Supramolecular Orange-Red- and Yellow-Emitting Ir(III) Complexes with TFSI and PF₆ Counteranions and Production of LEC Devices

Abstract

A series of orange-red- and yellow-emitting Ir­(III) complexes [Ir­(C∧N)2(N∧N)]­[PF6]/[TFSI], where C∧N = 2-phenylpyridine (ppy) (a), N∧N = 4,4′-bis­(4-fluorophenyl)-2,2′-bipyridine (Fpbpy) (1), and N∧N = 4,4′-dimethyl-2,2′-bipyridine (dmbpy) (3), are synthesized. The electrochemical and photophysical properties of the complexes [Ir­(ppy)2(Fpbpy)]­[PF6] (1aPF6), [Ir­(ppy)2(Fpbpy)]­[TFSI] (1aTFSI), [Ir­(ppy)2(dmbpy)]­[PF6] (3aPF6), and [Ir­(ppy)2(dmbpy)]­[TFSI] (3aTFSI) are studied particularly to check their suitability in light-emitting electrochemical cells (LECs). All complexes show aggregation-induced phosphorescent emission (AIPE) due to strong intramolecular π–π interactions between the adjacent ppy ligands that is detected with single-crystal X-ray diffraction. Therefore, these complexes exhibit the highest photoluminescence efficiency in the solid phase. Furthermore, the relationship between the experimental results and time-dependent density functional theory (TD-DFT) calculations of 1aTFSI and 3aTFSI complexes is examined. The effects of TFSI and PF6 counteranions as well as methyl- and fluorophenyl-substituted bpy ligand on LEC device performances are investigated. LEC devices with 1aTFSI complex show the highest efficiency. The resonance effect of the TFSI anion is believed to result in the effective accumulation of ions through electrode interface. In particular, the LEC device with 1aTFSI was subjected to consecutive reverse bias applied every 5 min. Therefore, the effect of charge mobility and ion distribution in the device was interpreted. The maximum brightness, luminous efficiency, power efficiency, and external quantum efficiency values are 10109 cd/m2, 3.40 cd/A, 1.26 lm/W, and 1.71%, respectively. According to the first reverse bias application, there is about 7-fold increase in brightness and power efficiency at the end of 30 min. The turn-on time is decreased from 69.2 to 24 s.