Synthesis, characterization and third-order non-linear optical properties of novel fluorene monomers and their cross-conjugated polymers

We designed and synthesized two novel fluorene monomers of D-A-D (donor acceptor donor) type (M1 and M2), and their two corresponding polymers (PM1 and PM2) and a copolymer (CPM). These high molecular weight, film-forming polymers were obtained from metal-free, superacid-catalyzed reactions of the monomers with N-phenylisatin. The cubic NLO response (chi((3))) for these new compounds, in solid thin films, was measured through the use of third-harmonic generation (THG) Maker-Fringes technique at IR wavelengths given values of the order of 10 (12) esu from which, the corresponding second hyperpolarizabilities (gamma) were estimated to be of the order of 10(-33) esu for monomers and 10 (31) esu for polymers. Second hyperpolarizabilities have also been estimated theoretically at B3LYP/6-31G(d) level of theory in gas phase and related with the electronic structure of the synthesized molecules. (C) 2010 Elsevier Ltd. All rights reserved.