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

Förster共振能量传递是一个被广泛讨论和应用的光物理过程。其机制基于偶极子-偶极子相互作用，即由供体分子吸收的能量转移到受体分子。几年来，关于如何主动控制这种或类似的能量转移过程存在争议。主动控制是指在时间、时间和能量域上传递的动力学被一个可控的环境所改变，从而导致传递的增强或完全抑制。这一问题对于设计微、纳米级光子开关或光伏器件尤为重要。例如，光合复合体极高的能量转换效率基于复杂的能量传递途径，最终导致电子的产生或水的分裂。在之前的提案期间，我们开始通过精确可控的光子环境来分析和控制两个发色团之间的Förster-Transfer，这是通过可调谐的lambda/2- fabry - psamrot谐振器实现的。与等离子体结构相反，等离子体结构允许增强接近状态的光子密度，光子对量子系统的影响可以通过我们的可调谐微谐振器以非常精确和可重复的方式进行监测和操纵。通过对谐振腔中fret耦合系统的光谱和时间分辨测量，我们能够对能量传递动力学进行研究和理论建模。此外，我们能够确定单个fret -对不同的镜面分离的能量传递速率常数。因此，我们可以发现，与转移效率相比，我们的谐振器并没有改变fret速率常数。本文的目的是研究在可调谐半波长法布里-帕姆罗谐振器中，偶极子-受体分子对之间从低耦合状态到强耦合状态的能量转移。为了获得不受非均匀加宽、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，并在低温下分离供体-受体对。首先，我们将开发一个可调谐谐振器，使我们能够控制液氦温度下的光子环境。然后，单量子系统和偶极-偶极耦合模型系统将被光谱和时间分辨显微镜检查。为了研究这类系统的耦合动力学，我们计划在不同镜像分离的单个系统上进行脉冲激励的泵浦探测测量。数据分析是基于理论模型和模拟。

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.