All solutions were freshly prepared and were continuously stirred through the entire length of the experiment in a 2 mm optical path length quartz cell (Starna Cells, Inc.) using a Teflon-coated magnetic stirring bar. The sample was replaced with a fresh solution to maintain less than five percent decrease in absorbance through the entire length of the experiment, as monitored from the maxima of the lowest-energy band of the absorption spectra.