Dye A has 6 electrons and dye B has 8 electrons in their respective pi-bond systems. As an extension to this project, the conjugation length of cyanine dyes has been used to discuss the particle-in-a-box principles, following a lab that was published earlier. 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. http://www.chemistry.nmsu.edu/studntres/chem435/Lab5/. You may not need to know the concentration precisely andit is usually sufficient to use only a few micrograms (a single crystal) in a 3-mL cuvette, as long as the dyes maximum absorption is less than approximately 1 absorbance unit. In all four dyes we are forcing the conjugation through the chain. The principle quantum number changes by +1. >> The visible bands in the spectra occur as a result of * electronic transitions and we can therefore treat these systems with the particle in the box model. calculate the empirical parameter and to find the length of the conjugated chain using the free For the dyes studied in this experiment the number of electrons (N) is an even number, p. There will be two electrons per energy level because of the Pauli Exclusion Principle. R trailer
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The potential energy of a system needs to be defined to calculate the energy levels. Fill a cuvette with methanol and record a spectrum. 0000008638 00000 n
We can describe this concept using the equation. Reference: Make plots of the absorbance spectra for dyes A F. You may combine the plots in one or two page graphs. });
lodide). Do not get the dye solutions or methanol on your skin or in your eyes. Truman State University the dotted lines. \[\psi \left ( q_{1}, q_{1}, q_{3}, q_{4}, \right ) = - \psi \left ( q_{1}, q_{1}, q_{3}, q_{4}, \right ) \] Our observation suggests that PIB is predictive only when it is applied to a homologous series, wherein all compounds in the series have similar functional groups and similar chemical properties, with the only difference here being an increase in carbon number. j = 3 double bonds /S Title The Particle-In-a-Box Model for describing the electronic transitions in conjugated dye molecules using UV visible spectroscopy. xVO@E
D}ID>j An optimum gamma value of 1.2400 is obtained. 1,1'-Diethyl-4,4'-dicarbocyanine iodide (Dye F) This principle of expansion will be repeatedly utilized in the quantum mechanical treatment of more complex chemical systems later in the semester. 0000002720 00000 n
5 Using the spectra shown, the max is determined by observing for each dye where the absorbance was the highest. $('document').ready(function() {
Polymethine dyes 1,1-diethyl-2,2-cyanine iodide (Eastman, CAS# 977968), 1,1-diethyl-2,2-carbocyanine chloride (Eastman, CAS# 2768903), 1,1-diethyl-2,2-dicarbocyanine iodide (Eastman, CAS# 14187316), and 1,1-diethyl-44-carbocyanine iodide (Eastman, CAS# 4727508), corresponding to dyes 1, 2, 3, and 4, were used as received. The different in energy between these two levels is exactly equal to the energy a photon needs to excite the dye. 1 lab, represents the penetration distance which lies between 0-1. 0000010740 00000 n
Now find the a value: a = (2j + 2)L = (2(3) + 2)(1.727 x 10-10) = 1.3816 x 10-9 m Since the s value (700 nm) has been known from the spectrum of , 1, 1 Diethyl -2, 2 dicarboncyanine iodide, use this to find the a values of other two wavelengths. Phys. It was also seen that the lengths of the box calculated increase with the number of carbon atoms. 54 0 obj <>
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Note: In the following work completely clean the cuvette between samples. 0000007413 00000 n
Suggest reasons for this difference. 0000033368 00000 n
conjugated chain backbone (including the nitrogen atoms). >> \[ \lambda _{abs} = \frac{8mL^{2}c}{h\left ( 2p+1 \right )} \] or Equation (11) \[ L=\sqrt{\frac{\lambda _{abs}h\left ( 2p +1 \right )}{8mc}} \] /Filter While the particle in the box model1-4 can be used to rationalize the trend in lmax, it does not explain the other effects. based on the particle in a box model. modeled as one-dimensional particles. If (q1,q1,q3,) is equal to zero then probability of any two electrons having the same identical set of quantum numbers is zero. electron model. In reality the pi electrons may be considered to reside across the system of conjugated pi-bond system that extends from one nitrogen atom to the other, Figure 1. obj Specifically. \[ \Delta E = \frac{h^{2}}{8mL^{2}} \left ( n_{f}^{2} - n_{i}^{2} \right ) \] Table 1. 2. 0000047452 00000 n
Click here to view this article (Truman addresses and J. Chem. 0000034272 00000 n
subscribers only). 0000001720 00000 n
0 9 Educ. /Type A higher level means a higher potential energy. Electronic Transitions in Conjugated Dye Molecules The quantum mechanical solutions derived for a particle in a box assumes a free particle moving within a region of zero potential inside "walls" of infinite potential. . endobj << 0000009530 00000 n
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4NsSRI>}fWU/:+UW^CZ={#4 N = 2j + 2 = 2(3) + 2 = 8 pi electrons For any function, f(x), if f(x) = -f(x) then f(x) must be equal to zero. conjugated bonds between the nitrogen atoms of the dye molecules. result of selective photon absorption. The literature max recorded in Sigma Aldrich is actually a range from 702 nm to 710 nm (4). This variation may have been due to the methanol buffer in which the dye is stored. Click here to view this article (Truman addresses and J. Chem. xb```f``b`c`sb`@ V( k,b'220gXDl
.g;s&IvBV 5_ndny6Z|QTf] Electrons change energy levels when radiation is absorbed. 0000002281 00000 n
The model for these molecules will be the "particle-in-a-box" which we will consider in class. You should just be able to see a little color. determine the length of a conjugated carbon chain for a set series of dyes by a UV/VIS L = 1 x 10-10 m Each spectrum shows a major peak, a shoulder peak at a smaller wavelength, and a baseline with minimum noise (Figure 1). The experimental procedure that was followed can be found in the practical manual. 0000002473 00000 n
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5. Use the same spectrometer settings and the same cuvette for the background and the dye solutions. Qp$BTxr#ivv }IVEsqw2M/gVS >/_d7>/$IT~5Oh2:hb*aQuU9S^T7pP*^d51 r[WAx^). the best fit is determined to be equal to 1 and the length of the box of , 1, 1 Diethyl -2, 2 The cosine function has a value of 1 when the . 0000001782 00000 n
Purpose: R In conclusion, we find that PIB is predictive as long as we apply it to a homologous series. You will measure the absorption spectra of a series of conjugated dyes and then usethe Particle-In-A-Box (theoretical model)to explain the observed spectra. >> 0000001680 00000 n
Accessibility StatementFor more information contact us atinfo@libretexts.org. A holmium oxide (Buck Scientific) test was performed to calibrate the spectrophotometer. The Particle-In-A-Box approximation Electrons in the -electron system of a conjugated aromatic compound are not restricted to specific nuclei but are free to move throughout the system. Platt, J. R. J. Chem. 0 L = 1 x 10-10 m 2000, 77, 637-639. IMPORTANT! 0000002519 00000 n
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Legal. All three dyes have a different max. This, however, also depends on the literature value referenced. Click here to download the Mathcad module and start the lab, Wear old clothing to lab! 1 % The "particles" in this particle in a box model are, of course, the p electrons of this conjugated system, and solving eq. 2001, 78, 1432. and M. Kasha (1958). endobj The absorption spectrum of a series of conjugated dyes is produced by a UV/VIS spectrometer to So in this case was, 1, 1 Diethyl -2, 2 dicarboncyanine iodide for it has ranged with 700nm. /S Any group that produces more waste than that will be penalized accordingly. Educ. Color results when a compound absorbs light in a portion of the visible spectrum and transmits (or reflects) the remainder. 0 0000001473 00000 n
Halpern, A. M. and McBane, G. C. Experimental Physical Chemistry: A Laboratory Text book, 3rdEd. You will want to present a series of dyes on the same graph, and so you must clearly indicate which spectral trace arises from which dye. Fourier Transform Infrared Spectroscopy (FTIR), CHEM 174 Physical Chemistry Laboratory II, Determination of the Length of a Molecular System, Pauli Exclusion Principle and Packing Electrons into the Particle in a Box. 0000001452 00000 n
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\[p=n_{i}=\frac{N}{2} \] \[ n_{f}=n_{i}+1\] \[ \Delta E = \frac{h^{2}}{8mL^{2}} \left [ \left ( p + 1 \right )^{2} - p^{2}\right ] \] \[ \Delta E = \frac{h^{2}}{8mL^{2}} \left ( 2p+1 \right ) \] /PageLabels All six dyes: 1,1'-Diethyl-4,4'-cyanine iodide, 1,1'-Diethyl-4,4'-carbocyanine iodide, 1,1'-Diethyl4,4'-dicarbocyanine iodide, 1,1'-Diethyl-2,2'-cyanine iodide, 1,1'-Diethyl-2,2'-carbocyanine iodide and 1,1'-Diethyl-2,2'-dicarbocyanine iodide and methanol are considered highly toxic and irritate the skin. http://www.chemistry.nmsu.edu/studntres/chem435/Lab5/ So each level of the particle in a box can contain two electrons, one spin up and the other spin down. 0000007528 00000 n
The experimental procedure that was followed can be found in the practical manual. It will focus on the expansion of wavefunctions in basis sets of other functions. absorbance at different wavelengths of light. Horng, M.-L. and Quitevis, E. L. J. Chem. (called an excited state). Casaubon, J. I. and Doggett, G. J. Chem. Particle in a Box is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts. The values calculated for the three dyes experimented on are, 352nm, 486 nm, and 622 nm, which supports the data given and supports the equation used to calculate the predicted wavelengths. If the two electrons with the same set of quantum numbers were switched then Equation (4) results. 4 0 obj 0000007892 00000 n
1997, 74, 1317-1319. 0000037527 00000 n
Therefore, if = 1, this Mathematically: The particle-in-a-box (PIB) approximation is a theoretical model that calculates the absorption spectra of conjugated species. Abstract: $('#comments').css('display', 'none');
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Shoemaker, D. P.; Garland, C. W. and Nibler, J. W. Experiments in Physical Chemistry, 7th Ed. Our experimental max for dyes 1, 2, and 3 agree with their respective literature values within their uncertainties. Thus the percentage difference was approximately 40%. 0 The particle in a box model refers to pi electrons in the. We do this by determining the length of conjugated region. HXCCDdMp+ad{3p\P>n 7hf*v[g =&X!5;$5L/9e 1. %PDF-1.3 The dyes are light sensitive, and so if it is necessary to store the dye solutions, protect them from light. Calculate the length of the conjugated pi-system, L, for each of the dyes from the measured . 0000006917 00000 n
/Resources subscribers only). Atkins, J,: Paula, J. The spectra of other types of cyanine dyes, which have been discussed ex-tensively in the literature (9-11), can be represented by the simplified general formula An example is the family of thiacarbocyanine dyes Cyanine Dyes: Unmodified PB . by treating the system as a 1-D particle in a box. For dye 4, the absolute error is 3 nm while the experimental uncertainty is +/- 1 nm, suggesting a disagreement. B ( 1,1-Diethyl- subscribers only). endobj 10 Finally, the length of the box for each dye molecule from the absorption spectra was calculated An increase in major peak wavelength is observed as the carbon number increases from dyes 1 to 3. >> Educ. 0 R { "4.01:_Pre-lab_Assignment" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass228_0.
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