Solid-state fluorophores featuring a combined hybridized local and charge transfer excited state and aggregation-induced emission as efficient emitters for electroluminescent devices

Abstract

Solid-state fluorophores with high fluorescence efficiency and charge transportation have always been of great interest as emitters for organic light-emitting diodes (OLEDs). Mostly, donor (D)-acceptor (A) molecules holding prominent intramolecular charge transfer exhibit low fluorescence quantum yield. Here, we report a series of D–A–D type hybridized local and charge transfer (HLCT) excited state fluorophores (TBz, T2FBz, TFBz, TBBz, TPyBz, and TNz) containing benzo[c][1,2,5]thiadiazole (Bz) and its derivatives (5,6-difluoro-2,1,3-benzo[c][1,2,5]thiadiazole (2FBz), 5–2,1,3-benzo[c][1,2,5]thiadiazole (FBz), naphtho[1,2-c:5,6-c']bis([1,2,5]thiadiazole) (BBz), [1,2,5]thiadiazolo[3,4-c]pyridine (PyBz), and naphtho[2,3-c][1,2,5]thiadiazole (Nz)) as acceptor cores end-capped with tetraphenylethylene (TPE) as a donor and aggregation-induced emission (AIE)-luminogen. The different variations in the molecular structures of the cores render compounds with wide-ranging electronic and photophysical properties. The HLCT and AIE properties of these compounds are confirmed by theoretical calculations, solvatochromic behaviors, and transient decay lifetimes analyses. They show intense fluorescence emissions with good thermal stability and hole mobility, leading to effective utilization as emitters in OLEDs. The resulting devices demonstrate strong green to orange-red electroluminescent (EL) emissions with decent EL performance (Lmax of 6030–20220 cd m−1, CEmax of 6.26–13.18 cd A−1, and EQEmax of 3.51–5.11%). Among them, OLED fabricated with TBBz realized the best EL performance (Lmax of 11115 cd m−2, CEmax of, 12.03 cd A−1, EQEmax of 5.11%) with orange emission (λEL = 592 nm, CIE coordinates (0.53, 0.46)).