Synthesis, crystal structures and nonlinear optical properties of three TCF-based chromophores

Three new nonlinear optical (NLO) chromophores (1-3) with the same dialkylamino group as an electron donor and the same 2-dicyanomethylene-3-cyano-4-methyl-2,5-dihydrofuran (TCF) as an electron acceptor have been synthesized and characterized. The only difference in these three molecules lies in the length and nature of conjugation bridges. X-Ray single-crystal structural analyses show that 1 displays the best coplanarity between the two building blocks (conjugative bridge and TCF acceptor moieties) among three chromophores. The crystal packing reveals various antiparallel dimer structures which are stabilized by intermolecular pi-pi stacking, C-H center dot center dot center dot N and C-H center dot center dot center dot O interactions. Density functional theory (DFT) calculations demonstrate a linear relation between the first-order hyperpolarizability (beta) and the bond length alternation (BLA) for all investigated chromophores.