Ultrafast dynamics and temperature effects on the quantum efficiency of the ring-opening reaction of a photochromic indolylfulgide

Abstract The ultrafast ring-opening reaction of the molecular switch 1,2-Dimethyl-3-indolylfulgide dissolved in acetonitrile is investigated by temperature dependent quantum efficiency measurements and time-resolved transient absorption spectroscopy in the ultraviolet and visible spectral range. The photoreaction is found to be thermally activated with an activation energy of about 1640 cm − 1 . The transient absorption signal is bi-exponential with the time constants τ 1  = 0.7 ps and τ 2  = 12 ps. The fast time constant is due to solvation dynamics, while the main component τ 2 is attributed to the excited state lifetime and product formation. A long-lived intermediate state in the photoreaction can be excluded.