Moreover, the reversible feature of dynamic covalent motivated us to study how to control the cyclic oligomers to depolymerize through dynamic covalent reaction. Solvents have important effects on organic reaction [
19]. Thus, solvents effects and guest template were taken into account to investigate the reverse polymerization process of
BC7Se2. The mixture with a high content of cyclic oligomers was prepared by concentrating the
BC7Se2 solution in dichloromethane by a rotatory evaporator under light due to the polymerization of
BC7Se2 was under the control of its concentration. After drying under vacuum, the residue coated on the flask slowly switched from an oily shape to an elastic lump with yellow, which is different from the yellow powder of monomer
BC7Se2 (Fig. S20 in Supporting information). A series of the solution containing oligomers of
BC7Se2 with a concentration of 5 mmol/L calculated by the molecular weight of
BC7Se2 was prepared in CDCl
3, CDCl
3/CD
3CN = 1/2 (v/v), CD
3CN, DMSO-
d6 respectively under dark, the polarity of which range from low to high. Unfortunately, the oligomers of
BC7Se2 could not dissolve in CD
3CN. The changes for these four samples under light were monitored by
1H NMR spectroscopy. Before exposed to light, the Ar-H chemical shift of oligomers in the CDCl
3 (
Fig. 3B–a) was located downfield compared with monomer
BC7Se2 (
Fig. 3B–j). On the contrary, partial peaks of OCH
2 of oligomers mixture shifted upfield compared to monomer. And the signal for the proton of monomer
BC7Se2 is very weak in
Fig. 3B–a. These observations reconfirmed the polymerization of dynamic covalent reaction for this system is under control of concentration. While the solution of oligomers in CDCl
3 was kept under dark for 4 h, there were no significant changes in the
1H NMR spectrum (Fig. S19 in Supporting information), however, after exposed exposure to light, oligomers began to depolymerize to form monomer
BC7Se2 and took about 33 h to be entirely consumed in CDCl
3 (
Fig. 3) deduced from it is scarce to observed the
1H NMR peak (in the rectangle) for oligomers (
Fig. 3B–i). The results suggested that the depolymerization is dependent on light irradiation. And it took almost 194 h to complete this switch in the mixture solvents (CDCl
3/CD
3CN = 1/2, v/v) (Fig. S21 in Supporting information). In DMSO-
d6 with higher polarity, the content of the oligomers and monomer
BC7Se2 seemed to reach a balance, and the depolymerization reaction of oligomers stopped owing to there is no changes on the
1H NMR spectrum after the sample exposed to light for 33 h (Fig. S22 in Supporting information). Although there were no apparent signals for oligomers on its
1H NMR spectrum in CD
3CN before exposure to light, which was due to its weak solubility, there were more than two sets of chemical shifts after under light for 8 h (Fig. S23f in Supporting information). One set was attributed to monomer
BC7Se2. The other was considered as oligomers with small size due to the weak solubility of oligomers and the decomposition rate become slow after exposure to light for 55 h (Fig. S23i in Supporting information). These phenomena demonstrate solvent effect plays a crucial role in the depolymerization reaction.