highlight 8 2018

Linear conjugated quadrupolar molecules containing electron donor (D) and acceptor (A) subunits exhibit unusual excited-state properties. Upon photoexcitation in polar environments, the initial centrosymmetric charge distribution localizes on one of the branches due to solvation, a phenomenon known as excited-state Symmetry Breaking (SB). These dynamics can be observed directly using Time-resolved Infrared spectroscopy (TRIR) where vibrations localized on both branches are monitored over time after electronic excitation of the molecule. The above figure depicts TRIR spectra of a highly conjugated quadrupolar D-A-A-D molecule in weakly and strongly polar solvents. In toluene, two bands, α and β, are visible. They originate from to the outermost and the central carbon triple bonds, respectively. In DMF, symmetry is broken and α rapidly transforms into a new band, γ, which corresponds to the SB state where the electronic excitation is concentrated on one of the branches. These results show that conjugation length increases the effect of SB and reinforces the notion that TRIR constitutes the best tool to investigate these dynamics.

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Eric Vauthey

Physical Chemistry Department - Sciences II - University of Geneva
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