Multi-functional photonic crystals of modular nanosheets.

Photonic crystals with periodically ordered nanoscale building blocks can exhibit structural colors, offering a promising optical platform. Among various building blocks, colloidal nanosheets have attracted increasing attention owing to their intrinsic two-dimensionality and stimuli-responsiveness. However, integrating multiple functionalities into nanosheet-based photonic crystals remains challenging due to the structural and colloidal requirements of the nanosheets. Here, we established a universal modular strategy for synthesizing functional hybrid nanosheets and subsequently constructed multi-functional photonic crystals via their self-assembly. By electrostatically integrating negatively charged titanate nanosheets with positively charged nanoparticles, including gold nanoparticles, gold nanorods, and fluorescent silica nanoparticles, we successfully synthesized functional hybrid nanosheets. The enhancement of electrostatic repulsion between these nanosheets enabled the formation of multi-functional photonic crystals with modularly integrated structural color, plasmonic absorption, and fluorescence. Finally, we demonstrated three-dimensional visualization of the photonic nanostructures using confocal microscopy and reversible modulation of the optical properties using magnetic fields and light. This work provides a versatile platform for designing next-generation smart photonic materials with integrated functionalities.