title: Symmetry-Breaking Charge Transfer and Hydrogen Bonding: Toward Asymmetrical Photochemistry.
abstract: 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 S1state 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 S1state is substantially reduced. This is attributed to the formation of an excited asymmetric tight H-bond complex.
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30, Quai Ernest-Ansermet, 1211, Geneva 4, Switzerland.
authors.forename: Bogdan
authors.identifier: 0000-0003-2895-7915
authors.initials: B
authors.lastname: Dereka
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30, Quai Ernest-Ansermet, 1211, Geneva 4, Switzerland.
authors.forename: Arnulf
authors.identifier: 0000-0002-1828-5206
authors.initials: A
authors.lastname: Rosspeintner
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224, Warsaw, Poland.
authors.forename: Maciej
authors.initials: M
authors.lastname: Krzeszewski
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224, Warsaw, Poland.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Gryko
authors.affiliation: Department of Physical Chemistry, University of Geneva, 30, Quai Ernest-Ansermet, 1211, Geneva 4, Switzerland.
authors.forename: Eric
authors.identifier: 0000-0002-9580-9683
authors.initials: E
authors.lastname: Vauthey
keywords: charge transfer; photochemistry; quadrupolar molecules; solvation; ultrafast vibrational spectroscopy