Onset of exciton–polariton behavior observed in individual fibers of pseudoisocyanine J-aggregates by sub-micron scale reflectance spectroscopy

We report results on reflection microscopy and local spectroscopy of aggregates of pseudoisocyanine chloride prepared in thin film of polyvinylsulfate. The aggregates assemble into fiber-like structures of relatively high reflectivity of up to 20%. Locally, the fibers show a large variety of reflectance spectra from sharp peaks at the position of the absorption J-band to broad bands with further structures near their maxima. Polarization experiments confirm that transition dipoles responsible for the J-band are oriented along the fibers. A simple theoretical model taking into account polariton-like excitations and finite dimensions of the fibers is used to simulate the experimental results.