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Symmetry‐Breaking Charge Transfer and Hydrogen Bonding: Toward Asymmetrical Photochemistry
Author(s) -
Dereka Bogdan,
Rosspeintner Arnulf,
Krzeszewski Maciej,
Gryko Daniel T.,
Vauthey Eric
Publication year - 2016
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201608567
Subject(s) - photoexcitation , symmetry breaking , chemistry , photochemistry , excited state , charge (physics) , hydrogen bond , molecule , polarity (international relations) , infrared , spectroscopy , infrared spectroscopy , chemical physics , polar , atomic physics , physics , organic chemistry , biochemistry , quantum mechanics , cell , astronomy , optics
Symmetry‐breaking charge transfer upon photoexcitation of a linear A‐π‐D‐π‐A molecule (D and A being electron donating and accepting groups) could be visualized using ultrafast time‐resolved infrared spectroscopy by monitoring the CN stretching modes on the A units. Whereas in apolar solvents, the S 1 state remains symmetric and quadrupolar, symmetry breaking occurs within ca. 100 fs in polar solvents as shown by the presence of two CN bands, instead of one in apolar solvents, with a splitting that increases with polarity. In protic solvents, symmetry breaking is significantly amplified by H‐bonding interactions, which are the strongest at the CN group with the highest basicity. In strongly protic solvents, the two CN bands transform in about 20 ps into new bands with a larger splitting, and the lifetime of the S 1 state is substantially reduced. This is attributed to the formation of an excited asymmetric tight H‐bond complex.

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