Structural, electronic and optical properties of multifunctional iridium(iii) and platinum(ii) metallophosphors for organic light-emitting diodes

An elaborated theoretical investigation on the optical and electronic properties of three fluorene-based platinum(II) and iridium(III) cyclometalated complexes Pt-a, Ir-a and Ir-b is reported. The geometric and electronic structures of the complexes in the ground state are studied with density functional theory and Hartree Fock approaches, while the lowest triplet excited states are optimized by singles configuration interaction (CIS) methods. At the time-dependent density functional theory (TD-DFT) level, molecular absorption and emission properties were calculated on the basis of optimized ground- and excited-state geometries, respectively. The computational results show that the appearance of triphenylamino (TPA) moiety at the 9-position of fluorene ring favors the hole-creation and leads to red-shifts of absorption and emission spectra. Moreover, Pt-a and Ir-b are nice hole-transporting materials whereas Ir-a has good charge-transfer balance, which render them useful for the realization of efficient OLEDs (Organic Light-Emitting Diodes). Obvious metal-to-ligand charge transfer (MLCT) occurs during low energy transitions, which is the decisive factor for the occurrence of spin-forbidden electron transition. The introduction of triphenylamino (TPA) units improves hole-creation ability and the extent of conjugation, leading to red-shifts in absorption and emission spectra.