Relaxation dynamics in the first excited singlet state of a cyanine dye: HITC

The S1 state relaxation dynamics of HITC were examined with 200 fs time resolution. The sample was excited at 780, 700, 650 or 600 nm, and the transmission at 780 nm was recorded. In the nondegenerate experiments there is an instantaneous ground state depletion and a stimulated emission signal with a bi-exponential rise with time constants of 300 ± 100 fs and 2.9 ± 0.3 ps. The degenerate experiments show the ground state depletion component and a small stimulated emission signal with a 1.1 ± 0.2 ps decay. The dynamics are assigned to vibrational relaxation and/or solvation effects.