*3.1. NMR Spectroscopy*

The binding interactions between each of the pyrrolidinopyridinium guests and Q[7] can be conveniently monitored using 1H NMR spectroscopic data recorded in neutral D2O solution.

In the case of C0, Figure 1 shows the changes observed in the 1H NMR spectrum of C0 as progressively larger amounts of Q[7] were added to the D2O solution at 25 ◦C. Spectrum A was obtained in the absence of Q[7], B with Q[7] at 0.326 (B), C with 0.487 equivalents with progressive increasing amounts up to spectrum I with 1.939 equivalents of Q[7] in D2O (D) at 20 ◦C. The peaks associated with protons a–d all experienced upfield shifts as increasing amounts of Q[7] was added (for specific shift changes, see Table A1, ESI). This is consistent with the complete encapsulation of C0 as depicted in the image shown top right, Figure 1. For the COSY NMR spectrum of this system with 1.939 equivalents of C0, see Figure A1, ESI.

**Figure 1.** Interaction of C0 and Q[7] (25 ◦C): 1H NMR spectra (400 MHz, D2O) of C0 (*ca*. 0.5 mM) in the absence (**A**), 0.191 equiv. (**B**), 0.326 equiv. Q[7] (**C**), 0.487 equiv. (**D**), 0.663 equiv. Q[7] (**E**), 0.838 equiv. (**F**), 0.930 equiv. (**G**), 1.570 equiv. (**H**), and 1.939 equiv. of Q[7] (**I**).

In the case of C2, similar analysis (Figure 2) of the system involving Q[7] and C2 revealed that the peaks associated with the ethyl chain, particularly the methyl group (f), did not undergo any significant changes. However, the remaining peaks associated with the protons of the pyridine and pyrrole rings did undergo an upfield shift (for specific shift changes, see Table A2). This situation, whereby the pyridine and pyrrole rings are accommodated within the cavity of Q[7] is reminiscent of that observed for Q[8] [23] and the same guest. There may be slight differences with regard to how much the alkyl chain protrudes out of the cavity for Q[7] *versus* Q[8], but the 1H NMR spectra sugges<sup>t</sup> the difference is small (the change of chemical shifts between these two systems is not obvious).

**Figure 2.** Interaction of C2 and Q[7] (25 ◦C): 1H NMR spectra (400 MHz, D2O) of C2 (*ca*. 0.5 mM) in the absence (**A**), 0.133 equiv. (**B**), 0.273 equiv. Q[7] (**C**), 0.453 equiv. (**D**), 0.595 equiv. Q[7] (**E**), 0.755 equiv. (**F**), 0.926 equiv. (**G**), 1.415 equiv. (**H**), and 1.733 equiv. of Q[7] (I).

In the case of C4, the 1H NMR titration spectra of C4/Q[7] in D2O are presented in Figure 3. There was a clear upfield shift of the signals of all protons in the pyridine ring, whilst the pyrrole ring and alkyl chain protons were also shifted upfield, though to a lesser degree (for specific shift changes, see Table A3, ESI). This indicates that the pyridine ring, pyrrole ring, and the alkyl chain are all accommodated within the cavity of Q[7], and that the Q[7] is capable of shuttling on the gues<sup>t</sup> C4 in a state of dynamic equilibrium. For the COSY NMR spectrum of this system with 1.939 equivalents of C4, see Figure A2, ESI. This shuttling situation is reminiscent of that observed for Q[8] and the same guest.

**Figure 3.** Interaction of C4 and Q[7] (25 ◦C): 1H NMR spectra (400 MHz, D2O) of C4 (*ca*. 0.5 mM) in the absence (**A**), 0.116 equiv. (**B**), 0.173 equiv. Q[7] (**C**), 0.331 equiv. (**D**), 0.474 equiv. Q[7] (**E**), 0.641 equiv. (**F**), 0.750 equiv. (**G**), 1.164 equiv. (**H**), and 1.653 equiv. of Q[7] (**I**).

In the case of C6, Figure 4 depicts the 1H NMR titration spectra of the C6/Q[7] in D2O. All the protons of the gues<sup>t</sup> experienced upfield shifts to varying degrees (for specific shift changes, see Table A4, ESI). There was little change on increasing the Q[7] concentration beyond the addition of 0.997 equivalents. The situation is consistent with the pyridine ring, pyrrole ring, and the alkyl chain all being accommodated within the cavity of Q[7], and with the Q[7] shuttling on the gues<sup>t</sup> C6 in a state of dynamic equilibrium. This contrasts with the situation observed for the same gues<sup>t</sup> and Q[8], in which the pyridine ring, the alkyl chain, and the N part of the pyrrole were accommodated within the cavity of Q[8], and the another part of pyrrole was at its portal; the alkyl chain was buried in the cavity of Q[8] in a twisted form. The reason for the different inclusion modes involving C6 is likely to be related to the smaller cavity size of Q7 versus Q8, which prevents the alkyl chain from bending in the cavity of Q7.

**Figure 4.** Interaction of C6 and Q[7] (25 ◦C): 1H NMR spectra (400 MHz, D2O) of C6 (*ca*. 0.5 mM) in the absence (**A**), 0.110 equiv. (**B**), 0.223 equiv. Q[7] (**C**), 0.363 equiv. (**D**), 0.461 equiv. Q[7] (**E**), 0.646 equiv. (**F**), 0.739 equiv. (**G**), 0.997 equiv. (**H**), and 1.494 equiv. of Q[7] (**I**).
