Theoretical Studies on the Ground- and Excited-State Structures and the Spectroscopic Properties of IrR(CO)(PH3)2(mnt) Complexes

MP2 and CIS methods were used to optimize the ground- and excited-state structures of IrR(CO)(PH3)(2)(mnt) complexes [mnt=maleonitriledithiolate; R=H (1), Me (2), and Br (3)]. The absorption and emission spectra were calculated using a TD-DFT method. The calculated results indicated that the lowest-energy absorptions of 1 similar to 3 at 430, 435 and 439 nm were all the admixture of the ILCT/LLCT/MLCT transitions. The emissions were red-shifted to 760, 770 and 800 nm, the origins of which are similar to those of the lowest-energy absorptions. The structure and spectroscopic properties of 2 and I are close with each other, but the introduction of Br for 3 changes the ground- and excited-state geometries and the compositions of frontier orbitals, which affects the emission spectra and transition characters.