Photoinduced electron-transfer quenching of excited singlet states of polycyclic aromatic hydrocarbons by organic acceptors

Abstract

The electron-transfer quenching of the singlet excited state of polycyclic aromatic hydrocarbons (PAHs) by organic electron acceptors (cyano-and nitrobenzenes) has been investigated in acetonitrile and methanol. Intermolecular electron-transfer rate constants were determined. They follow a Rehm–Weller type correlation with the overall Gibbs energy of reaction. When the rate constants are below the diffusion control limit, in nearly all cases they are higher in methanol than in acetonitrile. The triplet state and free radical ions are formed in the quenching reaction. The charge-separation efficiency was also determined in both solvents. Using Eigen's equation for the cage-escape rate constants the global back electron transfer was estimated and correlated with the Gibbs energy change for the back-electron-transfer reaction, to the triplet state.