Homoleptic Facial Ir(III) Complexes via Facile Synthesis for High-Efficiency and Low-Roll-Off Near-Infrared Organic Light-Emitting Diodes over 750 nm

Abstract

Despite the great potential for applications spanning from military night-vision displays and information-secured devices to civilian medical diagnostics and phototherapy, the development of highly efficient, stable, and low-cost near-infrared (NIR) emitting lumophores is still a formidable challenge. Herein, we report two novel NIR-emitting homoleptic facial Ir­(III) complexes based on extended π-conjugated benzo­[g]­phthalazine ligands, namely, tris­[1,4-di­(thiophen-2-yl)­benzo­[g]­phthalazine] iridium­(III) (Ir­(dtbpa)3, 1) and tris­[1-(2,4-bis­(trifluoromethyl)­phenyl)-4-(thiophen-2-yl)­benzo­[g]­phthalazine] iridium­(III) (Ir­(Ftbpa)3, 2). Actually, these two ligands not only enable simple one-pot synthesis of homoleptic Ir­(III) complexes without any catalyst under mild conditions, but also contribute to intense NIR-emission with high photoluminescence quantum yield up to 5.2% at 824 nm for 1 and 17.3% at 765 nm for 2, respectively. Single-crystal structure of 1 demonstrates desired facial form with short Ir–N and Ir–C bonds because of strong coordination and small steric hindrance of those highly conjugated C^NN ligands. Importantly, the incorporation of CF3 groups in 2 further leads to high thermal stability and a good ability to sublime, thus resulting in ultrapurity for highly efficient NIR-organic light-emitting diodes (NIR-OLEDs) with a high maximum external quantum efficiency of 4.5% at 760 nm and small efficiency roll-off remaining of 3.5% at 100 mA cm–2, values which rank with those of the most efficient NIR-OLEDs with small roll-off and peak emission over 750 nm. Notably, the content percentages of the noble metal in these two complexes (∼10% Ir) are markedly lower by about two-thirds than that of typical green-emitting tris­(2-phenylpyridine)­iridium (∼30% Ir). The findings may provide a new strategy to develop robust NIR emitters and achieve high efficiency, small roll-off, and low cost simultaneously in NIR-OLEDs for practical applications.

Using Simple Fused‐Ring Thieno[2,3‐d]pyrimidine to Construct Orange/Red Ir(III) Complexes: High‐Performance Red Organic Light‐Emitting Diodes with EQEs up to Nearly 28%

“…The relatively short phosphorescence lifetimes can decrease the triplet‐triplet annihilation and triplet‐polaron annihilation processes and thus may allow the fabrication of highly efficient OLEDs . More importantly, the radiative decay rates ( k r ) of these complexes ranging from 5.6 × 10 5 to 9.5 × 10 5 s −1 are rather high for iridium complexes . These high radiative rate constants would be beneficial for device performance, as the triplet excitons can decay rapidly through the radiative pathway.…”

Facile access to deep red/near-infrared emissive AIEgens for efficient non-doped OLEDs

“…, Pt 2+ , Os 3+ or Ir 3+ ), lanthanide complexes, organic small molecules, and conjugated polymers 5–7. Amongst these materials, transition-metal complexes with phosphorescence achieve DR/NIR luminescence easily because the energy level of the triplet excited state is intrinsically lower than that of the singlet excited state.…”

Efficient Near‐Infrared Electroluminescence at 840 nm with “Metal‐Free” Small‐Molecule:Polymer Blends

“…[7] In the search for ever-higher efficiencies, several classes of materials have been investigated, such as perovskite-structured methylammonium lead halides, [8][9][10] quantum dots, [11] and organometallic phosphorescent complexes. [12][13][14][15][16][17][18][19] However, although such hybrid materials afford substantial electroluminescence (EL) external quantum efficiency (EQE) in the NIR, in some cases exceeding 10% [8,10] or even 20% or so, [13] their use of heavy, toxic, and/or costly metals is not ideal for manufacturing, sustainability, environmental impact, and, in perspective, biocompatibility. Furthermore, in such hybrid systems, and in general in materials that leverage triplet excitons to boost the EQE, [20,21] exciton recombination dynamics typically fall in the hundreds of nanoseconds or even in the microsecond (or longer) range, which intrinsically limits the bandwidth when integrated in devices for telecommunications.…”