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Krohn, O.A.* ; Quick, M.* ; Ioffe, I.N.* ; Mazaleva, O.N.* ; Lenoir, D. ; Detert, H.* ; Kovalenko, S.A.*

Time-resolved photochemistry of stiffened stilbenes.

J. Phys. Chem. B 123, 4291-4300 (2019)
DOI PMC
Open Access Green as soon as Postprint is submitted to ZB.
Broadband transient absorption spectroscopy is used to study the photoisomerization of stiffened stilbenes in solution, specifically E/Z mixtures of bis(benzocyclobutylidene) (t4, c4) and (E)-1-(2,2-dimethyltetralinylidene)-2-2-dimethyltetraline (t6). Upon excitation to S 1 , all evolve to perpendicular molecular conformation P, followed by decay to S 0 , while the spectra and the kinetic behavior crucially depend on the size of the stiffening ring. In 4, contrary to all previously studied stilbenes, the trans and cis absorption and excited-state spectra are nearly indistinguishable, while the corresponding isomerization times are comparable: τ i = 166 ps for t4 and τ i = 64 ps for c4 in n-hexane, as opposed to 114 and 45 ps in acetonitrile, respectively. Faster isomerization in polar solvents agrees with the zwitterionic character of the P state. In t6, torsion to P is effectively barrier-less and completes within 0.3 ps, the S 1 → P evolution being directly traceable through the transient spectra of stimulated emission and that of excited-state absorption. In n-hexane, the P state is remarkably long-lived, τ P = 1840 ps, but the lifetime drops down to 35 ps in acetonitrile. The trans-to-cis photoisomerization yield for t6 is measured to be 20%, while for t4, it remains uncertain. We discuss the effects of stiffening and substitution on the formation and lifetime of the intermediate states through which the stilbene molecules evolve on the S 1 energy surface.
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Publication type Article: Journal article
Document type Scientific Article
Corresponding Author
ISSN (print) / ISBN 1520-6106
e-ISSN 1520-5207
Journal Journal of Physical Chemistry B
Quellenangaben Volume: 123, Issue: 19, Pages: 4291-4300 Article Number: , Supplement: ,
Publisher American Chemical Society (ACS)
Non-patent literature Publications
Reviewing status Peer reviewed
Institute(s) PPM-MEX-Molecular EXposomics (MEX)