You will record the UV-Vis absorption spectrum of each dye using either the Varian or Ocean Optics spectrometers available in the laboratory. Any group that produces more waste than that will be penalized accordingly. It is possible to obtain the absorption spectrum of all the dyes in Table 1 (all in the same solvent), and generate only 100 mL of waste. These dyes are typically $100-$300 per gram and so it is important not to waste the materials. IMPORTANT! You may not need to know the concentration precisely and it is usually sufficient to use only a few micrograms (a single crystal) in a 3-mL cuvette, as long as the dye’s maximum absorption is less than approximately 1 absorbance unit. ![]() Use the references 3 and 4 to develop an experimental procedure. The dyes are light sensitive, and so if it is necessary to store the dye solutions, protect them from light. Conjugated dyes are known sensitizers take care when handling the dyes and wash your hands after handling them. Representative members of the cyanine family of conjugated dyes.ĬAUTION! The toxicity of the dyes used in this lab should be considered unknown and as such all should be treated as toxic. Dyeġ,1'-diethyl-2,2'-carbocyanine chloride (pinacyanol)ġ,1'-diethyl-4,4'-carbocyanine iodide (cryptocyanine) Some references from the Journal of Chemical Education are included here to help you get started, 5-12 and please discuss your ideas with the instructor. To develop your hypothesis you must first read some articles describing the system, what is known about it, and some of the approaches that others have used to address these questions. Unfortunately, this experiment cannot be done with the equipment that we have in the laboratory, but it is possible to test a number of hypotheses using only a UV-Vis spectrometer, the dyes in Table 1 and common laboratory solvents. For example, your hypothesis might be that the dye’s large second hyperpolarizability is the source of dependence of l max on number of carbon atoms in the dye, which could be measured by light scattering. In this exercise you will explore the spectroscopy of the cyanine dye family, develop a testable hypothesis and then determine the validity of your hypothesis. While the particle in the box model 1-4 can be used to rationalize the trend in l max, it does not explain the other effects. The wavelength of maximum absorbance (l max) for the cyanine family of conjugated dyes, representative members of which are shown in Table 1, has a marked dependence on the number of conjugated carbons, 1,2 while some also exhibit changes in l max with solvent polarity, dye concentration and other factors.
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