An Insight of the Results Provided by Color-Tuning Studies Made on Ir(III) Complexes: A pi-Neutral CF3 Group Viewed by Adjusting Energies of pi-type Molecular Orbitals

The pi‐nature of a CF3 group can be understood through analysis of its bond orbitals (BOs) mixed into the pi‐type molecular orbitals of CF3‐substituted Ir(ppy)2MDPA+ complexes (ppy=2‐phenyl‐pyridine and MDPA=methylated 2,2′‐dipyridyl amine). It has been found that, through this natural bond orbital analysis, the parent’s molecular orbitals (MOs) can be stabilized by χρ*CF BO via negative hyperconjugation and, simultaneously, destabilized by electron lp(F) BO. Since these two competing pi‐effects are virtually counterbalanced as indicated by the vanishing values of crystal orbital overlap populations, the chemical substitution strategy originated from lowering of HOMO by using this electron‐withdrawing CF3 group has been found effective in color‐tuning to blue region. Based on reduced shielding effect due to de‐ creased χρ‐electron density, the reported position dependent CF3‐substitution effects on pi‐type MOs can also be understood through HOMO/LUMO wavefunction analysis. The pi‐neutral nature of a CF3 group viewed by adjusting HOMO/LUMO levels, further confirmed by COOP‐values, arises from the counterbalance of two opposing effects: the pressing‐down effects exerted by the CF antibonding bond orbital (σCF*) and the pushing‐up effects exerted by the one‐center bond orbital on F‐atom(s), LPF.