Fluorescent molecular switches, sensors, and nanostructures based on perylene diimide

In this thesis I explored the design, synthesis, and physical investigation of new molecular and nano scale structures and devices based on perylene diimide (PDI): A. A PDI trimer was designed to self-organize into fluorescent nanofibers. The orientation of the trimer was determined by polarized scanning confocal microscopy to be perpendicular to the axis of the fibers, in agreement with molecular mechanics calculations. Strongly red-shifted fluorescence from these fibers indicates a high degree of electronic delocalization, and breaking up this delocalization by photobleaching blueshifts the emission toward that of an isolated noninteracting molecule. The delocalization along these nanofibers and the ability to study the electronic structure using fluorescence make them potentially useful in nanoscale devices.; B. Biologically important redox centers, nicotinamide and quinone, have been incorporated into molecular redox switches. The switch based on nicotinamide is strongly fluorescent in its oxidized state, but non-fluorescent in the reduced state due to photoinduced electron transfer (PET) from the reduced nicotinamide to a photoexcited PDI. Switching of the fluorescence has been demonstrated by chemical, electrochemical, and biological methods. Ab initio quantum chemical calculations of orbital energy levels provided invaluable guidance to the design.; C. A rigid PDI tetramer shows several discrete emission colors at single-molecule level. Experiments and theoretical calculations support an internal Stark effect (ISE) mechanism: intramolecular or interfacial PET leads to the formation of an ion pair, which generates large local electric fields; consequently, the electronic energy levels of nearby chromophores are significantly altered, resulting in large redshifts in the emission spectra.; D. Two other systems, biphenyl-PDI and carbazole-PDI, have been designed to probe the dependence of PET on structures. For the biphenyl-PDI system, PET from the biphenyl to the PDI is favorable in a coplanar model compound, but not in a perpendicular one. For the carbazole-PDI system, PET from the carbazole to the PDI has been systematically modulated by a series of electron-withdrawing groups on the carbazole. In both systems density function theory calculations accurately predict the PET behaviors based on orbital energy levels.