Dynamics of charge-transfer state formation in supercritical fluid solvent

The rate of the intramolecular charge-transfer state formation has been determined for 4-(N, N-dimethylamino)-benzonitrile (DMABN) in supercritical CF₃H by means of a time-correlated single-photon counting technique. The rate constant increases rapidly with increasing CF₃H density, indicating the importance of the polar environment offered by the CF₃H molecules which are clustering around a DMABN molecule. With increasing clustering number, the activation barrier is lowered and hence the rate increases exponentially. The observation is semiquantitatively interpreted on the basis of a molecular dynamics simulation of clustering in supercritical solutions.