Investigation on photoexcited dynamics of IR-140 dye in ethanol by femtosecond supercontinuum-probing technique

Transient absorption and emission spectra of IR-140 dye (5,5'-dichloro-11-diphenylamine-3,3'-diethyl- 10,12-ethylene-thiatricarbocyanine-perchlorate) in ethanol have been investigated by using the pump supercontinuum-probing technique of 130 fs time resolution. Excited at a wavelength of 807 nm, two peaks at 820 and 840 nm in the emission spectra were observed. The decay of stimulated emission (SE) at 840 nm can be fitted by a dual-exponential function. Meanwhile, a new transient absorption band ranging from 500 to 650 nm was observed and attributed to the transition between the excited singlet states. Its relaxation process could also be fitted by a dual -exponential function. Both relaxation processes of SE and excited-state absorption were probing wavelength-dependent and included a fast relaxation with a decay time of about several picoseconds and a slow relaxation with decay time longer than 0.1 ns. The prime energy structure was proposed according to the relaxation process and transient spectra of IR-140.