Derivatives of Cyanonaphthyl-Substituted Phenanthroimidazole as Blue Emitters for Nondoped Organic Light-Emitting Diodes

Abstract

New multifunctional blue-emissive materials with superior thermal properties, viz., 4,4′-bis(1-(4-naphthyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)binaphthyl (NPIBN), 4,4′-bis(1-(4-cyanonaphthyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)biphenyl (CNPIBP), and 4,4′-bis(1-(4-cyanonaphthyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)binaphthyl (CNPIBN) have been synthesized. The said molecules show high photoluminescence quantum yield (Φ s/f : NPIBN-0.75/0.68, CNPIBP-0.85/0.76, and CNPIBN-0.90/0.88). The fabricated nondoped/doped device with CNPIBN/4,4′-bis(carbazol-9-yl)biphenyl: CNPIBN display maximum efficiencies (η ex 4.96/5.4%; η c 7.46/7.56 cd A –1 ; η p 6.85/6.91 lm W –1 ) at low turn-on voltage (3.5/3.8 V). Nondoped devices based on D−π–A architecture, 4-(2-(5-(9 H -carbazol-9-yl)thiophen-2-yl)-1 H -phenanthro[9,10- d ]imidazol-1-yl)naphthalene-1-carbonitrile exhibit maximum efficiencies (η ex 2.32%; η c 4.00 cd A –1 ; η p 3.42 lm W –1 ) compared to 4-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)-1 H -phenanthro[9,10- d ]imidazol-1-yl)naphthalene-1-carbonitrile (η ex 2.01%; η c 3.89 cd A –1 ; η p 3.15 lm W –1 ).

Realization of switching between TADF and HLCT emissions through modulation of the intramolecular charge transfer character

“…[20][21][22] The enhancement of both TADF and HLCT fluorescent emissions is achieved by increasing the number of singlet excitons through triplet-to-singlet conversion by means of the reverse intersystem crossing (RISC) process. 9,23,24 However, TADF and HLCT emitters differ in the proportion of CT excitation in their singlet excited states and the source of triplet excitons. TADF emitters have predominantly CT character in the lowest singlet excited state (S 1 ) which will greatly diminish the singlet-triplet energy gap (DE ST ).…”

Efficient M-shaped blue emitters having a high conjugation extent with improved roll-off efficiency

“…S1, ESI†). 13,14 The hole and particle overlap for TPA–2SPPITPA was found to be larger than that of TPA–2PPITPA ; hence, TPA–2SPPITPA has higher oscillator strength than TPA–2PPITPA. From NTO analyses of TPA–2SPPITPA and TPA–2PPITPA, the computed oscillator strength, vertical transitions and HONTOs/LUNTOs are depicted in Fig.…”

Regulation of Singlet and Triplet Excitons in a Single Emission Layer: Efficient Fluorescent/Phosphorescent Hybrid White Organic Light-Emitting Diodes

“…The rigid geometry of DDIBPPIN limits the flexibility, and minimized k nr transition results in higher η PL efficiency. 27 The interring torsion angles of highly twisted molecular conformation suppress the intermolecular π–π stacking in solid state, and thus aggregation-induced fluorescence quenching was reduced. At this small interring torsion angle, the extended conjugation is limited and also the amount of charge transfer is increased.…”

“…The small HOMO and LUMO overlap of DDIBPPIN leads to small ΔEST, which enhanced the excition utilization (η s ) through upconversion of triplet (nonradiative) to singlet (radiative). The rigid geometry of DDIBPPIN limits the flexibility, and minimized k nr transition results in higher η PL efficiency . The interring torsion angles of highly twisted molecular conformation suppress the intermolecular π–π stacking in solid state, and thus aggregation-induced fluorescence quenching was reduced.…”