Radiative lifetime and electronic relaxation of 9-cyanoanthracene in rare-gas clusters and in rare-gas matrices

Abstract

Laser-induced fluorescence (LIF) excitation spectra and fluorescence lifetimes were measured for rare-gas (Ar, Kr and Xe) clusters of 9-cyanoanthracene (9CNA) generated in supersonic free jets and for 9CNA isolated in rare-gas matrices at 15 K. The natural radiative lifetime, τr, of the 9CNA clusters was not influenced greatly by complexation with rare-gas atoms of any kind. The values obtained for the most highly coordinated clusters were 26.5±0.3, 28.2±0.6 and 28.4±0.3 ns for Ar, Kr and Xe, respectively. These values are approximately equal to the value for τr at the electronic band origin of the bare 9CNA molecule, but are almost two times larger than the radiative lifetimes of 9CNA found in the rare-gas matrices at 15 K, in which the radiative lifetimes measured are correlated satisfactorily through the square of the refractive index. Nevertheless, the relaxation process from higher vibronic levels as well as the spectral band positions of these clusters are similar to those found in the rare-gas matrices.