• solid-state photochemistry;
  • metastable linkage isomers;
  • metastable states;
  • molecular photo-switchable species

Over the last 30 years, the single-crystal photocrystallographic technique has been developed to determine the three-dimensional crystal and molecular structures of metastable species which have been generated in the crystal photochemically. Transition-metal complexes that have been investigated using this methodology include complexes that contain nitrosyl, dinitrogen, sulfur dioxide and nitrite ligands, all of which form new linkage isomers in the solid state when photoactivated by light of the appropriate wavelength. Both steric and electronic factors determine the level of the conversion from the ground-state structure to the metastable isomeric structure, and both the `reaction cavity' size and the nature of the intermolecular interactions are shown to be among the key factors that influence the percentage conversion.