Then, the successful assembly of FMR with CB[8] inspired us to further study the assembling behaviors of (
E)-SSB-(
E)-FMR with CB[8]. As displayed in
Fig. 1a, a Job plot for the complexation of (
E)-SSB-(
E)-FMR with CB[8] revealed 1:1 host–guest stoichiometry, exhibiting a peak at molar fraction 0.5. By a
1H NMR spectral comparison of (
E)-SSB-(
E)-FMR and the sample containing (
E)-SSB-(
E)-FMR and equivalent CB[8] (
Fig. 1b), the protons (H
b˗H
g) on FMR segments displayed obvious upfield shifts, indicating these parts were located in the cavity of CB[8]. Furthermore, absorption maximum of (
E)-SSB-(
E)-FMR manifested apparent bathochromic shift from 380 nm to 408 nm with the change in absorbance upon sequential addition of CB[8] and simultaneously, the color of (
E)-SSB-(
E)-FMR aqueous solution was changed from light yellow to deep yellow (
Fig. 1c and Fig. S4 in Supporting information), implying occurrence of assembling behaviors between (
E)-SSB-(
E)-FMR and CB[8]. The absorption band between 430 nm and 750 nm which appeared in the assembly composed of FMR and CB[8] disappeared in UV–vis spectrum of the sample containing (
E)-SSB-(
E)-FMR and CB[8], implying that their assembling models were different. Based on UV–vis absorption spectral titration above, the complex stability constant (
KS) was determined to be 1.14 × 10
8 L/mol (
Fig. 1c, inset), where the absorbance changes upon stepwise addition of CB[8] to the aqueous solution of (
E)-SSB-(
E)-FMR were analyzed by using the nonlinear least-squares fitting method [
32]. To further ascertain their assembling behaviors, DOSY-NMR spectra were subsequently performed to investigate which model (polymers, oligomers or small-size supramolecular assemblies) was formed by (
E)-SSB-(
E)-FMR and CB[8]. As shown in Fig. S5 and Table S1 (Supporting information), diffusion coefficients of (
E)-SSB-(
E)-FMR/CB[8] (2.04 × 10
−10 m
2/s) and (
E)-SSB-(
E)-FMR (2.21 × 10
−10 m
2/s) were obtained through their DOSY-NMR spectra. According to the Stokes–Einstein equation (
D =
kBT/(
6pƞR)) [
33], the average size of the assembly (
E)-SSB-(
E)-FMR/CB[8] was estimated to be equal to (
E)-SSB-(
E)-FMR and 3 times sum of CB[8] by assuming the complexes as being hydrodynamically spherical. Diffusion coefficients of the assembly also didnot change significantly along with change of its concentration (Table S1 and Fig. S5), which implied that (
E)-SSB-(
E)-FMR/CB[8] was a small-size supramolecular complex.
1H–
1H ROESY of the (
E)-SSB-(
E)-FMR/CB[8] assembly (Fig. S6 in Supporting information) showed that proton correlations of H
f,g–H
h,i and H
h,i–H
e between two adjacent (
E)-SSB-(
E)-FMR molecules, indicating that pyridine fraction of one guest molecule and styrene part of the other guest molecule were arranged in parallel in the cavity of CB[8] and giving a rational assembling pattern (
Fig. 1b). Moreover, the ESI-MS of the assembly revealed two charge states including 3
+ and 4
+ (Fig. S7 in Supporting information). These evidences all proved that (
E)-SSB-(
E)-FMR and CB[8] formed a 2:2 quaternary supramolecular complex (
Scheme 1). (
E)-SSB-(
E)-FMR and CB[8], unlike the reference compound FMR, tended to form 2:2 complex due to its suitable molecular rigidity, angles between building-blocks and linker length [
34,
35].