Photochemical reactions which can be activated by the simultaneous absorption of two photons provide a means for singlestep fabrication of complex three-dimensional microstructures. These types of structures are needed for a wide range 1 applications, including microfluidics, electrooptics, and micro-electromechanical systems (MEMS). We have shown that chromophores can be engineered to have both large two-photon absorptivities as well as an efficient means for activating chemical processes,

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... as radical polymerization, subsequent to the photoexcitation. Chromophores designed following this strategy two-photon-activate the radical polymerization of acrylates at lower incident laser powers than conventional UV initiators. Efficient two-photon photopolymer resins based on these chromophores were used in the fabrication of complex microarchitectures, such as photonic bandgap structures and tapered waveguides. We have devised a strategy which allows this approach to be extended to other chemical systems.