Manipulating charge-transfer character and tuning emission color with electron-withdrawing main-group moieties in iridium-based electrophosphors: A theoretical investigation

A new way has been investigated for tuning the optical and electronic performance of cyclometalated iridium(III) phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2-phenylpyridine) with various main group moieties in [Ir(ppy-X)2(acac)] (X = POPh2, SO2Ph, GePh3, OPh, OPh(CF3)3, SOPh). The geometric and electronic structures of the complexes in the ground state are studied with time-dependent density functional theory (TD-DFT) and Hartree-Fock method, whereas the lowest singlet and triplet excited states are optimized by the configuration interaction singles method. At the TD-DFT level, absorptions and phosphorescence properties of the studied molecules were calculated on the basis of the optimized ground- and excited-state geometries, respectively. The various main group moieties produce a remarkable influence on their optoelectronic properties. The calculated data reveal that the studied molecules have improved charge transfer rate and balance and can be used as hole and electron transport materials in organic light-emitting devices. In particular, the work can provide valuable insight toward future design of new and relatively rare luminescent materials with enhanced electron-injection and electron-transporting features.