Photoinduced energy-electron transfer studies with naphthalene diimides

Seven derivatives of naphthalene diimides, synthesized, have shown similar photophysical properties. Low fluorescence quantum yields (0.002-0.006) and short fluorescence lifetimes (5-18 ps) have suggested rapid intersystem cr ossing processes from excited singlet state. Quenching of fluorescence emis sions of aromatic donor molecules, i.e. naphthalene, phenanthrene and pyren e, at rates reaching to diffusion Limits in acetonitrile (2-8 x 10(10) M-1 s(-1)), have proven the electron acceptor capacities of naphthalene diimide s. Photooxydation of styrene to benzaldehyde, in presence of naphthalene di imide (NDI) molecule, is found to occur at similar rates with respect to pe rylene diimides. Addition of ferric and cupric ions to NDI, have enhanced t he formation rate of benzaldehyde by about two-fold. Photooxidation of alph a-terpinene with naphthalene diimide, produced only p-cymene, no endoperoxi de adduct was identified. Naphthalene diimides appear to produce no singlet oxygen, and photooxidation probably occurs on radical chain reactions of s uper oxide anion radical. But the electron transfer electron via excited tr iplet or singlet state, remains to be unclear. (C) 2000 Elsevier Science S. A. All rights reserved.