Abstract
Photochromic stimuli-responsive coordination polymers that offer on-demand molecular structure modifications are promising building blocks for next generation of multi-functional materials. Getting closer to some applications requires these materials to be in condensed phases, which is yet lacking. In this work, ≈ 300 - 450 nm colloidal particles made of a coordination polymer that includes dimethyldihydropyrene (DHP) as photoswitchable units have been synthesized. ZnDHP particles exhibit a photochromic behavior based on the reversible conversion of “closed” DHP units into “open” cyclophanediene (CDP). Ring opening in the condensed phase was triggered by visible light illumination while back-conversion was performed by either heating or irradiation with UV light. Experiments were monitored by UV–vis spectroscopy. Results showed good reversibility of the system with < 5 min back-conversion under UV irradiation. Nanostructure of the particles was studied by TEM and SAXS. Particles are made of 10 – 25 nm dense parallelepipedic nanoparticles organized into a slightly loose network. SAXS analysis demonstrates that ZnDHP particle structure is resilient to ZnCDP conversion. Finally, ability of ZnCDP-O2 particles to release singlet oxygen during their back-conversion to ZnDHP particles is demonstrated by EPR experiments.
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