Electron Push–Pull Effects on Intramolecular Charge Transfer in Perylene-Based Donor–Acceptor Compounds

Abstract

A series of asymmetric donor-acceptor (D-A) perylene-based compounds, 3-(<i>N</i>,<i>N</i>-bis(4'-(R)-phenyl)amino)perylene (<b>Peri</b>-<b>DPA</b>(<b>R</b>)), were successfully prepared to explore their intramolecular charge transfer (ICT) properties. To induce ICT between the donor and acceptor, diphenylamine (DPA) derivatives (electron donor units) with the same functional groups (<b>R</b> = CN, F, H, Me, or OMe) at both para positions were linked to the C-3 position of perylene to produce five <b>Peri</b>-<b>DPA</b> derivatives. A steady-state spectroscopy study on <b>Peri</b>-<b>DPA</b>(<b>R</b>)s exhibited a progressively regulated ICT trend consistent with the substituent effect as it progressed from the electron-withdrawing group to the electron-donating group. In particular, a comparative study using a D-A-D (donor-acceptor-donor) system demonstrated that not only the electron push-pull substituent effect but also subunit combinations influence photophysical and electrochemical properties. The different ICT characters observed in Lippert-Mataga plots of <b>D</b>-<b>A</b>(<b>CN</b>) and <b>D</b>-<b>A</b>-<b>D</b>(<b>CN</b>) (CN-substituted <b>D</b>-<b>A</b> and <b>D</b>-<b>A</b>-<b>D</b>) led to the investigation on whether ICT emission of two systems with differences in subunit combinations is of the same type or of a different type. The femtosecond transient absorption (fs-TA) spectroscopic results provided direct evidence of ICT origin and confirmed that <b>D</b>-<b>A</b>(<b>CN</b>) and <b>D</b>-<b>A</b>-<b>D</b>(<b>CN</b>) exhibited the same transition mix of ICT (from donor to acceptor) and reverse ICT (rICT, from arylamine to CN unit). Density functional theory (DFT)/TD-DFT calculations support the presence of ICT for all five compounds, and the experimental observations of rICT presented only for CN-substituted compounds.