Bringing Far-Field Subdiffraction Optical Imaging to Electronically Coupled Optoelectronic Molecular Materials Using Their Endogenous Chromophores.

We demonstrate that subdiffraction resolution can be achieved in fluorescence imaging of functional materials with densely packed, endogenous, electronically coupled chromophores by modifying stimulated emission depletion (STED) microscopy. This class of chromophores is not generally compatible with STED imaging due to strong two-photon absorption cross sections. Yet, we achieve 90 nm resolution and high contrast in images of clusters of conjugated polymer polyphenylenevinylene-derivative nanoparticles by modulating the excitation intensity in the material. This newfound capability has the potential to significantly broaden the range of fluorophores that can be employed in super-resolution fluorescence imaging. Moreover, solution-processed optoelectronics and photosynthetic or other naturally luminescent biomaterials exhibit complex energy and charge transport characteristics and luminescence variations in response to nanoscale heterogeneity in their complex, physical structures. Our discovery will furthermore transform the current understanding of these materials' structure-function relationships that have until now made them notoriously challenging to characterize on their native, subdiffraction scales.