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Water‐Soluble Spiropyrans with Inverse Photochromism and Their Photoresponsive Electrostatic Self‐Assembly
Author(s) -
Moldenhauer Daniel,
Gröhn Franziska
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201605621
Subject(s) - photochromism , spiropyran , merocyanine , chemistry , photochemistry , aqueous solution , cationic polymerization , dynamic light scattering , hydrolysis , ultraviolet visible spectroscopy , self assembly , supramolecular chemistry , fluorescence spectroscopy , visible spectrum , fluorescence , polymer chemistry , materials science , organic chemistry , nanotechnology , nanoparticle , molecule , optics , physics , optoelectronics
A new type of light responsive nanoscale assemblies based on water‐soluble spiropyrans is presented. We have synthesized four anionic spiropyrans bearing multiple sulfonate groups and investigated their photochromic behavior in aqueous solution. Depending on the pH, either inverse photochromism (acidic conditions) or normal photochromism (alkaline conditions) is found. Kinetic data for the interconversion of the spiropyran and merocyanine isomers including the subsequent slow hydrolysis have been obtained by UV/Vis spectroscopy. The results show that the spiropyrans undergo hydrolysis in both alkaline and acidic solution, while in the latter the rate is far slower than in the former. This prolonged hydrolytic stability together with the inverse photochromism under acidic conditions makes the sulfonated spiropyrans suitable to build photoresponsive nanostructures with cationic polyelectrolytes. We show how the self‐assembly process is driven by electrostatic interactions and how the spiropyrans’ photochromic property allows the size control of the supramolecular objects by visible light. The assembly size is characterized by dynamic light scattering and TEM. In addition, UV/Vis and fluorescence spectroscopy and ζ ‐potential measurements help to explain the size change upon visible light irradiation.