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 PtL 1 Cl [L 1 = 1,3‐di(2‐pyridyl)‐5‐methyl‐benzene] ( 1 ), PtL 2 Cl [L 2 = 1‐(2‐pyridyl)‐3‐(1‐pyrazolyl)‐5‐methyl‐benzene] ( 2 ), and PtL 3 Cl [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 CH 2 Cl 2 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% π*(pyrazolyl) and 47.8% π*(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 3 ILCT/ 3 MLCT/ 3 LLCT characters, respectively. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010