Absorption and fluorescence spectroscopic investigation of indocyanine green

Absorption spectra, fluorescence quantum distributions, fluorescence quantum yields and degrees of fluorescence polarization vs, dye concentration were determined for indocyanine green in methanol, water and aqueous albumin solution. The monomer fluorescence quantum yield is limited to a few per cent by internal conversion. In water, dimerization starts at low concentrations (approximately 3 x 10(-8) mol dm(-3)) and lowers the fluorescence quantum yield. The strong affinity of the dye to albumin shifts the onset of dimerization to higher concentrations. in methanol, dimerization is weak and closely spaced pair formation dominates at high concentrations. Dye adsorption to albumin and dye aggregation in the solvents were analysed experimentally and theoretically.