This
applet shows the energy levels and wave functions
for electrons confined to a one-dimensional box.
This is a simple model to explain the absorption
spectra of conjugated dyes.
A dye will absorb photons having
energy equal to the difference between the lowest
unoccupied energy level and the highest occupied
energy level. Click on the "show excited
state" and "show ground state"
buttons to see this difference. The red arrows
represent electrons in different energy levels.
A dye with longer conjugation is
modeled by increasing the box length. Click on
the x-axis and drag right or left to change the
length of conjugation in the dye.
Exercise.
Consider a dye with conjugated bonds as in the
figure below.
The
dye has 8  -electrons that are
"free" to move along the
-N-C-C-C-C-C-N- skeletal structure. Estimate the
length of the conjugated-bond chain assuming
carbon-carbon and carbon-nitrogen bond lengths of
about 0.14 nm and including a bond length at each
end of the chain. Enter these values into the
applet below (using the mass of the electron) and
determine the wavelength of absorption expected
for a molecule with this conjugated component.
How does the estimated wavelength of absorption
compare to a typical experimental value of 416 nm
for this type of molecule?
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