Supramolecular structural control: photochemical reactions between styrylpyridine derivative and cucurbit[7,8]urils

The use of cucurbit[n]urils to control the photochemical reactions of styrylpyridine salts has become a new strategy in supramolecular chemistry. In an aqueous solution, styrylpyridine derivatives (CHP) can form supramolecular complexes of the 1 : 2 and 2 : 1 type with cucurbit[8]uril (Q[8]) and cucurbit[7]uril (Q[7]), respectively. Given the photosensitivity of the CHP, the CC bond of the CHP undergoes a cis-trans isomerization reaction and a [2 + 2] cycloaddition reaction under 365 nm UV irradiation in an aqueous solution. After binding with Q[8], the photo-induced [2 + 2] cycloaddition reaction rate of the CHP is greatly increased, while after binding with Q[7], the CC bond of the CHP only undergoes a cis-trans isomerization reaction, i.e. no further photo-induced [2 + 2] cycloaddition reaction occurs. Competitive experiments demonstrated that CHP is more inclined to combine with Q[7], and thus when Q[7] and Q[8] coexist in the system, the inhibition of the [2 + 2] cycloaddition reaction of CHP by Q[7] is not disrupted. The characteristics of this supramolecular catalysis and supramolecular protection make it applicable to catalyze or inhibit reactions required under specific circumstances.