Optical properties and dynamics of a photochromic bisthienylethene in solution and in a polymer film

Optical switching dynamics and fatigue were investigated for a photochromic molecular switch, bis(5-pyridyl-2-methylthien-3-yl)perfluorocyclopentene (PMTFC). Femtosecond transient absorption was measured using 270 nm pump and broadband visible probe pulses for samples in ethanol solution and as a dispersion film of poly(butyl acrylate-co-acrylic acid). The optical switching occurs in ≤3 ps in both cases. The spectral evolution observed in solution within 20 ps is absent in the film, suggesting that the switching dynamics are sensitive to the molecular environment. PMTFC in the copolymer film demonstrated evidence of fatigue after ∼1500 complete cycles of optical switching.