| Recently, the scientific researchers endeavor to design and develop new type of luminescent devices with high efficient, high stability, high brightness. The transition metal materials have good performance, such as long luminescent life and single color.So far, a number of d8 and d10 complexes have been synthesized with well-known structures. It was found that many d8 complexes exhibit intensive luminescence and can be applied in the optical materials; their long lifetime of phosphoresce makes them be used as photosensitizer, photochemical catalysis and optical sensor; their interaction with DNA leads to the application in the molecular pharmacy. The experimental studies show potential applications of transition metal complexes in many fields. Lack of theoretical support, insight into the luminescent process and microscopic mechanism is only empirical, which results in experimental deviation from reality. Thus, systematic studies on the d8 complexes in theory to rationalize and predict experimental phenomena are of practical significance.The electronic excited states of molecules have higher energy and unsteady characteristics, which easily emit the energy to recur the steady ground state in a short time. So it is difficult for experiment to obtain reliable information about the excited states of molecules. Theoretical chemists attempt various electronic structure theories of excited states to seek the method that can accurately predict excited-state electronic structures and be applied in the calculations of relatively large molecules without consuming excess computational resources. So far, CIS (Single excitation configuration interaction), unrestricted DFT and TD-DFT (Time-dependent density functional theory) methods have been widely used to treat the electronic excited states of large molecular systems.The advanced technique applied in experiments greatly promotes the development of modern computational chemistry. On one hand, the comparison between calculation and experiment can test the reliability and accuracy of electronic structure theory, showing the dependence of theory on experiment; on the other hand, to develop the electronic structure theory is to support and/or supplement the known experimental results, and further to predict the potential results, indicative of theoretical forward looking and independence.The electronic structures and spectroscopic properties of [(4'-XC≡Ctrpy)PtCl]+ (trpy = 2,2':6',2"-terpyridine; X = H (1), methyl (Me) (2), and phenyl (Ph) (3) were studied by the ab initio method. The ground- and excited-state structures were optimized by the B3LYP and CIS level, respectively. The absorption and emission spectra in the dichloromethane solution were obtained by using the TD-DFT (B3LYP) method associated with the PCM model. The molecular orbital energy of the HOMOs of 1–3 with the d(Pt), p(Cl),π(trpy), andπ(XC≡C) character, are sensitive to the substituents on the acetylide ligand, but those of the trpy-based LUMOs with theπ*(trpy) character vary slightly. The lowest lying distinguishable absorption bands of 1, 2, and 3 are at 404 nm (3.07 eV), 405 nm (3.06 eV), and 447 nm (2.77 eV), they are all attributed to the MLCT/LLCT (ligand to ligand charge transfer) transitions. The lowest-lying emission at 503 nm for 1 is mainly attributed to the 3ILCT perturbed by the 3MLCT and 3LLCT transitions, but those at 535 nm for 2, and at 558 nm for 3 are mainly attributed to the 3LLCT perturbed by the 3ILCT and 3MLCT transitions. The different electron-donating ability of H, Me, and Ph is responsible for the differences in emission character. Moreover, the calculation results show that the phosphorescent color can be tuned by adjusting the substituents. Both the lowest-energy absorptions and emissions of 1-3 are red-shifted in the order 1 < 2 < 3 consistent with the electron-donating order H < Me < Ph.
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