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 π-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 v(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 π-character of a bond, is confirmed by the higher Raman intensity of the v(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−Δρ plot, which highlights the changes in the bonding situation of the ph−py bond induced by complex forming.