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Issue 5, 2008
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Triplet and ground state potential energy surfaces of 1,4-diphenyl-1,3-butadiene: theory and experiment

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Abstract

Relative energies of the ground state isomers of 1,4-diphenyl-1,3-butadiene (DPB) are determined from the temperature dependence of equilibrium isomer compositions obtained with the use of diphenyl diselenide as catalyst. Temperature and concentration effects on photostationary states and isomerization quantum yields with biacetyl or fluorenone as triplet sensitizers with or without the presence of O2, lead to significant modification of the proposed DPB triplet potential energy surface. Quantum yields for ct-DPB formation from tt-DPB increase with [tt-DPB] revealing a quantum chain process in the ttct direction, as had been observed for the cttt direction, and suggesting an energy minimum at the 3ct* geometry. They confirm the presence of planar and twisted isomeric triplets in equilibrium (K), with energy transfer from planar or quasi-planar geometries (quantum chain events from tt and ct triplets) and unimolecular decay (kd) from twisted geometries. Starting from cc-DPB, ϕcctt increases with increasing [cc-DPB] whereas ϕccct is relatively insensitive to concentration changes. The concentration and temperature dependencies of the decay rate constants of DPB triplets in cyclohexane are consistent with the mechanism deduced from the photoisomerization quantum yields. The experimental ΔH between 3tt-DPB* and 3tp-DPB*, 2.7 kcal mol−1, is compared with the calculated energy difference [DFT with B3LYP/6-31+G(d,p) basis set]. Use of the calculated ΔS = 4.04 eu between the two triplets gives kd = (2.4–6.4) × 107 s−1, close to 1.70 × 107 s−1, the value for twisted stilbene triplet decay. Experimental and calculated relative energies of DPB isomers on the ground and triplet state surfaces agree and theory is relied upon to deduce structural characteristics of the equilibrated conformers in the DPB triplet state.

Graphical abstract: Triplet and ground state potential energy surfaces of 1,4-diphenyl-1,3-butadiene: theory and experiment

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Publication details

The article was received on 22 Jan 2008, accepted on 06 Mar 2008 and first published on 03 Apr 2008


Article type: Paper
DOI: 10.1039/B801075G
Citation: Photochem. Photobiol. Sci., 2008,7, 566-577

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    Triplet and ground state potential energy surfaces of 1,4-diphenyl-1,3-butadiene: theory and experiment

    J. Saltiel, O. Dmitrenko, Z. S. Pillai, R. Klima, S. Wang, T. Wharton, Z.-N. Huang, L. J. van de Burgt and J. Arranz, Photochem. Photobiol. Sci., 2008, 7, 566
    DOI: 10.1039/B801075G

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