Ligand‐Engineered Nanoclusters as Photoinitiator and Mechanical Reinforcement for Two‐Photon Polymerization

ABSTRACT Although two‐photon polymerization (TPP) is a flexible micro‐nanoscale 3D printing technique, conventional polymeric resists contain permanently embedded organic photoinitiators that adversely affect the mechanical properties of printed structures. Here, we report a novel type of ligand‐engineered nanoclusters, which serve simultaneously as the photoinitiators in the TPP resist and as mechanical reinforcement after polymerization. Uniform nanoclusters are liganded with both reactive and photosensitive molecules to achieve combined functions. An enhanced two‐photon absorption of 22.45 GM (Goeppert‐Mayer) suggests synergistic photoenergy conversion between the nanocluster core and photosensitive ligands. The stable dispersion of the nanoclusters enables high‐fidelity 3D printing with a resolution of 141 nm. Covalently bonded interfaces between the nanoclusters and the crosslinked polymer matrix enable outstanding mechanical stiffness and strength for the printed microscale structures. In situ mechanical tests reveal that the well‐incorporated nanoclusters result in a 75% enhancement in stiffness and a 105% enhancement in strength. Such a convenient ligand‐engineering strategy can go beyond photoinitiation and mechanical reinforcement, enabling new potentials of the TPP technique for the fabrication of high‐performance micromechanical devices with diverse applications.