Insight into regulation of emission color and photodeactivation process from heteroleptic to homoleptic Ir(III) complexes

Abstract

The phosphorescent process of two heteroleptic ((DMDPI)2Ir(tftap) and (tftap)2Ir(DMDPI)) and one homoleptic (Ir(DMDPI)3) Ir(III) complexes (See Fig. 1) is theoretically investigated by density functional theory (DFT) and quadratic response (QR) time-dependent density functional theory (TDDFT) calculations including spin-orbit coupling (SOC). Two or three triplet excited states are confirmed for three complexes, respectively. On the basis of the respective optimized triplet geometry, the emissive wavelength is determined by the ΔSCF-DFT method. Furthermore, the radiative rate constant (kr) is also calculated corresponding to each triplet state. Combination of kr and emissive energy, the emission rule is determined. It is found that complex (DMDPI)2Ir(tftap) follows the dual emission scenarios, while complexes (tftap)2Ir(DMDPI) and Ir(DMDPI)3 obey the Kasha rule. The nonradiative rate constant (knr) is qualitatively evaluated by the construction of triplet potential surface via metal centered (3MC d-d) state. Finally, the sequence of quantum yield is compared by both kr and knr. The quantum yield of homoleptic Ir(III) complex Ir(DMDPI)3 is higher than that of heteroleptic Ir(III) complexes (DMDPI)2Ir(tftap) and (tftap)2Ir(DMDPI). However, the emissive wavelength of Ir(DMDPI)3 is in the red color region rather than blue color.