Single-crystal-to-single-crystal E --> Z isomerization of tiglic acid in a supramolecular framework.

The single-crystal-to-single-crystal E --> Z photoisomerization of tiglic acid (2,3-dimethylacrylic acid) occurs in the supramolecular crystals CECR-HTA x 2MeOH x 1.5H(2)O (1) (where HTA = tiglic acid, CECR = C-ethylcalix[4]resorcinarene) with the preservation of the crystal lattice, indicating the ;scaffolding effect' of the molecular framework, which holds the crystal together notwithstanding the change in shape of the embedded guest molecules. A photostationary state is reached at a concentration of ca 30% of the Z isomers. A kinetic analysis shows the Z --> E back-reaction to proceed with a larger rate constant than the E --> Z isomerization.