Saturable absorption and absorption recovery of indocyanine green J-aggregates in water

Abstract

Concentrated aqueous indocyanine green solutions form J-aggregates (absorption peak at 890 nm). Nonlinear energy transmission measurements using femtosecond pulses of a cw mode-locked Ti:sapphire laser were performed to determine the number density, the ground-state absorption cross section, and the excited-state absorption cross section of the J-aggregate chromophores (Frenkel excitons). The chromophore number density 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 quantum yield measurements are discussed