Substituent-effect investigation of facial and meridional tris(phenylbenzimidazolinato) Ir(III) carbene complexes: A theoretical perspective

- The geometrical structures are hardly affected by substitution effect.
- The absorption intensity is enhanced for mer-Ir(R-pmb)3 compared to fac-Ir(R-pmb)3.
- The CN and Ph substitutions cause significant red shift on emissions.
- The emissive nature is dominated by ligand with large structural change upon S0 → T1.

A DFT/TDDFT investigation was carried out to understand the electronic structures and photophysical properties of a series of facial and meridional Ir(III) complexes fac-Ir(R-pmb)3 and mer-Ir(R-pmb)3 (R = H, CF3, CN, OCH3, tBu, Ph, respectively) bearing phenylbenzimidazolinato ligand. Substitution effects and fac-mer isomer factors were both investigated. The results herein show that the variation of substituent on the phenyl ring does not cause obvious effects on the metal-related bond lengths and absorption spectra of these complexes. However, the HOMO and LUMO energy levels are affected significantly by the substitution effects. Meanwhile, the most intense absorptions of mer-Ir(R-pmb)3 are found to be blue shifted (∼10 nm) compared with their fac isomers, and the absorption intensities of mer Ir(III) complexes are l enhanced. In addition, we also find that both the electron-donating and electron-withdrawing substituents lead to a red shift on the emissions of these fac and mer Ir(III) carbene complexes and the emissive natures are controlled by the chelate ligand with significant structural changes upon S0 → T1 excitation.