Iridium Complexes with Terdentate Ligands: Cyclometalated vs. Polypyridine Analogues; Hybrid vs. ``Pure'' DFT

The present investigation has a twofold aim. In the first place, the ground-state spectroscopic features of three IrIII polypyridyl complexes were studied by computational means, in order to elucidate the nature of their UV-visible spectra and electrochemical behaviour. Coincidentally, the limited but variegated set of molecules was employed to analyse how different exchange-correlation functionals model the properties of interest in the presence of transition metal atoms. These iridium complexes involve various terdentate ligands: a N[logical and]N[logical and]N bonded ttpy derivative (ttpy = 4[prime]-tolyl-2:2[prime],6[prime]:2[double-prime]-terpyridine), a C[logical and]N[logical and]C bonded dppy derivative (dppy = 2,6-diphenyl-pyridine), a C[logical and]N[logical and]N pbp derivative (pbp = 6-phenyl-2:2[prime]-bipyridine). The axially-symmetric-homoleptic or heteroleptic-arrangement gives the low-lying excited states of these molecules a unique directional nature. Analysis of the electronic transitions calculated by first-principle method based on time-dependent density functional theory (TDDFT) gives insight on their steady-state visible absorption bands. The comparison of generalised-gradient approximation (GGA) functionals (BLYP and G96LYP) with hybrid GGA functionals (B3LYP and PBE0) values the consequences of the nonlocal Hartree–Fock exchange embedded in the latter