D–π–A type π-conjugated photoacid generators through the para-to-meta substitution strategy show high efficiency in photoinitiated cationic polymerization reactions at 405 nm and 800 nm excitation.

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

We investigated methodically the one- and two-photon absorption properties of a series of multibranched triphenylamine-based chromophores incorporating 4-(methylthio)styryl fragments as external substituents. Some relevant structure–property relationships relative to these highly fluorescent compounds have been derived based on emission anisotropy measurements, quantum chemical calculations and the use of the exciton coupling theory. Even though branching effects lead to a cooperative enhancement of the two-photon absorption (2PA), all compounds exhibit relatively low-to-moderate 2PA cross-sections (δ ≤ 100 GM) in the NIR region. However, the ‘so-called’ one-photon resonance enhancement effect leads to a remarkable increase of δ by more than one order of magnitude in the visible range. This strong 2PA ability has been associated with an efficient photosensitization of iodonium salt to elaborate a new bicomponent photoacid generator, which is readily two-photon activable at 532 nm. In the visible range, the strong enhancement of the efficiency of the two-photon induced polymerization is clearly demonstrated as compared with that observed in the NIR region

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