Radiation Laboratory and Chemistry Department of Notre Dame, Notre Dame, Indiana 46556, USA
Department of Physical Chemistry and the Fritz Haber Research Center for Molecular Dynamics1. The Hebrew University, Jerusalem 91904. Israel
Abstract:
A laser photolysis study of ZnTPP (P) oriented in nematic and isotropic cyanohexylbiphenyl (6CB) as a function of added 1.4-benzoquinone (Q) is reported. In the absence of Q, enhancement of triplet absorption below the clearing point (nematic phase) is observed. It is attributed to the improved alignment of the optical transition in the ordered matrix and also to the increase in the intersystem crossing efficiency. T?S1. In the presence of Q in the nematic phase. An additional increase in triplet absorption is noticed. This result is interpreted in terms of a triplet radical pair P+√…Q?√]T,RP formation which is facilitated by the ordering in the liquid crystal, thus providing an additional channel for triplet formation. The triplet PT in 6CB (nematic or isotropic) is quenched with a second-order rate of ≈108 M?1 s?1 as compared to 2 × 109 M?1 s?1 in toluene.