Multifunctional Phenanthroimidazole Derivatives to Realize High‐Performance Deep‐Blue and White Organic Light‐Emitting Diodes

Abstract

Deep blue emitters with high quantum yield, good stability, and multifunctionality are still the key technology for white organic light‐emitting diodes (WOLEDs). To address this, two multifunctional deep‐blue materials 4‐{2‐[4′‐(1,4,5‐triphenyl‐4,5‐dihydro‐1H‐imidazol‐2‐yl)‐biphenyl‐4‐yl]‐3a,11b‐dihydro‐phenanthro[9,10‐d]imidazol‐1‐yl}‐benzonitrile (CPD) and 4‐(2‐{4′‐[1‐(4‐tert‐butyl‐phenyl)‐4,5‐diphenyl‐4,5‐dihydro‐1H‐imidazol‐2‐yl]‐biphenyl‐4‐yl}‐3a,11b‐dihydro‐phenanthro[9,10‐d]imidazol‐1‐yl)‐benzonitrile (tCPD) based on phenanthroimidazole units are designed, synthesized, and characterized. Both the materials show high quantum yields and good stabilities. The deep‐blue fluorescent devices using CPD and tCPD as emitters show maximum external quantum efficiency (EQE) of 5.80% and 4.71% along with Commission Internationale de I'Eclairage (CIE) coordinates of (0.15, 0.07) and (0.15, 0.09), respectively. Two‐color based WOLEDs are demonstrated by doping Ir(MDQ)2acac into CPD and tCPD with a low doping concentration, both devices show high EQEs of 16.4% and 16.6% and CIEs of (0.49, 0.34) and (0.48, 0.32), respectively. Furthermore, three‐color based fluorescence/phosphorescence‐WOLEDs (F/P‐WOLEDs), with reasonable exciton management, are fabricated to enhance exciton utilization and improve device performance. CPD‐based WOLED shows high efficiencies of 49.4 cd A−1, 53.5 lm W−1, 19.0%, and CIE coordinate of (0.46, 0.46). With the same structure, tCPD‐based device also shows high efficiencies of 40.6 cd A−1, 47.2 lm W−1, 19.4% along with CIE coordinate of (0.43, 0.45). These results are among the best of reported deep‐blue OLEDs and F/P‐WOLEDs.

Efficient donor–acceptor emitter based nonsymmetrical connection for organic emitting diodes with improving exciton utilization

“…The singlet-triplet energy gap (DE ST ) is greater than $0.8 eV suggesting that TADF behavior was eliminated. 42 The wide vibrational emission peak with small red shi by increasing solvent polarity informed the strong CT of excited state relative to ground state 43,44 which reveal that these emitters are different from common D-A molecules with prominent solvation effect. [45][46][47][48] The red shied emission is due to twisted conformation which enable for charge transfer from donor to accept or via linker.…”

“…The m-CNPPI and p-CNPPI was adopted as a host to fabricate PHOLEDs which endowed triplet energy (E T ) of these materials exhibit high quantum yield in lm (f lm ) to ensure that the triplet excited state energy m-CNPPI (2.66 eV) and p-CNPPI (2.61 eV) is high enough to excite phosphorescent dopant (green/red). The green device (l EL -504 nm) based on p- [65][66][67][68][69] Moreover, p-CNPPI and m-CNPPI also have a small excited-state dipole moment which can relieve host dopant dipole-dipole interaction explaining the reason for low roll-off efficiency in PHOLEDs adopting them as host materials. 41 These ndings are greatly helpful to construct lowcost uorescent materials with subtle molecular modication.…”

Strategic tuning of excited-state properties of electroluminescent materials with enhanced hot exciton mixing

“…The PL spectra of CADPPI and DPIAPPB show red shi due to the strong CT character of the excited state than the ground state and stabilized by polar solvents. 51,52 The emission of CADPPI and DPIAPPB is observed at 468 and 473 nm in solid with full-width at half-maximum (FWHM) is around 30 nm: the red-shi cannot be due to aggregation in solid state and might be from change in excited state conguration. 53 The small red shi in lm of DPIAPPB and CADPPI compared to solution show suppressed p-p* stacking.…”

Pure-Blue Fluorescence Molecule for Nondoped Electroluminescence with External Quantum Efficiency Approaching 13%

“…The incorporation of a CN group can efficiently adjust the electron-withdrawing ability of PI and further lower the charge injection barrier. 41 The anthracene the formation of "hot-exciton" channels and improves device efficiency. Thus, this twisting bipolar D-π-A molecule can effectively interrupt conjugation and inhibit the ACQ effect in a solid state, simultaneously improving color purity and photoluminescence quantum yield (PLQY).…”