New NLO active cyclopalladated chromophores in main-chain polymers q F. Cariati a , U. Caruso b , R. Centore b , A. De Maria b , M. Fusco b , B. Panunzi c, * , A. Roviello b , A. Tuzi b a Universit  a degli Studi di Milano, Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, via Venezian 21, 20133 Milan, Italy b Universit  a degli Studi di Napoli ‘‘Federico II’’, Dipartimento di Chimica, Complesso Universitario di Monte S. Angelo, 80126 Naples, Italy c Universit  a degli Studi di Napoli ‘‘Federico II’’, Dipartimento di Scienza degli Alimenti, via Universit  a 100, 80055 Portici (Naples), Italy Received 24 July 2003; accepted 2 August 2003 Abstract Four new OH-functionalized orthopalladated complexes bearing an electron-donor and an acceptor group in a trans-like ar- rangement with respect to the metal have been prepared and characterized. The ligands are Schiff bases, bound as C,N- or N, O-chelating moieties. Four new polyesters were obtained by polycondensation from the monomeric complexes and pentyloxyte- rephthaloyl chloride. Two ‘‘model’’ complexes, each one related to one monomer, were also synthetized, in order to obtain further and more detailed characterization data, and in particular to perform measurements of lb. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Cyclopalladated complexes; Nonlinear optics; Main-chain polymers 1. Introduction A significant part of the research in the field of nonlinear optics is being focused on the design of new chromophoric coordination compounds [1–3]. Metal complexes can possess a large NLO response due to the attainment of low-energy excited states with dipole mo- ment significantly different from the ground-state dipole moment. Most of these excited states are involved in metal-to-ligand and/or ligand-to-metal charge-transfer and have large oscillator strengths. In these cases, charge transfer is expected to provide a substantial contribution to the second order molecular hyperpolarizability [3]. The NLO properties of several types of transition metal complexes have been previously examined by the authors [4–6]. In particular, a series of cyclopalladated derivatives of Schiff bases was prepared, developing a synthetic strategy to obtain thermally stable and soluble non-centrosymmetric coordination compounds, with fair second order NLO response. Variation in molecular design of cyclopalladated complexes was used to obtain information on the correlations between structure and NLO properties. In this work, we describe further de- velopments in this area. Four metal complexes with the general formula re- ported in Scheme 1 have been prepared, characterized and successively used as monomers in the preparation of a series of polyesters. It is to note that the above complexes are organo- metal derivatives. Organometallics can form polymers or can be included in polymers, just as simple organic molecules, and the use of NLO active monomers is ex- pected to produce NLO active materials. The synthesis of Pd(II) based organometal side-chain NLO active polyacrylates has already been described [4]. A variety of examples of metallic main-chain polymers, with the second order NLO active units in the polymeric back- bone, have been reported in the literature, but most of them contain non-organometal coordinated groups, as in the case of bis(salicylaldiminate) derivatives of cop- per, nickel and cobalt [8] or zinc [9]. Very few examples Inorganica Chimica Acta 357 (2004) 548–556 www.elsevier.com/locate/ica q Supplementary data associated with this article can be found, in the online version, at doi:10.1016/S0020-1693(03)00495-X. * Corresponding author. Tel.: +39081-674170; fax: +39081674367. E-mail address: bpanunzi@chemistry.unina.it (B. Panunzi). 0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0020-1693(03)00495-X