Sensitizers, photochemical photographic

An illustration of the technological significance of the relaxation phenomenon can be taken from photographic chemistry. Dyes of the cyanine class where Y = S, 0, CH—CH— n = 0,1,2,3...X = haUde, etc, are used as spectral sensitizers to extend photochemical response of the photographic silver hahdes, which only absorb blue and ultraviolet light, into the visible spectral regime. 

As will be apparent, the principal interest in this ring system is as a source of carbocyanine dyes. In the last few years over 40 patents have been listed in Chemical Abstracts describing their use as sensitizers and desensitizers of direct positive photographic emulsions, A further dozen or so patents claim their use as sensitizers for electrophotographic recording materials. Other uses for the ring system are as fungicides and as initiators of photochemical polymerization of vinyl monomers. ... 

Much has already been published on the problem of the photosensitivity of nonsllver photographic systems based on organic photochemical reactions. Before starting with the discussion of the theoretical sensitivity value. It Is worthwhile to comment a little on the specific meaning of sensitivity. 

A correlation of the photosensitivities of several organic photochemical systems with this theoretical value is given in Table 1, where the sensitivity of some silver halide materials were Included for comparison. It Is trivial to state that the success of classical photographic systems, considered from the point of view of their photosensitivity, lies in the possibility of chemical amplification of the latent image. It seems therefore evident that the only chance for organic photochemical systems to realize a significant penetration Into the broad application field of silver systems with sensitivities of 10 ergs/cm and less Is to find some way to amplify the primary photochemical effect - that is, to find photochemical reactions with an overall... 

D. Coster, and 0. Stelhng studied the X-ray spectrum and D. M. Yost, the absorption of X-rays. I. PlotnikofE and M. Karshulin measured the absorption spectrum and the region of photochemical sensitivity for soln. of potassium chromate in colloidion films—with methyl alcohol as acceptor. A. Kailan found that an aq. soln. of potassium chromate is reduced by radium rays more slowly than potassium dichromate. E. Montignie observed that after exposure to ultra-violet light, potassium chromate affects a photographic plate. 

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