Exploring the influence of different ancillary ligands of heteroleptic Ir(III) complexes on the phosphorescent properties: Emissive rule and photodeactivation dynamics

Abstract The complexity of emissive process for five heteroleptic Ir(III) complexes (dfpypy)2Ir(LˆX), where dfpypy = 4-methyl-2',6'-difluoro-2,3'-bipyridine and LˆX = picolinate (1), dipivaloylmethanate (2), picolinic acid N-oxide (3), N,N'-di-tert-butylbenzamidinate (4), or 5-(4′-methylpyridine-2'-yl)-3-trifluoromethyl-1,2,4-triazole (5) (See Fig. 1), is unveiled by density functional theory (DFT) and quadratic response (QR) time-dependent (TD)DFT calculations including spin-orbit coupling (SOC). Besides the emission wavelength, we would like to pay intense attention on the emissive rule. It is found that the emission likely originates from different triplet states rather than only from the lowest Kasha state for complexes 1, 2, 3, and 5, which indicates they obey dual emission scenarios. In contrast, complex 4 follows the Kasha rule. Different from the total qualitative study, the quantum yield is semi-quantitatively determined in this work. The radiative decay rate constants (kr) from possible emissive states are quantitatively determined by the quadratic response method. The triplet potential energy surfaces are constructed to elucidate the factors that affect the temperature-dependent nonradiative rate constants (knr). Complex 4 have the higher quantum yields in all the investigated complexes because of the larger kr and smaller knr. The metal-centered (3MC) triplet state in the deactivation pathways is confirmed to play a vital role in determining the quantum yield.