Fading mechanism of azomethine dyes for image formation in color photography. Reaction mechanism of photo-fading of model dyes with benzophenone in ethanol.

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In order to elucidate fading mechanisms of azomethine dyes for image formation in color photography, remarkable photo-fading reactions of model dyes with benzophenone (BP) in degassed ethanol are investigated by flash photolysis. In these solutions, the BP lowest triplet state abstracts a α-hydrogen of a ethanol molecule and produces a BP kethyl radical (KR). Then the KR initiates the fading reaction by addition of a hydrogen to an azomethine group of a dye molecule. The second order decay constant of KR is found to be (1.3±0.2) ×108M-1s-1 and the second order fading constant of the cyan dye to be (5.2±0.8) ×108M-1s-1. Effects on the fading reaction by KR scavengers such as dietyl maleate and methyl viologen (MV) are investigated. It is concluded that the fading reaction is not initiated only by KR but also by other radicals such as CH3CHOH, and that the latter process makes probably a large contribution to the fading reaction. Moreover MV and AgNO3 show interesting effects on the dye fading and the KR decay.
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