The effect of J-aggregate size on photoinduced charge transfer processes for dye-sensitized silver halides Original Research Article

The excited state dynamics of J-aggregated cyanine dyes adsorbed to silver halide microcrystals as spectral sensitizers were investigated. The rates of charge transfer, fluorescence, and non-radiative relaxation were studied as a function of surface morphology, halide, and degree of dye aggregation. The dye aggregation was controlled using a statistical dilution method: the sensitizing dyes studied (pseudoisocyanine [PIC] and a thiacarbocyanine [RTHC]) were diluted with structural homologues that do not absorb light at the wavelength of interest. As a general rule, the rate of charge transfer was observed to increase as the aggregate size increased. In spite of this trend, a strong enhancement in the rate of non-radiative relaxation as the aggregates become larger causes the net photographic efficiency of J-aggregate sensitization to decrease with increasing aggregate size.