The spectroscopy and photochemistry of the excimer-emitting 9-cyanoanthracene crystal; The importance of multiphonon processes

A study of the spectroscopy and photochemistry of crystalline 9-cyanoanthracene is reported. This crystal gives rise to excimer emission; at 77 K the excimer has a lifetime of 160 ±5 ns and the emission spectrum is of gaussian shape. There is, prior to reaction, transfer of excitation energy by a process occurring at the excimer—exciton level and involving an activation energy of about 420 ^cm?1. Radiationless deactivation of the excimer involves an activation energy of 660 cm^?1. These experimental observations are in good agreement with the predictions of theories based on the model of strong exciton—phonon coupling. The photoreaction occurs at specific sites which are believed to be head-to-tail defects.