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.