Temperature Dependence of Intersystem Crossing in Crystalline Anthracene

Blue-light-excited delayed fluorescence is used to study the temperature dependence of monomolecular intersystem crossing in crystalline anthracene. The associated rate constant k is found to obey an equation of the form k = k1 + k2exp(− E / kT), where E = 900 ± 100 cm−1 and k2 / k1 = 800 ± 200. A calculation of the relevant Franck–Condon factors using the method developed by Siebrand gives good agreement with experiment. At temperatures less than 90°K, the delayed fluorescence appears to be dominated by trapping effects similar to those reported in red-light-excited measurements.