Student Project Abstracts 2005 - Pluto - University of Washington

CHARACTERIZATION OF THE PHOTODECOMPOSITION OF THE CF3-FTC CHROMOPHORELab. No electric poling was applied to these slides, and concentrationsof 5%, 10%, 15%, and 25% chromophore in amorphouspolycarbonate (APC) were made to illustrate the behavior of decayas chromophore interactions change directly with concentration.A slide was placed at a precise location on the stage of a polarizingmicroscope, and at a precise angle, denoted as 0 degrees.The microscope light source was a tungsten bulb, set at a constantintensity setting. Other light sources considered and tested werethe differential interference contrast (DIC) microscope and a xenonarc lamp. A beam of light was focused onto the thin film ofCF3-FTC/APC and a spectrum was taken by the charge coupleddevice (CCD) absorbance spectrophotometer. The rotating stagewas then turned 90 degrees counterclockwise, and a second spectrumwas taken. This set of absorbance measurements at 0 and 90degrees were repeated to improve statistical error, and the stagewas left at the angle of 90 degrees. A comparison of the orthogonalmeasurements will assay the degree of dichroism in the photolyzedregion of the films. For the next 24 hours, this setup was leftundisturbed, while a timed acquisition program gathered spectraevery hour. At the conclusion of 24 hours, four more spectra weretaken at 0, 90, 0 and 90 degrees. This was repeated for samplesof all concentrations. A few samples were also tested in 3.5 hourexperiments using the polarizing microscope’s condensing lens.Figure 1.3. The changes in absorbance of CF3-FTC in 24hours is shown at approximately 660 nanometers.The timed acquisitions of absorbance by the chromophoredid provide some interesting data. It can be concluded that noanisotropy is induced by spin coating the films. Measurementsof absorption at 0 and 90 degrees before photolysis show statisticallyinsignificant differences; no dichroism is observed. As timeprogressed in the experiments the absorbance at 660 nanometers(indicative of CF3-FTC) decreased steadily while the absorbancein the region of the decomposition products (around 440 nm) increased.Most trials exhibited predictable exponential decay of thechromophore, but many trials showed a poor fit to an exponentialgrowth model for the decomposition products. Measurements ofabsorption at 0 and 90 degrees after photolysis showed no signsof induced anisotropy. As there should be induced dichroism, thefact that there is none at all is curious and raises questions.Figure 1.2. Experimental DesignRESULTS AND DISCUSSIONKnowledge of decomposition product structure will guideother photodecomposition research. The spectroscopic studiesused in this research held potential for being convenient to usewith the poled or unpoled films of dye doped polymer. In actuality,practical limitations kept these three forms from providinguseful information. All three sets of spectra yielded from thesetechniques were indecipherable. The infrared spectrometer produceda very weak spectrum due to both moisture in the KBrpellet and heterogeneous dispersion of the polymer film. TheATR spectrometer also gave very weak spectra because of poorcontact between the internal reflectance element and the film ofchromophore doped polymer. Lastly, the Raman microscope andspectrometer gave very weak spectra, caused by fluorescence ofthe chromophore. Raman spectrometers are very susceptible tointerference by fluorescence.Figure 1.4. No anisotropy is shown after 24 hours of polarized photolysis.Figure 1.5. All concentrations of chromophore decay exponentially.112 CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005