(Figure Presented) Seeing is believing: Treatment of a tetrathiafulvalene- functionalized calix[4]pyrrole 1 with chloride anions in CHCl produces bowl-like receptor 1·Cl, which is able to encapsulate C in a 2:1 barrel-like manner. The color of C ⊂(1·Cl) (green in CH Cl) differs dramatically from its constituents (yellow and magenta for 1 and C, respectively), thus allowing its formation to be monitored visually.
