Recently, photo-controlled reversible addition-fragmentation chain transfer (RAFT) polymerization has been successfully applied in digital light processing 3D printing. It provides a convenient way to tune the surface properties of the 3D printed object. However, so far, 3D micro-and nanostructures and reconfigurations based on photo-induced RAFT polymerization have not been presented. In this work, one macro-photoiniferter, synthesized by photocontrolled RAFT polymerization is applied, to 3D direct laser writing. Thanks to the exquisite spatial control of the photoreaction, 3D microstructures with feature sizes of around 500 nm are successfully obtained. Taking advantage of the presence of dormant polymeric RAFT agents, photo-induced postmodification of the printed microstructures is highlighted via the elaboration of multi-chemistry patterns including thermo-responsive ones. These results open new perspectives in multi-material and 4D micro-printing.

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Novel sulfonium-based D-p-A photoacid generators (PAGs) with a benzene oligomer (from one to four) as a p-conjugated system that are highly photosensitive in the near-ultraviolet region (365 nm) were prepared.The maximum absorption and molar extinction coefficients of the PAGs redshifted and enhanced with the increasing length of the conjugated systems. The quantum yields of PAGs were high (three of them were over 0.6) and improved by adjusting the number of the phenyl rings. The quantum chemical calculation results proved that the molecular configuration and nature of the frontier orbitals are crucial factors which affect PAG performance. Photopolymerization kinetic results demonstrated that these sulfoniumbased PAGs were highly efficient cationic photoinitiators, and the i-line sensitivities were evaluated based on the photolithographic performance of the PAG-containing SU-8 resins. In addition, the two-photon absorption cross sections (d 700 nm > 400 GM) matched the requirements needed in the 3D fabrication of polymer microstructures. † Electronic supplementary information (ESI) available: Details of the organic synthesis and characterization, photodecomposition, photoacid generation, TGA curves, photopolymerization, photolithography and two-photon absorption. See