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'-tetr achloro-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 fluore scence lifetime has been measured between 4 and 300 K with different s olvent mixtures and different cooling procedures. At very low temperat ures, the lifetime is nearly constant under different conditions. Betw een 50 and 300 K the lifetime depends on solvent mixture and cooling p rocedure indicating that the microscopic environment of the J-aggregat e determines the fluorescence decay. At room temperature the fluoresce nce lifetime depends linearly on the reciprocal viscosity as would be expected for a diffusion controlled deactivation process under the Sto kes-Einstein approximation. From the data, a hydrodynamic volume of 5 X 10(-28) m(3) can be derived. In contrast to the behavior of pseudois ocyanine (PIC) aggregates, it has been impossible to burn holes in the J-band of TDBC under the given experimental conditions. We conclude t hat this discrepancy is due to the different aggregate structure of bo th dyes. In the monomer band of TDBC in ethanol/methanol glass, howeve r, holes can be burnt with prolonged irradiation.