Precise control of energy transfer between single dipole-coupled molecules in a tunable half-wavelength Fabry-Pérot resonator at cryogenic temperatures

• Applicant: Professor Dr. Alfred J. Meixner
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2011 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 196392417

The Förster resonance energy transfer is an intensively discussed and often applied photo-physical process. Its mechanism bases on dipole-dipole interaction, whereby the energy absorbed by a donor-molecule is transferred to an acceptor-molecule. Since several years, there is a controversial debate about how this or similar energy transfer processes can be controlled actively. Active control means that the dynamics of the transfer in time time and energy domain are to be altered by a controllable environment leading either to an enhancement or complete suppression of the transfer. This issue is especially of great importance for the design of micro- or nanoscopic photonic switches or for photovoltaic devices. As an example, the extremely high energy conversion efficiency of photosynthetic complexes grounds on sophisticated energy transfer pathways, which finally leads to the generation of electrons or the splitting of water.During the previous proposal period we started to analyze and control the Förster-Transfer between two chromophores by an accurately controllable photonic environment, which was realized by a tunable lambda/2-Fabry-Pérot-resonator. In contrast to plasmonic structures, which allow to enhance of the photonic density of states in close proximity, the photonic impact on quantum systems can be monitored and manipulated in a very precise and reproducible manner by our tunable microresonators. By means of spectral and time resolved measurements on FRET-coupled systems in our resonators we were able to study and theoretically model the energy transfer dynamics. Also, we were able to determine the energy transfer rate constant of single FRET-pairs for various mirror separations. Thus, we could find out that the FRET-rate constant is not altered by our resonators in contrast to the transfer efficiency. The goal of the following proposal is to investigate dipole-coupled energy transfer between pairs of donor-acceptor molecules from the low coupling regime to strong coupling in a tunable half wavelength Fabry-Pérot resonator. In order to gain high quality data which are not hampered by inhomogeneous broadening, overlapping vibronic bands or conformational changes, the experiments will be performed at the single-molecule level with isolated donor-acceptor pairs at cryogenic temperatures. First, we will develop a tunable resonator which allows us to control the photonic environment at liquid helium temperatures. Then, single quantum systems and dipole-dipole coupled model systems shall be examined by spectrally and time resolved microscopy. For studying the coupling dynamics of such systems we are planning to perform pump-probe measurements with pulsed excitation on single systems for various mirror separations. Data analysis is based on theoretical models and simulations.

• DFG Programme: Research Grants