Ultrasensitive nonlinear vibrational spectroscopy of complex molecular systems

In this work we use polarization-resolved pump-probe and two-dimensional infrared (2DIR) spectroscopy to study the conformational changes and the vibrational population dynamics in complex molecular systems.
In the first part of this thesis we investigate elastin-like polypeptides, which are a new class of biocompatible molecules known for their promising application in drug delivery, tissue engineering and recombinant protein purification. When heated above their lower critical solution temperature, these peptides undergo a sharp, reversible transition to an insoluble phase. We study the molecular origin of this transition by using 2DIR spectroscopy to probe the amide I’ vibration, which is sensitive to the conformation and the solvation state of the peptide backbone.
In the second part we demonstrate how the sensitivity of nonlinear vibrational spectroscopy can be increased by more than 4 orders of magnitude by exploiting the nearfield of infrared gold nanoantennas. In addition to performing a proof of principle experiment, we also develop an intuitive and didactic model which explains the observed linear and nonlinear infrared signals.
In the last part we study methylammonium lead halide perovskites, which are a new class of solution-processable, cheap, high-efficiency solar-cell materials. Many of the remarkable optoelectronic properties of these materials are attributed to the fast reorientational dynamics of the methylammonium cation. We use a combination of 2DIR spectroscopy and molecular dynamics simulations to characterize the timescale and nature of these ultrafast motions.