Transient Glass Formation around a Quadrupolar Photoexcited Dye in a Strongly H‐Bonding Liquid Observed by Transient 2D‐IR Spectroscopy. Issue 52 (26th November 2018) - Dereka, Bogdan
Abstract: Intermolecular H‐bonding dynamics around a photoexcited quadrupolar dye is directly observed using transient 2D‐IR spectroscopy. Upon solvent‐induced symmetry breaking, the H‐bond accepting abilities of the two nitrile end‐groups change drastically, and in extremely protic (superprotic) solvents, a tight H‐bond complex forms at one end. The time evolution of the 2D C≡N lineshape in methanol points to rapid, 2–3 ps, spectral diffusion due to fluctuations of the H‐bonding network. Similar behavior is observed in a superprotic solvent shortly after photoexcitation of the dye. However, at later times, the completely inhomogeneous band does not exhibit spectral diffusion for at least 5 ps, pointing to a glass‐like environment around one side of the dye. About half of the excited dyes show this behavior attributed to the tight H‐bond complex, whereas the others are loosely bound. A weak cross peak indicates partial exchange between these excited state subpopulations. Abstract : Frozen but not for long : A few picoseconds after its excitation, a quadrupolar dye forms a tight and asymmetric hydrogen‐bond complex with the solvent. Transient 2D‐IR spectroscopy reveals that this results in a dramatic slowing down of the solvent dynamics on one side of the dye. The surrounding solvent exhibits a glass‐like behavior.