Rational design of orange-red iridium(iii) complexes by an isomer engineering strategy for improved performance of white organic light-emitting diodes?

Journal of Materials Chemistry C Pub Date: 2022-08-22 DOI: 10.1039/D2TC02249D

Abstract

White organic light-emitting diodes (WOLEDs) achieving high electroluminescence (EL) performance and tiny efficiency roll-off concurrently have been highly desired for practical application. Orange-red luminescence is well-known as an important component of WOLEDs, however, the development of such materials with high efficiency is still challenging due to the relatively poor emission caused by the energy-gap law and the concentration quenching phenomenon. Herein, two orange-red emitting iridium(III) complexes Ir(pq)2pbi and Ir(piq)2pbi with isomeric cyclometalated ligands, i.e. 2-phenylquinoline and 1-phenylisoquinoline, are designed and synthesized. The structural modulation adjusts not only the conjugation degree but also the molecular packing of both complexes, resulting in distinctly different photophysical and EL performance. The utility of Ir(pq)2pbi in a monochromic device shows a current efficiency (ηc) of 36.7 cd A?1, a power efficiency (ηp) of 22.6 lm W?1, and an external quantum efficiency (ηext) as high as 16.0% along with negligible efficiency roll-off, which are much better than those of Ir(piq)2pbi. Two-color complementary WOLEDs based on Ir(pq)2pbi as a dopant realize an ηc of 39.8 cd A?1, an ηp of 31.3 lm W?1, and an ηext of 17.3% with a low ηext roll-off ratio of 2.3%, respectively. Such excellent electroluminescence performance for monochromic and WOLEDs suggests the potential of Ir(pq)2pbi for further display application and will guide further molecular design in the future.

Graphical abstract: Rational design of orange-red iridium(iii) complexes by an isomer engineering strategy for improved performance of white organic light-emitting diodes
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