An Introduction to Two-dimensional Electronic Spectroscopy and its Applications

Abstract

This thesis is written as an introductory compilation of two-dimensional electronic spectroscopy (2DES) and its applications. It introduces the concepts of 2DES where the aim is to provide an overview of the technique and a few of its more prominent applications for those who are not already familiar with the technique. 2DES is a third-order optics technique that utilizes three interactions with laser pulses and involves four transition dipole interactions and is thus a so-called four wave mixing (FWM) technique. A set-up utilizing a diffractive optics (DO) element and a local oscillator (LO) for heterodyne detection in a boxcar geometry is described. Theoretical description of 2DES is based on nonlinear response function formalism in the third order of perturbation theory. Basic concepts regarding the formalism and the projection of the mathematics as visualizable by double-sided Feynman diagrams will be explained. Research performed by multiple scientists has been focused on understanding the ultra-fast energy transfer efficiency in photosynthetic organisms and artificial systems. Some early studies suggested that the biological systems utilize electronic quantum coherent behaviour to improve the efficiency. This has however not been confirmed in other studies. One topic under inquiry is the very nature of coherent oscillations observed in the experiments. The chlorosome, Fenna-Matthew-Olson (FMO) protein and reaction centre (RC) of green sulphur bacteria has been of particular interest in the division of Chemical Physics and will therefore be mentioned throughout the discussion.

Popular Abstract

Spectroscopy is a well-known technique used in many different scientific fields. Spectroscopy is derived from the Latin “spectron” which means spirit or ghost, and from the Greek “σκοπιεν” which means “to see”. [17] The kind of spectroscopy that is described in this thesis utilizes electromagnetic radiation (light) to see how microscopic objects not visible for the naked eye behave.

There are research problems that seem to delimit the very frontiers of science. One of these problems has for a few decades been in understanding the very fast processes of light-harvesting in some photosynthetic organisms. Ultra-fast spectroscopy techniques have provided the means for scientists to understand how processes on the time scale of femtoseconds (11 000,000,000,000,000 ⁄s) occur. Two-dimensional electronic spectroscopy (2DES) is one example of an ultrafast technique that takes on this challenge in a very effective manner.

We are in a global crisis of a rising energy demand and at the same time confronting the threat of climate change with rising global temperatures. Solar energy is a trustworthy source (at least for a few billion years) that provides Earth with energy at a rate of 120 000 TW and could thus, if used suitably, cover the needs of mankind with energy in an environment-friendly and sustainable manner. [4]

Photosynthesis has been refined for more than three billion years by evolution of the photosynthetic organisms. However, earth is bombarded with so much light that these processes were limited selected for by some organisms living on land. A few organisms have to the contrary developed a higher degree of efficiency in these steps of the photosynthesis because of environmental necessity. Green sulphur bacteria are one example of bacteria that has optimized this ability in order to survive in the dark places where they dwell – deep underwater – where the supply of photons has been a limited commodity in profit for the most well-adapted.

The quantum efficiency of the initial light-harvesting process in some photosynthetic organisms almost equals unity, [4] and is thus of great interest when it comes to developing artificial methods of converting light into other forms of energy, e.g. electricity. Detailed knowledge of these biological processes is thus an important area of research for further improvement in the areas of synthetic biology and biomimicry. With this technology we could imitate and improve the optimized principles of light-harvesting found in biological systems as well as improve the suboptimal ones. [4]

2DES techniques provide the efficient means for extracting information on light-matter interactions within multi-pigment systems, including photosystems in the bacterial cells such as the green sulphur bacteria. Exciton dynamics and the interpretation of quantum beatings have been questions under inquiry by many scientists for a few decades. [23] New techniques within the area of 2DES have been developed to elucidate the details of the complete dynamics within biological systems and the question regarding the nature of the quantum coherence found in the energy-transfer process. This is demonstrated in this thesis with an analysis of the reaction center in green sulphur bacteria, which showed that information about energy levels, energy transfer and quantum coherences can be obtained. 2DES is, furthermore, well used to investigate non-biological systems.

• author: Eliasson, Nora
• supervisor: Donatas Zigmantas
• organization: Department of Chemistry
• course: KEMK09 20161
• year: 2016
• type: M2 - Bachelor Degree
• subject: Chemistry
• keywords: Light-harvesting, Photophysics, KEMK09, Green Sulphur Bacteria, Spectroscopy, Photosynthesis, Two-dimensional, Optics, Laser, chemical physics, kemisk fysik
• language: English
• id: 8883509
• date added to LUP: 2016-07-01 13:47:28
• date last changed: 2016-07-01 13:47:28