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POLARIZED UV‐ABSORPTION SPECTRA OF RETINAL ISOMERS—II. ON THE ASSIGNMENT OF THE LOW AND HIGH ENERGY ABSORPTION BANDS
Author(s) -
Drikos G.,
Rüppel H.
Publication year - 1984
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.1751-1097.1984.tb04559.x
Subject(s) - retinal , absorption band , excited state , spectral line , chemistry , absorption spectroscopy , transition dipole moment , polarization (electrochemistry) , absorption (acoustics) , crystal (programming language) , molecular electronic transition , molecular physics , atomic physics , optics , physics , molecule , biochemistry , organic chemistry , astronomy , computer science , programming language
The polarized UV‐absorption spectra of all‐ trans retinal and both crystal forms of 11‐ cis , 12‐s‐ cis retinal (presented in the previous paper, Part I) are analyzed using Lowry‐Hudson functions to describe the band profiles. The polarization ratios of the polarized bands is used to determine the direction of the corresponding transition moments. For all‐ trans retinal the polarization spectra show that the absorption between 23 and 36 X 10 3 cm −1 is caused by three overlapping bands labeled S, A and B. For 11‐ cis retinal the B‐band is also clearly resolved whereas the S and A bands are separated with much less certainty than for all‐ trans retinal. Comparing these bands with the excited state manifold resulting from semiempirical CI‐calculations including double excitations, the S‐band could be assigned to the 1 A g − → 1 A g ‐* and the A‐band to the 1 A g − → 1 B u +* transition. However, no transition is found in this manifold which could positively be assigned to the B‐band because the transitions predicted in this spectral region have negligible oscillator strengths. In all the crystal spectra a further band C is observed around 39 X 10 3 cm −1 which is particularly pronounced in the case of 11‐ cis retinal. For this band an assignment to the 1 A g − → 1 A g +*‐transition is proposed.