Femtosecond reaction dynamics of a photochromic dithienylethene derivative

The dynamics of the photochromic ring-closure reaction of 1,2-bis[5-formyl-2-methyl-thien-3-yl]perfluorocyclopentene (CHO-BMTFP) in dichloromethane were monitored by fs transient absorption spectroscopy. The open isomer was excited using a 260 fs pump pulse tuned to the S₀-S₁ absorption transition at 308 nm. A temporally delayed white-light continuum probe pulse measures the rise dynamics of the ground-state absorption spectrum of the closed isomer which exactly displays the monoexponential dynamics of the ring-closure reaction with a time constant of about 2.3 ps. These spectroscopic data are discussed in terms of a model potential calculated in the collective electronic oscillator (CEO) approach.