SHORT AND EXCITATION-INDEPENDENT FLUORESCENCE LIFETIMES OF J-AGGREGATES ADSORBED ON AGBR AND SIO2

Excitation intensity independent fluorescence lifetimes of cyanine dye J-aggregates adsorbed on octahedral microcrystals of AgBr and on silica gel have been observed to be as short as 5 and 25 ps, respectively. The fluorescence lifetime of the aggregate/SiO2 systems at 4 K is about 120 ps and attributed to the pure radiative lifetimes of the J-aggregate in the adsorbed state; thus the very short fluorescence lifetimes at ambient temperatures seem to be dominated by a fast nonradiative decay channel. The fluorescence lifetimes of the aggregate/microcrystalline AgBr systems are dependent on the size of the J-aggregate, which itself was determined from spectroscopic and kinetic data. The necessity for the development of an inert reference system without electron transfer is discussed for elucidation of the rate of electron transfer of J-aggregates adsorbed on AgBr microcrystals. © 1990 American Chemical Society.