Inclusion Properties and Solid-State Behavior of Thiophene-Condensed Host Compounds

A series of new clathrate host molecules, each containing thiophene rings as a rigid and bulky substituent, has been synthesized based on the "wheel and axle"-type of host design. The interest in these hosts is focused on the continuous change in the length of the "axle" part together with their electron-donating ability. Moreover, the tertiary alcohol moiety in the "wheel" part can undergo the substitution reactions in the solid state. Thus, the host : guest ratio and the conformation of the host molecules exhibit novel dependences on the number of the condensed thiophene rings. Guest exchange via gas solid contact has been achieved in the clathrates which provide a channel-type inclusion void. Isostructural and polymorphic transformation of the host lattices has been found upon gas-solid contact. Pseudo-polymorphic change was also observed in guest release. Ternary crystals exhibited novel site-selectivity for random inclusion of two alcohol guests. The donor character of the hosts can afford three-component charge-transfer complexes enclathrating solvent molecules. Cogrinding the host and the acceptor enhanced the solid-state charge transfer interactions, which have been associated with the nucleophilic substitution in the solid state induced by gas-solid contact. These results indicate one future direction for research on crystalline inclusion complexes.