Terpyridine Zn(II), Ru(III) and Ir(III) complexes as new asymmetric chromophores for nonlinear optics: first evidence for a shift from positive to negative value of the quadratic hyperpolarizability of a ligand carrying an electron donor substituent upon coordination to different metal centres

The synthesis of 4-(C6H4-p-NBu2)-2,2:6,2-terpyridine and the strongly enhanced second-order NLO response of its Zn(II), Ru(III) and Ir(III) complexes are reported, evidencing for the first time a shift from positive to negative value of the ligand quadratic hyperpolarizability by varying the nature of the metal centre.