Cationic Iridium(III) Complexes with Benzothiophene-Quinoline Ligands for Deep-Red Light-Emitting Electrochemical Cells

Recent advances of organic emitters in deep-red light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) are kind of easily fabricated and low-cost light-emitting devices that can efficiently convert electric power to light energy. Compared with blue and green LECs, the performance of deep-red LECs is limited by the high non-radiative rate of emitters in long-wavelength region. While various organic emitters with deep-red emission have been developed to construct high-performance LECs, including polymers, metal complexes, and organic luminous molecules (OLMs), but this is seldom summarized. Therefore, we overview the recent advances of organic emitters with emission at the deep-red region for LECs, and specifically highlight the molecular design approach and electrochemiluminescence performance. We hope that this review can act as a reference for further research in designing high-performance deep-red LECs.

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

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.