Interaction between cucurbit[8]uril and viologen derivatives

Abstract

The interaction between cucurbit[8]uril (Q[8]) and a series of symmetric viologen derivatives having aliphatic substituents of variable length [N,N′-dialkyl-4,4′-bipyridinium dianions; alkyl = CH3(CH2)n–, n = 0 (MV2+), 1 (EV2+), 2 (PV2+), 3 (BV2+), 4 (FV2+), 5 (HV2+) or 6 (SV2+); BPY2+ = diprotonated 4,4-bipyridine], determined by 1H NMR and electronic absorption spectroscopy methods, is described. Some different binding models were observed in this work when compared to the interactions between cucurbit[7]uril (Q[7]) and these guests. The experimental results revealed that the binding site of the guests by Q[8] depended strongly on the length of the aliphatic substituents on the 4,4′-bipyridinium nucleus. While a 1:2 complex was observed for Q[8]-BPY2+ under acidic conditions, a 1:1 complex was formed for Q[8]-viologen derivatives with chains shorter than four carbon atoms. However, multiple Q[8] molecules could be threaded on the longer-chain FV2+, HV2+ or SV2+ molecules to form 2:1 and even possibly 3:1 complexes.