名称:
Structures of transient species in the photochromic reaction of 1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indoline]: Time-resolved resonance Raman study of isotopically substituted analogues
摘要:
Time-resolved resonance Raman spectra of seven kinds of isotopically substituted analogues of 1,'3',3'-trimethylspiro[2H-1-benzopyran-2,2'-indoline] in the photomerocyanine form have disclosed that only the vibrations of the cleaved benzopyran part are resonance enhanced significantly in cyclohexane and in acetonitrile solutions with 460-390 nm probe light. Dramatic changes in the resonance Raman spectra of the photomerocyanine on going from non-hydrogen-bond donor solvents to hydrogen-bond donor solvents can be interpreted as being due to changes in the relative contribution of ortho-quinoidal and zwitterionic forms in the resonance hybrid structure of the photomerocyanine: in cyclohexane and in acetonitrile the contribution of the ortho-quinoidal form is substantial, while in methanol the zwitterionic form is stabilized by hydrogen bonding with the solvent and the photomerocyanine takes an almost zwitterionic structure.
DOI:
10.1016/0584-8539(94)e0059-j