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

We perform two-dimensional electronic spectroscopy on chlorophyll (Chl) and molecules in aprotic solvents of different Lewis basicity. By analyzing the ultrafast spectral diffusion dynamics of the Q transition, we show that a certain timescale of the spectral diffusion dynamics is affected by the solvents' Lewis basicity. Control experiments with Chlorin-e6-a Chl molecule analog-and time-dependent density functional theory calculations confirm that we are directly probing the fluctuation dynamics of the dative bond between the solvent's lone pair and the Mg center in Chls that is responsible for the Lewis basicity.

Glass formation of a DMSO-water mixture probed with a photosynthetic pigment.

Despite their extensive industrial usage, glass-forming liquids are not fully understood, and methods to investigate their dynamical heterogeneity are sought after. Here we show how the appearance of a second component in the visible absorption spectrum of a photosynthetic pigment upon cooling can be used to probe the glass transition of a dimethylsulfoxide-water mixture. The changes in the relative ratio of the two components with respect to temperature follow a sigmoid curve, and we show that the second component arises due to protonation of the pigment at low temperatures.