A novel family of twisted molecular luminescent materials containing carbazole unit for single-layer organic electroluminescent devices

A novel family of twisted naphthalimide–carbazole dyads (NI–VK) and triads (NI–VK–NI) with moieties capable of carrier-balance and electroluminescence was synthesized. The key molecular structure design includes the use of carrier-transporting fragments, together with aliphatic side groups that can eliminate the recrystallization tendency and favor the formation of stable amorphous state. It shows that there exists an effective singlet–singlet energy transfer in dyads (NI–VK) and triads (NI–VK–NI) due to the overlap between the absorption of naphthalimide moiety and the emission of carbazole moiety. Such promising twisted emitters with glass-transition temperature of Tg>115 °C, which can generate stable cation and anion radicals for exciton recombination, were successfully utilized in single-layer electroluminescent (EL) device to avoid the layer–layer exciton quenching and micro-cavity effect. The single- and multi-layer devices fabricated with these compounds have been studied in an effort to improve the device efficiency and to gain insight into the luminescent mechanism. As for typical preliminary single-layer EL devices, only emission from naphthalimide was observed with maximum luminescence of 260 cd/m2 at the driving voltage of 18 V.