Synthesis and non-linear optical properties of some novel nickel derivatives

The synthesis of a new nickel complex with an extended multi-sulfur dithiolene ligand Ni(etodddt)(2) (etodddt = 4,5-(1,4-oxathiane-2,3-diyldithio)-1,3-dithiole) is described. It is characterized analytically and spectroscopically. The structure of the compound is determined by single crystal X-ray crystallography. Its redox potentials are determined using cyclic voltammetry and are compared with similar dithiolene complexes. Several other nickel derivatives are synthesized: bis(5,6-dihydro-1,4-dithiine-2,3-dithiole) nickel (Ni(dddt)(2)) and bis(6,7-dihydro-5H-[1,4] dithiepine-2,3-ddithiole) nickel (Ni(pddt)(2)). The non-linear optical response of the synthesized dithiolenes is measured in the visible (532 nm) and in the infrared (1064 nm) using the Z-scan technique with picosecond laser pulses. Both the refractive and absorptive parts of the third-order susceptibility chi((3)) are determined and the second-order hyperpolarizabilities c of the dithiolenes are determined and compared between them and with other reported in the literature data. The second hyperpolarizabilities of the synthesized metal derivatives are calculated by employing a series of computational approaches, involving density functional theory and a semi-empirical method. The. first strong transition of the derivatives is attributed mainly to HOMO-LUMO pair connected with the intramolecular charge transfer pi --> pi*. Similar trends are observed between the experimental and the theoretical second hyperpolarizabilities, although the former are much larger due to resonance enhancement. The reported analysis demonstrates the complementarity of both experimental and theoretical results. It is shown that modest substitution of Ni(SCH)(4), for example substitution of four H atoms by two S2C2H4 groups, leads to a very large increase of the second hyperpolarizability. (C) 2010 Elsevier B. V. All rights reserved.