Single-particle two-photon absorption imaging and enhancement determination for organic nanoparticles

The lack of characterization regimes available for the rapid single-particle assessment of two-photon (TPA) response in nanomaterials remains a critical barrier to nonlinear optical device development. This is particularly true of nonemissive species whose TPA must often be characterized in the bulk. In this study, self-assembly is used to produce uniform nanoparticles from a novel porphyrin dimer, which is known to exhibit both severe fluorescence quenching and two-photon cross section (TPACS) enhancement when assembled into macromolecules. We present here the first reported use of fiber aperture near-field optical microscopy (NSOM) for the purpose of characterizing directly the TPA of nonemissive nanoparticles, observing directly a 5-fold enhancement in TPA response. This assembly/characterization regime provides a fast and fully actualized method for the generation of low-scatter optical-limiting organic nanomaterials where domain size, morphology control, and TPA enhancement are all critical to applic...