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Solvatochromism and Photo-Induced Intramolecular Electron Transfer
Katelyn J. Billings; Bret R. Findley1
1Department of Chemistry and Physics, Saint Michael’s College, Colchester, VT 05439
ABSTRACT COMPOUNDS STUDIED SAMPLE RESULTS
Our proposed research is intended to develop a laboratory exercise for
publication, suited for a physical chemistry class. The exercise centers around
the study of solvatochromism, which affects both emission and absorption in Plot of v ct vs Df from Steady State Fluorescence
(for Coumarin 153)
intramolecular photo-induced electron transfer. The method itself involves steady
state absorption and steady state fluorescence measurements and allows for the 25000.0015
determination of the change in dipole moment between the
excited and ground states of the covalently linked electron donor and acceptor. It N 20000.0015
also provides for an experimental measurement of polarity for solvents and y = -8464.7x + 22022
15000.0015
Coumarin 153 2
v ct
solvent mixtures. R = 0.8905
10000.0015
3
BACKGROUND 5000.0015
O 0.0015
When dealing with intramolecular photo-induced electron transfer (PET),
•An electron donor and acceptor are covalently linked together (A-D complex) Reichardt’s Dye 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45
•The donor or acceptor is locally excited by a photon (h1) Df
4-amino-N-
•The complex undergoes electron transfer methylphthalimide
•As a result the positively charged donor cation is bonded to the negatively
charged acceptor anion. Our Experimental Δμ : 7.05D Literature values1:
CALCULATING THE CHANGE IN DIPOLE MOMENT1: Given that: ρ = 3.9Ǻ Theoretical Δμ = 3.9D
•This A--D+ excited state complex follows one of two potential pathways
whereby it returns to the ground state D-A complex Experimental Δμ = 6.0D
•releasing either a photon via fluorescence (h2) OR 2D 2 1 n2 1
•heat ct ct (0)
~ ~
Df Where: Df 2
A - D + ΔH hc (4 0 )
3
2 1 4n 2 LAB SETUP & CONCLUSIONS
h1 kET A- - D+ ~
A- D A *- D
•vct = frequency of maximum emission in cm-1 •Δf = the solvent factor (change in Students will:
~ the reaction field)
A-D + h2 •vct (0)= frequency of maximum emission in the •Run steady state absorption and fluorescence spectra for:
gaseous phase in cm-1 •ε = the solvent dielectric constant •Reichardt’s Dye &
•Δμ = difference in excited and ground state •n = the refractive index •Coumarin 153 OR
As one alters the polarity of the solvent, the fluorescence produced undergoes
dipole moment •4-amino-N-methylphthalimide
a wavelength (or color) change in a process known as solvatochromism. •ρ = the radius of the solute cavity •h = Planck’s constant
•4πε0 = gas permittivity constant
Which will be dissolved in Chlorobenzene, DCM, DMSO, & Acetonitrile
•Bathochromic shift: the wavelength of emission shifts towards •c = speed of light •Graph the results and calculate Δμ.
the red end of the spectrum (lower photon energy),
•Hypsochromic shift: the wavelength shifts towards the blue end of TABLE OF CONSTANTS In conclusion this lab will help students as:
the spectrum (higher photon energy). It gives them a good introduction to photo-induced intramolecular electron
Compound ρ (Ǻ) ε (@ 25˚C)5 η (@ 25˚C)5 transfer, which has applications to photovoltaic and solar cells,
For solutes with non-polar ground states: nanotechnology and many chemical and biological processes.
• Changes with the solvent polarity stabilize the excited A-—D+ complex Cu153 3.92 -- -- It provides them with a quantitative method for analyzing solvatochromism.
4-ANMP 3.33 -- -- • It deepens their understanding of basic physical chemistry topics.
•This lowers the energy gap between excited A-—D+ and ground A-D states
• emission spectra for a particular D-A complex is indicative of the polarity Reichardt's Dye 7.84 -- --
of the solvent and the dipole moment of the excited A-—D+ complex. FUTURE PLANS
Chlorobenzene -- 5.621 1.52185
•Calculate the change in dipole moment for Reichardt’s Dye, as it does NOT have a non-
Dichloromethane -- 8.93 1.42115 polar ground state.
A* —D
Dimethyl Sulfoxide -- 46.45 (20˚C) 1.47933 (20˚C) •Reevaluate our data—Check Fluorimeter calibration/correction for accuracy.
Electron
Transfer A- —D+ •Test lab and submit for publishing.
Solvent Acetonitrile -- 35.94 1.34163
Relaxation A- —D+
E hυ1 ACKNOWLEDGEMENTS
SAMPLE DATA
hυ2
The authors would like to thank the NASA Vermont Space Grant initiative for
Fluorescence Spectra for Coumarin 153 funding this research project.
A —D A —D
REFERENCES
(1)Hermant, R. M.; Bakker, N. A. C.; Scherer, T.; Krijnen, B.; Verhoeven, J. W. J. Am.
EXPERIMENTAL PROCEDURE Chem. Soc, 1990, 112, 1214-1221.
•Take fluorescence measurements for solvatochromic dyes in a variety of **Note the Bathochromic Shift (2) Maroncelli M., Fleming, G. R. J. Chem. Phys, 1987, 86, 6221-6239.
solvents (with different polarities).
(3) Chapman, C. F.; Fee, R. S.; Maroncelli, M. J. Phys. Chem., 1995, 99, 4811-4819.
•Plot ct, the maximum emission frequency in cm-1, versus Δf, a solvent (4) Mente, S. R.; Maroncelli, M. J. Phys. Chem B., 1999, 103, 7704-7719.
polarity parameter.
(5) Riddick, J. A; Bunger, W. B.; Sakano, T. K. Organic Solvents: Physical Properties and
•Slope of this line ultimately yields Δμ, the difference in excited and ground Methods of Purification; Wiley Interscience: New York, 1986; Vol. 2.
state dipole moment of the solute.
