Portrait of David Parker Craig

23: Molecular Crystals and Light: Chemical Reactions in Cages (1982)

David Parker Craig


The Liversidge Research Lecture, delivered before the Royal Society of New South Wales, 20th May 1982. Reproduced by permission of the Royal Society of New South Wales from J. Proc. Roy. Soc. N.S.W., 1982, 115, 61-7.

"The kinetics, mechanisms, and stereochemistry of solid state photochemical reactions are different in fundamental ways from reactions in fluids, and constitute a distinct set of problems. Molecules in crystals below the melting point are confined by intermolecular forces to sharply defined regions, or 'cages'. Reactions take place between molecules within such cages in positions and orientations known from crystal structure analysis or in positions related to the perfect crystal structure by dislocations or local disordering."

"New concepts are being developed to advance understanding in this field. The best known is that of 'topochemistry', which is that static lattice constraints restrict the products of a photochemical reaction to those preformed in the parent crystal. Also recent theory leads to the proposal that there may be impulsive molecular displacements following light absorption and lasting only a few picoseconds that bring neighbour molecules close together and promote chemical change or excimer formation. The theory of this concept of 'dynamical preformation' is described and possible examples discussed."

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