Rhodamine 800 has different optical absorption spectra in various organic solvents and in aqueous solution in the visible and near-infrared regions. The absorption maximum at 683 nm in acetone shifts to 696 nm in DMSO without a significant change of the overall spectral profile. The fluorescence intensity of Rhodamine 800 varies markedly with the solvent, and decreases to less than one-fifth when the solvent is changed from acetone to water without a significant change of the emission peak.