Color and fluorescence switchable 2D and 3D printed hybrid materials

We introduce an ink system for light-driven 3D printing that consists of electrostatically stabilized inorganic-organic hybrid nanoparticles (IOH-NPs), a crosslinking monomer and a photoinitiator, enabling the printing of color- and fluorescence-switchable 3D objects. Nanoparticles (NPs) are often prone to aggregation in photoresins, causing significant light scattering that hinders the printing process. Furthermore, the particles may degrade upon exposure, resulting in the loss of their properties. These issues result in poor printing quality or a loss of functionality. By carefully selecting NPs and resin composition, we successfully incorporate IOH-NPs into a soft-matter 3D network, enabling a fast pH-dependent color and fluorescence change over a wide pH range. In-depth characterization of the printed structures <i>via</i> imaging, spectroscopic and spectrometric techniques reveals that the IOH-NPs remain intact after printing, exhibiting repeatable color and fluorescence switching. We further demonstrate that multi-material objects can be fabricated entailing both color-switchable and non-switchable structural elements. The hybrid materials for 3D printing introduced here enable tunable optical properties and hold promise for applications in sensors or optical devices.