Fano Resonances in Metal–Organic Framework ZIF-8 Derived from Liquid-Crystal-Templated Nanoporous ZnO Films

Nanoporous zinc oxide (ZnO) thin films have attracted considerable attention and are widely used in advanced photonic and chemical applications. Although various methods exist for producing large area nanoporous ZnO thin films, they often require complex, costly equipment, and a simple one-pot synthesis is still lacking. Developing a simple and accessible fabrication method would therefore facilitate and broaden their application in optoelectronics, photocatalysis, and as templates for advanced functional materials, including metal–organic frameworks (MOFs). In this study, we report an approach for fabricating large-area nanoporous ZnO thin films using lyotropic liquid crystals (LLCs) as templates, which are subsequently converted into microporous ZIF-8 films, enabling the observation of pronounced Fano resonances in J-aggregate coated ZIF-8 films. The nanoporous ZnO thin films were prepared using a hexagonal LLC phase composed of a metal ion source Zn(NO3)2·6H2O, a nonionic surfactant C12E10, and water. Calcination at 450 °C yielded nanoporous ZnO films, which were subsequently converted into localized ZIF-8 crystals and uniformly coated with J-aggregate dyes, enabling the observation of Fano resonances and highlighting their strong potential for photonic applications. Therefore, we propose that microporous ZIF-8 crystals, with their porous structure and the localization of the electromagnetic field within them, serve as an ideal dielectric platform for studying light–matter interactions in the weak coupling regime.