Two-dimensional electronic spectroscopy signatures of the glass transition

F Fuller,J P Ogilvie,P F Tekavec,K L M Lewis,J A Myers

doi:10.1155/2010/342156

Abstract

Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump–probe geometry with a pulse shaper [Optics Express15(2007), 16681-16689;Optics Express16(2008), 17420-17428], we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longer waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency–frequency correlation function [Optics Letters31(2006), 3354–3356]. Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreting temperature-dependent dynamics of biological systems.

Highlights

Two-dimensional electronic spectroscopy (2DES) is a useful tool for studying the dynamics of complex biological systems
Many commonly used solvents for biological samples will undergo a phase transition to a glassy state, and this transition can have a large effect on solvation dynamics and spectral diffusion
Two-dimensional electronic spectroscopy can serve as a probe of the liquid-glass phase transition through a number of different measures

Summary

Introduction

Two-dimensional electronic spectroscopy (2DES) is a useful tool for studying the dynamics of complex biological systems. Its ability to resolve ultrafast dynamics has been shown to be useful in photosynthetic systems, which contain many coupled chromophores that absorb in similar wavelength ranges [2]. Low-temperature 2D studies of these systems can give additional insight in resolving individual excitations and couplings where broad, room-temperature peaks overlap. Many commonly used solvents for biological samples will undergo a phase transition to a glassy state, and this transition can have a large effect on solvation dynamics and spectral diffusion. K.L.M. Lewis et al / Two-dimensional electronic spectroscopy signatures of the glass transition follow the frequency–frequency correlation function that reflects the fluctuating solvent environment of the reporter dye [6]

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