W, the solvent is rotary evaporated and the solid stirred in 40 ml of HC1 2M for 4 hours in the dark, the solid is filtered and dried at 80°C under vacuum for giving a yield of 82% of pure Ru (dcbH2) 2Cl2 3. Process of claims 1 and 2 characterized in that all the quantities can be scaled up by a factor ranging from 10 to 100.

X is a mono-dentate ligand of the type: CN-, NCS-, py, NC- (CH2) 2-CN, NC-(CH2) 3-CN, NC-(CH2) 4-CN, halide, CO, NO, pyridine, 4-cyanopyridine, dicyanobenzene, H20, NH3 or NO2-, characterized in that an amount of 50-500 mg of commercially available hydrated ruthenium trichloride and a 70-700 mg amount of the trpy (COOH) 3 ligand are suspended in 7-70 ml of dimethylformamide in a 50-200 ml glass reactor, the mixture is irradiated with a microwaves for 5-15 min by using a power in the range 250-700 W, the solvent is rotary evaporated and the solid redissolved in a small volume of methanol and reprecipitated with diethylether, giving 440 mg of the trichloro species, corresponding to a yield of 80%.

addition of 0.1 M tetrabutylammonium hydroxide solution, the solution is filtered and the (TBA) 3 [Ru [trpy (COOH) (COO- ) z] (NCS) 3 complex precipitated in the pH range 4.8-5.0 by addition of acid, keeping the solution in an ice bath, the solution is then filtered giving a solid product formation yield of 75-80%.

aromatic spacer group, e. g., methylene or phenyl); 1,10- phenanthroline unsubstituted or substituted by one or two -COOH,-B (OH) 2-PO3H2, or-R-PO3H2 groups (where R is as defined above) ; or 2,2'-biquinoline unsubstituted or substituted by one or two-COOH,-B (OH) 2-PO3H2, or-R-PO3H2 groups (where R is as defined above), characterised in a) reacting a pentachlororuthenium complex or ruthenium trichloride hydrate for 3-6 hours with an excess of potassium or sodium oxalate in water at 60-100°C, b) adding the mixture of step (a) with a 1.5-2 fold molar excess of (PO3R2)n(CH2)mbpy, where R represents ethyl or methyl group to obtain the complex Ru[(PO3H2)n(CH2)mbpy]2(C2O4), c) refluxing the Ru[(PO3H2)n(CH2)mbpy] 2 (C, Oj complex of step (b) during 6-12 hours, in a solvent such as acetonitrile, methanol, tetrahydrofurane or acetone in the presence of a 10-40 fold molar excess of acid, of hydrochloric acid, in order to hydrolyse the phosphonate ester groups and at the same time to get the substitution of the oxalate ligand with two solvent molecules, to form the complex ion [Ru[(PO3H2)n(CH2)mbpy]2 (S) 21'* I wherein S represents the solvent; the solution is rotary evaporated to dryness and the solvent complex is made to react at reflux for 2-4 hours, in solvents such as, methanol, ethanol or water, with an excess of mono-dentate ligand (X) or bi- dentate ligand (Y) to obtain the desired dye, for giving a yield from 50% to 80%.

c) the Ru[(PO3H2)n(CH2)mbpy]2(C2O4) complex of step (b) is refluxed for 8 hours in a solvent such as acetonitrile, methanol, tetrahydrofurane or acetone in the presence of a 20 fold molar excess of hydrochloric acid, the solution is rotary evaporated to dryness and the solvent complex is made to react at reflux for 2 hours in solvents for giving a yield from 75% to 80%.