highlight 5 2021

Laporte rule applies to centrosymmetric molecules and states that one-photon transitions, which conserve the parity of the wavefunction (g↔︎g, u↔︎u), are forbidden. We demonstrated in a recent publication (J. Phys. Chem. Lett., 2021, 12, 4067−4071) that this rule can be used to monitor excited-state symmetry breaking (ES-SB). 

The above figure shows the result of a global analysis of the electronic transient absorption spectra measured with a centrosymmetric dicyanoanthracene derivative in a non-polar (left) and a polar (right) solvent. In the near IR region of the transient spectra, which is free from complications due to overlapping ground-state bleach and stimulated emission, we observe the rise of initially Laporte-forbidden Sn←S1 transitions upon ES-SB in polar solvents. 

This novel approach for following ES-SB is more general than that based on TRIR spectroscopy as it does not require the presence of well-localized vibrational marker modes in the molecule. It is also more direct than the measurement of the instantaneous emission transition dipole moment, which required sufficiently long-lived excited states.

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Eric Vauthey

Physical Chemistry Department - Sciences II - University of Geneva
30, Quai Ernest Ansermet - CH-1211 Geneva 4 (Switzerland)

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