DFT/TDDFT study on the electronic structures and optoelectronic properties of a series of iridium(III) complexes based on quinoline derivatives in OLEDs

The electronic structures and photophysical properties of several heteroleptic iridium(III) complexes Ir(C^â̂§N) ₂(acac) with acetylacetonate (acac) ligand, including 1 [C ^â̂§N = 2-phenylisoquinoline], 2 [C ^â̂§N = 2-biphenyl-4-yl-quinoline], 3 [C ^â̂§N = 2-(fluoren-2-yl)-quinoline], 4 [C ^â̂§N = 2-dibenzofuran-3-yl-quinoline], 5 [C ^â̂§N = 2-dibenzothiophen-3-yl-quinoline], and 6 [C^â̂§N = 2-phenanthren-2-yl-quinoline], have been investigated by density functional theory (DFT) and time-dependent DFT. They show a wide color tuning of photoluminescence from orange-red (λ = 601 nm) to saturated red (λ = 685 nm). The calculated absorption and emission properties of complexes 1 and 2 are in good agreement with the available experimental data. Complex 6 has the smallest ionization potentials (IP) value, which is consistent with its highest occupied molecular orbital energy level, and thus its hole injection is easiest. Corresponding to its lowest unoccupied molecular orbital energy level, the assumed complex 5 has the large electron affinities value and enhanced electron injection ability compared to the others. These calculated results show that the assumed complex 3 may possess better charge transfer abilities than others and is the potential candidate for an efficient electrophosphorescent polymer-based red-emitting material.