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Substituent-controlled photoisomerization in retinal chromophore models: Fluorinated and methoxy-substituted protonated Schiff bases ☆

Paper ID Volume ID Publish Year Pages File Format Full-Text
28091 44059 2007 16 PDF Available
Title
Substituent-controlled photoisomerization in retinal chromophore models: Fluorinated and methoxy-substituted protonated Schiff bases ☆
Abstract

The effect of substitution on the intrinsic (i.e. in vacuo) photoisomerization ability of retinal chromophore models has been explored using CASPT2//CASSCF minimum energy path computations to map the S1 photoisomerization paths of two substituted minimal models of the retinal chromophore: the 2-cis-penta-2,4-dieniminium and the all-trans-epta-2,4,6-trieniminium cations, which have been modified using fluorine or methoxyl substituents as representative examples of electron-withdrawing and electron-releasing groups, respectively. A systematic analysis has been performed involving substitutions in all the possible positions along the chain. It is shown that the photochemical reactivity and photoisomerization efficiency of these systems may be tuned or indeed changed, although this effect strongly depends on the position of the substituent. In particular, we have shown that (i) most of the systems preserves qualitatively the reactivity of the parent (i.e. unsubstituted) compound; (ii) substitution at positions C4 or C6 leads to a different relaxed excited state structure of the chromophore and in general to a very flat photoisomerization path (or to a tiny S1 energy barrier in some cases); (iii) the nature of the TICT state (i.e. the S1 → S0 decay funnel) may be turned from a conical intersection into an excited state minimum; (iv) for the C4 methoxy-substituted system the isomerization path as well as the S1/S0 decay funnel involve an unusual torsional angle. Thus, substitution turns out to be a good tool not only to tune the optical properties (i.e. the absorption and emission features) of the chromophore (as we have already shown in a previous work: I. Conti, F. Bernardi, G. Orlandi, M. Garavelli, Mol. Phys. 104 (2006) 915–924), but it may also play a crucial role in tuning and controlling photoisomerization selectivity and efficiency, affecting excited state lifetime and reaction rate. A rationale for these effects is presented, which provides a basis for understanding reactivity properties and the intrinsic photochemical behavior of substituted retinal chromophores.

Keywords
MEP, minumum energy path; PES, potential energy surface; CI, conical intersection; PSB, protonated Schiff base; PSB11, 11-cis Retinal protonated Schiff base; PSBT, all-trans Retinal protonated Schiff base; OBF, one-bond-flip; IRD, initial-relaxation-direc
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Substituent-controlled photoisomerization in retinal chromophore models: Fluorinated and methoxy-substituted protonated Schiff bases ☆
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 190, Issues 2–3, 15 August 2007, Pages 258–273
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
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Any Questions? feel free to contact us