Lab 5: Modeling Conjugated Dyes with the Multielectron Particle-in-a-Box CH109 - Semester 2017 1 Lab #5: Modeling Conjugated Dyes with the Multielectron Particle-in-a-Box 1. You MUST bring a completed pre-lab before you will be allowed to start the lab. Correct the wavelength scale using the calibrations given in the class handout. The dyes are light sensitive, and so if it is necessary to store the dye solutions, protect them from light. It is advisable not to try to do the peak picking in Excel; it is fairly tedious. For the recalibration include a plot of the known wavelengths as a function of the measured wavelengths and the linear fit with your report. Atkins, J,: Paula, J. We can describe this concept using the equation. 3. 0000007157 00000 n
2. Finally, the length of the box for each dye molecule from the absorption spectra was calculated /Parent GCD210267, Watts and Zimmerman (1990) Positive Accounting Theory A Ten Year Perspective The Accounting Review, Subhan Group - Research paper based on calculation of faults. All of the conjugated dyes used have the largest absorbance at different wavelengths of light. 0000005432 00000 n
Do not get the dye solutions or methanol on your skin or in your eyes. White light is a mixture of all wavelengths of the visible spectrum. In the free electron model, represents a constant for a series of dyes of a given type.1 In this lab, represents the penetration distance which lies between 0-1. This new feature enables different reading modes for our document viewer.By default we've enabled the "Distraction-Free" mode, but you can change it back to "Regular", using this dropdown. Dye A has 6 electrons and dye B has 8 electrons in their respective pi-bond systems. The absorption spectrum of a series of conjugated dyes is produced by a UV/VIS spectrometer to calculate the empirical parameter and to find the length of the conjugated chain using the free electron model. Soltzberg, L. J. J. Chem. Hence, gamma should be calculated using only compounds from a homologous series (9). In this video you will learn how to calculate the maximum wavelength of absorption for a conjugated dye using the particle in a box (PIB) model. The particle-in-a-box (PIB) approximation is a theoretical model that calculates the absorption spectra of conjugated species. Thus the percentage difference was approximately 40%. 1949, 17, 1198. Phys. 1,1'-Diethyl-4,4'-cyanine iodide (Dye D) 1991, 68, 506-508. 0000008846 00000 n
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13. 9. 0000008957 00000 n
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In conclusion, we find that PIB is predictive as long as we apply it to a homologous series. Using the spectra shown, the max is determined by observing for each dye where the absorbance was the highest. Note: In the following work completely clean the cuvette between samples. Conjugated dyes are known sensitizers; take care when handling the dyes and wash your hands after handling them. /Transparency 61 0 obj
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2000, 77, 1221-1224. Conclusion : 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. 0000006031 00000 n
absorbance at different wavelengths of light. Identify the wavelength of the maximum absorbance, max, for each dye. dyes. 0 _________________________________________________________________________________________________. &P?ED Hp*^hZ{6@Lb"cx:+R+. lab, represents the penetration distance which lies between 0-1. length (m) << Platt, J. R. J. Chem. Color results when a compound absorbs light in a portion of the visible spectrum and transmits (or reflects) the remainder. The experimental procedure that was followed can be found in the practical manual. 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. II8b iDE;@8H%XDIc#,Olf4w73yTjHfHf`a Ch :n@| e~G)
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3. Bring a floppy disk to record your data. a Molar absorption coefficient in methanol at the absorption maximum (from reference 2).. P = # of carbon atoms in chain of conjugation. Image 1. determine the length of a conjugated carbon chain for a set series of dyes by a UV/VIS Then we use the number of pi electrons to determine the energy level of the highest occupied molecular orbital and the lowest unoccupied molecule orbital. For a molecule to absorb a photon, the energy of the impinging photon must match the energy difference between the initial state and some excited state of the molecule. 4 (an appropriate eigenfunction for eq. To test the robustness of the PIB model against four conjugated polymethine dyes, 1,1-diethyl-2,2-cyanine iodide (dye 1), 1,1-diethyl-2,2-carbocyanine chloride (dye 2), 1,1-diethyl-2,2-dicarbocyanine iodide (dye 3), and 1,1-diethyl-4,4-carbocyanine iodide (dye 4), I measured their absorption spectra 523 +/- 1 nm, 604 +/- 1 nm, 706 +/- 1 nm, and 706 +/- 1 nm at room temperature using a UV-Vis spectrophotometer, and calculated their PIB approximations and lengthening parameter gamma using an in-house MATLAB subroutine. 0000007549 00000 n
% If the two electrons with the same set of quantum numbers were switched then Equation (4) results. 0000001452 00000 n
IMPORTANT! The calculated length of 1, 1 Diethyl -2, 2 dicarboncyanine was 1 x 10-10 m. The You will record the UV-Vis absorption spectrum of each dye using either the Varian or Ocean Opticsspectrometers available in the laboratory. Clearly identify which curve corresponds to which dye and label lmax for each compounds. I got a 89%, which is close to being the bottom of my class :( But I worked hard for it, and thought I did well, so Im posting it here for you to see. An optimum gamma value of 1.2400 is obtained. 0 0000008795 00000 n
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a = (2j + 2)L, j = 2 double bonds /MediaBox Abstract In this experiment, the penetration length can be determined experimentally and refined with experimental data. model for the electrons. 0000001680 00000 n
8. https://chem.libretexts.org/Courses/Howard_University/Howard%3A_Physical_Chemistry_Laboratory/13._Particle_in_a_Box. 1,1'-Diethyl-2,2'-dicarbocyanine iodide (Dye C) Olsson, L. F. (1986). We also plot the literature and theoretical max against p for dyes 1, 2, and 3. 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. state of the molecule. << 1,1'-Diethyl-4,4'carbocyanine iodide (Dye E) Figure 1: The absorption spectra of each conjugated dye. /Filter 0 The wavelength of maximum absorbance (lmax) 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 lmax with solvent polarity, dye concentration and other factors. 2001, 78, 1432. Fill a cuvette with methanol and record a spectrum. Purpose: Moog, R. S. J. Chem. For dyes 1 and 3, the absolute percent errors are 8.79% and 3.64%, respectively, while the absolute percent error is the greatest for dye 4 (21.7%). Halpern, A. M. and McBane, G. C. Experimental Physical Chemistry: A Laboratory Text book, 3rdEd. 0000044295 00000 n
To test the robustness of the PIB model against four . 0000002519 00000 n
m"^}U%SzjFmV[luPym}jc^mvV;G;u4Xt4\VIZiYV+_;k|/l"#[bG EuL qf>Y#tLbJ( ]WIkrF'd kHP|o9ra+3Igeu
* w[VI[fSQ13M4/V# UMVyTp?8f34M3)0w^p2/&xX:~ q*j BI{J9LCL'u"/|&46W'LJUuW~Fb>L Educ. because of the poor solubility of these dyes in non-polar solvents and in water. You MUST fill out the cover sheet fully and correctly to receive credit. /Creator [ 1 In this A higher level means a higher potential energy. Although the theoretical max gives a similar trend we see in our max measurements, it seems that there is a good agreement between the experimental and theoretical max for dyes 1, 2, and 3, and not for dye 4. To calculate the length of the box, assume that the molecule is linear and use 154 pm and 135 pm for C-C and C = C bond lengths respectively. The different in energy between these two levels is exactly equal to the energy a photon needs to excite the dye. 0000007528 00000 n
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electron model. 0000001838 00000 n
subscribers only). HTMo0vnY?;vkZpH=z(YYPD:*?oi6A6oR0%J*e,uD|.j'NZ1NlD'Z{ ]^>IlrcN" YGHI4Hr4&y Ls43)i3 ef=:(+K)U\2%=+MQ5~P4zihve1\^v'M( 7v.OFz`\71+k(MmM]u36vU[q%pZ%qJf{7*`#u& sqJbY=rB1+C7R'rKyM^]L*HVZ4qcKs. 0000005032 00000 n
We do this by determining the length of conjugated region. $('document').ready(function() {
(The dyes are CONCENTRATED.) How spectroscopic measurements may be used to derive some molecular properties (in this case the length of a conjugated pi-bonded system in dye molecules). Educ. Accessibility StatementFor more information contact us atinfo@libretexts.org. 0000034252 00000 n
Educ. HXCCDdMp+ad{3p\P>n 7hf*v[g =&X!5;$5L/9e subscribers only). Pope, M., C.E. 1,1'-Diethyl-2,2'-carbocyanine iodide (Dye B) For x = 0 and x = L, i.e. %PDF-1.4 Any group that produces more waste than that will be penalized accordingly. Title: Particle in a Box: Absorption Spectrum of Conjugated Dyes The figure also shows the change in state caused by the absorption of a photon. 0000006052 00000 n
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Fill out the worksheet given below as you do the following. The experiment has been revised to suit our laboratory environment. In conclusion, my results suggest that PIB is predictive of the experimental only when it is applied to compounds in a homologous series. B ( 1,1-Diethyl- This, however, also depends on the literature value referenced. The purpose of this experiment is to measure the absorption spectra of two series of cyanine dyes and diphenyl polyenes, and to try to correlate the experimental observations using a simple quantum mechanical model. Band breadth of electronic transitions and the particle-in-a-box model. Particle in a box Pre-Lecture Assignment You must show all working to receive full credit. Electrons change energy levels when radiation is absorbed. 1 I found a large absolute percent error in the PIB approximation for dye 4 with respect to the experimental, and a breakdown in the positive linear association between the number of carbons framed by nitrogen atoms in the dyes and the experimental wavelengths when dye 4 is added to dyes 1, 2, and 3. observing for each dye where the absorbance was the highest. Im in the Class of 2020, and a week ago I turned in my final lab report for college. Educ. Click here to view this article (Truman addresses and J. Chem. These dyes are typically $100-$300 per gram and so it is important not to waste the materials. 5 0000009530 00000 n
Why compounds have color. Farrell, J. J. J. Chem. The dyes are light sensitive, and so if it is necessary to store the dye solutions, protect them from light. It will focus on the expansion of wavefunctions in basis sets of other functions. The results from a classic experiment in the undergraduate physical chemistry laboratory, the particle-in-a-box model for spectroscopic transitions of conjugated dyes, is compared to computational results obtained using a molecular mechanics structural approach and the extended Hckel molecular orbital picture. Three things need to be considered to calculate the energy changes from Equation 5. \[E = n^{2} \frac{h^{2}}{8mL^{2}}\] \[n=1,2,3 \] ] Kirksville, Missouri 63501 Click here to view this article (Truman addresses and J. Chem. 0000002771 00000 n
Part A In the free electron model, represents a constant for a series of dyes of a given type. %PDF-1.3 /Names Physical Chemistry Laboratory 0 Dye A Dye B. subscribers only). Abstract: The literature max recorded in Sigma Aldrich is actually a range from 702 nm to 710 nm (4). 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. Figure 2 shows that there is a potential energy barrier at the nitrogen atoms and there are wells at each atom; however to a reasonable degree of accuracy the potential energy of the conjugated pi-bonded system can be approximated by a particle in a box potential.
