Light to dissolve: (R)- and (S)-diamides bearing a hydrogen-bonding framework (red in picture) and a trans-azobenzene unit (blue) form an insoluble heterochiral aggregate, which can be dissolved by photoisomerization of the azobenzene unit to the cis conformation by UV irradiation (365 nm). The insoluble aggregate was formed again by subsequent irradiation with visible light (>422 nm). The precipitation and dissolution is manifestly reversible.
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