The results of the dynamics analysis are shown in Figure . 8. Note that data points at later time delays are more off-trend because of the lower IR signal resulting from the population relaxation. All the fitting parameters are listed in Supplementary Tables , and 3. The amplitude A 1 is related to the amide I frequency fluctuations, where a larger amplitude indicates increased disorder in the local environment. The time constant τ 1 represents the timescale of the motions within the local environment. The offset y 0 , also known as static inhomogeneity, is related to the solvent-inaccessible amide I modes, whose dynamics are slower than the investigated time window. It is worth noting that the offset from the fitting also depends on the selected frequency region because of the peak overlap of different backbone structures. Because we select three frequency regions to reveal the solvent dynamics around the three secondary structures, the offset from the fitting cannot be directly compared across the three structures. It is also discovered that the CLS of β -sheet decays very fast within 0.3 ps and plateaus afterwards, making it difficult to accurately extract decay constants for β -sheet. Therefore, only the values of the offset y 0 are listed for β -sheet in Supplementary Table .