Control by one drop of solvent: selective preparation of guest release/trap-triggered interconvertible molecular crystals.

Interconvertible molecular crystals 1close and 1open composed of 4-pyridyl-1,3-indanedione dimer 1 were selectively obtained. Thermal removal of solvent molecules in 1open afforded 1close. Further dipping of 1close in a specific solvent reproduced 1open. No crystallinity loss was observed even though both processes involved a drastic change of molecular packing arrangements.