Dual Hybridized Local and Charge Transfer Characteristic Fluorophore as an Efficient Nondoped Emitter for Electroluminescent Device

Abstract

Hybridized local and charge transfer (HLCT) is an attractive strategy for achieving efficient electroluminescence (EL) in electrofluorescent devices by the conversion of triplet‐state (T) to singlet‐state (S) excitons via a reverse intersystem crossing, giving rise to a high exciton utilization efficiency exceeding the spin statistical limit. Excellent device performance is reached using thermally evaporated emissive layers. However, for potential large‐scale commercialization, it is crucial to attain comparable device performances using low‐cost solution‐processing techniques. Herein, a new concept of dual HLCT characteristic fluorophore (BCBF) with a high solid‐state fluorescence as a nondoped emitter for a simple structured solution‐processed EL device is presented. BCBF is effectively formulated by π‐conjugation linking two HLCT fragments with a highly soluble hole‐transporting aromatic moiety. Its dual HLCT and photoluminescence (PL) properties are experimentally and theoretically probed by the solvatochromic effect and density functional theory (DFT) calculations. The molecule exhibits an intense yellow–green emission with a good solution‐processed film‐forming quality and a high solid‐state fluorescence quantum yield of 80%. BCBF is successfully utilized as a nondoped emissive layer in a solution‐processed double‐layered organic light‐emitting diode (OLED), which shows excellent EL performance (brightness of 47 580 cd m−2, current efficiency of 15.78 cd A−1, and external quantum efficiency of 7.20%).

Anthracene derivatives with strong spin–orbit coupling and efficient high-lying reverse intersystem crossing beyond the El-Sayed rule

“…As can be seen, 2MIQ-NPA shows a single linear relationship over the entire solvent polarity, defining that the excited state dipole ( μ e ) calculated by the Lippert–Mataga equation is only 2.27 D. Previous studies have suggested that when the excited state dipole is greater than 10 D, it can be assigned as CT characteristics. 17,37 However, our NTO and experimental results indicate that the LE characteristic is dominant in the singlet excited state of 2MIQ-NPA .…”

Rational molecular design of phenanthroimidazole–azine derivatives for efficient non-doped blue organic light-emitting diodes with low-efficiency roll-off

“…Accordingly, HLCT-based OLEDs can achieve efficiencies above the spin statistical limit or an external quantum efficiency (EQE) of >5%, whereas the inherent short exciton lifetime of HLCT emitters owing to the faster rate of RISC brings about a small efficiency roll-off in the devices. 10 To date, many HLCT-based blue OLEDs with high EQEs with Commission Internationale de l’Eclairage (CIE y ) of (0.06–0.30) have been reported; 10 b ,11 however, deep blue HLCT materials that simultaneously bring about high EQE, good color purity and low-efficiency roll-off, particularly at high luminance are still rare. 10 c ,12…”

“…Phenanthroimidazole (PI) is a common building block for blue-emissive fluorescent materials, especially HLCT blue-emissive materials, due to its bipolar nature and appropriate energy level. 10 a ,13 In most PI-based HLCT materials, PI is employed as an electron acceptor and integrated with triarylamine-based donors (triphenylamine and carbazole). 10 a ,13 a Some of them produced high-performance non-doped deep blue OLEDs.…”

“…10 a ,13 In most PI-based HLCT materials, PI is employed as an electron acceptor and integrated with triarylamine-based donors (triphenylamine and carbazole). 10 a ,13 a Some of them produced high-performance non-doped deep blue OLEDs. Liu et al in 2017 designed and synthesized two triarylamine-PI-based HLCT emitters and achieved OLEDs with an intense deep-blue color with CIE coordinates of (0.15, 0.06) and an EQE as high as 7.20%.…”

A deep-red fluorophore based on naphthothiadiazole as emitter with hybridized local and charge transfer and ambipolar transporting properties for electroluminescent devices

“…So far, based on this concept, several D-A-type fluorophores have been designed and investigated including some DR/NIR materials [37][38][39][40][41]. Inevitably, these materials displayed high PLQY and exceptional OLED device performance [42][43][44][45]. Even though the radiative transition rate is improved for the HLCT fluorophores, the non-radiative transition process is still an obstacle to lowering the PLQY, particularly for the DR/NIR emitters [20,46].…”