Absorption Spectrum Of Conjugated Dyes

1574 Words Mar 23rd, 2015 7 Pages
Absorption Spectrum of Conjugated Dyes
Bashar Baraz
Lab Partners: whole class
Physical Chemistry II

Abstract: The highly conjugated system of the cyanine dyes makes it a very good compound in the development of more efficient solar cells. In this experiment, the maximum wavelength was measured for nine dyes using a UV-Vis spectrum. The result that were obtained agreed with Kuhn’s model for the less polarizable end groups such as 3,3 '-diethyloxadicarbocyanine and 3,3 '-diethyloxatricarbocyanine. That suggested that these two compounds were not as easy to polarize compared to the rest of the dyes. The rest of the dyes required the use of the empirical parameter α to provide more reliable predictions of the wavelengths. This was due to the highly polarized ends of the dyes which needed the adjustment of the parameter to get more accurate results. The series with the higher polarizable end groups’ absorbed higher wavelength light than the less polarized groups. This supported the idea of the one-dimensional box. Also, higher wavelength was determined to be associated with longer conjugated carbon methine chains between the Nitrogen atoms. Kuhn’s free electron model was very reliable for this system.
The conjugated electron system in polymethine dyes allows these compounds to absorb light in the visible region of the electromagnetic spectrum. Many of the carbocyanine dyes contain a different number of methine carbons with two…
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