During the synthesis of bis(
B21C7)-substituted
ZE [
37], a wrong molar ratio of
B21C7-NH2 and acid (1:1) was applied (
Scheme 1). Firstly, a labile intermediate compound (
O-acylisourea ester) was formed
via the reaction of EDC with the carboxyl group of
TA. Secondly,
B21C7-NH2 partially substitutes the EDC group of
O-acylisourea ester
via a nucleophilic attack to produce amide. Finally, the residual EDC groups of
O-acylisourea ester may undergo cyclic electronic displacement (N→O displacement) to generate
N-acylurea (Fig. S1 in Supporting information) [
38]. Therefore,
OE instead of
ZE was monitored and isolated. Compared with
ZE and
TE, OE is a glue-type material with high viscosity and poor fluidity (
Fig. 1a), as confirmed by various rheology measurements. As shown in
Fig. 1e and Figs. S25-S27 (Supporting information),
OE displays excellent temperature-dependent rheological behavior, which can be attributed to the bulk state and thermal stable feature of
OE. In addition, the composite viscosity of
OE was increased by 10
5 times as the testing temperature decreased from 80 ℃ to 10 ℃, and this rheological behavior was reversible (
Fig. 1e). This observation can be ascribed to the existence of dynamical non-covalent interactions in the system, such as hydrogen bonding, van der Waals forces, and F–F interactions. In contrast, neither
ZE nor
TE exhibits any viscosity in a wide temperature range (from −80 ℃ to 100 ℃). In our previous studies, it has been demonstrated that benzo-21-crown-7 is essential to realize strong adhesion [
39-
41]. Thus,
TE did not show any adhesion property due to the absence of the crown ether ring [
41]. Meanwhile, as a 1,4-disubstituted compound,
ZE favors aggregating together (strong cohesion), which dramatically attenuated the adhesion capacity to surfaces (weak adhesion) [
41].