PRESSURE-INDUCED PHASE-TRANSITIONS IN PENTACENE DOPED PARA-TERPHENYL PROBED BY CHANGES IN THE IMPURITY ABSORPTION-SPECTRUM

The pressure dependence (0-10 kbar) of the low temperature (15 K) abso rption spectrum of pentacene impurities in a para-terphenyl host cryst al is used to investigate the pressure and/or temperature induced tric linic to monoclinic phase change of the para-terphenyl host crystal. D ue to the characteristic absorption spectrum of pentacene in these two crystal phases, the pentacene impurity proves to be a sensitive probe of the structure of the surrounding para-terphenyl matrix.