Theoretical Studies on Structures and Spectroscopic Properties of Bis-Cyclometalated Iridium Complexes

The series of iridium(III) complexes Ir(C ∧ N) 2 LX (C ∧ N = bzq, LX = acac, 1; C ∧ N = thp, LX = acac, 2; C ∧ N = tpy, LX = acac, 3; C ∧ N = bzq, LX = dbm, 4; acac = acetoylacetonate, bzq = benzoquinoline, tpy = 2-(4-tolyl)pyridine, thp = 2-(2‘-thienyl)pyridine and dbm = dibenzoylmethanate) have been investigated theoretically to explore their electronic structures and spectroscopic properties. Their structures in the ground and excited states have been optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The calculated bond lengths of Ir−N, Ir−C, and Ir−O in the ground state agree well with the corresponding experimental results. Upon excitation, the bond lengths of Ir−N and Ir−C lengthen by 0.03 Å and that of Ir−O shortens by 0.01 Å compared with those in the X 1 A ground states. This is consistent with the variation trend of corresponding vibration mode in the ground and excited states. At the TD-DFT and PCM levels, 1 − 4 give rise to absorptions at 484, 462, 452, and 536 nm and phosphorescent emissions at 541, 589, 499, and 540 nm, respectively. The transitions of 1 − 3 are attributed to [d(Ir) + π(C ∧ N)] → [π*(C ∧ N)] charge transfer, whereas those of 4 are related to [d(Ir) + π(C ∧ N)] → [π*(LX) + π*(C ∧ N)]. It is shown that the emissions are significantly dominated by the metal participating in the frontier molecular orbitals and affected by the C ∧ N ligands but are hardly perturbed by the LX ligands.