文摘
We have investigated and quantified the role that the glycol chain length has on the strength of the noncovalent bonding interactions taking place between cyclobis(paraquat-p-phenylene) (CBPQT<sup>4+sup>) and five different monopyrrolo-tetrathiafulvalene (MPTTF) derivatives that only differ in the length of the N-substituted glycol chain. The MPTTF derivatives were used to form [2]pseudorotaxanes by mixing them with CBPQT<sup>4+sup>. The binding constants (K<sub>asub>) associated with the complexation process leading to the formation of the [2]pseudorotaxanes were obtained using the UV–vis−NIR dilution method and the [2]pseudorotaxanes were characterized structurally using <sup>1sup>H NMR spectroscopy. These experimental investigations clearly indicate that the glycol chains provide additional stability to the [2]pseudorotaxanes findings that were further supported by density functional theory (DFT) studies. The DFT calculated superstructure of the [2]pseudorotaxane 3⊂CBPQT<sup>4+sup> reveal that [C–H···O] hydrogen bonding interactions between the acidic α-H protons in CBPQT<sup>4+sup> and the oxygen atoms present in the glycol chain can take place on the exterior of the [2]pseudorotaxane. However, the length of the glycol chain is of paramount importance and the present studies show that the first and second oxygen atom in the [2]pseudorotaxanes 2–5⊂CBPQT<sup>4+sup> are engaged in [C–H···O] hydrogen bonding interactions with CBPQT<sup>4+sup>, whereas the third and fourth oxygen atoms are not.