Zinc(II) Bisterpyridine Complexes: The Influence of the Cation on the π-Conjugation between Terpyridine and the Lateral Phenyl Substituent

The synthesis and photophysical properties of an ethynylphenyl -substituted terpyridine ligand L and its corresponding zinc(II) complex [Zn(L)(2)](PF6)(2), serving as model compounds for self-assembling Zn(II)based metallopolymers suited for photoluminscent and electroluminescent devices, are presented. The UV-vis spectra are characterized, and the photoluminescence quantum yields are determined. The ground-state structures are calculated by means of DFT, and the structural key features are approved by experimental as well as by DFT-calculated Raman spectra. Special attention is paid to the pi-electron delocalization between phenylene (ph) and pyridine (py) and, in particular, to changes in the ph-py bond due to complexation. The DFT-calculated ph-py bond shortening in [Zn(L)(2)](PF6)(2) compared to L correlates well with the higher wavenumber of the nu(ph-py(trig)) vibration, which involves strong ph-py bond stretching. The higher ellipticity in the ph-py bond due to complexation, calculated according to Bader's QTAIM indicating the pi-character of a bond, is confirmed by the higher Raman intensity of the nu(ph-py(trig)) vibration. The electron density distributions in the ph-py bond between [Zn(L)(2)](PF6)(2) and L are compared in an inter-Delta rho plot, which highlights the changes in the bonding situation of the ph-py bond induced by complex forming.