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Chem 42013 Lab 04: UV-Visible Absorption Spectra of Conjugated Dyes 0.1g 2.22104 Materials 4.54.3 454.3 454.34 HzC CH3 1,1'-diethyl-2.2-cyanine iodide 306.4 1.1'-diethyl-4,4-cyanine iodide soe.s 1,1-diethyl-4,4'-carbocyanine iodide 3,3-Diethyl-9-methylthiacarbocyanine iodide Procedure Dye solutions need to be approximately 10% Min methanol using the smallest volumetric flasks available. Obtaining small volumes of such low concentrations will require more than one dilution step. One possible method is to make a 10-4 M solution in a 100 ml volumetric flask, then dilute that to the desired concentration in a 10 mL volumetric flask. You and your lab partner(s) are welcome to use any method you choose, but I must approve your calculations before you begin. I recommend that the class as a whole prepares diluted "stock" solutions of each dye, and then each lab group prepares their own diluted solution of each. It is important to dilute the solutions properly, because if the dye solutions are too concentrated, it is possible for dimers to form in solution. The dimers will absorb at different wavelengths than the monomers, and therefore interfere with your spectral analysis. To verify that you solution has primarily monomers, also perform a 1:4 dilution of the 10-M solution and measure the absorption spectra from 300 nm to 800 nm on the UV-visible spectrophotometer (note the actual name and model of both the 10% M solution and the more dilute solution. If the hear is the same for both solutions it is confirmation that even the more concentrated solution contains monomers and not dimers. However, if the hmm is significantly different for the two solutions, then it is likely there is significant dimer formation. In this instance, take your most dilute solution and perform another 1:4 dilution. Measure the absorbance again to ensure the peak has not shifted with the further dilution. 1
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Table II should include: • the n associated with the HOMO (nHomo) • the PIB energy of the HOMO (ExoMO) • the n associated with the LUMO (TLUMO) • the PIB energy of the LUMO (ELUMO) the difference in energy between the HOMO and LUMO (AE) Table III should include the theoretical wavelength oux (in nm) • the experimental wavelength wax (in nm) the literature wavelength (in nm) the percent difference of the theoretical wavelength and the experimental wavelength, the percent difference of the experimental wavelength and the literature wavelength