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 ( χ (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 ( γ) 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. [Display omitted]