Theoretical studies upon the electronic structures and spectroscopic properties for a series of luminescent terpyridyl platinum(II) phenylacetylide complexes

A comprehensive calculations were carried out to get a deep insight into the ground- and excited-state electronic structures and the spectroscopic properties for a series of [Pt(4-X-trpy)CCC6H4R]+ complexes (trpy = 2,2′,6′,2″-terpyridine; X = H, R = NO2 (1), Cl (2), C6H5 (3) and CH3 (4); R = Cl, X = CH3 (5) and C6H5 (6)). MP2 (second-order Møller-Plesset perturbation) and CIS (single-excitation configuration interaction) methods were employed to optimize the structures of 1-6 in the ground and excited states, respectively. The investigation showed that substituted phenylacetylide and trpy ligands only give rise to a small variation in geometrical structures but lead to a sizable difference in the electronic structures for 1-6 in the ground and excited states. The introduction of electron-rich groups into the phenylacetylide and/or terpyridyl ligands produces two different low-lying absorptions for 1 and 2-6, i.e., Pt(5d) → π∗(trpy) metal-to-ligand charge transfer (MLCT) mixed with π → π∗(CCPh) intraligand charge transfer (ILCT) for 1 and Pt(5d)/π(CCPh) → π∗(trpy) charge transfer (MLCT and LLCT) for 2-6. Remarkable electronic resonance on the whole Pt-CCPh-NO2 moiety for 1 may be responsible for the difference. Solvatochromism calculation revealed that only LLCT/MLCT transitions showed the solvent dependence, consistent with the experimental observations.