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

Förster共振能量转移是一个广泛讨论和经常应用的光物理过程。它的机制是基于偶极-偶极相互作用，即供体分子吸收的能量被转移到受体分子。几年来，关于如何主动控制这种或类似的能量转移过程，一直存在着争议。主动控制意味着转移在时间、时间和能量域上的动力学将被可控环境改变，从而导致转移的增强或完全抑制。这一问题对于微纳尺度光子开关或光伏器件的设计尤为重要。例如，光合作用复合体极高的能量转换效率源于复杂的能量传递途径，最终导致电子的产生或水的分裂。在前面的提议期间，我们开始分析和控制两个生色团之间的Förster转移，通过精确可控的光子环境，这是通过可调的Lambda/2-Fabry-Pérot共振器实现的。与等离子体结构不同，等离子体结构允许在近距离增强光子态密度，而光子对量子系统的影响可以通过我们的可调微谐振器以非常精确和可重现的方式进行监控和操作。通过对谐振腔中FRET耦合系统的光谱和时间分辨测量，我们能够研究和理论模拟能量传递动力学。此外，我们还能够确定不同镜面分离条件下单个FRET对的能量转移速率常数。因此，我们可以发现，与传输效率相反，我们的谐振器没有改变FRET速率常数。以下方案的目的是研究半波长可调谐F-P腔中偶极耦合的能量传递。为了获得不受不均匀展宽、重叠振动带或构象变化影响的高质量数据，实验将在单分子水平上进行，在低温下进行分离的施主-受体对。首先，我们将开发一种可调谐谐振器，使我们能够在液氦温度下控制光子环境。然后，对单量子系统和偶极-偶极耦合模型系统进行光谱和时间分辨显微镜研究。为了研究这类系统的耦合动力学，我们计划在不同镜片分离的单个系统上进行脉冲激发的泵浦-探测测量。数据分析建立在理论模型和模拟的基础上。

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.