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

Abstract 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.