Bimolecular Ionization of the Triplet State of Aromatic Hydrocarbons in Solution

Abstract

The production of free ionic carriers due to bimolecular triplet encounters of anthracene, naphthalene, phenanthrene, and pyrene in solvents methyltetrahydrofuran (MTHF), tetrahydrofuran (THF), benzonitrile (C₆H₅CN), and acetonitrile (CH₃CN), whose dielectric constants fell between 6.2 and 36.7, was verified. The probability of producing free carriers per triplet–triplet collision from phenanthrene was found to be 1.9 × 10⁻⁴, 1.9 × 10⁻³, and 0.41 in MTHF, THF, and CH₃CN, respectively. The probability of free carrier production in fluid THF was found to be 1.4 × 10⁻², 1.3 × 10⁻², and less than 10⁻⁴, respectively, for triplets of anthracene, pyrene, the tetracene. The significance of escape of carriers from a Coulomb well was delineated and shown to be of maximal concern for media whose dielectric constant was less than 15. Similarly, carrier escape was shown to be primarily responsible for the lack of observed photocurrents from these aromatic hydrocarbons in n‐hexane and cyclohexane.