Non-aggregating solvatochromic bipolar benzo[f]quinolines and benzo[a]acridines for organic electronics

A novel series of light emitting and thermally stable non-aggregating benzannulated quinolines and acridines were designed and prepared from ketene-S,S-acetal under mild conditions through C–C bond formation. Photophysical and electrochemical analyses of these bipolar N-heterocyclic compounds revealed intense solvatochromism due to the intramolecular charge-transfer character, exemplary for 9b, which covered PL ranging from blue (480 nm) to green (501 nm) to yellow (562 nm) to orange (589 nm) using aprotic solvents of varying polarity. Organic light emitting devices with a device configuration of ITO/PEDOT:PSS (40 nm)/NPB (20 nm)/(N-heterocyclic compound) (50 nm)/BCP (7 nm)/LiF (0.7 nm)/Al (200 nm) were successfully prepared. The optoelectronic properties of these compounds were altered by controlled tuning of donor–acceptor and aromatic π-conjugation in benzo[f]quinolines and benzo[a]acridines, which exhibited a low turn-on voltage with electroluminescence ranging from blue (6c: λEL 455 nm) to green (8a: λEL 496 nm) to yellow (11: λEL 545 nm) to red (9b: λEL 630 nm).