The ultrafast dynamics of near-infrared heptamethine cyanine dye in alcoholic and aprotic solvents

The ultrafast dynamics of a synthesized near-infrared heptamethine cyanine dye has been studied in the typical alcoholic and aprotic solvents using the femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP FD) technique. The faster decay on the hundreds of the femtosecond time scale and the slower decay on the order of picosecond are found. The intramolecular vibrational redistribution (IVR) and the ultrafast solvent inertial relaxation should account for the faster decay, while the slower decay is attributed to the diffusive solvent relaxation. The time constants of the slower decay increase with the hydrogen-bonding energy in alcoholic solvent, and the time constants of the slower decay decrease with the dipole moments of the aprotic solvent molecules due to the interactions between the aprotic molecules and the excited dye molecule.