For practical applications of poled electrooptic polymers, highly efficient and thermally stable nonlinear optical (NLO) chromophores are required. We describe here a concise synthesis and characterization of a series of donor−acceptor chromophores incorporating a bithiophene moiety in the conjugated bridge. They display a suitable thermal stability and significantly enhanced molecular nonlinearity as compared to their monothiophene analogues and are among the most efficient yet stable NLO chromophores prepared so far.

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A series of phenylbithiophene stilbenes and phenyltetraenes were synthesized and their first-order molecular hyperpolarizabilities determined. Optical nonlinearities up to μβo=9300×10−69 C m5/V were measured at 1907 nm. We show that intermolecular interactions have a large influence on the optical nonlinearity of the molecules in solution and in guest-host polymers with polymethylmethacrylate and polyquinoline as the host. We propose the use of a bulky donor group and a side chain perpendicular to the molecule’s conjugate bridge to reduce aggregation. Electro-optic coefficients as high as r33=30 pm/V at 1.55 μm in polymethylmethacrylate with 25 wt % chromophore loading were measured.

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than to the quantity of active materials. Further device optimization based on such models is under way. ExperimentalPolymer Synthesis: The synthetic path to poly(3-(4¢-(1²,4²),7²-trioxaoctyl)phenyl)thiophene) (PEOPT) is described in Scheme 1. Treatment of p-bromophenol with 1-chloro-2-(2-methoxyethoxy)ethane afforded compound 1, which on Pd(0) catalyzed coupling [6] with 3-thiopheneboronic acid [7] gave 2 as a dark crystalline solid. After passing the crude product dissolved in CH 2 Cl 2 through a short column of silica gel and subsequent recrystallization from MeOH, the monomer (2) was obtained as a pure white crystalline solid (m.p. = 76.1±76.9 C). The polymerization of 2 was performed by slow addition of a slurry of FeCl 3 in CHCl 3 to a solution of the monomer in CHCl 3 at room temperature [8]. The ratio of monomer/FeCl 3 used was 1:6. PEOPT was obtained as a dark solid after precipitation from methanol. The polymer was carefully dedoped and the lower molecular weight and irregular compounds were removed by Soxhlet extraction with methanol and diethyl ether [6]. Size exclusion chromatography (SEC) of the polymer dissolved in tetrahydrofuran (THF) resulted in a molecular weight M n = 20 000 and M w = 56 000 relative to polystyrene standards. The 1 H NMR spectrum of PEOPT was used to estimate the head-to-tail density, which was found to be >85 %. The CHCl 3 solution of the polymer was deep red, while it became darker upon evaporating the solvent. The UV-vis. spectrum of a spin-cast film of the polymer on glass showed an absorption maximum at 476 nm. Annealing of this film with heat or CHCl 3 vapors at room temperature resulted in a change of color accompanied by a red shift of the absorption maximum to 552 nm.