Spin–lattice relaxation and intersystem crossing in single molecules of terrylene embedded in a p-terphenyl crystal

Thermal evolution of fluorescence intensity correlation functions of single molecules of terrylene in a p-terphenyl crystal was studied and double-exponential decay at 5 K was found to change to a mono-exponential decay above 17.5 K. Such behavior was attributed to spin–lattice relaxation (SLR), which couples the long-lived zero-field triplet spin sublevel TZ with the short-lived and experimentally unresolved TX and TY sublevels. For two of the studied molecules, which were probably deformed from planar symmetry, we observed overpopulation of the spin sublevel TZ and activation of the SLR at temperatures above 20 K. The SLR rate constant exhibited Raman relaxation.