A family of conjugated polymers with fused structures consisting of three to five
thiophene rings and with the same alkyl side chains has been synthesized as a means to
understand structure - property relationships. All three polymers showed well extended
conjugation through the polymer backbone. X-ray diffraction study of the polymer thin
films suggests that the polymer with the even number of fused thiophene rings forms a
tight crystalline structure due to its tilted side chain arrangement. On the other hand, the
polymers with the odd number of fused thiophene rings packed more loosely.
Characterization in a field-effect transistor configuration showed that the mobility of the
polymer with the even number of rings is one order of magnitude higher than its oddnumbered
counterparts. Through this structure - property study, we demonstrate that
proper design of the molecules and properly arranged side chain positions on the polymer
backbone can greatly enhance polymer electronic properties
A novel class of organic electro-optic(EO) acceptors has been synthesized by a facile high yield synthetic route. These tricyanovinyldihydrofuran type of acceptors have been used to prepare high mb chromophores. Due to the three dimensional shape of the acceptor, these so called 'fish hook' chromophores have been proven to be highly soluble and processable by minimizing chromophore-chromophore electrostatic interactions. Preliminary EO characterization as a guest in polycarbonate film has given r33 values of 70 pm/v at 1550nm for one of these chromophores. We believe this to be the highest value EO coefficient to be reported at this wavelength.
The full potential of second order nonlinear polymers can be utilized in electro-optic polymer modulators with a DC biased operation scheme to greatly reduce the V(pi ). This technique makes use of the total achievable electro-optic coefficient, which can be more than three times as high as the residual value after the fast partial relaxation following corona or contact poling. As the result of the DC bias and with high (mu) (beta) chromophores, a low V(pi ) of 1.5 V was achieved with 2 cm long birefringent waveguide modulators at the wavelength of 1.3 micrometer. Results of 200 degrees Celsius stability experiment indicate that this scheme also enables electro-optic polymer devices to meet the stability required for high temperature hermetic sealing because the polymer does not need to be poled before device packaging.
During the past five years, (pi) -conjugated organic polymers, such as poly[p-phenylene vinylene] (PPV) and polythiophenes, have become attractive alternatives to semiconducting materials as light-emitting diodes. Various approaches to tuning emission wavelength have been proposed, such as controlling the conjugation length by employing polymer oligomers or via steric effects in the fully conjugated polymers, or by using substituent effects to fine-tune the band gap. In the present study, we demonstrate that these features can be designed into copolymeric structures in which (pi) -conjugated emitters of carefully controlled length alternate with various non-emitting flexible spacers which improve solubility and thus processibility. These copolymers display predictable emission characteristics which can also be fine-tuned by incorporation of electronic substituent effects.
We measure the magnitude and phase of the degenerate third-order nonlinear optical susceptibility (chi) (3)llll of solutions of various bis-thienyl polyenes (n-BTP) with the number n of the conjugated double bonds ranging from 3 to 9. We study both neutral and bipolaronic (i.e., doubly ionized) forms of n-BTP. We find that, within experimental error, (chi) (3)llll is proportional to nb where b-5.5 at 532 nm for our neutral n-BTP samples which have 3 <EQ n <EQ 9, and b-14 at 1.06 micrometers for the bipolaron state samples which have 6 <EQ n <EQ 9 where the probing laser wavelength is close to an absorption band. We calculate (chi) (3)llll of the bipolaronic n-BTP assuming it is associated with this absorption band acting as a two-level system and find good agreement with experiment.
Third order nonlinear optical susceptibility of solutions of a triphenodithiazine derivative in dichloromethane has been measured at several different wavelengths utilizing sub-picosecond degenerate four-wave mixing. The values of the second hyperpolarizability, (gamma) , for the neutral and for the oxidized form (dication) are reported. The measurements performed at the wavelengths corresponding to the absorption maxima of the neutral and the dication forms (578 nm and 800 nm, respectively) indicate a twofold increase of the (gamma) /(sigma) figure of merit (where (sigma) is the absorption cross section) for the dication molecule. Time resolved experiments reveal different dynamics of photoexcitation relaxation in the neutral and the oxidized molecules.
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