Electronic structures and spectroscopic properties of [Pt(CNMe)2(CN)2]n (n = 1-4): A theoretical exploration of promising phosphorescent materials

Abstract

The structures of [Pt(CNMe)2(CN)2]n (n = 1-4) in the ground states (S0) and lowest-energy triplet excited states (T1) were calculated by using the second-order Møller-Plesset perturbation (MP2) and density functional theory (DFT) methods, respectively. The MP2 results show that the formation of the dimer causes a significant red shift in emission energy, and the frequency calculations reveal that a weak metal-metal interaction exists in the S 0 state, which is greatly enhanced in the 3[d σ·pσ] excited state. The aggregation of [Pt(CNMe)2-(CN)2]n (n = 1-4) was explored by using the slate-type VWN functional in the DFT method. The 3B u→1Ag transition in the dimer at 509 nm corresponds to the experimental higher-energy emission at 530 nm in CH 3CN solution, while the 3A′→ 1A′ transitions in the trimer and tetramer at 557 and 650 nm, respectively, are responsible for the low-energy emission at 584 nm observed experimentally. The analyses of the Wiberg bond indices for the Pt-Pt bond indicate that the dimer may be the most stable form in solution and that the oligomer species (n = 3 and 4) can be treated as a special dimer in which the excess z electron ligand is bonded to the Pt atoms of the central dimer. © Wiley-VCH Verlag GmbH & Co. KGaA, 2007.