Measuring Ultrafast Spectral Diffusion and Correlation Dynamics by Two‐Dimensional Electronic Spectroscopy

Abstract

The frequency fluctuation correlation function (FFCF) measures the spectral diffusion of a state's transition while the frequency fluctuation cross‐correlation function (FXCF) measures the correlation dynamics between the transitions of two separate states. These quantities contain a wealth of information on how the chromophores or excitonic states interact and couple with its environment and with each other. We summarize the experimental implementations and theoretical considerations of using two‐dimensional electronic spectroscopy to characterize FFCFs and FXCFs. Applications can be found in systems such as the chlorophyll pigment molecules in light‐harvesting complexes and CdSe nanomaterials.

Line-shape analysis of double-quantum multidimensional coherent spectra

“…In addition, peak lineshapes on a two-dimensional spectrum provide extremely valuable information. For example, one can determine a correlation function [19] (which is related to the spectral diffusion) by measuring the elipticity of the elongated peaks on a single quantum two dimensional spectrum as a function of the time delay between B and C pulses [20,21]. We note that over the years several methods have been developed to interpret lineshapes of singlequantum multidimensional coherent spectra [13,[20][21][22].…”

CLS Next Gen: Accurate Frequency–Frequency Correlation Functions from Center Line Slope Analysis of 2D Correlation Spectra Using Artificial Neural Networks

“…Two-dimensional correlation spectroscopy (2D CS) has become a powerful tool for studying the dynamics of a wide range of chemical systems. While developed first in 2D nuclear magnetic resonance, ultrafast laser equipment has enabled 2D CS to be performed in the infrared , (2D IR) and more recently for electronic spectroscopy at ultraviolet/visible frequencies (2D ES). , 2D IR spectroscopy has been used to examine the dynamics of liquids ,− and solute–solvent interactions, − protein dynamics, , and even the dynamics of crystalline solids , and interfaces. , The development of 2D ES has permitted the study of photoactive systems including dye molecules, photovoltaics, , quantum dots and wells, , and photosynthetic pathways. − A large family of related techniques are also being developed, including 2D electronic-vibrational and vibrational-electronic, heterodyne-detected 2D vibrational sum frequency generation, , and 2D terahertz, which all arise from the same theoretical framework…”

“…A 2D CS spectrum is a correlation plot between the frequencies of an ensemble of chromophores at an initial time and the frequencies of the chromophores after a “waiting time” T w . , There is a high density of information in a 2D spectra, such as the appearance of cross peaks from coherence transfer , or chemical exchange ,, and decay in the amplitudes of peaks due to population relaxation and orientational relaxation . Of particular interest in 2D IR, and increasingly in 2D ES, is the time evolution of the 2D line shape. If the spectrum is inhomogeneously broadened, the distribution of frequencies in the line shape typically corresponds to the distribution of chemical environments of the chromophore.…”

Observing the Fluctuation Dynamics of Dative Bonds Using Two-Dimensional Electronic Spectroscopy

“…The two main types of Chls, Chls a and b , with the molecular structures shown in Figure a,b, have been investigated under various studies using both steady-state − and time-resolved techniques. − The solvation relaxation timescales of Chls were reported to be in the range of several picoseconds. Recently, using advanced spectroscopic techniques, − the relaxation dynamics of Chls have been resolved in more details at various timescales spanning from sub-ps to tens of ps with several processes, including those involving hydrogen bonding and solvent polarity. , However, the assignments to specific molecular processes have remained elusive. Here, we perform 2DES measurements that study a specific molecular process, that of the fluctuation dynamics of a dative bond between the lone pair of a Lewis base and the Mg 2+ center of a Chl molecule.…”

“…The slowest timescale of nanoseconds is undetermined, as it is outside of our observed T w range. This long-lived component is usually assigned as a measure of the structural inhomogeneity of the chromophore and usually relaxes at a nanosecond timescale. − The second and third diffusion lifetimes, τ 2 and τ 3 , in the timescale of several to tens of ps are assigned to solvation relaxation processes. However, exact assignments to the molecular mechanisms of these processes remain elusive, and there are very limited evidential studies about the solvation mechanism at the molecular scale. , …”