Superradiance of Aggregated Thiacarbocyanine Molecules

Emission lifetime and steady-state spectral measurements of aggregated and monomeric 3,3‘-diethyl-5,5‘-dichloro-9-phenylthiacarbocyanine (DDPT) in methanol and aqueous solutions at room temperature have been conducted. We deduce that in aqueous solution DDPT molecules that maintain their monomer emission lifetime and spectral properties exist intimately with molecules that are coherently interconnected in the excitonic structure. Simultaneous superradiance and monomer fluorescence from DDPT molecules occur and allows for a direct comparison of superradiance emission properties of aggregated molecules to the emission properties of the single molecule. We have found that the fluorescence lifetime of the aggregate is excitation wavelength dependent, and are led to conclude that superradiance by aggregated molecules and energy transfer from monomeric species to the aggregate play important roles in determining the optical dynamics of the aggregated system. We also report some of the photophysical properties of DDPT.