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 T-g > 115 degreesC, 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 nticro-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/m(2) at the driving voltage of 18 V. (C) 2003 Elsevier Science B.V. All rights reserved.