Atomic force microscopy and solid state photolyses: phase rebuilding

Abstract

Atomic force microscopy (AFM) was used for the study of the mechanism 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 transport 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 Å) and trans-stilbene (d=5.720 Å) are not reactive, because no phase-rebuilding mechanism is available, while anthracene (d=6.038 Å) does form a photodimer. The phase-rebuilding mechanisms on two natural faces of antharacene are analysed and interpreted on the molecular level. The formation of three different photoproducts from 2,5-dibenzylidenecyclopentanone shows two different phase-rebulding mechanisms on the morphologically dominant face and there are extraordinarily wide molecular rotations of the highly skewed (46°, 131°) reactants in the crystal. Photolyses of polymeric foils of styrene-isopropyl-acrylate copolymer and polystyrene give rise to very nanostructures in the surface region that can be imaged by AFM.