Thermal energy assisted heavy atom effect: fluorescence quenching of 9-cyanoanthracene in the supercritical fluid of Xe

The fluorescence lifetime, τf, of 9-cyanoanthracene (9CNA) in the supercritical fluid (SF) of Xe (6.8 MPa at 293 K) is found to be 2.39 ± 0.13 ns, which is much shorter than the 17.78 ± 0.43 ns measured in SF of CO2. This large decrease in τf is interpreted in terms of the vibronic-level-dependent heavy atom effect which is revealed by a comparison of the absorption and fluorescence excitation spectra measured for the 1:1 van der Waals complex of 9CNA with Xe generated in a supersonic jet. The effect of the temperature on τf observed in Xe is concordant with the vibronic-level-dependent heavy atom effect.