title: Stepwise Two-Photon-Gated Photochemical Reaction in Photochromic [2.2]Paracyclophane-Bridged Bis(imidazole dimer).
abstract: Stepwise two-photon processes not only have great potential for efficient light harvesting but also can provide valuable insights into novel photochemical sciences. Here we have designed a [2.2]paracyclophane-bridged bis(imidazole dimer), a molecule that is composed of two photochromic units and absorbs two photons in a stepwise manner. The absorption of the first photon leads to the formation of a short-lived biradical species (half-life = 88 ms at 298 K), while the absorption of the additional photon by the biradical species triggers a subsequent photochromic reaction to afford a long-lived quinoid species. The short-lived biradical species and the long-lived quinoid species display significantly different absorption spectra and rates of the thermal back-reaction. The stepwise two-photon excitation process in this photochromic system can be initiated even by incoherent continuous-wave light irradiation, indicating that this two-photon reaction is highly efficient. Our molecule based on the bridged bis(imidazole dimer) unit should be a good candidate for multiphoton-gated optical materials.
authors.affiliation: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Mutoh
authors.affiliation: ‡Itoh Optical Industrial Co.,Ltd., 3-19 Miyanari-cho, Gamagori, Aichi 443-0041, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakagawa
authors.affiliation: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Sakamoto
authors.affiliation: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: †Department of Chemistry, School of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara, Kanagawa 252-5258, Japan.|§CREST, Japan Science and Technology Agency (JST), K's Gobancho 7, Gobancho, Chiyoda-ku, Tokyo 102-0076, Japan.
authors.forename: Jiro
authors.initials: J
authors.lastname: Abe