Highly Linearized Twisted Iridium(III) Complexes

Abstract

Improving the spatial alignment of emitting molecules has long been a goal of organic-light-emitting-diode development to improve device efficiencies and to generate polarized emission. Herein we describe a simple approach employing Sonogashira coupling with alkyne iridium(phenylpyridine)2(acetylacetone) synthons (2-5) to generate eight linear iridium complexes (6-13) with crystallographically determined lengths of up to 5 nm. By embedding these 'long' complexes into a polymer matrix and stretching it an improvement of polarization ratio of an unstretched and stretched film up to 7.1 times was achieved. Additionally, through the inclusion of 'twists' in the complexes the electronic coupling between the iridium center and substituent was controlled giving a system where the emission behavior is independent of the length.

Tuning Emission Lifetimes of Ir(C^N)2(acac) Complexes with Oligo(phenyleneethynylene) Groups

“…34 Complex 9 in comparison exhibited only a broad featureless emission at λ emis = 500−750 which was not resolved at low temperatures, indicating a pure 3 MLCT emission character as was previously reported. 27 In addition to the emission character, there was a notable shift in the highest energy emission, i.e., λ emis 7 < 6 < 8 < 9. Complex 7 had the emission most similar to that of the parent Ir(ppy) 2 (acac) owing to the combination of the substitutions occurring on the phenylene ring, i.e., HOMO-dominated, and the substitution was in the meta position (5′ in Figure 1) relative to the ppy axis, resulting in a break in conjugation.…”

“…Unlike the acac chelate, the position of substitution on the ppy ligand is a factor that must be considered, as any modifications to the pyridyl group directly impact the LUMO, while modifications to the phenylene group alter the HOMO. The complexes were prepared using a known approach, 27,32 To provide a series of complexes, where OPE3 is attached to the ppy ligand but also electronically decoupled, a series of durylene-linked complexes dOPE3 (Figure 4) were synthesized. Using the same synthetic approach as that used for the pOPE3 complexes, duryl-ethynyl-TIPS ligands were first formed.…”

“…In this study, we examine various approaches for controlling REET to tune the emission lifetime, independently of the emission energy and PLQY (Φ). The simple rod molecule bis­(phenylethynyl)­benzene (BPEB) has T 1 at 2.53 eV close to that of Ir­(ppy) 2 (acac) at 2.55 eV, so a BPEB-type framework could be used as a triplet sensitizer . Therefore, an oligo­( para -phenyleneethynylene) motif (OPE3) as a generic model of BPEB is employed here as the triplet sensitizer for three different architectures: (i) attaching OPE3 to the ancillary acac ligand (acac is typically passive in the photophysics of the system) to electronically decouple the sensitizer from the emitter, (ii) integrating OPE3 with the ppy ligand at different positions (the HOMO is most affected by modifications made to the phenylene ring, whereas the LUMO is governed by pyridyl modifications), and (iii) attaching OPE3 to ppy via duryl groups to electronically decouple the sensitizer from the emitter.…”

Divergent Approach for Tris-Heteroleptic Cyclometalated Iridium Complexes Using Triisopropylsilylethynyl-Substituted Synthons

“…A mixture of 2-phenyl-4-((triisopropylsilyl)­ethynyl)­pyridine (HppyTIPS) and 2-phenylpyridine (Hppy) (1:2.5 equiv) was reacted with IrCl 3 ·3H 2 O (2.5 equiv) under standard conditions to form the dimer mixture. This was in turn reacted with acetylacetone, under basic conditions, to give the statistical mixture of Ir­(ppy) 2 (acac), Ir­(ppyTIPS) 2 (acac) ( 1 ), and Ir­(ppyTIPS)­(ppy)­(acac) ( 2 ).…”

“…Building on this work, we report an additional approach for the divergent synthesis of tris -heteroleptic iridium complexes. Previously, we have demonstrated the utility of ethynyl-triisopropylsilylane (TIPS)-substituted bis -heteroleptic complexes to produce iridium complexes with high aspect ratios . In this report, we sought to combine the use of a TIPS-substituted ligand with the statistical mixture approach to develop a synthon that could be used for divergent synthesis.…”