Synthesis and nonlinear optical properties of novel multi-branched two-photon polymerization initiators

Efficient Witting and Pd-catalyzed Heck coupling methodology are employed to synthesize three multi-branched two-photon photopolymerization initiators diphenyl-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to DPVPA), phenyl-bis-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to BPVPA) and tris-(4-{2-[4-(2-pyridin-4-yl-vinyl)-phenyl]-vinyl}-phenyl)-amine (abbreviated to TPVPA). The experimental results confirm that all these compounds are good two-photon absorbing chromophores and operative two-photon photopolymerization initiators. The calculated two-photon absorption cross sections of DPVPA, BPVPA and TPVPA for the lowest excited state are 59.3, 30.2 and 42.4 × 10⁻⁵⁰ cm⁴ s photon⁻¹, respectively. A microstructure using BPVPA as initiator has been fabricated under irradiation of 200 fs, from a 76 MHz Ti∶sapphire femtosecond laser at 820 nm. The possible photopolymerization mechanism is discussed.