NDLI: Blue-green emitting cationic iridium complexes with 1,3,4-oxadiazole cyclometallating ligands: synthesis, photophysical and electrochemical properties, theoretical investigation and electroluminescent devices

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Song, Xiangzhi Wang, Zhen Duan, Lian He, Lei Pan, Chunyue Yan, Jun Tang, Ruiren
Description	Author Affiliation: Wang Z ( College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan Province 410083, P. R. China. helei06@csu.edu.cn trr@mail.csu.edu.cn.)
Abstract	Two cationic iridium complexes, namely $[Ir(dph-oxd)_{2}(bpy)]PF_{6}$ (1) and $[Ir(dph-oxd)_{2}(pzpy)]PF_{6}$ (2), using 2,5-diphenyl-1,3,4-oxadiazole (dph-oxd) as the cyclometallating ligand and 2,2′-bipyridine (bpy) or 2-(1H-pyrazol-1-yl)pyridine (pzpy) as the ancillary ligands, have been synthesized, and their photophysical and electrochemical properties have been comprehensively investigated. In solution, both complexes emit efficient blue-green light. For complex 1, the light emission in a neat film is remarkably red-shifted; in solid state, it gives an intriguing piezochromic phenomenon. Compared with archetype $[Ir(ppy)_{2}(bpy)]PF_{6}$ (ppy is 2-phenylpyridine), complex 1 shows a largely stabilized HOMO (highest occupied molecular orbital) level, induced by the electron-deficient 1,3,4-oxadiazole (oxd) heterocycle of dph-oxd, which results in an enlarged energy gap and blue-shifted emission. Compared with complex 1, complex 2 shows an enhanced LUMO (lowest unoccupied molecular orbital) level, caused by the electron-rich pzpy ancillary ligand, but they exhibit similar emission energy in solution. For both complexes, theoretical calculations reveal that their blue-green emission in solution arises primarily from the $^{3}π–π$ states centered on dph-oxd; moreover, complex 1 bears close-lying $^{3}π–π$ and $^{3}CT$ (charge-transfer) states, underlying its remarkably red-shifted emission in the neat film and unique piezochromic behavior in the solid state. Solid state light emitting electrochemical cells (LECs) based on complexes 1 and 2 give efficient yellow and green-blue light, with peak current efficiencies of 18.3 and 5.2 cd $A^{−1},$ respectively. It is demonstrated that oxd-type cyclometallating ligands are promising as an avenue to stabilize the HOMOs and tune emission properties of cationic iridium complexes to a large extent.
ISSN	14779226
Issue Number	36
Journal	Dalton Trans.
Volume Number	44
e-ISSN	13645447
Language	English
Publisher	Royal Society of Chemistry
Publisher Date	2015-09-28
Publisher Place	Great Britain (UK)
Access Restriction	Subscribed
Subject Keyword	Chemistry
Content Type	Text
Resource Type	Article
Subject	Inorganic Chemistry

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