Three-dimensional microfabrication using two-photon-activated chemistry

Photochemical reactions which can be activated by the simultaneous absorption of two photons provide a means for single-step fabrication of complex 3D microstructures. These types of structures are needed for a wide range of applications, including microfluidics, electrooptics, and micro-electromechanical systems. 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, such 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

Design of Organic Molecules with Large Two-Photon Absorption Cross Sections

A strategy for the design of molecules with large two-photon absorption cross sections, δ, was developed, on the basis of the concept that symmetric charge transfer, from the ends of a conjugated system to the middle, or vice versa, upon excitation is correlated to enhanced values of δ. Synthesized bis(styryl)benzene derivatives with donor-π-donor, donor-acceptor-donor, and acceptor-donor-acceptor structural motifs exhibit exceptionally large values of δ, up to about 400 times that of trans-stilbene. Quantum chemical calculations performed on these molecules indicate that substantial symmetric charge redistribution occurs upon excitation and provide δ values in good agreement with experimental values. The combination of large δ and high fluorescence quantum yield or triplet yield exhibited by molecules developed here offers potential for unprecedented brightness in two-photon fluorescent imaging or enhanced photosensitivity in two-photon sensitization, respectively

Theoretical Design of Organic Chromophores with Large Two-Photon Absorption Cross-Sections

Design strategies and structure-property relationships for two-photon absorption in conjugated molecules are described on the basis of correlated quantum-chemical calculations. We first focus on stilbene derivatives with centrosymmetric structures. We found that derivatization of the conjugated molecule with electroactive groups in a quadrupolarlike arrangement leads to a large increase in the two-photon absorption cross section, δ. Quantum-chemical description provides rich insight into the mechanisms for the two-photon absorption phenomenon