46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015;
Columbus, Ohio
Session C1: DAMOP Thesis Prize
2:00 PM–4:00 PM,
Tuesday, June 9, 2015
Room: Regency Ballroom
Chair: John Bollinger, National Institute of Standards and Technology
Abstract ID: BAPS.2015.DAMOP.C1.2
Abstract: C1.00002 : Non-Adiabatic Mechanism for Photosynthetic Energy Transfer and All-Optical Determination of Concentration using Femtosecond Lasers
2:30 PM–3:00 PM
Preview Abstract
Abstract
Author:
Vivek Tiwari
(University of Colorado, Boulder)
Understanding the fundamental physics of light-harvesting in both, natural
and artificial systems is key for the development of efficient
light-harvesting technologies. My thesis addresses the following topics, i.)
the mechanism underlying the remarkably efficient electronic energy transfer
in natural light harvesting antennas, ii.) a femtosecond time-resolved
photonumeric technique to quantitatively characterize transient chemical
species. This talk will concentrate on the first project, while briefly
touching the key ideas of the second project.
Light harvesting antennas use a set of closely spaced pigment molecules held
in a controlled relative geometry by a protein. It is shown that in certain
antenna proteins the excited state electronic energy gaps between the
pigments are resonant with a quantum of pigment vibrational energy. With
such a vibrational-electronic resonance, anti-correlated motions between the
pigments lead to a strong coupling between the electronic and nuclear
motions, that is, breakdown of the Born-Oppenheimer approximation, over a
wide range of pigment vibrational motions. It is shown that the 2D
spectroscopic signatures of the resulting unavoidable nested non-adiabatic
energy funnel on the excited states of photosynthetic antennas are
consistent with all the reported 2D signatures of long-lived coherent
oscillations, including the ones that are not explained by prior models of
excited state electronic energy transfer. Extensions that account for both
resonant and near-resonant pigment vibrations suggest that photosynthetic
energy transfer presents a novel design in which electronic energy transfer
proceeds non-adiabatically through clusters of vibrations with frequencies
distributed around electronic energy gaps.
I will also briefly talk about our experiments demonstrating quantitative
time-resolved measurement of \textit{absolute} number of excited state molecules. Based on
these measurements, an all-optical technique that simultaneously determines
concentration and extinction coefficient of an unknown sample is presented.
Unlike prior analytical techniques, any requirements such as sample
isolation, physical handling or in situ calibrant are eliminated allowing
possible extensions towards characterizing transient chemical species.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2015.DAMOP.C1.2