i‐Indigo‐Based Self‐assembled Microparticles and Their Conversion to Nanoparticles

Abstract

AbstractMicroscopic particles (MPs) are used to scatter and reflect UV light. It is well established that inorganic MPs such as TiO2 and ZnO produce carcinogens. Therefore, organic MPs are explored for UV absorption. Conjugated chromophores with differing lipophilicity usually self‐assemble into nanoscopic structures. In our previous experiments, unsymmetrical i‐Indigo was found to self‐assemble into 500 nm particles. We hypothesized that the size of the self‐assembled particles can be increased by increasing the lipophilicity difference between the side chains. Toward this objective, we have chosen the i‐Indigo core with TEG and alkyl chains as side chains. As a result, the i‐Indigo molecules were found to self‐assemble into 3 μ spheres in solution. By substituting side chains with different lipophilicity, i‐Indigo microparticles with the size of 5 μ are prepared. A careful analysis showed that the spheres are similar to a soccer ball, and they deflate upon drying on the substrate surface. The judiciously chosen side chain binds with a metal‐ion (Cs+) and forms nanoscopic assemblies. After Cs+ binding, the size of the particles is decreased drastically to 100 nm. The simple addition of ions converts microscopic assemblies into nanoscopic assemblies.