A separate class of solid materials

A separate class of solid materials that could change color in reaction to solvent vapors is called vapochromic. some porous organometallic or coordination complexes had been identified as vapochromic pigments, most of which are derived from square planar Pt(II) and Au(I) compounds. Vapochromism is due to the intercalation of solvent molecules into crystals, and color or luminescence changes from relatively weak reactions in solids, consisting of the coordination of solvent molecules to metal bonds, π-π stacking, hydrogen bonding, and nonspecific host−guest reactions. the limitations of vapochromic materials, however, remain within the very slow response time due to the slow diffusion of vapor molecules into the solid materials, and the weak interactions involved that limit their selectivity and sensitivity as sensors. One potential solution is possible to develop nanoscale and porous coordination complexes that can successfully reduce diffusion time and increase surface area for analyte exposure, therefore improving interactions that occurred at the solid−gas interface.