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Excited-State Symmetry Breaking in a Quadrupolar Molecule Visualized in Time and Space
Bogdan Dereka1, Arnulf Rosspeintner1, Rafał Stężycki2
1Department of Physical Chemistry, University of Geneva , 30 Quai Ernest-Ansermet, CH-1211 Geneva 4, Switzerland.
Abstract:
The influence of the length of the push-pull branches of quadrupolar molecules on their excited-state symmetry breaking was investigated using ultrafast time-resolved IR spectroscopy. For this, the excited-state dynamics of an A-π-D-π-A molecule was compared with those of an ADA analogue, where the same electron donor (D) and acceptor (A) subunits are directly linked without a phenylethynyl π-spacer. The spatial distribution of the excitation was visualized in real time by monitoring C≡C and C≡N vibrational modes localized in the spacer and acceptor units, respectively. In nonpolar solvents, the excited state is quadrupolar and the excitation is localized on the π-D-π center. In medium polarity solvents, the excitation spreads over the entire molecule but is no longer symmetric. Finally, in the most polar solvents, the excitation localizes on a single D-π-A branch, contrary to the ADA analogue where symmetry breaking is only partial.
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