Controllable isomerization of a light-sensitive spiropyran unit via the assembly of pyrenyl-modified rod-coil amphiphiles

Abstract

New types of supramolecular light-responsive assembly systems have been constructed upon the addition of pyrene functional groups to spiropyran-derived amphiphilic rod-coil molecules. These molecules are composed of hydrophobic pyrene, biphenylacetylene and aldehyde-modified spiropyran group as rod building block as well as flexible oligoether chains with non lateral methyl or lateral methyl as coil segment. Our self-assembly investigations revealed that compared to molecules with noncovalently linked pyrene groups, these molecules were arranged relatively compactly during their aggregation via the strong π-π stacking effect provided by the pyrene groups. Meanwhile, we found that the steric hindrance effect of the methyl side chains at the rigid-flexible interface loosely stack the molecules to form nanostructures with a larger curvature in 99 % aqueous solution. Notably, the strong π-π stacking intermolecular interaction of the pyrene and ring-opening isomer induce the formation of nano-assemblies under stimulation with ultraviolet (UV) light, which subsequently block the ring-closing process of the spiropyran in solution, resulting in the construction of new organized disc-like structures and spherical micelles. Interestingly, the solution of complexes formed between rod-coil molecules with pyrene group and 2, 4, 5, 7-tetranitro-9-fluorenone (TNF) displayed good fluorescence sensing performance for TNF in both an organic solvent and mixed solvent system with a high-water content, which has the potential to be developed into sensors suitable for multi-nitro electron acceptor molecules.