Revealing the role of 1,2,4-triazolate fragment of blue-emitting bis-tridentate Ir(III) phosphors : photophysical properties, photo-stabilities, and applications

Novel bis-tridentate Ir(III) complexes are of great interest in the development of blue-emitting organic light-emitting diodes (OLEDs) due to their rigid and robust molecular architecture. In this work, both the functional 6-pyrazolyl-2-phenoxypyridine (pzyPx) and 6-(1,2,4-triazolyl)-2-phenoxypyridine (tazPx) were used as chromophoric chelates in the construction of the blue-emitting Ir(III) phosphors. Accordingly, the substitution of pzyPx with tazPx chelates retains the desired characteristics, i.e. both high quantum yields (>92%) in solution and shortened radiative lifetime (τ_rad) (from 19.8 to 2.5 μs), respectively. The theoretical calculation reveals that the triazolate moiety contributes considerably to the radiative transition, to which the greater iridium involvement in T₁ → S₀ transition of tazPx-based complex is responsible for the shortened τ_rad. Consequently, enhanced photostabilities in degassed toluene and competitive performances with maximum EQE of 19.2% with CIE coordinates of (0.17, 0.22) were observed from the tazPx-based complex Px-33.