Dye Aggregation Identified by Vibrational
Coupling Using 2D IR Spectroscopy
Tracey A. Oudenhoven,† Yongho Joo,‡ Jennifer E. Laaser,†,¶ Padma Gopalan,‡ Martin T.
Zanni*,†
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, and
Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison,
Wisconsin 53706
Email: zanni@chem.wisc.edu
*To whom correspondence should be addressed
†
University of Wisconsin-Madison Chemistry
‡
University of Wisconsin-Madison Materials Science and Engineering
¶
Current address: University of Minnesota, Twin Cities Chemistry
Supplemental Information
Figure S1: Waiting time 2D IR spectra for ReC and ReCC in ethanol and acetonitrile solutions.
a),d),g) at waiting time = 0 ps, b),e),h) at waiting time = 1 ps, and c),f),i) at waiting time = 3.5 ps
for ReC and ReCC respectively.
Figure S2: Normalizing constant exponential fits to waiting time 2D IR data. a), b) ReC samples
with waiting time = 3.5 ps (a-acetonitrile solution, b-ethanol solution); c),d) ReC plots of
normalization constant, a, of same samples as first column (c-acetonitrile solution, d-ethanol
solution); e), f) ReCC samples with waiting time = 3.5 ps (e-acetonitrile solution, f-ethanol
solution); g),h) ReCC plots of normalization constant, a, of same samples as first column (gacetonitrile solution, h-ethanol solution).
Exponential decay data analysis
In order to better resolve 2D IR cross peaks, we have developed a method to emphasize the cross
peak presence. For a series of waiting time spectra, the intensities at each pixel of the 2D IR
spectrum are fit to a least squares single exponential function (Equation 1).
𝑓(𝑥) = 𝑎 𝑒 −𝑏∗𝑡𝑖𝑚𝑒 + 𝑐
(Equation 1)
Figure S3a shows the intensity for a representative pixel on one of the diagonal peaks for a
sample of amorphous deposits along with the fit using Eq 1. Figure S3b-d shows three different
contour plots created from the exponential fitting: one plotting the leading normalizing constant
(a), one plotting the time constant of the exponential (b), and one plotting an offset (c). Each of
these parameters was visualized in a 2D plot (an example is given in Fig. S3). The plot of the
normalization constant, a, was found to give the relative intensities of the diagonal peaks much
like at a waiting time of 0 ps, but with particular sensitivity and increased intensity to the
presence of cross peaks. The plot of the time constant, b, was not found to give clear cross peak
information, probably due to universal fitting parameters for the whole spectrum. However, the
time constant plot does show that the diagonal peaks have uniform decay, which would be
expected in these systems. Lastly, the plot of the offset, c, vaguely resembles the input 2D IR
spectra; however, with an intensity greater than a factor of ten lower than the normalization
constant plot. In this study, we used the normalization constant plots in order to identify the
location of cross peaks to measure relative intensities and coherent oscillations of the actual 2D
IR data.
Figure S3: Example exponential fits of Equation 1 to one set of 2D IR data, namely ReC
amorphous deposits on sapphire. (a) Exponential fit to diagonal peak. Contour plots of (b)
normalization constant, a, (c) time constant, b, and (d) offsets, c.
Figure S4: Comparison of cross peaks to noise from 2D IR data for ReC amorphous deposits.
Blue – lower cross peak, Green – upper cross peak, Red – data from (pump,probe) (2048,1946).