文摘
We report the photochemistry of two ring-open isomers, namely TTC and TTT, of a bidirectional photoswitchable spiropyran, 6,8-dinitro-1鈥?3鈥?3鈥?trimethylspiro[2H-1-benzopyran-2,2鈥?indoline] (6,8-dinitro BIPS). Both isomers are capable of ring closure after excitation with visible fs laser pulses, as disclosed by pump-wavelength-dependent transient absorption experiments in the visible spectral range. The main isomer TTC has its maximum absorption at 560 nm, whereas the minor isomer TTT is red-shifted (600 nm). The excited-state lifetimes differ strongly (蟿 鈮?900 ps for TTT and 蟿 鈮?95 ps for TTC), nevertheless the quantum efficiencies for ring closure (40% for TTC and 35% for TTT) and isomerization (1鈭?% for TTC and 1鈭?% for TTT) are comparable. With regard to the bidirectional photoswitching capabilities, 6,8-dinitro BIPS is the first molecular switch based on a 6蟺-electrocyclic reaction where both ring-open isomers are capable of ring closure.
