ATOMIC-FORCE MICROSCOPY AND SOLID-STATE PHOTOLYSES - PHASE REBUILDING

Atomic force microscopy (AFM) was used for the study of the mechanisms of phase rebuilding in photodimerizations in crystals and of photoreactions on polymer surfaces. The AFM features that are found upon photochemical reactions in the surface regions indicate far-reaching (up to 100 nm) molecular transports which are well directed in space and depend on the crystal face. Thus, not only proximity considerations (topochemistry) but more importantly phase-rebuilding mechanisms are crucial for solid state photoreactivity and this depends on the bulk crystal structure. 2-benzylidenecyclopentanone (d = 4.123 angstrom) and trans-stilbene (d = 5.720 angstrom) are not reactive, because no phase-rebuilding mechanism is available, while anthracene (d=6.038 angstrom) does form a photodimer. The phase-rebuilding mechanisms on two natural faces of anthracene are analysed and interpreted on the molecular level. The formation of three different photoproducts from 2,5-dibenzylidenecyclopentanone shows two different phase-rebuilding mechanisms on the morphologically dominant face and there are extraordinarily wide molecular rotations of the highly skewed (49-degrees, 131-degrees) reactants in the crystal. Photolyses of polymeric foils of styrene-isopropyl-acrylate copolymer and polystyrene give rise to very uniform nanostructures in the surface region that can be imaged by AFM.