Synthesis, structure and two-photon absorption properties of a new multi-branched two-photon photopolymerization initiator

A new free-radical photonpolymerization initiator Tris-[4-(2-pyridin-4-yl-vinyl)-phenyl]-amine (TPPA) has been synthesized and characterized by 1H NMR spectra,13C NMR spectra and elemental analyses. X-ray diffraction analyses reveal that TPPA belongs to monoclinic system, P21/n space group with a=15.851 (3), b=9.7932 (18), c=20.084 (6) Å, α=90, β=107.241 (12), γ=90°, V=2977.6 (12) Å3, Z=4, T=293 (2) K, Dc=1.237 g cm−3, R1=0.0569, wR=0.1245. The calculated two-photon absorption cross-section is 33.6×10−50 cm4 s photon−1. The experimental results confirm that TPPA is a good two-photon absorbing chromophore and operative two-photon photopolymerization initiator. When pumped with 820 nm laser irradiation, TPPA shows strong two-photon induced fluorescence. A microstructure has been fabricated under irradiation using a 200 fs, 76 MHz Ti: sapphire femtosecond laser at 820 nm. The possible photopolymerization mechanism is discussed.