ENERGY MIGRATION PHENOMENA IN J-AGGREGATES .1. FLUORESCENCE LIFETIME MEASUREMENTS AND HOLE-BURNING EXPERIMENTS ON J-AGGREGATES OF A BENZIMIDOCARBOCYANINE DYE

The photophysics of the J-aggregates of the cyanine dye 5,5',6,6'-tetrachloro-1,1'-diethyl-3,3'-bis (4-sulfobutyl)-benzimidazolocarbocyanine (TDBC) has been investigated with fluorescence lifetime measurements and hole-burning experiments. The temperature dependence of the fluorescence lifetime has been measured between 4 and 300 K with different solvent mixtures and different cooling procedures. At very low temperatures, the lifetime is nearly constant under different conditions. Between 50 and 300 K the lifetime depends on solvent mixture and cooling procedure indicating that the microscopic environment of the J-aggregate determines the fluorescence decay. At room temperature the fluorescence lifetime depends linearly on the reciprocal viscosity as would be expected for a diffusion controlled deactivation process under the Stokes-Einstein approximation. From the data, a hydrodynamic volume of 5 X 10(-28) m(3) can be derived. In contrast to the behavior of pseudoisocyanine (PIC) aggregates, it has been impossible to burn holes in the J-band of TDBC under the given experimental conditions. We conclude that this discrepancy is due to the different aggregate structure of both dyes. In the monomer band of TDBC in ethanol/methanol glass, however, holes can be burnt with prolonged irradiation.