Phosphorescent Pt(II) Emitters for OLEDs: From Triarylboron‐Functionalized Bidentate Complexes to Compounds with Macrocyclic Chelating Ligands

Abstract

The development of organic light-emitting diodes (OLEDs) has attracted enormous research efforts from both academia and industry in the past decades and tremendous progress has been made. However, the low operation lifetime of the blue phosphorescent OLEDs remains as one of the greatest bottlenecks limiting further applications of OLEDs. To address this problem, design and synthesis of triplet emitters with high phosphorescence quantum yield (F P ) and adequate thermal, chemical, electrical and ultraviolet (UV) stabilities are vital. This review summarizes the progress we made on the development of efficient and robust phosphorescent emitters based on cyclometalated Pt(II) compounds, particularly the ones with blue emission, starting from complexes with triarylboron-functionalized bidentate ligand to molecules incorporating tetradentate and macrocyclic ligands, with emphasis on their structure-property relationships.

Cyclometalated Platinum(II) β‐Diketonate Complexes with Extremely High External Quantum Efficiency for White Organic Light‐Emitting Diodes

“…[67] This may be the origin of the higher PLQY of 3. [55,59] The HOMOs energy levels are −5.29 eV for 1, −5.26 eV for 2, and −5.29 eV for 3, as shown in Figure 6. These values for 1-3 are much higher than those for their analogues, such as (dfpypy)Pt(acac) (E HOMO = −6.00 eV) and even (dfppy)Pt(acac) (E HOMO = −5.72 eV), as shown in Figure 7.…”

“…Moreover, it is typical for Pt(II) compound emission bearing a dimesitylboron as a substituent at C^N ligand and is in agreement with previous reports. [55,59,60] Well-resolved emission spectra are obtained at 77 K for each of the complexes, as shown in Figure 5. Sharp vibronic progressions, with peaks at 465/497/526 nm for 1, 467/501/537 nm for 2, and 505/542 nm for 3, were observed, indicating that these emissions mainly originated from ligand-centered triplet states.…”

“…Based on a previous report, we suggest that this might be due to the enhancement of a MLCT transition by an electron deficient triarylboron unit as well as by the synergistic coupling of the boron center with an electronaccepting pyridine ring. [55,59] Thermal stability is an important consideration for OLED materials because vapor deposition techniques are often used in OLED device fabrication. [65,66] Thermogravimetric analysis of complexes 1-3 confirmed that the stability of the Pt(II) complex with dimesitylboron substituents is higher than the unsubstituted and TMS-substituted analogs (Figures S17-S19, Supporting Information).…”

Tuning the through-space charge transfer emission in triarylborane and triarylamine functionalized dipeptide organogels

“…[9][10][11][12] So far, numerous triarylboron functionalized organic and organometallic compounds with a donor-p-acceptor (D-p-A) skeleton have been developed. [13][14][15][16][17][18][19] Due to the intense through bond charge transfer (TBCT) transition, these compounds are usually highly emissive, making them especially suitable for the fabrication of organic-light-emitting-diodes (OLEDs). 18,20 Recently utilization of through space charge transfer (TSCT) emission from nonconjugated polymers has been proved to be an emerging strategy for thermally activated-delayed-fluorescence (TADF) emitter development, [21][22][23][24][25] and these non-conjugated polymers are believed to be third generation OLED emitters to supplant the state-of-the-art phosphorescent emitters.…”

Highlights on Gold TADF Complexes

“…Emitting materials for organic light-emitting diodes (OLEDs) have been a significant focus of academic and industrial research in recent years [1][2][3][4][5][6]. In this respect, thermally activated delayed fluorescence (TADF) represents a promising concept for harvesting both singlet and triplet excitons ( Figure 1) [7][8][9][10][11][12].…”