THE MECHANISM OF SINGLET TO TRIPLET TRANSITIONS OF PENTACENE GUESTS IN PARA-TERPHENYL AND BENZOIC-ACID CRYSTALS

In this paper we examine the effect of the different site configurations on the S1 squiggly arrow pointing right T1 intersystem crossing (ISC) of pentacene in p-terphenyl (ptp) and benzoic acid (bza) crystals by measuring site-selectively the fluorescence quantum yield of pentacene as function of temperature in the range 4.2-140 K. The local structures of the four sites (O1, O2, O3, O4) for pentacene in ptp are simulated using the Buckingham (exp-6) potential. The present study provides a rationalization for the temperature dependent ISC rates of pentacene at O1 and O2 in ptp and pentacene in bza as well as for the enhanced, temperature independent ISC rates of pentacene at O3 and O4 in ptp.