Light-Controlled Aggregation and Gelation of Viologen-Based Coordination Polymers

Ditopic bis-(triazole/pyridine)viologens are bidentate ligands that self-assemble into coordination polymers. In such photo-responsive materials, light irradiation initiates photo-induced electron transfer to generate pi-radicals that can self-associate to form pi-dimers. This leads to a cascade of events: processes at the supramolecular scale associated with mechanical and structural transition at the macroscopic scale. By tuning the irradiation power and duration, we evidence the formation of aggregates and gels. Using microscopy, we show that the aggregates are dense, polydisperse, micron-sized, spindle-shaped particles which grow in time. Using microscopy and time-resolved micro-rheology, we follow the gelation kinetics which leads to a gel characterized by a correlation length of a few microns and a weak elastic modulus. The analysis of the aggregates and the gel states vouch for an arrested phase separation process, a new scenario to supramolecular systems.

Automated summary

Ditopic bis-(triazole/pyridine)viologens self-assemble into coordination polymers under light irradiation, leading to mechanical and structural transitions at the macroscopic scale. Adjusting irradiation conditions can result in the formation of aggregates and gels, with aggregates being dense, polydisperse, micron-sized, spindle-shaped particles. Analysis of these states shows an arrested phase separation process, presenting a new scenario for supramolecular systems.