C _2v symmetrical two-photon polymerization initiators with anthracene core: Synthesis, optical and initiating properties

A series of C _2v symmetrical two-photon absorption compounds with anthracene core, 2,7-bis[2-(4-substituted phenyl)-vinyl]-9,10- dipentyloxyanthracenes designated as I, II and III (the substituted groups at the 4-position of phenyl of I, II and III were dimethylamino, methyl and cyano, respectively) were designed and synthesized as initiators in two-photon induced polymerization (TPIP). The anthracene ring was modified by linking vinylphenyl groups to the 2,7-position to extend conjugation system length and two pentyloxy groups to the 9,10-position to serve as electronic donors. Two-photon absorption cross section of I was around 300 GM, which was much larger than the 10 GM of II and 29 GM of III at 800 nm. I of 0.18% molar ratio in resin composed of methacrylic acid and dipentaerythritol hexaacrylate exhibited a dramatically low threshold of 0.64 mW compared with commercial photoinitiator benzil at a scanning speed 10 μm s ^-1. Moreover, the threshold of photoinitiator I was only increased to 2.53 mW at a scanning speed of 1000 μm s ^-1. The dependency of threshold on the concentration and exposure time was in accordance with theoretical calculation. Finally, a reasonable mechanism of the two-photon initiating process was proposed. This study provides good prospects for developing low threshold photoinitiator in TPIP.