SATURABLE ABSORPTION AND ABSORPTION RECOVERY OF INDOCYANINE GREEN J-AGGREGATES IN WATER

Concentrated aqueous indocyanine green solutions form J-aggregates (ab sorption peak at 890 nm). Nonlinear energy transmission measurements u sing femtosecond pulses of a cw mode-locked Ti:sapphire laser were per formed to determine the number density, the ground-state absorption cr oss section, and the excited-state absorption cross section of the J-a ggregate chromophores (Frenkel excitons). The chromophore number densi ty was found to be approximately one sixteenth of the molecule density (coherent exciton extension over approximately sixteen molecules). In a Michelson-type transmission correlation measurement a ground-state absorption recovery time of (4.5 +/- 1) ps was deduced. The absorption and emission dynamics including results from previous fluorescence qu antum yield measurements are discussed.