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DIPHENYLPOLYENE DYE SPECTRA

DIPHENYLPOLYENE DYE SPECTRA. UV-VISIBLE SPECTROSCOPY PARTICLE IN THE BOX. QUANTUM MECHANICAL MODEL. Delocalized pi electrons in a conjugated dye molecule are constrained to move along the C-C backbone.

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DIPHENYLPOLYENE DYE SPECTRA

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  1. DIPHENYLPOLYENE DYE SPECTRA UV-VISIBLE SPECTROSCOPY PARTICLE IN THE BOX

  2. QUANTUM MECHANICAL MODEL • Delocalized pi electrons in a conjugated dye molecule are constrained to move along the C-C backbone. • What energy states are the pi electrons in? The particle in the box model provides the answer. • En = n2h2/8mL2 where L is the length of the dye molecule, m is the electron mass, h is Planck’s constant and n is 1,2 ,3…

  3. QM Model - 2 • Light absorbed by the dye molecule will cause the electron to be promoted from ni to nf. • The energy of this transition is ΔE = (nf2 -ni2)h2/8mL2 = hc/ • Measure the absorption spectra for three dye molecules (with increasing L values)

  4. BEER’S LAW • Beer’s Law describes the dependence of absorption intensity on dye molecule concentration, [J]. • A = ε [J]ℓ where ε is the molar absorption coefficient and ℓ is the cell path length. • A linear least analysis of A vs [J] yields ε.

  5. Analysis • Calculate the Particle in the Box predictions for absorption wavelength and compare them to the experimental values. • Modify the Box model using a factor α. • Use the absorbance vs dye concentration data to determine the extinction coefficient for one dye.

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