Facile one-step synthesis of efficient hybridized local and charge transfer emitter for ultraviolet electroluminescence with low roll-off.

Ultraviolet organic light-emitting diodes (UV-OLEDs) have attracted increasing attention in the applications of phototherapy, high-density information storage, sterilization, photocuring and so on, yet the development of efficient short-wavelength emitters remains challenging due to the irreconcilable contradiction between fluorescence efficiency and short molecular conjugation length. Here, we design and synthesize a simple yet efficient donor-acceptor-donor (D-A-D) type UV emitter D3CZ4F featuring a hybridized local and charge transfer state, via a facile one-step coupling reaction. The multiple intramolecular non-covalent C-H⋯F locking interactions enhance molecular rigidity as well as promote the planarization of the excited state geometry, leading to a large oscillator strength of 1.3989 and a high solid-state photoluminescence quantum yield of 86%. Consequently, the doped device with D3CZ4F as an emitter not only emits high color-purity UV emission at 388 nm with color coordinates of (0.165, 0.025), but also furnishes a maximum external quantum efficiency (EQE) of up to 8.97% and a small roll-off with the EQE of 8.15% at 500 cd m-2. Moreover, the non-doped device achieved a surprised EQE of 7.33% with an emission peak at 390 nm and color coordinates of (0.164, 0.027), respectively.