Photophysical properties of the non-alternant polycyclic aromatic hydrocarbons periflanthene and 1,16-benzoperiflanthene in solution

Abstract

Photophysical properties of periflanthene (PF) and 1,16-benzoperiflanthene (BPF) were studied in solution. Particular emphasis was placed on temperature and solvent effects on the fluorescence of PF and on the triplet state properties of both molecules. PF is only weakly fluorescent (Φ F = 0.015) and deactivation from the S 1 state occurs almost exclusively by internal conversion (IC) (Φ IC = 0.98), whereas BPF with Φ F = 0.52 exhibits rather strong fluorescence (the quantum yields are given for benzene solutions at room temperature). From the spectral shapes of the fluorescence emissions of PF and BPF and from the effects of temperature and solvent changes on the PF fluorescence, it can be inferred that considerable mixing of two close-lying, lowest singlet excited states profoundly affects the photophysics of the two molecules. The involvement of two excited states in the fluorescence is most pronounced in PF for which a schematic energy level diagram is proposed.