Lessons learned in tuning the optoelectronic properties of phosphorescent iridium(iii) complexes

Abstract

This perspective illustrates our approach in the design of heteroleptic cationic iridium(iii) complexes for optoelectronic applications, especially as emitters in electroluminescent devices. We discuss changes in the photophysical properties of the complexes as a consequence of modification of the electronics of either the cyclometalating (C^N) or the ancillary (N^N) ligands. We then broach the impact on these properties as a function of modification of the structure of both types of ligands. We explain trends in the optoelectronic behaviour of the complexes using a combination of rationally designed structure-property relationship studies and theoretical modelling that serves to inform subsequent ligand design. However, we have found cases where the design paradigms do not always hold true. Nevertheless, all these studies contribute to the lessons we have learned in the design of heteroleptic cationic phosphorescent iridium(iii) complexes.

From Ligand to Phosphor: Rapid, Machine‐Assisted Synthesis of Substituted Iridium(III) Pyrazolate Complexes with Tuneable Luminescence

“…A family of such fluorinated pyrazole‐iridium complexes has not been reported. Enhancing the electron withdrawing capability of the coordinating phenyl unit is known to blueshift the emission wavelength of luminescent Ir III complexes . Our approach is outlined in Scheme , and features the input of the appropriately fluorinated aniline(s) into the continuous flow apparatus for the ligand synthesis phase.…”

Facile Synthesis of Luminescent Ir–Pt–Ir Trimetallic Complexes

“…Cyclometalated iridium complexes have emerged as champion molecular phosphors for a number of applications, exhibiting good photostability, thermal stability, and high photoluminescence quantum yields over the entire visible spectrum . They are synthetically versatile, allowing facile tuning of the emission color via modification of the cyclometalating (C^N) and/or ancillary ligand structure . Several examples of polynuclear cyclometalated iridium complexes have been reported recently, as well as some supramolecular structures where cyclometalated iridium is combined with another photoactive metal complex .…”

Thermally Activated Delayed Fluorescence Materials: Towards Realization of High Efficiency through Strategic Small Molecular Design

“…The strategy of utilizingcyano-substituted phenyl-or heterocycle-rings has been proven to be quite useful in creatinge fficient TADF materials during the past few years. As eries of TADF moleculesb ased on two substitution positions of cyanounits was reported by Adachie tal.,w ith 3, 3'-bicarbazolyl as EDG (3,2, ( Figure 2b). [28] The substitution positions of cyano-groups evidently affects the dihedral angles between EDG and EWG, consequently resulting in distinct energy differences between S 1 and T 1 .T he 3,5-IPPNDCz has smaller steric hindrance compared to 2,6-IPNDCz,w ith twist angles between the cyano-substitutedp henylr ings and bicarbazolyl-unit of 698 for 2,6-IPNDCz and 508 for 3,5-IPNDCz,r espectively.Aslightly larger HOMO and LUMO separation degree wase xpected accordingt ot heoretical calculation, subsequently leading to smaller DE ST for 2,6-IPNDCz (0.06 eV), and also slightly better device performances with the EQE max data of 9.6 %f or 2,6-IPNDCz and 9.2% for 3,5-IPNDCz-based OLEDs, respectively,u nder the same device configuration.…”

“…Fluorescent materials are, however, intrinsically unable to harvest the triplet excitons generated during the electroluminescence (EL) process, which constitutes three quarters of all electrically generated excitons. Therefore, the first generation OLED can only theoretically achieve 25 % internal quantum efficiency (IQE), unable to satisfy the requirements of commercial applications. The second generation of OLEDs introduces the heavy‐metal incorporating complexes, such as iridium(III) and platinum(III) complexes, which are capable of manifesting both singlet and triplet excitons, consequently achieving 100 % internal quantum efficiency due to the strong spin‐orbit coupling (SOC) effect induced by heavy noble metal centers .…”