Solvent tuning of photochemistry upon excited-state symmetry breaking

Bogdan Dereka, Denis Svechkarev, Arnulf Rosspeintner, Alexander Aster, Markus Lunzer, Robert Liska, Aaron M. Mohs and Eric Vauthey ()
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Bogdan Dereka: University of Geneva
Denis Svechkarev: University of Nebraska Medical Center
Arnulf Rosspeintner: University of Geneva
Alexander Aster: University of Geneva
Markus Lunzer: Institute of Applied Synthetic Chemistry, TU Wien
Robert Liska: Institute of Applied Synthetic Chemistry, TU Wien
Aaron M. Mohs: University of Nebraska Medical Center
Eric Vauthey: University of Geneva

Nature Communications, 2020, vol. 11, issue 1, 1-11

Abstract: Abstract The nature of the electronic excited state of many symmetric multibranched donor–acceptor molecules varies from delocalized/multipolar to localized/dipolar depending on the environment. Solvent-driven localization breaks the symmetry and traps the exciton in one branch. Using a combination of ultrafast spectroscopies, we investigate how such excited-state symmetry breaking affects the photochemical reactivity of quadrupolar and octupolar A–(π-D)2,3 molecules with photoisomerizable A–π–D branches. Excited-state symmetry breaking is identified by monitoring several spectroscopic signatures of the multipolar delocalized exciton, including the S2 ← S1 electronic transition, whose energy reflects interbranch coupling. It occurs in all but nonpolar solvents. In polar media, it is rapidly followed by an alkyne–allene isomerization of the excited branch. In nonpolar solvents, slow and reversible isomerization corresponding to chemically-driven symmetry breaking, is observed. These findings reveal that the photoreactivity of large conjugated molecules can be tuned by controlling the localization of the excitation.

Date: 2020
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DOI: 10.1038/s41467-020-15681-3

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