Electron-Transfer Reduction Properties and Excited-State Dynamics of Benzo[ghi]peryleneimide and Coroneneimide Derivatives

A series of benzo[ ghi ]perylene and coronene derivatives substituted by electron-withdrawing imide and ester groups were systematically synthesized considering (i) number of imide and ester groups, (ii) five- and six-membered imide groups, and (iii) the peripheral positions. The spectroscopic, electrochemical, and photophysical properties of these molecules were investigated in full detail by steady-state and time-resolved spectroscopy, cyclic voltammetry, quantum yield measurements of fluorescence and intersystem crossing, electron spin resonance (ESR), and density functional theory calculations. The synthetic introduction of proper substituents on the polycyclic aromatic hydrocarbon ring therefore enables us to successfully control the electrochemical and photophysical behaviors. The steady-state absorption and fluorescence spectra also become red-shifted and broadened as compared to those of reference unsubstituted benzo[ ghi ]perylene and coronene. Regarding the electrochemistry, with an increase in the number of imide groups, the reduction potentials are significantly shifted to the positive direction, which indicates the large enhancement of electron-accepting properties. Then, absorption spectra of mono- and diradical anions of coronenetetraimide (Cor(Im) 4 ), which were generated by the electrochemical reduction, extended to the near-infrared region (up to ∼1000 nm). The ESR measurements of one-electron reduced species of Cor(Im) 4 demonstrate that more spin is relatively localized on the nitrogen atom in six-membered imide than that in five-membered imide. Finally, systematic comparison of quantum yields and rate constants of the excited-state dynamics also reveals that the intersystem crossing pathway was accelerated in both benzo[ ghi ]peryleneimide and coroneneimide derivatives, whereas the fluorescence property was dependent on the number of substituents and structural symmetry. This is in sharp contrast to the high quantum yield (ca. ∼1) of fluorescence of perylenediimides.