Molecularly-defined macrocycles containing azobenzene main-chain oligomers: modular stepwise synthesis, chain-length and topology-dependent properties

The synthesis and properties of macrocyclic structures have attracted continuous attention since the cyclic topology effect may offer unique performances. As is well-known, the properties of polymers/oligomers are dependent on molecular weight (chain length). Therefore, the precise synthesis of molecularly-defined macrocycles is undoubtedly a prerequisite to precisely explore the structure–property relationship. Herein, a series of molecularly-defined macrocycles with main-chain azobenzene-containing oligomers (sixth generation) is prepared efficiently, based on click chemistry and a stepwise chain-growth strategy. The cyclic topology and chain-length effects on the properties/functions of the cyclic oligomers are investigated in detail by comparison with the linear analogues. This work undoubtedly illustrates an example for demonstrating properties/functions dependent on both cyclic topology and chain-length, allowing in-depth insight into the structure–property relationship. Moreover, the current modular strategy can be extended to various molecularly-defined macrocycles with a wide variety of functions.