����������� In thisinvestigation you will certainly measure the absorption spectra that a series of cyaninedyes.� Your speculative observationswill be examined in the frame of a straightforward quantum mechanically model, theparticle in a box model.� before thelaboratory you must familiarize yourself v the structures of the moleculesto it is in studied.�

Experimental Method:

The water you will be using in thisexperiment room toxic.� You should becareful in working v them, and avoid acquiring the options on yourskin.� In addition, these water willslowly degrade in the existence of light, for this reason you need to keep the options inthe dark once they are not in use.� Themanufacturers case 97% purity because that the 3 dyes detailed below.� friend should acquire spectra of the threecyanine dyes indicated in Table 1.

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1,1 "-diethyl-4,4"-cyanine iodide

Table 1.

Dye

M.W. (g mol-1)

e(105M-l cm-l)a

P

1,1 "-diethyl-2,2"-cyanine iodide

454.4

0.75

3

1,1"-diethyl-2,2"-carbocyanine iodide

480.4

1.95

5

1,1 "-diethyl-2,2"-dicarbocyanine iodide

506.4

2.13

7

aMolar absorption coefficient in methanol at theabsorption best (from reference 2).

P = # that carbon atoms in chain that conjugation.

N = p + 3 = # that conjugated � electron in cyaninechain

����������� We will certainly usemethanol as the solvent.� The molarabsorptivities (extinction coefficients) the these dyes are rather high, for this reason planyour dilutions to minimization the usage of the solutes and also solvent.� pick final concentrations such thatA~0.5-1.0 because that a standard, 1-cm pathlength cuvette. (Remember Beer"s Law: A = ecl.).� document spectra versus a solvent reference,scanning from 400-800 nm.� keep in mind thecolors that the stock solutions and also any alters in shade that occur when thesolutions are diluted.� You will certainly beusing the s Optics UV-Visible spectrometer to document the spectrum of eachdye.

����������� attract thesemolecules in HyperChem and also using a semiempirical CI calculation calculation theelectronic spectrum.� ar thisspectrum in your notebook.� What doesthe structure look like?�� check out themolecular orbitals the this collection of compounds.

����������� Determinehow the bit in a crate formulation can explain the absorption spectra ofthese water in the free electron model.�Develop a formula top top this basis.

Analysis:

����������� Yourcomputer notebook should encompass a concise review of the data, i.e., a tablecomparing your measurements of lmax v the lmaxdetermined native the cost-free electron model.�In to compare experiment and also theory, the wavelength of best absorptionfirst have to be calculated with a = 0, i.e., no mediate for finish effects.� you then should fit the data to the bestpossible a,using a non-linearleast squares fit within SigmaPlot (Regression Wizard- Equation category �User-Defined).� document data ~ above thequality of the to the right as indicated by Sigma Plot.�You likewise should analyze the lmax because that the members ofthe 1,1"-diethyl-4,4"-cyanine iodide series provided in Table 2. (data obtainedfrom Fisher and also Hamer).

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Table 2.

Dye

lmax

P

1,1"-diethyl-4,4"-cyanine iodide

593

7

1,1 "-diethyl-4,4"-carbocyanine iodide

704

9

1,1"-diethyl-4,4"-dicarbocyanine iodide

810

11

1,1 "-diethyl-4,4"-tricarbocyanine iodide

932

13

P # of carbon atom in chain the conjugation

N = ns + 3 = # that conjugated ir electron in cyanine chain

����������� similar to the2,2" series, usage the complimentary electron model to calculate the lmax�swith a= 0 and also with the ideal a figured out by a non-linear least squares fit. (Do notdespair if her a"slie somewhat external the 0 aa"s because that the two series and try to explain any differences based on differences in the molecularstructures.� You additionally should comment onthe appropriateness the the complimentary electron/particle-in-a-box design for describingthe spectra that the cyanine dyes.� Youranswer come this question should go past simply stating even if it is the design is"good" or "bad."