PURPOSE: To improve the sensitivity of a photosensitive material to long wavelengths, more particularly rays in a region in excess of nearly 600nm by consisting a photopolymn. initiation system of a specific cyanine dyestuff and s-triazine compd.

CONSTITUTION: The photopolymn. initiation system of the photopolymerizable compd. consisting of an addition-polymerizable ethyleneic unsatd. compd. and the photopolymn. initiation system consists of the cyanine dyestuff in which the absorption max. wavelength in a polar org. solvent is larger than 580nm and the s-triazine compd. having at least one halogenated methyl group. The good sensitivity is obtd. in this way in the region in excess of 600nm and further up to a near IR region.