Anisotropic Optical Properties of Thin-Film Thiacarbocyanine Dye Aggregates

Optical properties of thin films of aggregated thiacarbocyanine (TCC) dyes have been studied by means of spectroscopic ellipsometry and polarized IR spectroscopy. The experimental results reveal a strongly anisotropic response of the films, as quantified in the reported anisotropic dielectric functions over a wide range of frequencies. The studied TCC films exhibit both J-aggregate and H-aggregate absorption bands with different polarization properties. A strong dielectric resonance arising from the J-aggregate electronic excitations was found to be polarized along the film. The observations are consistent with the preferential orientation of aggregate filaments along the films. We have also used the measured anisotropic properties in model calculations of energy transfer into thin films of Jaggregates to illustrate the potential importance of accurate optical characterization in engineering aggregate-based hybrid nanostructures for optoelectronic applications.