Time- and Solvent-Dependent Self-Assembly of Photochromic Crystallites

Molecular self-assembly provides complex structures and enables the tuning of system features on the nanoscale. Guided assembly, induced by external stimuli, gives hierarchical but static arrangements, limiting the exploitation in several fields. A dynamic arrangement can confer improved and smarter properties, but adaptive self-assembly requires new molecules and the knowledge of kinetics effects. The interest in adaptive self-assembly is constantly growing and comprises environmental-, chemical-, and field-adaptive molecules. Thus reversible adaptive self-assembly systems, which can be build and destroyed for several times, attract large attention. To contribute in this field, we report the particular post-solvato-control on solid habit morphology of the vinyl-terminated spiropyran derivative named 1-(5-hexenyl)-3,3-dimethyl-6'-nitro-1,3-dihydrospiro[2H-indole-2,2'-[2H][1]benzopyran. For this molecule, the formation of supramolecular structures is solvent- and time-governed and exhibited reversible isomerization upon UV irradiation. We observed different solid habits by varying solvent polarity as well as an increasing degree of arrangement with time. Light-induced precipitation in nonpolar solvent afforded spherical merocyanine aggregates under mild conditions. This example of kinetics-controlled photochromic system has the potential to drive toward adaptive and dynamic self-assembly systems, with application in material science and for polymer functionalization.