The Study of Supersensitization by Measuring Fluorescence and Electron Spin Resonance

Abstract

Examination has been made of the supersensitization of 5,6-dichloro-l-ethyl- 3,3'-bi-(y-sulphopropyl) 5’-t rift uoro-methyl benzimidazolo-tliiacarbocyanine betaine, triethylaminium salt (dye A) by anhydro-i,1’-diethyl-3,3’-disulphobu- lyt-5,5’ dicyanoimidazolo carbocyaninc hydroxide (dye B). The steady-state fluorescence measurements and sensitometric measurements have shown that the relative fluorescence quantum yield and spectral sensitization efficiency for the /-aggregate of dye A adsorbed on AgBrl emulsion grains are a function of the amount of added supersensitizer, and the fluorescence yield decreases as the photographic efficiency increases. This implies that the major effect of the supersensitizer studied is to increase the rate for the primary sensitization step. The lime-resolved fluorescence measurements have quantitatively given the change in the rate of the primary spectral sensitization step. Determination of the light-induced ESR signals of dye A, and dye A plus dye B, absorbed on AgBrl emulsion grains indicates that a positive hole trapped by dye A was transferred to the supersensitizer (dye B). All of the above results support Gilman’s hole-trapping mechanism for supersensitization.