Efficient 1-(thiophen-2-yl)isoquinoline-based ionic iridophosphors with bulky counterions for solution-processed deep-red electroluminescence

Abstract

A pair of high-efficiency deep-red emissive ionic iridophosphors (Ira and Irb) showing high photoluminescence quantum yields (PLQYs) are rationally designed by using 1-(thiophen-2-yl)isoquinoline as the cyclometalating ligand. Two bulky tetraarylborate anions (tetraphenylborate and tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) are selected to improve their PLQYs in both solution and aggregated states, which enables efficient electroluminescence via a solution-processed approach. The variation of the tetraarylborate anions also aims to tune the photophysical properties of these deep-red emissive iridophosphors. Both ionic iridophosphors emit intense deep-red room-temperature phosphorescence in both solution and aggregated states. The phosphorescence spectra of both complexes are similar (630 nm with a shoulder emission of 686 nm) in CH₂Cl₂, originating from the same cationic species of the complexes. Both complexes show high PLQYs in CH₂Cl₂ (0.41 for Ira, 0.43 for Irb) and neat films (0.27 for Ira, 0.34 for Irb). Moreover, they serve as triplet emitters to evaluate their performance in solution-processed deep-red electroluminescent devices. The maximum external quantum efficiencies for the deep-red electroluminescence are 7.3% with an emission maximum of 649 nm for Ira, and 10.2% with an emission maximum of 635 nm for Irb, respectively, implying that they are good candidates for high-performance electroluminescence.