Picosecond pump-probe spectroscopic study of electronic energy relaxation in H-aggregates of 1,1'-diethyl-2,2'-dicarbocyanine (DDC) on colloidal silica



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Texas Tech University


Polarized transient bleaching measurements of H-aggregates of l, l'-Diethyl-2.2'-Dicarbocyanine (DDC) on colloidal silica were performed using picosecond time-resolved pump-probe spectroscopy. The aggregates were nonfluorescent but exhibited a broad absorption band, between 550 and 600 nm, which was blue-shifted from the monomer band at 711 nm. These spectral properties are consistent with the simple theory for one-dimensional excitons. The transient bleaching signals can be filled well by a stretched exponential function. The nonexponential signals are attributed to a distribution of aggregates with different lifetimes, with the most probable lifetime being equal to 120-130 ps. The absorption anisotropy was constant and equal to 0.30 ± 0.04. The anisotropy is discussed in terms of the coherence properties of excitons.