Determination of the barrier to intramolecular exciplex formation in a jet-cooled, bichromophoric molecule |
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Authors: | B. Wegewijs R. M. Hermant J. W. Verhoeven A. G. M. Kunst R. P. H. Rettschnick |
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Affiliation: | The laboratory of Organic Chemistry and the Laboratory of Physical Chemistry, University of Amsterdam, Nieuwe Achtergracht 129 and 127, 1018 WS Amsterdam, The Netherlands |
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Abstract: | The emissive properties of a bichromophor molecule (1) are reported. This contains an anilino group as an electron donor (D) and a 1-cyanonaphthalene group as an electron acceptor (A) interconnected by a saturated hydrocarbon bridge of limited flexibility, which holds D and A far apart in the electronic ground state. The emission spectrum of 1, both in solution and in the gas phase, indicates that quantitative formation of an intramolecular exciplex between D and A occurs. This exciplex formation was studied as a function of excitation energy in molecules of 1 isolated in a supersonic free jet. A barrier of 1700 ± 200 cm−1 was found between the Franck-Condon excited conformation and the conformation of the exciplex. Although this value is significantly higher than that reported earlier for exciplex formation between chromophores connected by a simple polymethylene chain (≈ 900 cm−1) it is much lower than the barrier predicted for folding the bridge in 1 sufficiently to bring D and A in close contact. A tentative explanation of this discrepancy is given. |
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