THE EFFECT OF J-AGGREGATE SIZE ON PHOTOINDUCED CHARGE-TRANSFER PROCESSES FOR DYE-SENSITIZED SILVER-HALIDES

The excited state dynamics of J-aggregated cyanine dyes adsorbed to si lver halide microcrystals as spectral sensitizers were investigated. T he rates of charge transfer, fluorescence, and non-radiative relaxatio n were studied as a function of surface morphology, halide, and degree of dye aggregation. The dye aggregation was controlled using a statis tical dilution method: the sensitizing dyes studied (pseudoisocyanine [PIG] and a thiacarbocyanine [RTHC]) were diluted with structural homo logues that do not absorb light at the wavelength of interest, As a ge neral rule, the rate of charge transfer was observed to increase as th e aggregate size increased, In spite of this trend, a strong enhanceme nt in the rate of non-radiative relaxation as the aggregates become la rger causes the net photographic efficiency of J-aggregate sensitizati on to decrease with increasing aggregate size.