CMDITR Review of Undergraduate Research - Pluto - University of ...

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Objective The goal of the research was twofold: to synthesize different NLO materials (chromophores), and to make a preliminary test of these and other chromophores (supplied by Sei-Hum Jang) to determine chromophores or their structure characteristics which are suitable for the photo-crosslinking processes. As only one finished chromophore was synthesized, this paper will deal primarily with UV testing of chromophores. Research Methods Synthesis For the synthesis of chromophore GIM2 – a simple chromophore – tricyanofuran (TCF) acceptor (previously synthesized) was attached to diethylamine benzaldehyde in a Knovenagel condensation (Figure 1). The Chromophores Compounds chosen for testing were four chromophores synthesized by Dei-Hum Jang of the Jen group, chromophore GIM2, and EA-FTC (Figure 2). Jang’s chromophores, abbreviated SHJ1-SHJ4 each contained a nitrogen ring acceptor, which was theorized to be more stable than the traditional TCF acceptor on GIM2 and EX-FTC. SHJ1’s π-bridge used a thiophene ring, SHJ2-SHJ4 and GIM2 used a phenyl. SHJ2 was eventually removed from the study because it had not yet been fully characterized. Solution Preparation To make the initial doped polymer solutions, glass vials were wrapped tightly with black electrical tape to make them light proof. Then, in a darkened room, 45 ± 10mg of various chromophores with and without ethylene linkages were combined with one, two, or no molar equivalents of hydroxychalcone and the polymer APC (Amorphous poly-carbonate: Poly [Bisphenol A carbonate-co-4,4’-(3,3,5-trimethyl cyclohexl-idene) diphenol carbonate]) in the weight proportions 15% chromophore to 85% APC. The solvent cyclopentanone was added in the weight proportions 88% solvent to 12% total solids (typically 2-3ml cyclopentanone.) The vial was then capped, sealed with Parafilm ® , wrapped in aluminum foil for additional light protection, and placed on a vial spinner and allowed to dissolve overnight (though SHJ4 required at least a week and extra cyclopentanone to dissolve enough.) Spin-coating Plates After the polymer-chromophore solution was well dissolved, it was filtered through a 0.2µm syringe-filter and allowed to fall dropwise onto a glass microscope plate spinning at 3000- 3500rpm to make a thin, even film on the plate. Care was taken to avoid contact with bright light. The plates were then placed in an unheated vacuum oven overnight or longer to remove the cyclopentanone residue. Testing Plates The removable plastic base of the UV-vis spectrophotometer was unscrewed, and a spincoated chromophore plate was taped to the surface. I took an initial scan of the spectrum from 205-1000nm, then placed the base with plate in a high-intensity UV light box (emits 203-350nm wavelength light) for 1-, 2-, 4-, or 10-minutes, then recorded the temperature of the inside of the box and took another scan of the spectrum. UV exposure was continued for a combined time total of between 20 and 50 minutes. The absorbances at the λmax of the chromophore and of the chalcone were recorded and graphed on Excel. A regression line was fitted to each set of data points. Then, since 44 CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004
absorbance is proportional to concentration, the slopes for the different time intervals were normalized per chromophore by dividing by initial absorbance. Results Ideally, conditions for the 1-, 2-, 4-, 10- minute intervals would dictate that the normalized slopes would be identical, with a better resolution of the decomposition curve for 1-minute intervals. However, going from 1- minute to 10-minutes, the slope often increased by a whole order of magnitude. Reasons for this could be temperature (during the 10-minute intervals, the temperature in the UV light-box often went above 50°, while in the 1-minute intervals, the temperature rarely rose above 33°), or the multiple starts and stops during testing (each time the plate was taken out of the UV light-box so it could be scanned on the spectrophotometer, the crosslinking reaction came to a stop and had to start back up again with a smaller concentration of chalcone than before.) Regardless, though the magnitude of the slope increased considerably from 1- to 2- to 4- minutes, only a 12—25% difference was evident between 4- and 10-minutes. Between the plates with chalcone and plates without, except EZ-FTC, chalcone seemed to increase the decomposition by a whole order of magnitude. Though each chromophore has a different extinction coefficient, making cross-comparison difficult, even a cursory visual evaluation showed the chromophores with ethylene linkages to be less stable that the SHJ chromophores without ethylene linkages, both with chalcone and without. The absorbances of the ethylenelinked compounds seemed to drop to half within 20—30 minutes, while the compounds lacking ethylene linkages appeared to decompose minimally. EZ-FTC, in particular, not only showed a steep decomposition that appeared to be at least an order of magnitude greater than SHJ1, but also showed an abnormally high amount of unlinked chalcone (implying that EZ- FTC absorbed and reacted with the UV light before the chalcone could). As EZ-FTC decreased, a new peak near 400nm also appeared (this behavior seems like it may be a mild analogue to the instability found in D. Casmier’s thiazole-forward molecules.) Conclusions Due to the time limitations on the research, some data was not satisfactory or completely consistent. However, it seems that with or without chalcone, chromophores lacking ethylene linkages are markedly more stable than the conventional EZ-FTC-style chromophores with ethylene linkages. More rigorous and extensive testing and re-testing will be required to say definitively, possibly using inert-gas atmosphere, temperature-controlled conditions, and real-time absorbance monitoring that does not require taking the chromophore out of the UV light-source. In light of the inherent instability which seems to exist with UV-exposure of ethylenelinked chromophores and hydroxyl-chalcone, I recommend that future photo-crosslinking studies look into using chromophores that do not include the vulnerable ethylene linkage. References 1. Lu, J. and J. Yin. 2003. J. Polym. Sci. 41:2:303-312. 2. Ramireddy, A.V., K. Subramanian, V. Krishnasamy and J. Ravichandran, 1996. J. Eur. Polym. 32,:8:919-926. CMDITR Review of Undergraduate Research Vol. 1 No. 1 Summer 2004 45
Page 1 and 2: CMDITR Review of Undergraduate Rese
Page 3 and 4: Welcome to the premier issue of the
Page 5 and 6: Extended Abstracts Table of Content
Page 7 and 8: wt % THV 220A). The glass tube was
Page 9 and 10: Fiber cladding preparation In order
Page 11 and 12: Acknowledgements Brian Ratliff, Gra
Page 13 and 14: Figure 2. Synthesis of the dendrime
Page 15 and 16: Toward the Synthesis of a Magnetic
Page 17 and 18: Results and Discussion Synthesis of
Page 19 and 20: years, (13) decomposes into a yello
Page 21 and 22: References 1. (a) MacDiarmid, A.G.
Page 23 and 24: suggests that any effects of these
Page 25 and 26: Electrospinning of Piezoelectric Ma
Page 27 and 28: varies and is close to the critical
Page 29 and 30: Synthesis of Azaindoly-phenanthroli
Page 31 and 32: Experimental Physical Measurements.
Page 33 and 34: [60] fullerene enable close packing
Page 35 and 36: Crystallization. We attempted to cr
Page 37 and 38: number of solvents including aceton
Page 39 and 40: References 1. Dalton, L.R. 2003. No
Page 41 and 42: though the beads were moving becaus
Page 43: Feasibility of Hydroxy-Chalcone Lin
Page 47 and 48: Results Linear Dichroism Metripol c
Page 49 and 50: Pararosaniline Xylene Cyanole FF Cr
Page 51 and 52: the source of the light emitted by
Page 53 and 54: Figure 6. UV and PL spectra of the
Page 55 and 56: Method The hybrid chromophore will
Page 57 and 58: Results The ligand was synthesized
Page 59 and 60: Following the cooling down, the pro
Page 61 and 62: Two-Photon Induced Free Radical Pol
Page 63: Future Work When the results of the

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