Multifunctional Materials Serving as Efficient Non‐Doped Violet‐Blue Emitters and Host Materials for Phosphorescence

Abstract

Efficient multifunctional materials acting as violetblue emitters, as well as host materials for phosphorescent OLEDs, are crucial but rare due to demand that they should have high first singlet state (S 1 ) energy and first triplet state (T 1 ) energy simultaneously. In this study, two new violet-blue bipolar fluorophores, TPA-PI-SBF and SBF-PI-SBF, were designed and synthesized by introducing the hole transporting moiety triphenylamine (TPA) and spirobifluorene (SBF) unit that has high T 1 into high deep blue emission quantum yield group phenanthroimidazole (PI). As the results, the nondoped OLEDs based on TPA-PI-SBF exhibited excellent EL performance with a maximum external quantum efficiency (EQE max ) of 6.76 % and a violet-blue emission with Commission Internationale de L'Eclairage (CIE) of (0.152, 0.059). The device based on SBF-PI-SBF displayed EQE max of 6.19 % with CIE of (0.159, 0.049), which nearly matches the CIE coordinates of the violet-blue emitters standard of (0.131, 0.046). These EL performances are comparable to the best reported nondoped deep or violet-blue emissive OLEDs with CIEy < 0.06 in recent years. Additionally, the green, yellow and red phosphorescent OLEDs with TPA-PI-SBF and SBF-PI-SBF as host materials achieved a high EQE max of about 20 % and low efficiency roll-off at the ultra-high luminance of 10 000 cd m À 2 . These results provided a new construction strategy for designing high-performance violet-blue emitters, as well as efficient host materials for phosphorescent 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

“…11,12 Although some efforts have been made via rational molecular design or device engineering, external quantum efficiencies (EQEs) usually lie below 7% in simple non-doped NUV-OLEDs. 3,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Moreover, most of the NUV-OLEDs suffer from serious efficiency roll-off at a high luminance level and poor color purity (the full width at half maximum (FWHM) value exceeding 50 nm), due to the intermolecular aggregation, strong intramolecular charge transfer (CT) effect, and unbalanced carrier injection, transport, and recombination.…”

Rational molecular design of phenanthroimidazole-based fluorescent materials towards high-efficiency non-doped deep blue OLEDs

“…29,30 With the introduction of the PI unit, the carrier transport balance of the resulting molecules could be significantly promoted, which reduces the necessity of D-A molecular structure construction. Meanwhile, PI possesses a rigid structure and near-ultraviolet emission, 29,31,32 all of which favour the construction of deep blue molecules.…”

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.…”