Vapochromic and semiconducting solids of a bifunctional hydrocarbon

This study explores a bifunctional hydrocarbon, which has two non-planar dibenzocycloheptatriene moieties linked by three cumulative C–C double bonds. This flexible conjugated molecule can adopt two conformations, namely, syn and anti, in its crystals. Of particular interest is that the molecule’s solids not only function as p-type semiconductors with field effect mobility of 0.02 cm2 V−1 S−1 but also exhibit vapochromic behavior with high selectivity. Upon selectively trapping specific volatile molecules, such as toluene and m-xylene, in the crystal lattice, the guest-free crystals of the syn conformer change to the clathrate crystals of the anti conformer accompanied by a change of color from red to orange. The unique combination of the two useful functions of this molecule can be attributed to its cycloheptatriene and cumulene moieties, both of which have rarely been used in building blocks for organic functional materials.