© Ultrafast Systems LLC /Vernier Software & Technology
32
Figure 16:
Ground state absorption spectrum of mercury dithizonate (trans conf.) in ethanol
Procedure
Obtain and wear goggles. Prepare a 25 mL stock solution of HgDz in ethanol with sufficient solute
to provide absorbance of ~1/cm at 500 nm (roughly 10
-5
M). Prepare 25 mL of 0.01 M stock solution of
TFA in ethanol. Prepare at least 5 sample solutions, each containing 3 mL of HgDz stock, aliquots of TFA
stock in the range of 0–1 mL and sufficient ethanol to bring total volume to 4.0 mL. These sample
solutions will all have the same concentration of HgDz and varying concentrations of TFA in the range
0–0.02 M TFA. Place ~4 mL of the [TFA] = 0 M sample solution in a 10 mm x 25 mm rectangular
borosilicate cuvette with all faces polished and proceed to photoexcitation.
Photoexcitation of an air-saturated ethanol solution of the Hg complex with the dithizone ligand in
the cis-form induces cis-to-trans isomerization, and the compound changes color from orange to blue
(
λ
max
= 605 nm).
