Rational Molecular Design of Multifunctional Blue‐Emitting Materials Based on Phenanthroimidazole Derivatives.

Abstract

High-performance deep-blue emitters with external quantum efficiencies (EQEs) exceeding 5% are still scarce in organic light-emitting diodes (OLEDs). In this work, by introducing a [ 1,2,4]triazolo [1,5-a]p yridine (TP) unit at the N1 position of phenanthroimidazole (PI), two luminescentm aterials, PTPTPA and PTPTPA,w ere obtained. Systematic photophysical analysis showed that the TP block is suitable for constructingh ybridized local and charge-transfer( HLCT) emitters. Its moderate electron-withdrawing ability and rigid planar structure can enhancet he CT component while ensuring color purity.I na ddition, compared with PTPTPA,t he additional phenyl ring of PTPBPTAn ot only increased the oscillator strength,b ut also decreased the Stokes shift. TDDFT calculations pointed out facile reverse intersystem crossing processes in PTPTPA from high-lying triplet states to the singlet excited state. An ondoped device based on PTPTPA as emitter showed impressive performance with EQE max of 7.11% and CIE coordinates of (0.15, 0.09). At the same time, it was also an efficient host for yellow and red phosphorescent OLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dyes into PTPTPA,awhite OLED with ah igh EQE of 23.85 %w as achieved. The successful design of PTPTPA not only provideda no ptimization choice for OLED emitters, but also demonstrated thee mpirical rules for the design of multifunctional deep-blue emitters.

A new multifunctional fluorescent molecule for highly efficient non-doped deep-blue electro-fluorescence with high color-purity and efficient phosphorescent OLEDs

“…[12][13][14] Hence, HLCT is a very feasible strategy for building deep-blue molecules. Actually, on the basis of the molecular design strategy of HLCT, great efforts have been made to develop highly efficient non-doped deep-blue fluorescence emitters such as carbazole, [15][16][17][18][19] imidazole, [20][21][22][23][24][25] triazole, 26,27 and oxadiazole 28,29 derivatives. For example, Su et al constructed a molecule named PhPBI having high device performance with an EQE max of 6.1% and CIE of (0.148, 0.140).…”

Impact of peripheral groups on pyrimidine acceptor-based HLCT materials for efficient deep blue OLED devices

“…Subsequently, a series of light-emitting molecules based on PPI were reported by changing the substituents at the 1 and 2 positions of imidazole. 3,[6][7][8][9][10][11][12][13][14][15][16][17][18] However, the class of PPI acceptors is relatively single, significantly limiting the development of such materials. Although some other acceptors, 19 such as pyrene-imidazole 20,21,[22][23][24] and 9,10-diphenylimidazole, [25][26][27] have been developed, there is still a need to develop more effective acceptor planes for expanding this HLCT material system.…”

A large-scale deep-blue tetraphenylbenzene-bridged hybridized local and charge transfer fluorophore exhibiting small efficiency roll-off and low amplified spontaneous emission threshold

“…With the rapid development of high and ultrahigh definition displays, highly efficient and stable blue organic optoelectronic materials have been a major requirement for applications in organic light-emitting diodes (OLEDs) and organic solid-state lasers (OSSLs). [1][2][3][4][5] However, although extensive efforts have been devoted, owing to the intrinsic wide bandgap characteristics, high-performance and cost-effective deep-blue emitters and devices meeting the requirement of Commission Internationale de l'Eclairage (CIE) y coordinate value o0.06 are really rare. 6 So far, blue phosphorescent and thermally activated delayed fluorescence (TADF) OLEDs have realized high external quantum efficiencies (EQEs) exceeding 25%, [7][8][9][10][11] but the emitters have to be dispersed into an appropriate host matrix to alleviate the concentration quenching effect, [12][13][14] which not only requires a stable host and adjacent layers with high triplet state energy (E T ) higher than that of the emitters, but is also related to host-guest doping technology, posing the phase separation risk and increasing the production costs.…”

“…Designing an excellent deep-blue emitter should indeed meet several criteria with regard to color quality, efficiencies, stability, and charge-carrier injection/transportation: 3,4,[23][24][25] (1) satisfying the standard of CIEy o 0.06 with good emission color purity, which is essential to develop high-end electronic displays such as (ultra-) high definition televisions, (2) a high photoluminescence quantum yield (PLQY), generally, the higher the PLQY is, the better the electroluminescence (EL) performance of the device will be achieved, (3) high thermal and morphological stabilities, which is beneficial for extending the lifetime of OLEDs, and (4) suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, which can ensure efficient hole and electron injection, transportation, and recombination within the emissive layer. To achieve deep-blue emission, the p-conjugation length of molecules must be limited, which in turn imposes restraint on the molecular size.…”