Donor-Acceptor Pentacene Analogues With Near-Infrared Emission and Tunable Aromaticity

Strategic substitution of the 5 and 12 positions in pentacene with an electron-donating nitrogen and electron-accepting phosphine oxide, sulfone and carbonyl groups results in highly polarized para-quinodimethane (pQDM) derivatives with large dipole moments exceeding 10 D. These push-pull systems feature narrow HOMO-LUMO gaps (1.0-1.7 eV), reversible redox properties and near-infrared (NIR) absorption and emission with maxima between 800 and 1100 nm. Remarkably, the polarization induces aromaticity switching: unlike their non-aromatic double-donor and double-acceptor counterparts, the donor-acceptor analogues develop weak aromatic character in the central quinoidal ring, which is further enhanced in polar solvents, as confirmed by theoretical calculations, NMR spectroscopy and X-ray crystallography. These findings demonstrate how molecular polarization can modulate aromaticity and electronic structure, providing a design platform for functional quinoidal π-systems with tunable optical and redox properties.