Photodimerization in the solid state

Abstract

Following a brief historical review of solid-state photochemistry current research is discussed under four parallel headings: first, analysis of the topochemical postulate according to which the course of the solid-state reaction and the stereochemistry of the photodimer (if any) can be predicted from the configuration and nearest-neighbour geometry of closest monomer molecules in the crystal lattice; secondly, the study of the lOCUS of the reaction, that is the dependence of the course of the reaction or (dimerization, cis -trans isomerization) on crystal texture (dislocation, grain and phase boundaries); thirdly, a better understanding of the packing principles of organic molecules in their crystal structure to enable us to construct photoreactive (or lightstable) crystal structures of any given monomer as well as mixed crystals of potentially codimerizable monomers for synthetic purposes or energy-transfer studies.Several approaches to this problem of 'crystal engineering' based on generalizations of packing modes of primary amides and of dichiorophenyl derivatives are outlined, and their application to a systematic photochemistry of the solid state discussed.

Crystal structures of polynuclear aromatic hydrocarbons. Classification, rationalization and prediction from molecular structure

“…The concept of crystal engineering which describes the deliberate design of organic crystal structures for specific physical and chemical purposes has therefore elicited much interest (Schmidt, 1971;Thomas, 1974;Scheffer, 1987;Desiraju, 1984Desiraju, , 1987aDesiraju, ,b, 1989. Two approaches to crystal engineering have been recognized.…”

Hydrogen bonding and perhalometallate ions: A supramolecular synthetic strategy for new inorganic materials

“…While having older roots in organic solid-state photochemistry and solid-state reactions (8), the primary focus of contemporary crystal engineering is the identification or design of molecular level building blocks whose interactions with other building blocks (including self recognition) exhibit some degree of predictability. These building blocks can then, in principle, be assembled systematically to give crystalline solids.…”

Crystal structures of 2,3,4aβ,6,7,8aβ-hexamethyl-4a,5,8,8a-tetrahydro-1-naphthoquin-4α (and 4β)-ol

“…In the solid state the molecules have well separated, non-parallel C=C bonds; C(2)... C(7) and C(3).-. C(6)intramolecular distances are 4.417 (2) and 4.400 (2) A, respectively, for the 43-ol, and 4.490 (3) and 4.471 (3) ~ for the 4/3-ol, outside the limit of 4.1 ,~ suggested for successful 2 + 2 photocycloadditions (Schmidt, 1971;Scheffer & Dzakpasu, 1978). The O(1)...H(81) intramolecular distance in the 43-ol is 2.45 (2) /~,, similar to those observed in several tetrahydronaphthoquinone derivatives (Phillips & Trotter, 1977), where photochemical conversion is initiated by H abstraction by carbonyl oxygen (Scheffer & Dzakpasu, 1978); the 4fl-ol conformer has no C=O...H interaction geometrically favourable for H abstraction by oxygen, and in fact none of the tetrahydronaphthoquinols studied exhibit this pathway in solution or in the solid state (Appel, Greenhough, Scheffer, Trotter & Walsh, 1980).…”