Binuclear iridium(iii) complexes for efficient near-infrared light-emitting electrochemical cells with electroluminescence up to 800 nm

Abstract

Near infrared (NIR) emitting optoelectronic devices have great potential for applications in communication, encryption technologies, night-vision display and photodynamic biomedical devices. Nevertheless, their development is currently hampered by the lack of efficient NIR-emissive materials. Herein, a novel class of cationic binuclear Ir(III) emitters (Ir-D1 and Ir-D2) based on a ditopic coordinating scaffold featuring the π-deficient thiazolo[5,4-d]thiazole and π-accepting moiety (either pyridine or pyrazine), is described and fully characterized using photophysical and computational techniques. Comparison with the parental mononuclear derivatives Ir-M1 and Ir-M2 is provided as well. Remarkably, the binuclear complexes display NIR photoluminescence in solution with a maximum up to λ_em = ca. 840 nm, which represent some rare examples of metal complexes emitting in this spectral region. Interestingly, NIR photoluminescence is retained in polymer-matrix thin-film for the binuclear counterparts. These findings prompt the successful use of these NIR emitters as electroactive materials in light emitting electrochemical cells (LECs). Binuclear complexes Ir-D1 and Ir-D2 yield electroluminescence peaking at λ_EL = 750 and 800 nm, respectively, and device performances that are the highest reported for LECs in this spectral region to date for molecular (i.e. non-excimer) emitters. This work demonstrates the superior performances of the binuclear design strategy for achieving efficient NIR electroluminescence.