Synthesis, characterization, and electro-optical properties of Zn II complexes with pi-conjugated terpyridine ligands

A series of nine zinc(II) complexes containing substituted 4'- phenyl-2,2':6',2"-terpyridines as ligands is synthesized and fully characterized. The ground-state structures of four examples are calculated by means of DFT and their structural features are confirmed by experimental Raman spectroscopy. Special focus is placed on the degree of p-electron delocalization between the terpyridine unit and the attached phenyl moiety. Applying Bader's quantum theory of atoms in molecules (QTAIM) and visualizing the electron-density distribution by intermolecular ¿¿ plots reveals an increase in ellipticity-and therefore p-electron delocalization for phenylvinyl-substituted derivatives compared to phenylethynyl-substituted ones. Experimentally, this is verified by spectroscopic means, because an increase in ellipticity goes along with a pronounced decrease of the HOMO-LUMO energy band gap. Overall, the lateral p-conjugated substituents are found to strongly influence the electro-optical properties of the complexes. In solution, the color of emission can be modulated from violet to cyan (425-487 nm) and high quantum yields (FPL up to 0.60) are observed. Thin solid films of the complexes in a matrix of poly(- methyl methacrylate) have been inkjet-printed, and their photophysical behavior (bright emission, FPL up to 0.30) reveals their potential as new emissive materials for applications in light-emitting devices. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA