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LASER PHOTOLYSIS OF RETINAL AND ITS PROTONATED AND UNPROTONATED n‐BUTYLAMINE SCHIFF BASE
Author(s) -
Fisher Michael M.,
Weiss Karl
Publication year - 1974
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.1751-1097.1974.tb06597.x
Subject(s) - chemistry , methylcyclohexane , photochemistry , flash photolysis , triplet state , intersystem crossing , anthracene , isomerization , protonation , singlet state , excited state , toluene , organic chemistry , reaction rate constant , kinetics , molecule , ion , physics , quantum mechanics , nuclear physics , catalysis
—The pulsed ruby laser (347 nm) flash photolysis technique has been used to measure the triplet‐triplet absorption spectra and triplet lifetimes of trans ‐retinal, N‐frans ‐retinylidene‐ n ‐butylamine (NRBA), and protonated NRBA (NRBAH + ) at room temperature. In methylcyclohexane solution, the triplet lifetimes are in the range 10–20 μs and decrease in the order NRBAH + > NRBA > trans ‐retinal. Intersy stem‐crossing efficiencies (φ ISC ) were determined by a comparison technique using anthracene and 1,2‐benzanthracene as reference compounds. For trans ‐retinal, φ ISC is 0–50 pM 0–05 in methylcyclohexane and 0–08 in methanol, which confirms that earlier values of 0–11 and 0–017 in these solvents are in error. For NRBA and NRBAH + in methylcyclohexane, Φ ISC values are 0008 and < 0–001, respectively. Evidence is presented for a significant solvent effect in the isomerization of retinal via the triplet state, and that cis φ trans isomerization occurs from the triplet state of NRBAH + . The relation between the intersystem‐crossing properties of model compounds and the photochemistry of rhodopsin is discussed.