Inter- and Intramolecular Electron-Transfer Reduction Properties of Coronenediimide Derivatives via Photoinduced Processes

Coronenediimide derivatives with five- or six-membered maleimide groups [denoted as Cor(5Im)₂ and Cor(6Im)₂] were employed as electron acceptors to examine the electron-transfer reduction properties through photochemical and electrochemical measurements. In steady-state absorption and fluorescence measurements, the spectra of Cor(5Im)₂ and Cor(6Im)₂ became remarkably broadened and red-shifted as compared to pristine coronene (Cor). These results are supported by electrochemical measurements and DFT calculations. The rate constants of photoinduced intermolecular electron transfer from various donor molecules to ³Cor(5Im)₂∗ or ³Cor(6Im)₂∗ are determined by nanosecond transient absorption measurements. Although the back-electron-transfer reactions examined in this study proceed with the diffusion-limited rate constant in benzonitrile (PhCN), the rate constants of forward electron-transfer reactions (k_et) increase with an increase in the driving force of electron transfer (-ΔG_et) to approach the diffusion-limited rate constant. When the driving force dependence of k_et was fit on the basis of the Marcus theory of electron transfer, the reorganization energy (λ) of the electron-transfer reduction of Cor(5Im)₂ and Cor(6Im)₂ are determined to be 0.77 and 1.15 eV, respectively. A new covalently perylene-linked donor-acceptor dyad was also synthesized to investigate the dynamics of ultrafast photoinduced intramolecular electron transfer.