Stepwise Two-Photon-Induced Fast Photoswitching via Electron Transfer in Higher Excited States of Photochromic Imidazole Dimer

Stepwise two-photon excitations have been attracting much interest because of their much lower power thresholds compared with simultaneous two-photon processes and because some stepwise two-Photon processes can be initiated by a weak incoherent,excitation light source. Here we apply stepwise two-photon optical processes to the photo chromic bridged imidazole dimer, whose solution instantly changes color upon UV irradiation and quickly reverts to the initial color thermally at room temperature. We synthesized a zinc tetrapherrylporphyrin, (ZnTPP)-substituted bridged imidazole dimer, and wide ranges of tune-resolved spectroscopic studies revealed that a ZnTPP-linked bridged imidazole dimer shows efficient visible stepwise two-photon-induced photo chromic reactions upon excitation at the porphyrin moiety. The fast photoswitching property combined with stepwise two photon processes is important not Only for the potential for novel photochromic materials that ate sensitive to the incident light intensity but also for fundamental-photochemistry using higher excited states.