PHOTOPHYSICAL PROPERTIES OF TETRACENE DERIVATIVES IN SOLUTION .3. THERMALLY ACTIVATED NONRADIATIVE PROCESSES AND TRIPLET-STATE PROPERTIES

Photophysical properties of several tetracene derivatives were studied in solution and in sucrose octa-acetate (SOA) glass. The photophysica l properties of rubrene (5,6,11,12-tetraphenyltetracene) in SOA glass are not significantly different from those in common solvents employed in our earlier studies. Deviating results by Song and Fayer are shown to be due to the neglect of (S1-S(n)) excited state absorption (ESA) and internal conversion (IC). It is demonstrated that the investigatio n of two temperature-dependent photophysical properties and, in partic ular, the direct detection of triplet state molecules allows the accur ate determination of the experimental activation energy E(a) (ISC) for thermally activated (S1-T2) intersystem crossing (ISC). For rurbrene in SOA glass E(a)(ISC) = 860 cm-1 was obtained. A consistent treatment of the photophysical processes is presented that allows the descripti on of the temperature-dependent non-radiative processes and of the inf luences of solvent and internal heavy atom (HAE) effects for the molec ules investigated.