Second order nonlinear optical properties of 4-styrylpyridines axially coordinated to A4 ZnII porphyrins: a comparative experimental and theoretical investigation

In this research, two 4-styrylpyridines carrying an acceptor -NO2(L1) or a donor -NMe(2)group (L2) were axially coordinated to A(4)Zn(II)porphyrins displaying in 5,10,15,20mesoposition aryl moieties with remarkable electron withdrawing properties (pentafluorophenyl (TFP)), and with moderate to strong electron donor properties (phenyl (TPP) < 3,5-di-tert-butylphenyl (TBP) < bis(4-tert-butylphenyl)aniline) (TNP)). The second order nonlinear optical (NLO) properties of the resulting complexes were measured in CHCl(3)solution by the Electric-Field-Induced Second Harmonic generation technique, and the quadratic hyperpolarizabilities beta(lambda)were compared to the Density Functional Theory (DFT)-calculated scalar quantities beta(||). Our combined experimental and theoretical approach shows that different interactions are involved in the NLO response ofL1- andL2-substituted A(4)Zn(II)porphyrins, suggesting a role of backdonation-type mechanisms in the determination of the negative sign of Electric-Field-Induced Second Harmonic generation (EFISH) beta(lambda), and a not negligible third order contribution forL1-carrying complexes