Theoretical Studies on the Electronic Structures and Spectroscopic Properties of a Series of Novel N-C-N-Coordinating Pt(II) Complexes

The electronic structures and spectroscopic properties of the three tridentate cyclometalated Platinum(II) complexes (PtLCl)-Cl-1[L-1 = 1,3-di(2-pyridyl)-5-methyl-benzene] (1), (PtLCl)-Cl-2 [L-2 = 1-(2-pyridyl)-3-(1-pyrazolyl)-5-methyl-benzene] (2), and (PtLCl)-Cl-3 [L-3 = 1,3-bis(1-pyrazolyl)-5-methyl-benzene] (3) were calculated to explore their spectroscopic nature. The geometry structures of 1-3 in the ground and excited states were optimized under the density functional theory (DFT) and the single-excitation configuration interaction (CIS) level, respectively. The absorption and emission spectra in CH2Cl2 solution were calculated by the time-dependent density-functional theory (TD-DFT) with the polarized continuum model solvent model. As revealed from the calculations, the LUMO of 1 and 2 are localized on phenyl and pyridyl, but that of 3 has 50.3% pi*(pyrazolyl) and 47.8% pi*(phenyl). The energy gap of the d-d state was much greater than that of the CT transitions. With the replacement of pyridyl by pyrazolyl, the electron-donating ability of N atom decreases, whereas the LUMO energy level increases. The lowest-energy absorptions and emissions are blue-shifted in the order 1 > 2 > 3, which are assigned as the ILCT/MLCT/LLCT and (ILCT)-I-3/(MLCT)-M-3/(LLCT)-L-3 characters, respectively. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 1605-1614, 2010