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COMPARISON OF THE PATHWAYS AND QUANTUM YIELDS OF DIRECT PHOTOISOMERIZATION OF UNPROTONATED AND PROTONATED N‐BUTYLAMINE SCHIFF BASES OF ISOMERIC RETINYLIDENEACETALDEHYDE WITH THOSE OF SCHIFF BASES OF ISOMERIC RETINAL: RATIONALIZATION OF THE SELECTION OF THE RETINYLIDENE CHROMOPHORE BY RETINOCHROME
Author(s) -
Mukai Yumiko,
Imahori Takumi,
Koyama Yasushi
Publication year - 1992
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1992.tb09719.x
Subject(s) - photoisomerization , isomerization , chemistry , photostationary state , protonation , acetonitrile , photochemistry , organic chemistry , ion , catalysis
— The pathways and quantum yields of direct photoisomerization of unprotonated and pro‐tonated n‐butylamine Schiff bases (SB and PSB) of isomeric retinylideneacetaldehyde (C22 aldehyde) were determined in n‐hexane, acetonitrile and methanol for the former and in acetonitrile and methanol for the latter. The results are compared with those of the Schiff bases of isomeric retinal (C20 SB and C20 PSB) reported previously (Koyama et al., Photochem. Photobiol. 54 , 433–443, 1991). The isomerization pathways and quantum yields of C22 SB are more or less similar to those of C20 SB, but conspicuous differences in the isomerization pathways are found between C22 PSB and C20 PSB. The homogeneous (exclusive) isomerization of the retinylidene chromophore from all‐trum to 11‐cis in retinochrome is rationalized not by C22 PSB but by C20 PSB. Almost complete one‐way isomerization from cis to trans of C22 SB (in n‐hexane) is ascribed to isomerization via the T 1 state, while mutual isomeritation between cis and tram of C22 PSB is ascribed to isomerization via the S 1 (B u ) state. The T I potential of C22 SB and the S 1 potential of C22 PSB are discussed based on photostationary state compositions.