Complex Formation between Sensitizing Dyes and Stabilizers: A Possible Contributing Factor in Supersensitization

Abstract

We have provided evidence, from fluorimetric titration and analysis of the spectral distribution of fluorescence. that representative symmetrical cyanine dyes, DTCI and DTDCI, form 1:1 complexes with photographic stabilizers, 2-methylbenzimidazole (MeBz), 2-mercaptobenzoxazole (MBO), tetraazaindene (TAI), and the conjugate anions of the latter two compounds, in solution. AM1 semi-empirical and molecular mechanics calculations are introduced to interpret these results. Complex formation is consistent with the reported role of these stabilizers in supersensitization given the following possibilities: (1) the complexes may be adsorbed to silver halide surfaces in preference to free dye; (2) incorporation of the complex can disrupt a J-aggregate of the dye, with concomitant decrease in recombination probability in the aggregate; and, (3) insofar as computations suggest a partial charge transfer character to the complexes, they may be energy trapping sites on the grain surface, where electron injection into the grain is facilitated.