Efficient initiators for two-photon induced polymerization in the visible range

We present two derivatives of biphenyl or fluorene symmetrically substituted, which could initiate the two-photon absorption (TPA) photopolymerization of acrylates in the visible range. Both compounds show broadband TPA between 500 and 650 nm with cross-sections of, respectively, 30 and 80×10−50 cm4 s photon−1 at 532 nm, the photoinitiation wavelength. Threshold energies and dynamic ranges for polymerization were measured in both cases. As expected, the fluorene derivative was slightly more efficient than the biphenyl one. Our initiators appeared to be orders of magnitude more sensitive than the commercial UV ones, commonly used for TPA photopolymerization.