Kinetics of J-aggregation of cyanine dyes in the presence of gelatin

The kinetics of formation of J-aggregates for 3,3'-bis[sulfopropyl]-R-4',5'-dibenzo-9-ethylthiacarbocyanines (R = 5-methoxy (1); R = 4,5-dibenzo (2)) and 3,3'-bis[sulfopropyl]-5,5'-diphenyl-9-ethyloxacarbocyanine (3) were studied in aqueous solution in the presence of gelatin at different pH values and at room and elevated temperatures. Addition of gelatin at concentrations of 0.0005-0.05 wt % to solutions of dyes 1-3 results in the production of J-aggregates in the tens of seconds to tens of minutes range. The rate of J-aggregate formation increases with increasing concentrations of dye and gelatin, correlates with the rate of decay of dimers, and is also dependent on the dye structure, temperature, and pH. The rate of J-aggregation is increased for 3 and decreased for 2 with an increase in temperature. For 2 and 3, the rate increases with increasing [HI] and reaches the maximum value at pH 3.3-4.3 for 3. The interaction of 1-3 with gelatin is considered to be a cooperative binding process, and J-aggregation is characterized by the time-dependent rate constant. Sigmoidaland nonsigmoidal-type kinetic curves of both formation of J-aggregates and decay of the dimers are best fitted with a stretched exponential function.