Theoretical Studies of the Spectroscopic Properties of [Pt(trpy)C⋮CR]+ (trpy = 2,2‘,6‘,2‘ ‘-Terpyridine; R = H, CH2OH, and C6H5)

Abstract

Electronic structures and spectroscopic properties of [Pt(trpy)C[triple bond]CR](+) (trpy = 2,2', 6',2' '-terpyridine; R = H (1), CH(2)OH (2), and C(6)H(5) (3) ) are studied by ab initio and DFT methods. The ground- and excited-state structures are optimized by the MP2 and CIS methods, respectively. The absorption and emission spectra in the dichloromethane solution are obtained by using TD-DFT (B3LYP) method associated with the PCM model. The calculations indicate that, for 1-3, the variation of the substituents on the acetylide ligand only slightly changes their structures in ground and excited states but leads to a sizable difference in the electronic structures. In both cases of absorption and emission, the energy levels of HOMOs for 1-3 are sensitive to the substituents on acetylide ligand and increase obviously with the introduction of the electron-donating groups; however, those of trpy-based LUMOs vary slightly. The lowest-energy emissions are attributed to triplet acetylide/Pt --> trpy charge transfer ((3)LLCT/(3)MLCT) transitions and the lowest-energy absorptions and emissions for 1-3 are red-shifted on the order of 1 < 2 < 3 when the electron-donating groups are introduced into the acetylide ligand. By comparison of the results obtained by using different functionals in TD-DFT method, the calculations indicate that the exchange-correlation functionals (B3LYP, B3P86 and B3PW91) involving Becke three parameter hybrid functionals are appropriate for the terpyridyl platinum(II) acetylide complexes to get the relatively satisfactory results for the absorption spectra. The underestimated excitation energies of lowest-lying absorption bands are probably due to insufficient flexibility in TD-DFT method to describe states with large charge transfer.