Ashwini K. Agrawal

Waveguiding in substrate supported and freestanding films of insoluble conjugated polymers

We demonstrate that waveguiding is possible in substrate supported and freestanding films of insoluble conjugated polymers. Photoresist gratings were used to couple 1.06–1.53 μm radiation into the waveguides allowing the refractive indices, the birefringence, and the linear losses to be measured.

Nonlinear Optical Properties of Ladder Polymers and Their Model Compound

The third order nonlinear optical properties of thin films of polybenzimidazobenzophenanthroline ladder (BBL) and semi–ladder (BBB) polymers and their model compound cis–BBB were investigated by picosecond, third harmonic generation. The χ (3) (−3ω, ω ω, ω) spectrum of BBL, BBB, and cis-BBB was obtained in the wavelength range 1.0–2.4µm and shown to exhibit a three–photon peak at respectively 1.695, 1.695, and 1.50 µm. The magnitude of the three–photon enhanced χ (3) was 6.40×10 −11 , 3.15×10 −11 , and 0.77×10 −11 esu, respectively, for BBL, BBB, and cis–BBB. The results show that the χ (3) of BBL and BBB is enhanced by a factor of 50 and 17, respectively, relative to the model compound cis–BBB at 1.05µm.

High Temperature Electrical Conductivity Of Solution-Cast Bbl Flims.

Thin films (18 μ thickness) of ladder polymer poly[(7-oxo-7H,10H-benz (d,e) imidazo (4′,5′:5,6) -benzimidazo (2,l-a) isoquinoline-3,4:10,ll-tetrayl)-10-carbonyl} (BBL), which were cast from an isotropie methanesulfonic acid solution of BBL, were characterized for electrical conductivity in the temperature range of 25–480 °C. The electrical conductivity was Measured in situ while the films were heated at a rate of 2 °C/Minute under vacuum. The in-plane conductivity of BBL films increased rapidly from below 10 −10 S/cm at the room temperature to 5 × 10 -3 S/cm at 280 °C and then increased slowly to a peak value of 5 × 10 -2 S/cm at about 460 °C. The out-of-plane conductivity of the films was comparable to their in plane conductivity at temperatures below 270 °C, however, was lower by a factor of 10 than in-plane conductivity at temperatures above 270 °C. This anisotropy in conductivity of BBL films is discussed with respect to the film morphology determined by wide angle x-ray scattering studies.