Tetraphenylethene modified [n]rotaxanes: synthesis, characterization and aggregation-induced emission behavior

A series of novel [n]rotaxanes based on a tetraphenylethene (TPE) backbone were constructed by a template-directed clipping approach and their structures were well-characterized. Investigation of their optical properties showed that these rotaxanes and their corresponding ammonium salts showed aggregation-induced emission (AIE) behavior. However, there were obvious differences as follows: (1) rotaxanes reached the aggregation state in the presence of less water compared with the corresponding ammonium salt; (2) the rotaxanes with a long alkoxyl chain on the pyridine unit of the crown ether formed the aggregation state in the presence of less water than for those without an alkoxyl substituent and (3) a smaller distance between the TPE unit and N-hetero crown ether component resulted in the aggregation state being reached more easily than when there is a longer distance. The results suggest that the mechanically interlocked structures can adjust the aggregation state of AIE molecules.