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Solvatochromism and Photo-Induced Intramolecular Electron Transfer

Solvatochromism and Photo-Induced Intramolecular Electron Transfer. Katelyn Billings, Dr. Bret Findley Saint Michael’s College. Abstract. Develop a laboratory exercise for a physical chemistry course Major topics covered Solvatochromism Intramolecular photo-induced electron transfer

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Solvatochromism and Photo-Induced Intramolecular Electron Transfer

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  1. Solvatochromism and Photo-Induced Intramolecular Electron Transfer Katelyn Billings, Dr. Bret Findley Saint Michael’s College

  2. Abstract • Develop a laboratory exercise for a physical chemistry course • Major topics covered • Solvatochromism • Intramolecular photo-induced electron transfer • Method • Steady state absorption • Steady state fluorescence • Goal • Determine the change in dipole moment between ground and excited electronic states • Compounds used • Coumarin 153 • 4-amino-N-methylphthalimide • 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate

  3. ReactionPathway Background A - D + heat k-ET, non-rad kET hυ1 A- - D+ A* - D A - D A* —D k-ET, rad Electron Transfer A- —D+ hυ2 A-D + Solvent Relaxation A- —D+ hυ1 E hυ2 A—D A—D Energy Diagram Key Terms • Solvatochromism Bathochromic Shift Hypsochromic Shift

  4. Experimental Method • Take fluorescence measurements for Coumarin 153 in a variety of solvents (with different polarities). • Plot , the maximum emission frequency in cm-1, versus Δf, a solvent polarity parameter. • Slope of this line yields Δμ, the difference in excited and ground state dipole moment of the solute. • We plan to make similar measurements with other compounds.

  5. ~ ~ Relevant Equations1 ~ ~ Where: • Δf = the solvent factor (change in the reaction field) • ε = the solvent dielectric constant • n = the refractive index • h = Planck’s constant • c = speed of light • vct = frequency of maximum emission in cm-1 • vct (0)= frequency of maximum emission in the gaseous phase in cm-1 • Δμ = difference in excited and ground state dipole moment • ρ = the radius of the solute cavity • 4πε0 = gas permittivity constant (1) Hermant, R. M.; Bakker, N. A. C.; Scherer, T.; Krijnen, B.; Verhoeven, J. W.; J. Am. Chem. Soc, 1990, 112, 1214-1221.

  6. 3 Solutes Studied N Coumarin 153 O Reichardt’s Dye 4-amino-N-methylphthalimide

  7. Fluorescence Spectra for Coumarin 153 Sample Results for Coumarin 153 Maroncelli value2: Theoretical Δμ = 3.9D Empirical Δμ = 6.0D (assuming ρ=3.9A) **Note the Bathochromic Shift Our Experimental Δμ : 7.05D (2) Maroncelli, Fleming. "Picosecond solvation dynamics of coumarin 153: The importance of molecular aspects of solvation." J. Chem. Phys. 86 (11)(1987): 6221-6239.

  8. Future Plans A Quick Review of the Lab • Run spectra for the Reichardt’s Dye and for Coumarin 153 or 4-amino-N-methylphthalimide • Solvents • Chlorobenzene • Dichloromethane • Dimethyl Sulfoxide • Acetonitrile • Calculate the change in dipole moment for Reichardt’s Dye • Reevaluate our data—Check Fluorimeter Calibration/Correction of max values • Test lab and submit for publishing

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