A novel diagnostics for polymer degradation based on near-field two-photon photoluminescence

By coupling femtosecond pulses to a hollow-pyramid aperture SNOM, we demonstrate nonlinear near-field two-photon photoluminescence imaging of organic semiconductors. We discover that two-photon excitation of the blue-emitting poly(9,9-dioctylflurorene) (PFO) selectively addresses the keto-defect units which are responsible for a shifted green-orange emission. We exploit this effect to map oxidized sites in the PFO film with high contrast and spatial resolution, introducing a novel tool for characterizing oxygen-induced degradation in electroluminescent materials.