Molecular strategies to read and write at the nanoscale with far-field optics.

Diffraction prevents the focusing of ultraviolet and visible radiations within nanoscaled volumes and, as a result, the imaging and patterning of nanostructures with conventional far-field illumination. Specifically, the irradiation of a fluorescent or photosensitive material with focused light results in the simultaneous excitation of multiple chromophores distributed over a large area, relative to the dimensions of single molecules. It follows that the spatial control of fluorescence and photochemical reactions with molecular precision is impossible with conventional illumination configurations. However, the photochemical and photophysical properties of organic chromophores can be engineered to overcome diffraction in combination with patterned or reiterative illumination. These ingenious strategies offer the opportunity to confine excited chromophores within nanoscaled volumes and, therefore, restrict fluorescence or photochemical reactions within subdiffraction areas. Indeed, information can be "read" in the form of fluorescence and "written" in the form of photochemical products with resolution down to the nanometre level on the basis of these innovative approaches. In fact, these promising far-field optical methods permit the convenient imaging of biological samples and fabrication of miniaturized objects with unprecedented resolution and can have long-term and profound implications in biomedical research and information technology.