Ralph H. Hill

Synthesis and characterization of carbazole polymers exhibiting large nonlinear absorption and refractive index

Abstract Poly-(N-[1-butane 4-sulfonate benzyl triethylammonium],-3,6-carbozolyl), PNBSC, the corresponding propane sulfonate derivative, PNPSC, and poly-(N-[2-pyrimido] 3,6 carbazolyl), PCZP were synthetized as candidates for non-linear optical materials. The radical cations of these polymers were distinguished by absorbances at 850–900nm and 1300 nm which were assigned to intramer and intermer charge transfer in the carbazole radical cations. Solutions of PNBCZ and PNPCZ in 0.1 and 1 M aluminum chloride - nitrobenzene or nitromethane or 2:1 aluminum chloride-n-butyl pyridinium chloride solvents, exhibited a complex with a sharp absorption peak at 700 nm and a very broad absorption centered at 1100 nm. Since these absorption characteristics are very similar to those appearing for oxidation with one electron oxidants such as NO + in protonic acids, a similar complexation must be taking place in both cases. The nonlinear optical properties of the aluminum chloride based solutions of PNBCZ and PNPCZ and nitrobenzene solutions of the radical cation of PCZP were measured with a degenerate four wave mixing experiment at 568 nm at the minimum of the linear absorption spectrum using 10 nsec wide pulses from a dye laser. The monomer unit based, nonlinear susceptibilities γ xxxx (all beams copolarized) and γ xyyx (probe and reflected phase conjugate polarized perpendicular to the pump beams) were 3.5→2.8×10 −29 esu and 9.0→5.7 × 10 −30 esu, respectively. We thus estimate that the electronic and reorientational contributions to the x 3 is on the order of 10 −7 − 10 −8 esu. Significant nonlinear absorption was also observed at 1060 nm using 5 nsec pulses. The data could be matched to a simple linear intensity dependence of the absorption coefficient only at lower intensities, whereupon values between 10 −6 →10 −5 cm/W/M (monomer unit based) were obtained. We suspect that such large nonlinearities are obtained through the introduction of delocalized charge transfer states into the polymer chain.

Optical properties of poly(2,5-dimethoxy-1,4-phenylene vinylene-co-2,5-thienylene vinylene) copolymer films and solutions

Abstract A copolymer system, poly(2,5-dimethoxy-1,4-phenylene vinylene-co-2,5-thienylene vinylene), prepared form various monomer feed ratios has been synthesized via a soluble precursor method. By preparing this copolymer, we hoped to achieve control, and hopefully reduction, of the bandgap relative to the parent homopolymers. In addition, the introduction of asymmetry into the backbone and the reduced bandgap should lead to materials with enhanced nonlinear optical properties. Optical absorption measurements on films and chloroform solutions of the eliminated copolymer systems indicate that the electronic and optical properties are intermediate to the parent homopolymers. Nonlinear optical absorption measurements show a power limiting effects indicating that these materials may be good candidates for more extensive NLO measurements.

Quasi-resonance enhancement of laser-induced-fluorescence diagnosis of endometriosis

Endometriosis, a common disease in women in the reproductive age group, is defined pathologically by the presence of endometrial tissue (inner lining of the uterus) outside the uterus. The displaced tissue is histologically identical to endometrium. In addition to being a highly prevalent disease, this disease is associated with many distressing and debilitating symptoms. Motivated by the need to improve diagnosis by endoscopic imaging instrumentation, we have previously used several drugs to cause selective laser-induced fluorescence of active surgically induced endometriosis in the rabbit model in vivo using ultraviolet-wavelength (351.1 and 363.8 nm) excitation from an argon-ion laser. In the present study we have investigated methods of enhancing differentiation between normal and abnormal tissue by using other excitation wavelengths. In addition to an enhanced capability for detecting abnormal tissue, there are several other advantages associated with using visible-wavelength excitation, such as deeper penetration into the tissue, as well as increased equipment performance, reliability, versatility, and availability. The disadvantage is that because only wavelengths longer than the excitation wavelength can be used for detection, some of the spectral information is lost. Because human endomeiriosis samples were somewhat limited in quantity, as well as specimen size, we used normal ovarian tissue for the laser-induced-fluorescence differentiation-enhancement studies. Positive enhancement of the laser-induced- fluorescence differentiation was found in human ovarian tissue in vitro utilizing 514.5-nm excitation from an argonion laser. Additionally, preliminary verification of this concept was accomplished in active surgically induced endometriosis in the rabbit model in vivo with visible argon-ion laser excitation of two tetracycline-based drugs. Future experiments with other drug treatments and excitation/detection parameters are planned.