BN-Substituted coronene diimide donor-acceptor-donor triads: photophysical, (spectro)-electrochemical studies and Lewis behavior

Boron/nitrogen substituted polyaromatic hydrocarbons ( PAH s) are unique materials, with similar molecular structures to their carbon/carbon analogs, but different electronic properties. We report how these may be tuned by substitution at the B and/or N atoms: the BN-PAH analogues we investigated are BN-substituted coronene diimide ( BNCDI ) acceptors, combined with electron-rich (hetero)arene substituents (donors) on the boron atoms at either side of the BNCDI , resulting in donor-acceptor-donor ( D - A - D ) triads. In comparison to the all-carbon coronene diimide, the implementation of two BN units led to a bathochromic shift of absorption/emission (44 nm) and luminescence quantum yields close to unity. The uniqueness of the BN-based D - A - D motif became clear as the substitution effect of the (hetero)arene substituents was investigated. The strong electron-donating triphenylamine motif had a minor influence on the absorption behavior but showed strongly solvent-dependent luminescence properties. This could be attributed to an intramolecular photoinduced electron transfer ( PeT ) process which was supported by a Rehm-Weller analysis and density functional theory computations. This process was not observed for the other substituents. Moreover, we probed the influence of the aryl substituent on the B-N bond itself by using (spectro)electrochemistry and analyzed the Lewis behavior of the BN unit. The species that formed showed strong absorptions across the whole UV/vis/NIR region. Boron/nitrogen substituted polyaromatic hydrocarbons ( PAH s) are unique materials, with similar molecular structures to their carbon/carbon analogs, but different electronic properties.