or where R ^1' is hydrogen and R ¹ is an active hydrogen-containing group, most preferably a hydroxyl group. Also preferred is that A is CH ₂ CHR ² R ^2' where both R ² and R ^2' are alkyl groups, most preferably C, to C ₄ alkyl groups, or one of R ² and R ^2' is an alkyl group, most preferably a C, to C ₄ alkyl group, and the other is an active hydrogen-containing group, most preferably a hydroxyl group.

These compounds possess large μ x β products (i.e., greater than 1 x lO^ ⁶ cm ⁶ ) and low molar absorbances at wavelengths longer than about 600 nm. They are soluble in common organic solvents such as pyridine or 1,2- dichloromethane.

When such molecules are reactants in the preparation of crosslinked polymers, difunctionality is a desirable characteristic. These NLO-active azo compounds advantageously have functionalities with differing reactivities which allows them to be reacted in a stepwise fashion. This stepwise reaction mechanism allows the azo compounds to be attached at either the electron donor or electron acceptor end, poled, and then attached at the opposite end to form a crosslinked polymer.

I. Preparation of Monomers

Synthesis of the azo monomers of the present invention requires the diazotization and coupling with an aniline-containing group of one of the following cyclic compounds (prepared as described in the Examples):

wherein R ⁷ through R ¹² , X, and Y are defined as above. Once the desired cyclic compound has been prepared, it is reacted with nitrous acid (i.e, sodium nitrite in an acidic medium) and an aniline or substituted aniline to form an azo monomer. Where an aniline is used in this diazotization, a second diazotization can be performed in order to form an extended conjugation azo monomer having the general formula:

wherein E is one of

with R ¹³ through R ¹⁷ , X', and Y' being defined as above and G being NO ₂ or SR ¹⁸ with R ¹⁸ being defined as above. Where G is SR ¹⁸ , the exocyclic sulfur atom can be oxidized with, for example, hydrogen peroxide to give the (5-

membered) cyclic sulfonyl structure which is one of the members of the group from which R ¹² (from Compound I) is selected.

Diazotization is a well known reaction. A full review can be found at, for example, Patai, The Chemistry of Diazonium and Diazo Groups. Wiley & Sons (1978).

Those skilled in the art will readily see that a variety of azo monomers can be prepared simply by varying the various R groups (from Compound I) and where they are positioned on the phenyl rings in the substituted nitro- aniline structure shown above. The substituents R ¹ and R ¹⁸ are independently selected from the class consisting of alkyl and R ²⁰ where R ²⁰ is (1) epoxide, diene, substituted maleimide, isocyanate, 2-oxazolin-5-one, aziridine, and acryloyl groups; (2) active hydrogen-containing groups; or (3) alkyl groups substituted with at least one active hydrogen-containing group. The sub¬ stituents R ¹ ', R ² , R ^2' , R ¹⁹ , and R ³ through R ⁶ are independently selected from hydrogen and the class from which R ¹ and R ¹⁸ are chosen. The substituents R ⁷ through R ¹¹ and R ¹³ through R ¹⁷ are independently selected from NO ₂ , SO ₂ R ¹⁸ , hydrogen, and the class from which R ¹ and R ¹⁸ are chosen.

At least one of R ³ , R ⁴ , R ⁷ , R ⁸ , and (when present) R ¹³ , R ¹⁴ , and R ¹⁹ from X or X' is preferably such that it inhibits alteration of the molecule at elevated temperatures (e.g., isomerization or thermal degradation) for extended periods of time. If this one or more groups is an alkyl group substituted with an active hydrogen-containing group, the alkyl chain thereof is preferably C ₂ or longer, more preferably C ₂ to C ₄ . If this one or more groups is an alkyl group that is not substituted with an active hydrogen- containing group, it is preferably a lower alkyl (i.e., to C ₄ ).

As mentioned above, the reactivities of R ²⁰ from proviso A (i.e., at least one of R ¹ , R ^1' , R ² , R ^2' , and R ³ through R ⁶ ) and R ²⁰ from proviso B (i.e., at least one of R ⁷ through R ¹⁹ with the exception of R ¹² ) must differ. Preferred among these compounds are those where R ¹¹ is R ¹² with R ¹² being NO ₂ or SO ₂ R ¹⁸ , preferably NO ₂ . Particularly preferred among these are those having the general formula

wherein G is a single bond or a CH(OH) group and one of the following is true:

(1) at least one of R ³ , R ⁴ , R ⁷ , and R ⁸ is an alkyl group, one of R ⁹ and R ¹⁰ is an active hydrogen-containing group or an alkyl group substituted with an active hydrogen-containing group, preferably

CH ₂ — J — OH where J is a single bond or a methylene group, and R ¹¹ is NO ₂ ;

(2) at least one of R ³ , R ⁴ , R ⁷ , and R ⁸ is an alkyl group, one of R ⁷ and R ⁸ is NO ₂ , and R ¹¹ is SO ₂ R ¹⁸ with R ¹⁸ preferably being an active hydrogen-containing group or an alkyl group substituted with an active hydrogen-containing group; and

(3) one of R ⁷ and R ⁸ is CH ₂ CH ₂ OH and R ⁿ is NO ₂ .

Most preferred among these compounds are those where R ³ or R ⁴ is a methyl group, R ⁷ or R ⁸ is a methyl group, whichever of R ⁹ and R ¹⁰ is para to the R ⁷ or R ⁸ methyl group is CH ₂ OH, and R ⁿ is NO ₂ .

These azo compounds display exceptional stability at elevated temperatures (as measured by monitoring X-^J when incorporated, either covalently or as a solute, in polymeric films. They also exhibit other desirable characteristics such as good solubility in common organic solvents. Where Z (from above) is the previously-described five-membered ring structure, R ¹² is preferably SO ₂ R ¹⁸ with R ¹⁸ being an alkyl group substituted with an active hydrogen-containing group.

See Examples 2-12, 14, 16-20, and 22-30 for further explanation of useful reaction conditions and reagents.

II. Preparation of Polymers

The azo compounds described above can be incorporated into linear polymers, either as part of the polymer backbone or as a side chain.

Where the azo compounds are to be part of the polymer backbone of a linear polymer, they can be homopolymerized or copolymerized with a coreactive monomer. For example, where one of R ¹ and R ² is an ester and R ⁶ contains a nucleophile (e.g., -NH ₂ or -OH), a reaction such as polyconden- sation can produce a homopolymer.

Where the azo compounds are to be part of a condensation copolymer, a difunctional monomer or oligomer that is coreactive with R ²⁰ from proviso B and R ²⁰ from proviso A may be preferred. Monomers that are reactive toward various R group combinations will be readily apparent to those skilled in the art and include isocyanates, thioisocyanates, epoxides, aziridines, and compounds comprising at least one α, 3-unsaturated group. The non-hydrogen, non-alkyl substiuents provide convenient points of attachment to linear polymers or oligomers. Once a linear polymer or oligomer with side chains is formed, it can be crosslinked, if desired, by subjecting it to any of a number of well known means for crosslinking polymers, such as heat, actinic radiation, and application of an external field. Alternatively, crosslinking can occur by reaction of a functionality other than that which reacted with the linear polymer, which will preferably be either an electron donor or acceptor group, with a coreactive monomer or oligomer. In a particularly preferred embodiment, R ²⁰ from proviso B can be either a diene or a dieneophile, such as a substituted maleimide, thus providing a convenient means of further reaction. Where R ²⁰ from proviso A differs in reactivity from R ²⁰ from proviso B, one of the functionalities can react with a multifunctional compound (e.g., a diisocyanate) and then, after the reaction conditions are changed (e.g., raising the temperature), a functionality which is less reactive than the first-reacting functionality can react. Regardless of which crosslinking means is chosen, the crosslinking step must be performed while the material is being subjected to an external field.

This poling ensures that the final material will have molecules with aligned dipoles.

An azo compound of the present invention can also be reacted with a multifunctional comonomer or oligomer to form a crosslinked polymer. Where a crosslinked polymer is desired, the relationship of R ²⁰ from proviso B and R ²⁰ from proviso A depends on the type of coreactant chosen. For instance, where a trifunctional coreactive monomer or oligomer is used with the reactivities of all functionalities being the same and R ²⁰ from proviso A coming from R ¹ and R ² (or R ^1' and R ^2' , or some combination of these substituents), the reactivity of R ²⁰ from proviso B must differ from and be greater than the reactivities of both the amino substituents where the reactivities of the amino substituents are the same. If the reactivities of the two amino substituents are not the same, however, R ²⁰ from proviso B need not be more reactive than both. Alternatively, where a difunctional coreactive monomer or oligomer is used, the reactivity of R ²⁰ from proviso B can be the same as that of one of the amino substituents, but the reactivity of the amino substituent that is not the same as that of R ²⁰ from proviso B must be greater than that of R ²⁰ from proviso B.

These restrictions on the interrelationships between the various R groups ensure that the two ends of the azo dye have functionalitites with different reactivities. This difference in reactivities allows for a stepwise reaction of the functionalities, i.e., the more reactive of the functionalities will react first and, after the reaction conditions are changed, the other functionality (ies) can be reacted. Typical coreactive monomers include isocyanates, thioisocyanates, epoxides, aziridines, 2-oxazolin-5-ones, substituted maleimides, compounds comprising at least one acryloyl group, and compounds comprising an a,β- unsaturated group. The coreactive compound can also be a linear polymer as described in section II. Because the azo compounds are attached to polymer chains at both ends of the molecule, and the second attachment (i.e., the crosslinking) occurs

as an external field is being applied, a film produced from such a crosslinked polymer is also NLO-active.

The azo dyes of the present invention (and polymers derived therefrom) are useful as components in optical devices such as electrooptical switches and modulators. Such devices can employ either branched or crosslinked polymers comprising at least one NLO-active azo group.

III. Preparing Films

A crosslinked film can be formed from an NLO-active compound having functionalities (which differ in reactivity) at the donor and acceptor ends of the compound.

NLO-active compounds that are useful in this process are those having a donor end and an acceptor end connected through a conjugated x-electron system and include substituted and unsubstituted azo compounds, substituted and unsubstituted stilbenes, merocyanines, hemicyanines, and nitroaniline derivatives. (Useful substituents include nitro, cyano, and benzimidazole groups). Each of the donor and acceptor ends is preferably substituted with at least one functional group, the reactivities of the functional groups at opposite ends being different. (If a coreactive monomer or oligomer with at least two functionalities having different reactivities is used, the functional groups of the NLO-active compound need not have differing reactivites.) A particularly preferred difunctionalized NLO-active compound is Compound I, described above.

Once such an NLO-active compound is provided, it can be reacted with a coreactive multifunctional monomer or oligomer which is reactive toward the functionalities at both ends of the NLO-active compound.

Particular multifunctional monomers useful in this step will depend on the functional groups with which the NLO-active compound has been functionalized. Potentially useful multifunctional monomers or oligomers include compounds having as functionalities isocyanate, thioisocyanate,

epoxides, aziridines, 2-oxazolin-5-ones, and substituted maleimide groups, although other functionalities will be apparent to those skilled in the art.

A typical multifunctional monomer or oligomer/NLO-active compound combination is an azo compound functionalized (on one end) with a secondary hydroxyl and (on the other) with a primary hydroxyl group and a multifunctional isocyanate, such as Tolonate ^™ HDT (Rhone-Poulenc, Inc.; Princeton, NJ). The isocyanate first reacts with the primary hydroxyl group to give an oligomeric urethane, from which can be produced a film. After the film is poled (by conventional means), the reaction conditions are changed (e.g., the reaction temperature is raised) while the external field is maintained, and the secondary hydroxyl group then reacts with free isocyanate. This second reaction, in combination with external field poling, provides a crosslinked film which is NLO-active.

Those skilled in the art will readily see which reaction conditions can be changed to suit particular multifunctional monomer/functionalized NLO- active compound combinations. Possibilities include, but are not limited to, changing temperature, changing pressure, and application of actinic radiation.

Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be construed to unduly limit this invention.

EXAMPLES

Structures of the compounds prepared according to the following Examples were confirmed by NMR analysis. Unless otherwise indicated, completeness of the described reactions was monitored by thin layer chromatography (TLC).

A chart showing the relationships between the following Examples is shown below.

GROUP A

GROUP B

13- -►14

GROUP C

GROUP D

Preparation of Azo Monomers

Examples 1, 13, 15 and 21 describe the syntheses of particular precursors of the azo dyes of the present invention, but similar precursors can be prepared with minor adjustments to the starting materials and procedures of these examples. Examples 2-12, 14, 16-20, and 22-29 describe the syntheses of azo dyes of the present invention.

Example 1: 2-acetamidomethyl-4-nitroaniline

To a room temperature solution of 10 g (82 mmole) 2-aminobenzyl- amine (Aldrich Chemical Co.; Milwaukee, WI) in 90 ml dry pyridine was added dropwise, with stirring, 20 g (0.20 mole) acetic anhydride (Aldrich). The resulting solution was stirred overnight (about 16 hours). Residual acetic anhydride and pyridine were removed by distillation under reduced pressure. The residue was recrystallized from chloroform to provide crystalline white needles with a melting point of 148 °C (95% yield).

This crystalline 2-acetamidomethylacetanilide was further reacted according to an adapted version of the procedure of Takami et al., Chem. Pharm. Bull , 22, 267 (1974). A mixture of 1.10 g concentrated nitric acid and 1.24 g concentrated sulfuric acid was added dropwise, with stirring, over an hour to a chilled (0° to -5°C) solution of 2.45 g (12.0 mmole) of the product from the above paragraph in 3.50 ml concentrated sulfuric acid. The mixture was stirred at 0° to 10° C for about three hours and then heated to about 65°-75°C for about an hour. When reaction was complete, the mixture was poured into cold water, which was vigorously stirred. The resulting light yellow precipitate was collected by suction filtration, washed with cold water, and recrystallized from methanol to give light yellow crystals with a melting point of l60°-161°C. Yield of 2-acetamidomethyl-4-nitroacetanilide was 51 %.

A suspension of 12.0 g (48.0 mmole) of this compound in 800 ml aqueous IN NaOH was heated under reflux for about 45 minutes and then cooled to room temperature. The resulting yellow precipitate was collected by suction filtration, washed well with cold water until the pH of the filtrate was neutral, and recrystallized from ethanol to afford bright yellow crystals having a melting point of 225°-226°C. Yield of 2-acetamidomethyl-4-nitroaniline was 91 %.

Examples 2 to 4 describe azo compounds which were prepared from the 2-acetamidomethyl-4-nitroaniline of Example 1.

Example 2: 4-(2'-acetamidomethyl-4'-nitrophenylazo)aniline

Diazotization of 10.0 g (47.8 mmole) 2-acetamidomethyl-4-nitroaniline (from Example 1) was effected in 40 ml concentrated HC1 by addition of a chilled (0°C) solution of 3.30 g (47.8 mmole) sodium nitrite in 10 ml distilled water. After addition was complete (about 30 minutes), the mixture was filtered. A chilled (0°C) solution of 10.0 g (47.8 mmoles) anilinemethylene- sulfonic acid, sodium salt (K & K Labs; Cleveland, OH) in 20 ml distilled water was added dropwise, with stirring, over a period of about an hour. After addition was complete, the solution was neutralized by dropwise addition of a 10% NaOH solution. The resultant orange solid was collected by suction filtration. Yield was 12.0 g (45% yield).

This solid was added to 800 ml aqueous IN NaOH. The mixture was refluxed for approximately 45 minutes and then cooled to room temperature. The resultant precipitate was collected by suction filtration, washed with cold water until the pH of the filtrate was neutral, and recrystallized from ethanol. The crystalline product (91 % yield) was reddish brown in color.

Example 3: 4-{(2'-acetamidomethyl-4'- nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]}aniline

Another diazotization of 10.0 g (47.8 mmole) 2-acetamidomethyl- 4-nitroaniline (from Example 1) was performed in 40 ml concentrated HC1 by addition of a chilled (0°C) solution of 3.30 g (47.8 mmole) sodium nitrite in 10 ml distilled water. After addition was complete (about 30 minutes), the mixture was filtered. A chilled (0°C) solution of 8.66 g (47.8 mmole) N,N-bis(2-hydroxyethyl)aniline (Aldrich) in 25 ml ethanol was added dropwise, with stirring, to the filtrate. After addition was complete, the mixture was stirred at room temperature for about an hour. The solution was then neutralized by dropwise addition of a 10% NaOH solution. The resulting deep red precipitate was collected by suction filtration and recrystallized from ethanol. The deep red, crystalline product had a melting point of 180°C. Yield was 45%.

Example 4: 4-(2'-acetamidomethyl-4'-nitrophenylazo)- (N-ethyl-N-hydroxyethyl)aniline

A third diazotization of 10.0 g (47.8 mmole) 2-acetamidomethyl- 4-nitroaniline (from Example 1) was performed in 40 ml concentrated HC1 by addition of a chilled (0° to 5°C) solution of 3.30 g (47.8 mmole) sodium nitrite in 10 ml distilled water. After addition was complete, the mixture was filtered. To the filtrate was added dropwise, with stirring, a solution of 7.90 g (47.8 mmole) N-ethyl-N-phenylethanolamine (K & K Labs) in 25 ml ethanol at 0° to 5°C. After addition was complete, the solution was neutralized by dropwise addition of a 10% NaOH solution. The resultant deep red precipitate was collected by suction filtration, washed well with water, and recrystallized from ethanol. The deep red crystals had a melting point of 185°-186°C. Yield was 45%.

Examples 5 to 7 and 8 to 9 describe diazo compounds prepared from the product of Example 2.

Example 5: 4-{[4-(2'-acetamidomethyl-4'-nitrophenylazo)-l- phenylazo]-[N,N-bis(2-hydroxyethyl)]}aniline

Diazotization of 14.96 g (47.80 mmole) 4-(2'-acetamidomethyl- 4'-nitrophenylazo)aniline (from Example 2) was effected in 40 ml concentrated HC1 by addition of a chilled (0°C) solution of 3.30 g (47.8 mmole) sodium nitrite in 10 ml distilled water. After addition was complete (about 30 minutes), the mixture was filtered. To the chilled (0°C) filtrate was added dropwise, with stirring, a solution of 8.66 g (47.8 mmole) N,N-bis(2- hydroxyethyl)aniline in 15 ml ethanol. After addition was complete, the solution was allowed to warm to room temperature and then stirred for about an hour. The solution was neutralized by dropwise addition of a 10% NaOH solution. The resulting purple precipitate was collected by suction filtration, washed with distilled water, and then recrystallized from ethanol to provide purple crystals (40% yield).

Example 6: 4-{[4-(2'-aminomethyl-4'-nitrophenylazo)- 1 -phenylazo] - [N , N-bis(2-hydroxyethyl)] } aniline

A mixture of 4.89 g (9.70 mmole) 4-{[4-(2'-acetamidomethyl-

4'-nitrophenylazo)-l-phenylazo]-[N,N-bis(2-hydroxyethyl)] }aniline (from Example 5), 15 ml methanol, and 15 ml 6N HC1 was heated under reflux, with stirring, for about 16 hours. After reaction was complete, the solution

was cooled in an ice bath and slowly neutralized by addition of a 10% NaOH solution. The resulting purple precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to afford purple plates (85% yield).

Example 7: 4-{[4-(2'-methylmethacryloylamide-4'- nitrophenylazo)- 1 -phenylazo]-[N,N-bis(2-hydroxyethyl)] }aniline

To a stirred, chilled (0°C) solution of 1.87 g (4.04 mmole) 4-{[4-(2'-aminomethyl-4'-nitrophenylazo)-l-phenylazo]-[N,N-b is(2-hydroxy- ethyl)]} aniline (from Example 6), 0.408 g (4.04 mmole) dry triethylamine, and 350 ml dry tetrahydrofuran was added dropwise with stirring a solution of 0.42 g (4.0 mmole) methacryloyl chloride (Aldrich) in 100 ml dry dichloro- methane. After addition was complete, the solution was stirred for about an hour at room temperature before solvent was evaporated under reduced pressure. To the purple residue was added 300 ml dichloromethane. After the solution was washed with 200 ml distilled water, the separated dichloro¬ methane layer was dried with anhydrous magnesium sulfate and filtered. The filtrate was evaporated under reduced pressure. The residue was purified by column chromatography on silica gel using a 9: 1 mixture of dichloromethane/ tetrahydrofuran as eluent. The final product was a purple solid (95% yield).

Example 8: 4-{[4-(2'-acetamidomethyl-4'-nitrophenylazo)-l- phenylazo] - [N-ethyl-N-hydroxyethyl)] } aniline

Diazotization of 14.96 g (47.80 mmole) 4-(2'-acetamidomethyl- 4'-nitrophenylazo)aniline (from Example 2) was effected in 40 ml concentrated HC1 by addition of a chilled (0° to 5°C) solution of 3.30 g (47.8 mmole) sodium nitrite in 10 ml distilled water. After addition was complete, the mixture was filtered. A solution of 7.90 g (47.8 mmole) N-ethyl-N-phenyl- ethanolamine in 25 ml ethanol was added dropwise, with stirring, to the chilled (0° to 5°C) filtrate. After addition was complete, the solution was neutralized by dropwise addition of a 10% NaOH solution. The resulting purple precipitate was collected by suction filtration, washed well with water, and recrystallized from ethanol to provide purple crystals (45% yield).

Example 9: 4-{[4-(2'-aminomethyl-4'-nitrophenylazo)-l- phenylazo]-[N-ethyl-N-hydroxyethyl)]}aniline

A mixture of 8.70 g (17.8 mmole) 4-{[4-(2'-acetamidomethyl-4'- nitrophenylazo)-l-phenylazo]-[N-ethyl-N-hydroxyethyl)]}anili ne (from

Example 8), 24 ml methanol, and 26 ml 6N HC1 was heated under reflux with stirring for about 16 hours. After reaction was complete, the solution was cooled in an ice bath "and slowly neutralized by addition of a 10% NaOH solution. The resulting purple precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to yield purple plates (85% yield).

Examples 10 to 12 describe diazo compounds prepared from the product of Example 3.

Example 10: 4-(2'-aminomethyl-4'-nitrophenylazo)- [N,N-bis(2-hydroxyethyl)]aniline

A mixture of 3.90 g (9.70 mmole) 4-{(2'-acetamidomethyl-4'- nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]}aniline (from Example 3), 15 ml methanol, and 15 ml 6N HC1 was heated under reflux with stirring for about 16 hours. After reaction was complete, the solution was cooled in an ice bath and slowly neutralized by addition of a 10% NaOH solution. The resulting deep red precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to yield deep red plates (85% yield) having a melting point of 180°C.

Example 11: 4-(2'-methylmethacryloylamide-4'- nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]aniline

To a stirred, chilled (0°C) solution of 1.45 g (4.04 mmole) 4-(2 ' -aminomethyl-4 ' -nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]aniline (from Example 10), 0.408 g (4.04 mmole) dry triethylamine, and 350 ml dry tetrahydrofuran was added dropwise, with stirring, a solution of 0.42 g (4.0 mmole) methacryloyl chloride (Aldrich) in 10 ml dry dichloromethane. After addition was complete, the solution was allowed to come to room temperature before being stirred for about an hour. After evaporating the solvent under reduced pressure, 300 ml dichloromethane was added to the deep red residue. The solution was washed with 200 ml distilled water. The separated dichloro¬ methane layer was dried with anhydrous magnesium sulfate and filtered. The filtrate was concentrated by distillation under reduced pressure. Using a 9: 1 mixture of dichloromethane/tetrahydrofuran as eluent, the resulting residue was purified by column chromatography on silica gel to provide a red solid (95% yield) having a melting point of 173°-174°C.

Example 12 describes a diazo compound derived from the product of Example 4.

Example 12: 4-(2'-aminomethyl-4'-nitrophenylazo)- (N-ethyl-N-hydroxyethyl)aniline

A mixture of 6.85 g (17.8 mmole) 4-(2'-acetamidomethyl-4'-nitro- phenylazo)-(N-ethyl-N-hydroxyethyl)aniline (from Example 4), 24 ml methanol, and 26 ml 6N HC1 was heated under reflux with stirring for about 16 hours. After reaction was complete, the solution was cooled in an ice bath and slowly neutralized by addition of a 10% NaOH solution. The resulting deep red precipitate was collected by suction filtration and recrystallized from ethanol to give deep red plates (85% yield) with a melting point of 200°C.

Example 13: 2-hydroxymethyl-4-nitroaniline

To a room temperature solution of 10 g (81 mmole) 2-aminobenzyl alcohol (Aldrich) in 90 ml dry pyridine was added dropwise, with stirring, 20 g (0.20 mole) acetic anhydride. The resulting solution was stirred, under a nitrogen atmosphere, for about 16 hours. Residual acetic anhydride and pyridine were removed by distillation under reduced pressure. The residue was recrystallized from a 9: 1 water/ethanol mixture to provide white crystalline needles (97% yield).

The crystalline 2-acetyloxymethylacetanilide from the above paragraph was further reacted according to the procedure of Takami et al., adapted as in Example 1, to make 2-acetyloxymethyl-4-nitroacetanilide. A mixture of

1.10 g (12.0 mmole) concentrated HNO ₃ and 1.24 g (12.0 mmole) concentrated H ₂ SO ₄ was added dropwise over an hour, with stirring, to a chilled (0° to -5°C) solution of 2.48 g (12.0 mmole) of the product from the above paragraph in 3.50 ml concentrated H ₂ SO ₄ . The mixture was stirred at 0°C to 10°C for about three hours, then at room temperature for about an hour. The mixture was poured into cold water, which was then vigorously stirred. The resulting light yellow precipitate was collected by suction filtration, washed well with cold water, and recrystallized from methanol to give light yellow crystals of 2-acetyloxymethyl-4-nitroacetanilide (55% yield). A suspension of 12.0 g (48.0 mmole) of the product from the preceding paragraph in 800 ml aqueous IN NaOH was heated under reflux for about 45 minutes and then cooled to room temperature. The resulting yellow precipitate was collected by suction filtration, washed with cold water until the pH of the filtrate was neutral, and recrystallized from ethanol to afford bright yellow crystals of 2-hydroxymethyl-4-nitroaniline (80% yield).

Example 14: 4-{(2'-hydroxymethyl-4'-nitrophenylazo)- [N-ethyl-N-(2-aminoethyl)]}aniline

A mixture of 50.0 g (0.413 mole) N-ethylaniline (Aldrich), 50.1 g (0.413 mole) N-(2-chloroethyl)-acetamide (Aldrich), 57.0 g (0.413 mole) potassium carbonate, and 100 ml 1-butanol was refluxed under nitrogen atmosphere, with stirring, for five days. After the solution was cooled and filtered, 1-butanol was evaporated under reduced pressure to give a brown oil. This oil was purified by column chromatography on silica gel (using dichloromethane as eluent) to give a white solid. The yield of N-ethyl-N- ethylacetamidoaniline was 65%.

A solution of 30.0 g (146 mmole) of the product from the above paragraph, 45 ml concentrated HC1, and 230 ml distilled water was refluxed for three days. The mixture was cooled, concentrated, made alkaline with a 10% NaOH solution, and extracted with chloroform. The chloroform extract was dried over anhydrous MgSO ₄ and concentrated under reduced pressure to give a light yellow oil. The oil was purified under reduced pressure to give a colorless to light yellow oil. Yield of N-ethyl-N-aminoethylaniline was 80%.

Diazotization of 4.0 g (24 mmole) 2-hydroxymethyl-4-nitroaniline (from Example 15) was performed in 70 ml 2N HC1 by addition of 1.64 g (23.8 mmole) sodium nitrite in 15 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about 30 minutes), the resulting solution was added dropwise to a solution of 3.90 g (23.8 mmole) N-ethyl-N-amino¬ ethylaniline (from the above paragraph) in 30 ml 2N HC1, with stirring, at 0°C. After this addition was complete, the solution was stirred at room temperature for about an hour before being neutralized by dropwise addition of a 10% NaOH solution. The resulting deep red precipitate was collected by suction filtration and recrystallized from ethanol to afford deep red crystals (50% yield).

Example 15: 4-aminophenyl-(2-acetamidoethyl)sulfone

o u o

H ^» ₂ N- {®{ ))- S — CH ₂ CH ₂ NHCCH ₃

O

To a room temperature solution of 10.30 g (82.00 mmole) 4- aminothiophenol (Aldrich) in 25 ml absolute ethanol was added dropwise, with stirring, under a nitrogen atmosphere 27 g (82 mmole) 21 % sodium ethoxide (Aldrich). After addition was complete (about 45 minutes), 9.12 g (82.0 mmole) N-(2-chloroethyl)acetamide was added dropwise to the solution. The resulting solution was stirred at room temperature for about two hours, then at 78°C for about four hours. The resulting mixture was filtered, and the filtrate

was concentrated by distillation under reduced pressure. Using an 8:2 mixture of dichlorornethane/tetrahydrofuran as eluent, the residue was purified by column chromatography on silica gel to provide a slightly yellow, viscous liquid. Yield of 4-aminophenyl-(2-acetamidoethyl)sulfide was 75 % . To a room temperature solution of 42 g (0.20 mole) of the product of the above paragraph in 220 ml dry pyridine was added dropwise, with stirring, under a nitrogen atmosphere 50.94 g (0.5000 mole) acetic anhydride. This solution was stirred for about 16 hours. Residual acetic anhydride and pyridine were removed by distillation under reduced pressure. Using a 9.5:0.5 mixture of dichloromethane/tetrahydrofuran as eluent, the resulting residue was purified by column chromatography on silica gel to provide a slightly yellow solid. Yield of 4-acetamidophenyl-(2-acetamidoethyl)sulfide was 98%.

To a room temperature solution of 51.64 g (0.2040 mole) of the product of the preceding paragraph in 256 ml glacial acetic acid was added dropwise, with stirring, 92.87 g (0.8160 mole) 30% hydrogen peroxide. The resulting solution was stirred at room temperature for about 16 hours, then at 80°C for about four hours. Residual glacial acetic acid and hydrogen peroxide were removed by distillation under reduced pressure. Approximately 200 ml ethyl-acetate (Mallinckrodt) was added to the residue, and the white precipitate was collected by suction filtration to give a white solid. Yield of 4-acetamido- phenyl-(2-acetamidoethyl)sulfone was 50%.

A mixture of 30 g (0.11 mole) of the product of the above paragraph, 106 ml concentrated HC1, and 53 ml distilled water was heated at 70°C for about 40 minutes. After reaction was complete, the solution was cooled in an ice bath and slowly neutralized by addition of a 40% NaOH solution. Liquid was removed by distillation under reduced pressure. The residue was extracted with 500 ml dichloromethane. The extract was dried with anhydrous MgSO ₄ and solvent was removed by distillation under reduced pressure. The residue was recrystallized from water to provide slightly yellow crystals (65% yield).

Examples 16 and 17 describe diazo compounds derived from the product of Example 15.

Example 16: 4-{[4'-(2-acetamidoethyl)sulfonyl-phenylazo]- (N-ethyl-N-hydroxyethyl)}aniline

Diazotization of 0.50 g (2.1 mmole) 4-aminophenyl-(2-acetamido- ethyl)sulfone (from Example 15) was performed in 30 ml 2N HCl by addition of 0.15 g (2.1 mmole) sodium nitrite in 5 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about 15 minutes), the resulting solution was added dropwise to a solution of 0.34 g (2.1 mmole) N-ethyl-N- hydroxyethylaniline (Aldrich) in 20 ml 2N HCl, with stirring, at 0°C. After addition was complete, the mixture was stirred at 0°C to 5°C for about an hour, then at room temperature for another hour. The resulting solution was neutralized by dropwise addition of a 10% NaOH solution. The resulting orange precipitate was collected by suction filtration and recrystallized from ethanol to provide orange crystals (90% yield).

Example 17: 4-[4'-(2-acetamidoethyl)sulfonylphenylazo]aniline

Diazotization of 2.0 g (8.4 mmole) 4-aminophenyl-(2-acetamido- ethyl)sulfone (from Example 15) was performed in 60 ml 2N HCl by addition of 0.60 g (8.4 mmole) sodium nitrite in 10 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about 15 minutes), the resulting solution was added dropwise to a solution of 1.76 g (8.40 mmole) aniline- methylenesulfonic acid, sodium salt (K & K Labs) in 30 ml distilled water,

with stirring, at 0°C. After addition was complete, the mixture was stirred at 0°C to 5°C for about an hour, then at room temperature for another hour. The resulting solution was neutralized by dropwise addition of a 10% NaOH solution. The resulting orange precipitate was collected by suction filtration and recrystallized from ethanol to provide orange crystals. Yield was 3.56 g (85% yield).

This orange solid was suspended in 15 ml methanol and 15 ml 6N HCl, and the mixture was heated under reflux, with stirring, for about two hours. After reaction was complete, the solution was cooled in an ice bath and slowly neutralized by addition of a 10% NaOH solution. The resulting orange precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to yield orange crystals (70% yield).

Example 18: 4-{[4'-(2-aminoethyl)sulfonylphenylazo]- (N-ethyl-N-hydroxyethyl) Janiline

A mixture of 4.0 g (9.6 mmole) 4-{[4'-(2-acetamidoethyl)-sulfonyl- phenylazo]-(N-ethyl-N-hydroxyethyl)}aniline (from Example 16), 15 ml methanol, and 15 ml 6N HCl was heated under reflux, with stirring, for about 16 hours. After reaction was complete, the solution was cooled in an ice bath and slowly neutralized by addition of a 10% NaOH solution. The resulting orange precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to yield orange crystals (65% yield).

Example 19: 4- { [4 ' -(2-acetamidoethyl) sulf onylphenylazo- 1 -phenylazo]-(N- ethyl-N-hydroxyethyl)} aniline

Diazotization of 2.0 g (5.8 mmole) 4-[4'-(2-acetamidoethyl)sulfonyl- phenylazo]aniline (from Example 17) was performed in 100 ml 2N HCl by addition of 0.40 g (5.8 mmole) sodium nitrite in 10 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about 15 minutes), the resulting solution was added dropwise, with stirring, to a chilled (0°C) solution of 0.96 g (5.78 mmole) N-ethyl-N-hydroxyethylaniline in 20 ml 2N HCl. After addition was complete, the mixture was stirred at 0°C to 5°C for about an hour, then at room temperature for another hour. The solution was neutralized by dropwise addition of a 10% NaOH solution. The resulting red precipitate was collected by suction filtration and recrystallized from ethanol to provide red crystals (81 % yield).

Example 20: 4-{[4'-(2-aminoethyl)sulfonylphenylazo- l-phenylazo]-(N-ethyl-N-hydroxyethyl)}aniline

A mixture of 1.0 g (1.9 mmole) 4-{[4'-(2-acetamidoethyl)sulfonyl- phenylazo-l-phenylazo]-(N-ethyl-N-hydroxyethyl)}aniline (from Example 19), 5 ml methanol, and 5 ml 6N HCl was heated under reflux, with stirring, for about 16 hours. After reaction was complete, the solution was cooled in an ice bath and slowly neutralized by addition of a 10% NaOH solution. The resulting red precipitate was collected by suction filtration, washed with dis¬ tilled water, and recrystallized from ethanol to yield red crystals (75% yield).

Example 21: 2-amino-5-(acetamidoethylthio)-l,3,4-thiadiazole

To a room temperature solution of 50 g (0.38 mole) 2-amino- 1,3,4- thiadiazole-5-thiol (Aldrich) in 150 ml absolute ethanol was added dropwise, with stirring, under nitrogen atmosphere 121.65 g (375.40 mmole) of 21 % sodium ethoxide (Aldrich). After addition was complete (about an hour), 45.64 g (375.4 mmole) of N-(2-chloroethyl)acetamide was added dropwise to the above solution in the same manner as in Example 15. The residue was recrystallized from acetone to provide white solids (72% yield).

Examples 22 and 23 describe azo compounds prepared from the thiadiazole of Example 21.

Example 22: 4-{[5'-(2-acetamidoethyl)thiothiadiazoleazo]- (N-ethyl-N-hydroxyethyl) } aniline

Diazotization of 50.0 g (229 mmole) 2-amino-5-(acetamidoethylthio)- 1,3,4-thiadiazole (from Example 21) was performed in 700 ml 2N HCl by addition of 15.82 g (229.4 mmole) sodium nitrite in 30 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about an hour), the resulting solution was added dropwise, with stirring, to a chilled (0°C) solution of 37.13 g (229.4 mmole) of N-ethyl-N-hydroxyethylaniline in 150 ml 2N HCl in the same manner as in Example 16. The resulting red precipitate was collected by suction filtration and recrystallized from ethanol to provide red crystals (95% yield).

Example 23: 4-[5'-(2-acetamidoethyl)thiothiadiazoleazo]aniline

Diazotization of 30 g (0.14 mole) 2-amino-5-(acetamidoethylthio)- 1,3,4-thiadiazole (from Example 21) was performed in 400 ml of 2N HCl by addition of 9.83 g (0.138 mole) sodium nitrite in 20 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about 45 minutes), the resulting solution was added dropwise, with stirring, to a chilled (about 0°C) solution of 28.83 g (0.1376 mole) anilinemethylenesulfonic acid, sodium salt in 30 ml distilled water as in Example 17. The resulting orange precipitate was collected by suction filtration and recrystallized from ethanol to provide 30 g (87% yield) of orange crystals. This orange solid was suspended in 100 ml methanol and 100 ml 6N

HCl, and the mixture was heated under reflux, with stirring, for about two hours in the same manner as in Example 17. The resulting orange precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to yield orange crystals (75% yield).

Example 24 : 4- { [5 ' -(2-acetamidoethy l)thiothiadiazoleazo] - (N-ethyl-N-acetyloxyethyl) } aniline

To a room temperature solution of 60 g (0.15 mmole) of 4-{[5'-(2- acetamidoethyl)thiothiadiazoleazo]-(N-ethyl-N-hydroxyethyl)} aniline (from

Example 22) in 168 ml dry pyridine was added dropwise, with stirring, under nitrogen atmosphere 38.80 g (0.381 mole) acetic anhydride as was 4- acetamidophenyl-(2-acetamidoethyl)sulfide (see Example 15). The residue was poured, with stirring, into cold water. The resulting precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to provide red crystals (95% yield).

Example 25: 4-{[5'-(2-acetamidoethyl)sulfonylthia- diazoleazo]-(N-ethyl-N-acetyloxyethyl)}aniline

To a room temperature solution of 60 g (0.14 mole) of 4-{[5'-(2- acetamidoethyl)thio-thiadiazoleazo]-(N-ethyl-N-acetyloxyethy l)}aniline (from Example 24) in 200 ml glacial acetic acid was added dropwise, with stirring, 62.57 g (0.550 mole) of 30% hydrogen peroxide in the same manner as in Example 23. Using acetone as eluent, the resulting residue was purified by column chromatography on basic aluminum oxide (Aldrich) to provide a deep red solid (65% yield).

Example 26: 4-{[5 '-(2-aminoethyl)sulfonylthiadiazoleazo]-(N-ethyl-N- hydroxyethyl) } aniline

A mixture of 10 g (0.21 mole) 4-{[5'-(2-acetamidoethyl)sulfonyl- thiadiazoleazo]-(N-ethyl-N-acetyloxyethyl)}aniline (from Example 25), 34 ml methanol, and 34 ml 6N HCl was heated under reflux, with stirring, for about 16 hours in the same manner as in Example 10. The resulting dark red precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to provide dark red crystals 70% yield.

Example 27: 4-{[5'-(2-acetamidoethylthio)thiadiazoleazo-l-phenylazo]- (N-ethyl-N-hydroxyethyl) } aniline

Diazotization of 10 g (0.28 mole) of 4-[5'-(2-acetamidoethyl)thio- thiadiazoleazo]aniline (from Example 23) was performed in 300 ml 2N HCl by addition of 1.95 g (28.3 mmole) sodium nitrite in 10 ml distilled water, with stirring, at 0° to 5°C. After addition was complete (about 30 minutes), the resulting solution was added dropwise, with stirring, to a chilled (0°C) solution of 4.66 g (28.25 mmole) N-ethyl-N-hydroxyethylaniline in 100 ml of 2N HCl. After addition was complete, the mixture was stirred at 0°C to 5°C for about an hour, then at room temperature another hour. The resulting solution was neutralized by dropwise addition of a 10% NaOH solution. The resulting deep red precipitate was collected by suction filtration and recrystallized from ethanol to provide deep red crystals (78% yield).

Example 28 : 4-{ [5 ' -(2-acetamidoethylthio)thiadiazoleazo- 1 -phenylazo]- (N-ethyl-N-acetyloxyethyl)}aniline

To a room temperature solution of 10 g (20 mmole) of 4-{[5'-(2- acetamidoethylthio)thiadiazoleazo-l-phenylazo]-(N-ethyl-N-hy droxy- ethyl)}aniline (from Example 27) in 22 ml dry pyridine was added dropwise, with stirring, under nitrogen atmosphere 5.10 g (50.0 mmole) acetic anhydride in the same manner as in Example 24. The residue was poured into cold water with stirring. The resulting precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to provide red crystals (98% yield).

Example 29: 4-{[5'-(2-acetamidoethylsulfonyl)thiadiazoleazo-l-phenylazo] - (N-ethyl-N-acetyloxyethyl)}aniline

To a room temperature solution of 10 g (19 mmole) 4-{[5'-(2- acetamidoethylthio)thiadiazoleazo-l-phenylazo]-(N-ethyl-N-ac etyloxy- ethyl)}aniline (from Example 28) in 50 ml glacial acetic acid was added dropwise, with stirring, 8.43 g (74.1 mmole) 30% hydrogen peroxide (Aldrich) in the same manner as in Example 25. The residue was recrystallized from ethanol to afford a dark violet solid (60% yield).

Example 30: 4-{[5 '-(2-aminoethylsulfonyl)thiadiazoleazo- l-phenylazo]-(N- ethyl-N-hydroxyethyl) Janiline

A mixture of 8 g (0.2 mole) 4-{[5'-(2-acetamidoethylsulfonyl)thia- diazoleazo- 1 -phenylazo]-(N-ethyl-N-acetyloxyethyl) }aniline (from Example 29), 40 ml methanol, and 40 ml 6N HCl was heated under reflux, with stirring, for about 16 hours in the same manner as in Example 26. The resulting violet precipitate was collected by suction filtration, washed with distilled water, and recrystallized from ethanol to provide deep violet crystals (68% yield).

Synthesis of Crosslinked Polymers

Example 31: Polymerization product of the dye of Example 10 and isophorone diisocyanate

A mixture of 0.125 g (0.348 mmole) 4-(2'-aminomethyl-4'- nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]aniline (from Example 10) and

0.065 g (0.38 mmole) isophorone diisocyanate (Aldrich) was dissolved in 2.00 g anhydrous dimethylformamide (DMF). To that solution was added 0.01 g dibutyltin dilaurate (Aldrich) and 0.01 g triethylenediamine (Aldrich).

Processing and poling was performed according to Francis et al. , Chem. Mater. , 5, 506 (1993). The resulting solution was held at 50°C for about an hour, filtered through a 0.2 μ filter, and spin-coated between coplanar chromium electrodes to provide a film. Under a nitrogen atmosphere, the film was poled at 1 kV and stored at a temperature of 120°C for 16 hours. The film was allowed to cool to room temperature, and the electric field was terminated.

Retention of polar orientation of the NLO-active dyes was manifested by the observation of SHG from the film after removal of the electric field.

Example 32: Polymerization product of dye from Example 12 and tolonate HDT

A mixture of 0.10 g (0.58 mmole) 4-(2'-aminomethyl-4'- nitrophenylazo)-(N-ethyl-N-hydroxyethyl)aniline (from Example 12) and 0.12 g (0.63 mmole) Tolonate™ HDT (Rhone-Poulenc Inc.; Princeton, NJ) was dissolved in 1.85 g dry pyridine. To this mixture was added 0.01 g dibutyltin dilaurate and 0.01 g triethylenediamine. The resulting solution was kept at room temperature for about an hour, filtered through a 0.2 μ filter, and spin-coated onto chromium electrodes. The processing and poling procedures described in Example 31 were performed.

Retention of polar orientation of the NLO-active dyes was manifested by the observation of SHG from the film after removal of the electric field.

Example 33: Polymerization product of the dye from Example 11 and tolylene-2 ,4-diisocyanate

A mixture of 0.12 g (0.29 mmole) 4-(2'-methylmethacryloylamide- 4'-nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]aniline (from Example 11), 0.055 g (0.32 mmole) tolylene-2,4-diisocyanate (Aldrich), 0.01 g dibutyltin diluarate, and 0.01 g triethylenediamine was dissolved in 1.85 g anhydrous DMF. The resulting solution was kept at 50°C for about four hours. Thereafter, 0.01 g 2-phenylacetophenone (Aldrich) was added. This solution was filtered through a 0.2 μ filter and spin-coated onto chromium electrodes. The film was poled at 1 kV, heated at 120°C under a nitrogen atmosphere, and irradiated with a UV light for 15 minutes. After about 16 hours, heating was stopped and the electric field was removed. The film was allowed to cool to room temperature. Retention of polar orientation of the NLO-active dyes was manifested by the observation of SHG from the film after removal of the electric field.

Example 34: Polymerization product of dye from Example 11 and tolonate HDT

A mixture of 0.124 g (0.58 mmole) 4-(2'-methylmethacryloylamide- 4'-nitrophenylazo)-[N,N-bis(2-hydroxyethyl)]aniline (from Example 11), 0.122 g Tolonate™ HDT, 0.01 g dibutyltin diluarate, and 0.01 g triethylenediamine was dissolved in 1.85 g dry pyridine. The solution was kept at room temperature for about an hour before 0.01 g of 2-phenylacetophenone was added. The film preparation and poling procedures of Examples 31 and 34 were followed.

Retention of polar orientation of the NLO-active dyes was manifested by the observation of SHG from the film after removal of the electric field.

Example 35: Thermal Stability Comparison

The thermal stabilities of several variations of Compound I from above (with Z being the six-membered ring moiety, A being CH ₂ CH ₂ R ² R ^2' , and R ¹ being OH) were compared. The results are shown below in Table I.

A film of each dye was prepared by dissolving about 15 mg of the dye and 285 g poly(methyl methacrylate) in 1.5 ml pyridine, spin coating the solution onto a glass substrate, and drying at 75 °C for about an hour. An absorption band of each film was measured from 350 to 700 nm. The films were then maintained at 100°C for several days during which time additional absorption spectra were taken to monitor changes in the peak absorbance of each film. Stable dyes exhibited less than 5% drop in peak absorbance after being held at 100°C for over 30 days.

TABLE I: Stability Data

Dye R ^1' R ² R ^2' R ³ R ⁴ R ⁸ R ⁹ R ¹¹ Stab 7

1 CH ₃ OH CH ₃ H H CH ₃ a NO ₂ YES

2 CH ₃ OH CH ₃ CH ₃ CH ₃ H a NO ₂ YES

3 H H H H CH ₃ H a NO ₂ YES

4 CH ₃ OH CH ₃ H H b H NO ₂ YES

5 H H H H H NO ₂ H c YES

6 H H H H H a H NO ₂ NO

a = CH ₂ OH b = CH ₂ CH ₂ OH c = S0 ₂ NHCH ₂ CH(OH)CH ₃

The absorbance band of the unstable dye had disappeared after seven days at 100°C.

The data in the Table show the stability imparted by use of a non- hydrogen group ortho to the azo linkage. When an alkyl group substituted with an active hydrogen-containing group is that group (and the only substituent on the phenyl rings), the use of a C ₂ or longer alkyl chain provides additional stability. (Compare Dyes 4 and 6.)

Various modifications and alterations of this invention which do not depart from the scope and spirit of this invention will become apparent to those skilled in the art. This invention is not to be unduly limited to the illustrative embodiments set forth herein.