Intramolecular charge-transfer reactions studied in a supercritical fluid of varying densities and in a molecular beam

Abstract

In a supercritical fluid solvent, the solvent molecules are found to gather around the solute molecule, even in a low density state. By using a simple model based on the solute–solvent interaction potential, the solvation number has been derived as a function of the fluid density. The correctness of the model has been examined by a comparison between the solvent spectral shifts measured in supercritical CF3H and those observed for van der Waals molecules in a supersonic beam. The formation of the charge-transfer (CT) state of N,N-dimethylaminobenzonitrile was then studied in supercritical CF3H. The increase in the intensity of the CT. emission, as well as the bathochromic shift of the emission maximum, with increasing fluid density suggests that the clustering of CF3H molecules strongly stabilizes the highly polar CT state. Thus solvation by polar molecules is shown to be an essential factor in facilitating CT state formation. However, on a microscopic level the location of the solvent molecules around the solute is also a crucial factor. This fact was demonstrated by the measurements of the emission spectra of various 9,9-bianthryl–acetone van der Waals complexes in a supersonic free jet.