Probing the Steric Effect of 2,6-disubstituted-4-phenylpyrilium Inclusion Complexes with Cucurbit{[}7]uril

2,6,-disubstitued-4-phenylpyrylium compounds form inclusion complexes with cucurbit[7]uril (CB[7]), a macrocyclic host made of repeating units of glycoluril. To study the effect of steric hindrance on the mode and extent of inclusion, four different 2,6-disubstituted-4-phenylpyrilium tetrafluoborate salts (1a-d) were synthesized and their complexation with cucurbit[7]uril was studied by 1H NMR. Based on the nature of the substituents at 2,6 positions (R = Me, i-Pr, t-Bu, Ph) of 4-phenylpyrylium tetrafluoborate salts, different degree of inclusion was observed and the extent of inclusion was further confirmed by measuring their binding constants with CB[7] via UV-Vis titrations