Translational motion in individual motor molecules

It is proposed to investigate the spontaneous dynamical behavior and the electron transfer induced translational switching of individual rotaxane motor molecules. The project comprises the design and synthesis of rotaxanes having strongly fluorescent and photostable groups in well-defined positions (in thread, in stoppers or attached to the moving ring), their achoring to glass cover slips, the implementation of fluctuation spectroscopic experiments, and the development of methods to drive these motor molecules by photoinduced electron transfer, coupled with single molecule fluorescence detection. Mechanically interlocked molecules which have multiple geometrical states that can be interconverted by an external stimulus are attractive for use as molecular switches and motors. A thorough understanding of the switching behavior of such systems is important. We aim to investigate the kinetics and thermodynamics of the underlying chemical processes under a variety of environmental conditions. Molecular motors and switches will play their role in nanotechnology at interfaces (or in otherwise confined spaces) and ? to remain on the nanoscale ? in small numbers of molecules acting in concert or as a small pool of workers. This motivates us to address the molecules on the smallest possible scale, that is, individually. Moreover, for single molecules much information can be obtained from the fluctuations of signals in time, and events that are rare under normal excitation conditions can be readily detected. We intend to explore these specific strengths of single molecule spectroscopy for fluorescence based detection of molecular movement, either occurring spontaneously, or triggered by photoinduced electron transfer. It is noteworthy that the requirements for the application of molecular photoswitches and for single molecule spectroscopy are similar: the molecules must be rock-stable, and have high probabilities for absorption and emission (high fluorescence quantum yield). The design and synthesis of such molecules, with built-in control over the co-conformational energetics, are a key step in the project.