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Diastereoselective photocyclization reactions based on a 6π-system have been demonstrated with terarylene molecules having a P-stereogenic moiety. A chiral benzo[b]phosphole chalcogenide unit was introduced as a central bridging part in a terarylene to form a photochromic dithiazolylbenzo[b]phosphole chalcogenide. The stereoselective photoreaction of terarylenes was controlled by the conformational preference in the photoprecursor open-forms, which was dictated by the intramolecular interactions involving the chiral phosphorus atom and its substituents. Dithiazolylbenzo[b]phosphole oxide showed moderate photocyclization quantum yield and diastereoselectivity, which were significantly improved by replacing the oxygen atom with a sulfur atom showing photon-quantitative reactivity in toluene. The conformational preferences, which play an important role in the photocyclization quantum yield and diastereoselectivity, were thoroughly investigated by means of DFT calculations, X-ray crystallography, NMR measurements and circular dichroism spectra. [ABSTRACT FROM AUTHOR]

The high reactivity of 6π-electrocyclization in polar solvents has remained one of the important challenges for diarylethenes because of the emergence of a twisted intramolecular charge transfer (TICT) state at the excited state in such polar media, which usually quenches the photocyclization reaction. Herein we report on the preparation and highly efficient photocyclization of 2,3-diarylbenzo[ b]thiophenes with nonsymmetric side-aryl units in a polar solvent. While the dithiazolylbenzo[ b]thiophene showed a suppressed quantum yield of 6π-electrocyclization of 54 % in methanol, the replacement of a thiazole unit with a thiophene ring led to a photon-quantitative 6π-cyclization reaction. The nonsymmetrical modification into the side-aryl units was considered to enhance the CH/π interactions between side-aryl units to support a photoreactive conformation in methanol. The stabilization of the photochromic reactive conformation is expected to suppress the formation of the TICT state at the excited state, leading to highly efficient photoreactivity. [ABSTRACT FROM AUTHOR]

The high reactivity of 6π-electrocyclization in polar solvents has remained one of the important challenges for diarylethenes because of the emergence of a twisted intramolecular charge transfer (TICT) state at the excited state in such polar media, which usually quenches the photocyclization reaction. Herein we report on the preparation and highly efficient photocyclization of 2,3-diarylbenzo[b]thiophenes with nonsymmetric side-aryl units in a polar solvent. While the dithiazolylbenzo[b]thiophene showed a suppressed quantum yield of 6π-electrocyclization of 54 % in methanol, the replacement of a thiazole unit with a thiophene ring led to a photon-quantitative 6π-cyclization reaction. The nonsymmetrical modification into the side-aryl units was considered to enhance the CH/π interactions between side-aryl units to support a photoreactive conformation in methanol. The stabilization of the photochromic reactive conformation is expected to suppress the formation of the TICT state at the excited state, leading to highly efficient photoreactivity., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We herein propose a new type of efficient neutral photoacid generator. A photoinduced 6π-electrocyclization reaction of photochromic triangle terarylenes triggers subsequent release of a Brønsted acid, which took place from the photocyclized form. A H-atom and its conjugate base were introduced at both sides of a 6π-system to form the self-contained photoacid generator. UV irradiation to the 6π-system produces a cyclohexa-1,3-diene part with a H-atom and a conjugate base on the sp(3) C-atoms at 5- and 6-positions, respectively, which spontaneously release an acid molecule quantitatively forming a polyaromatic compound. A net quantum yield of photoacid generation as high as 0.52 under ambient conditions and a photoinitiated cationic polymerization of an epoxy monomer are demonstrated.