• Toshihiro Nakayama

      Articles written in Journal of Chemical Sciences

    • Excited state dynamics of anthraquinones and electron transfer from ground-state triethylamine to the second and/or lowest excited triplet states of anthraquinones

      Kumao Hamanoue Toshihiro Nakayama

      More Details Abstract Fulltext PDF

      Picosecond laser photolysis of 1,8-dibromoanthraquinone (1,8-DBAQ) and 1,8-dichloroanthraquinone (1,8-DCAQ) in solutions at room temperature has revealed the existence of the second excitednπ* triplet [T2(nπ*)] states with a localized charge-transfer character between the halogen and oxygen atoms. The internal conversion (IC) times from theT2(nπ*) states to the lowest excited ππ* triplet [T1(nπ*)] states are 70–110ps for 1,8-DBAQ and 700–750ps for 1,8-DCAQ. In toluene and ethanol, an electron transfer from ground-state triethylamine (TEA) to triplet XAQ (anthraquinone and halogenoanthraquinones) forming the exciplexes [3(XAQ-TEA)*] has been found to occur via theT1 states of XAQ; these3(XAQ-TEA)* change to the contact ion pairs between the XAQ radical anions (XAQ) and the TEA radical cation. Neither free XAQ nor3(XAQ-TEA)* are produced via theT2 states of XAQ in toluene and ethanol. In acetonitrile, however, free XAQ and3(XAQ-TEA)* or the ion pairs (or the contact ion pairs) are produced via theT2 andT1 states of XAQ, respectively.

    • Amine-assisted photochemical dehalogenation of haloanthracenes (9-halo and 9,10-dihalo compounds) and their triplet formation

      Toshihiro Nakayama Kazuyasu Ibuki Kumao Hamanoue

      More Details Abstract Fulltext PDF

      Steady-state photolysis of haloanthracenes (XA; 9,10-dichloro, 9,10-dibromo, 9-chloro and 9-bromo compounds) in acetonitrile-amine (triethylamine or N,N-dimethylaniline) causes the consecutive reactions; 9,10-dihalo compounds→9-halo compounds→ anthracene. Although both the lowest excited singlet [1XA(S1)] and triplet [3XA(T1)] states of XA are quenched by amine, the appearance of absorption spectra due to the haloanthracene radical anions (XA-) within the duration of nanosecond pulse excitation indicates that the intermediates for dehalogenation of XA are XA- produced by a diffusion-controlled reaction of1XA(S1) with the ground-state amine yielding the singlet exciplexes [1(XA-amine)*] which decompose rapidly into XA- and the amine radical cations. Moreover, an amine-assisted formation of3XA(T1) has been attributed to the intersystem crossing from1(XA-amine)* to the triplet exciplexes [3(XA-amine)*] followed by decomposition into3XA(T1) and ground-state amine.

    • Photochemical reaction of [6]-l, 4-cyclophaneanthraquinone

      Sadao Miki F M Abdel-Latif Toshihiro Nakayama Kumao Hamanoue

      More Details Abstract Fulltext PDF

      [6]-1,4-Cyclophaneanthraquinone (CHAQ) has been synthesized and its photochemical reaction is studied. Nanosecond laser photolysis of CHAQ in EPA at room temperature reveals that both the lowest excited singlet and triplet states of CHAQ cause the intramolecular hydrogen-atom abstraction yielding the 1,4-biradical, i.e., the hydrogenatom abstraction by the carbonyl oxygen from the benzylic methylene of the cyclophane bridge. Since steady-state photolysis of CHAQ in EPA at 77 K reveals the formation of cyclophane-9-hydroxy-1,10-anthraquinone-1-methide (2), the results obtained by steadystate photolysis at room temperature are interpreted as follows: (1) In benzene,2 changes to a naphthoquinone derivative (6). (2) In EPA,2 yields its ethanol adduct (3) and there exists an equilibrium between3 (major) and6 (minor). (3) By a dark reaction,3 and/or6 revert very slowly to CHAQ.

  • Journal of Chemical Sciences | News

© 2021-2022 Indian Academy of Sciences, Bengaluru.