Single‐Step Fabrication of Smart 3D Microstructures Exploiting Naphthopyrans as Photoinitiators and Photochromic Molecules

ABSTRACT

Achieving robust photochromism inside 3D microstructures produced by two‐photon polymerization (TPP) is challenging, as many chromophores have their properties hindered upon polymerization. Here, we demonstrate the use of a naphthopyran–benzophenone compound simultaneously as a photoinitiator and photochromic chromophore for TPP‐based microfabrication using pentaerythritol tetraacrylate resin. The resulting photoresist exhibits reversible UV–vis photochromic properties in the liquid state and enables 3D microfabrication with 0.5 lateral and 2 axial feature sizes. To preserve photochromism post‐TPP fabrication, a single‐step fabrication process that encapsulates liquid photoresist within polymerized 3D structures is developed. These 3D microstructures display reversible optical switching under UV exposure, enabling controlled modulation of light transmission. This dual‐function behavior removes the need for post‐fabrication functionalization and highlights naphthopyran‐based compounds as promising materials for future potential applications in smart microsensors, and other miniaturized photonic technologies, including photonic integrated circuits.