Multiphoton-absorbing organic materials for microfabrication, emerging optical applications and non-destructive three-dimensional imaging

Non-resonant two-photon absorption (TPA) can be defined as the simultaneous absorption of two photons, via a virtual state, in a medium. TPA exhibits a quadratic dependence of absorption on the incident light intensity, resulting in highly localized photoexcitation. Recent developments in the design and synthesis of efficient, stable TPA organic materials are discussed. Microfabrication via two-photon induced free radical polymerization of acrylate monomers and cationic polymerization of epoxide monomers was accomplished using commercially available photoinitiators, and also a custom-made compound possessing high two-photon absorptivity. Two-photon facilitated photoisomerization of a fulgide in solution and in a polymer thin film demonstrated two-photon induced photochromism and its application in interferometric image recording, respectively. Greatly enhanced signal-to-noise ratios and resolution were achieved in the non-destructive three-dimensional two-photon fluorescence imaging of a polymer-coated substrate versus conventional single-photon laser scanning confocal microscopic imaging. Multifunctional TPA organic materials and fabrication of functional microstructures are also discussed.