Luminescence and absorption spectra under hydrostatic pressures in the range 0-50 kbar have been studied. The instability of free excitons occurs in tetracene, anthracene and phenanthrene crystals, while the instability of self-trapped excitons occurs in α-perylene and pyrene crystals. Experimental results lead to a conclusion that the exciton-phonon coupling constants in those materials are well expressed as a function of the intermolecular distance between nearest-neighbor, plane-parallel molecules.
"Pressure-Induced Exciton Instability In Organic Solids Probed By Fluorescence", Proc. SPIE 1054, Fluorescence Detection III, (17 May 1989); doi: 10.1117/12.951563; https://doi.org/10.1117/12.951563