Chloroform-selective vapochromic behavior based on crystal-state host–guest complexation of an organic cage

Abstract

Developing vapochromic materials capable of distinguishing molecules with minimal structural difference is important due to the complexity of environmental monitoring. This work reports an organic cage with vapochromic behavior upon exposure to halogenated methane (CH₂Cl₂, CHCl₃ and CCl₄) vapors. The vapochromic response of the organic cage is highly selective towards CHCl₃ molecules, although CH₂Cl₂ and CCl₄ molecules have very similar structures. Powder and single-crystal X-ray diffraction analyses reveal that this vapochromic behavior is attributed to the noncovalent interactions between hosts and guests to enhance the cage molecular conjugation, leading to a red-shift of its absorption band in the range of 450–800 nm. This work provides new insights into the design of novel reversible vapochromic systems based on a well-defined discrete organic cage as the main scaffold.