Cucurbit[7]uril Complexation Drives Thermal trans – cis ‐Azobenzene Isomerization and Enables Colorimetric Amine Detection

Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit[7]uril (CB[7]) results in the formation of purple‐colored CB[7] ⋅ cis ‐ 1⋅ 2 H + and CB[7] ⋅ cis ‐ 3⋅ 2 H + complexes, respectively. The high binding affinity and selectivity displayed by CB[7] toward 1 and 3 pays the >10 kcal mol −1 thermodynamic cost for this isomerization. We investigated the behavior of these complexes as a function of pH and observed large p K a shifts and high pH responsiveness, which are characteristic of cucurbit[ n ]uril molecular containers. The remarkable yellow to purple color change was utilized in the construction of an indicator displacement assay for biologically active amines 4 – 10 . This indicator displacement assay is capable of quantifying the pseudoephedrine ( 5 ) content in Sudafed tablets over the 5–350 μ M range.