J. Moll et al., FRACTAL APPROACH TO THE EXCITON-PHONON COUPLING AND STRUCTURE OF J-AGGREGATES, Physical review. B, Condensed matter, 55(9), 1997, pp. 5562-5565
We present a study on exciton-phonon coupling in molecular aggregates
at low temperature probed by photon-echo and resonance Raman experimen
ts. A large peak in the low-frequency Raman spectrum is interpreted as
a boson peak. Our results for the J aggregates of the dye 5,5', yl-3,
3'-di(4-sulfobutyl)-benzimidazolocarbocyanine indicate an anomalous vi
brational density of states with a spectral (or fracton) dimension of
1.44 at 3.9 K. The spectral dimension increases with temperature, sugg
esting that the topological dimension of the aggregates in solution is
1 and that an increase in temperature leads to an increase in effecti
ve branching of the aggregate.