Single-Molecule Traffic in Mesoporous Materials: Translational, Orientational, and Spectral Dynamics

摘要

The movement of individual TDI molecules in the channel structure of a porous material has been observed and characterized in detail using a combination of SMS methods. In a series of typical trajectories, we show how the simultaneous acquisition of spatial and orientational trajectories as well as orientational and spectral information gives a very detailed picture of the molecular traffic in a mesoporous material. The motion of the molecules was heterogeneous on many different length-scales and in time. The TDI molecules showed linear movement with their transition dipole moment aligned along their trajectories, reflecting well-ordered structural areas of the host. In other areas the motion of the TDI molecules was less structured and was characterized by jumps between regions where the molecule's dynamics were more confined. In these areas the simultaneous observation of orientation and spectral properties of the molecules revealed details of the guest-host interactions, that is, of adsorption sites. Hence, by correlating dynamical changes of position and orientation as well as orientation and emission spectra of single molecules, one is able to determine the nanoscaled heterogeneities of the mesoporous host. The methodology described in this paper gives novel insight into host-guest interactions within nanostructured materials. Thus, it represents an analytical tool that will be helpful in the design of nanoscopic devices with a high control of molecular dynamics.