Structurally Regulated Carbazole–Pyridine Derivatives Based on Space-Crowded Theory for Efficient Narrowband Ultraviolet Nondoped Organic Light-Emitting Diodes from the High-Lying Reverse Intersystem Crossing Process

Abstract

Achieving ultraviolet and narrowband emission simultaneously in nondoped organic light-emitting diodes (OLEDs) remains a tremendous challenge. Here, a "space-crowded donor−acceptor− donor" molecular design strategy is proposed for developing ultraviolet pure organic fluorophores by the nearby substituted positions at the phenyl linker between carbazole and pyridine units. Benefitting from the large steric hindrance effect, multiple intramolecular interactions, and low-frequency vibronic coupling dominated excited state property, all the emitters exhibit excellent fluorescence efficiencies at the solid state as well as the narrow full width at half maximums (FWHMs). Moreover, the effect of different substitution positions of pyridine on the structure−property relationship is also revealed. Consequently, the nondoped OLEDs exhibit an electroluminescence emission peak of 397 nm with FWHMs of 17 and 22 nm. Due to the high-lying reverse intersystem crossing process, external quantum and exciton utilization efficiencies of 3.6 and 54.55%, respectively, have been achieved based on the emitter with para-linkage. These findings may pave an avenue for the development of high-performance narrowband ultraviolet materials and OLEDs.

A record-high EQE of 7.65%@3300 cd m−2 achieved in non-doped near-ultraviolet OLEDs based on novel D′–D–A type bipolar fluorophores upon molecular configuration engineering

“…Several successful strategies have been proposed to weaken this effect for exploiting D–A-type NUV emitters, for example, incorporating a steric group, introducing a twisted bridge, and utilizing weak electron-donating/accepting groups. Based on these strategies, a series of D–(π)–A type, 41 donor–acceptor–donor (D–A–D) type, 42–45 acceptor–donor–acceptor (A–D–A) type, 46 and donor′–acceptor–donor (D′–A–D) type wide-bandgap organic emitters were reported in doped OLEDs (Fig. 1).…”

Effects of variation in phenylpyridinyl and di-tert-butyl-carbazolyl substituents of benzene on the performance of the derivatives in colour-tuneable white and exciplex-based sky-blue light-emitting diodes

“…27,28 The derivatives of carbazole and pyridine were reported as emitters for ultraviolet OLEDs with electroluminescence (EL) peaking at 394 nm and a narrow full-width at half maximum (FWHM) of 17 nm. 29 These emitters were characterised by their triplet harvesting abilities via high-laying tripletsinglet reverse intersystem crossing (RISC), allowing fabrication of OLEDs with an EQE of 3.6%. We modified this design strategy by exploiting variation in the number of pyridinyl and di-tert-butyl-carbazolyl substituents of benzene.…”

A spiroacridine-based thermally activated delayed fluorescence emitter for high-efficiency and narrow-band deep-blue OLEDs

“…Such a twisted molecular geometry in the ground state (S 0 ) can not only facilitate the formation of CT transition but also inhibit the tight molecular p-p packing and thus alleviate aggregation quenching. 23 Initially, to explore its photophysical characterization, the ultraviolet-visible (UV-vis) absorption and photoluminescence (PL) spectra of SAC-BOC were measured in dilute toluene (Tol) solution. As shown in Fig.…”

“…Such a twisted molecular geometry in the ground state (S 0 ) can not only facilitate the formation of CT transition but also inhibit the tight molecular π–π packing and thus alleviate aggregation quenching. 23…”