Ld. Bakalis et J. Knoester, Pump-probe spectroscopy and the exciton delocalization length in molecularaggregates, J PHYS CH B, 103(31), 1999, pp. 6620-6628
Using numerical simulations, we investigate to what extent the pump-probe s
pectrum can be used as a tool to determine the exciton delocalization lengt
h in disordered molecular (J) aggregates. We compare the delocalization len
gth obtained through heuristic arguments from the spectral separation betwe
en the bleaching and the one- to two-exciton induced absorption features in
this spectrum to the delocalization length obtained from the participation
ratio at the J band center. We find that up to a certain saturation length
these two delocalization lengths are indeed proportional. In the case of l
ong-pulse two-color pump-probe spectra, the slope of this linear scaling is
insensitive to the pump frequency; it is sensitive to the width of the pro
be pulse. Beyond the saturation length, which is determined by the homogene
ous line width of the exciton transitions, both the two-color and the short
-pulse pump-probe spectra saturate and no longer can be used as a measure f
or the delocalization length. The latter applies to the B850 ring of bacter
ial antenna complexes.