Light-Modulated Morphological Transformation of Spiropyran Derivative from Nanosphere to Nanorod.

The construction of tunable morphological systems has important implications for understanding the mechanism of molecular self-assembly. In this study, a spiropyran derivative M1 is reported with light-responsive assembly morphology, which can be tuned from nanosphere to nanorod by ultraviolet light irradiation. The absorption spectra show that M1 molecules are transformed from closed-ring (SP) isomers into open-ring (MC) isomers and start to form H-aggregates with increasing irradiation time. Density functional theory calculations indicate that MC-MC isomers possess stronger binding energy than SP-SP isomers. The MC isomers may thus facilitate the dissociation of the SP-SP aggregates and promote the change of self-assembled morphology with the aid of stronger π-π stackings and dipole-dipole interactions. The research gives an effective method for modulating the morphology of assemblies, with great potential for applications in smart materials.