Electron and energy transfer mechanisms for fluorescence modulation with photochromic switches

The electronic and structural changes associated with photochromic transformations can be exploited to modulate the emission intensity of fluorescent compounds on the basis of electron and energy transfer processes. Indeed, fluorescent and photochromic components can be joined covalently or noncovalently into molecular or supramolecular assemblies respectively and the emission of one component can be regulated by operating the other with optical stimulations. In fact, the photoinduced and reversible interconversion of the colorless and colored states of the photochromic component are accompanied by significant changes in absorption. These changes alter the degree overlap between the absorption band of a photochrome and the emission band of a fluorophore and, thus, activate or prevent the transfer of energy from the latter to the former. Here is presented a survey of diverse fluorophore\u2013photochrome conjugates, macromolecular constructs, supramolecular assemblies, photoswitchable nanoparticles and multilayer arrays which operate successfully with optical inputs

Building supramolecular nanostructures on surfaces: the influence of the substrate

Recent advances in supramolecular chemistry enable the construction of novel nanostructures in solution and the solid state. We present an investigation of the supramolecular organisation of a prototypical charged macrocycle — the self-complementary tetracationic cyclophane — on a surface using scanninng tunnelling microscopy. On the graphite surface the cyclophanes stand upright and self-organise into ordered nanotubes running along symmetry directions of the surface. The stacking of the cyclophanes within these nanotubes is quite different from the structural motifs found in the solid state. The findings open the possibility to use a surface to create previously unattainable structures and devices