Molecules with Exceptionally Small HOMO–LUMO Gaps

Mind the gap: HOMO–LUMO gaps less than 0.5 eV have been recently engineered in small organic molecules through extended conjugation and donor–acceptor covalent coupling approaches (see picture). Such compounds reveal a number of unusual electronic properties such as thermo-excited intramolecular electron transfer (in solution) and metallic conductivity (in the solid state).