Temperature Dependence of Crystalline Tetracene Fluorescence

A 100-fold increase in the fluorescence emission of crystalline tetracene is observed on cooling from room temperature to 4°K. Phase transformations and lattice distortions are reflected in a drastic change of the emission spectra: the high-temperature modification has an emission that resembles closely tetracene dimer fluorescence while the low-temperature modification fluorescence is nearly a mirror image of the absorption spectrum. The changes in the quantum yields are interpreted on the basis of the Dexter–Fowler model which predicts a considerable difference in the rates of radiationless transitions from different vibronic states.