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) absorption spectrum of pentacene impurities in a para-terphenyl host crystal is used to investigate the pressure and/or temperature induced triclinic to monoclinic phase change of the para-terphenyl host crystal. Due 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.