We performed an experimental investigation on the scattering and extinction properties of an aqueous solution of spermine-induced fractal $J$ aggregates, constituted by porphyrin molecules. In analogy with nanostructured particle composites, the dipolar moments of different porphyrins, not belonging to the $J$ aggregates, are coupled and generate a strong light scattering enhancement. Both the enhanced scattered intensity and the imaginary part of the polarizability of the system obey scaling laws with the optical spectral dimension $d_0=0.3$.

• Received 13 December 2004

DOI:https://doi.org/10.1103/PhysRevE.72.050401