NLO investigations of electroactive ligands and of their electroactive metal complexes

During this presentation, we will describe experimental as well as theoretical results of the third order nonlinear optical investigations of different electroactive ligands based on tetrathiafulvalene (TTF) derivatives and on dithiolates and their corresponding electroactive metal complex. The investigation and the comparison between the free TTF based ligands and their corresponding metal complexes show an increase of the NLO response and also with iron and ruthenium metal complexes a switch of the response from the RSA to SA behaviour [1]. In the case of dithiolates ligands, the third order nonlinear optical investigation of two corresponding gold dithiolene complexes, which differ by the nature of the counter cations by means of the Z-scan [2] and the Degenerate Four Wave Mixing (DFWM) [3] techniques under 532 nm, 30 ps laser excitation show a significant modification of the nonlinear optical response between the two metal complexes [4]. Energy and concentration dependent measurements have been performed in order to allow complete and accurate characterization of the nonlinearity. Moreover ab-initio quantum mechanical calculations have been done in order to compute the electric dipole moment, the dispersion-free and frequency-dependent dipole polarizability and the second hyperpolarizability values. The significant modification of the NLO response suggests a clear effect of the counter cation. In particular in the case of the Au-Mel molecular system the precise-charge assisted hydrogen-bonded cation-anion interaction is playing an important effect of the NLO response. These facts have been also verified with the theoretical calculations. The possibility to modify the nonlinear optical response by complexation with metal cation and/or by the use of different counter ions that affects the structural arrangement of the materials open new prospects for their use in photonic applications.