PICOSECOND POLARIZED PUMP-PROBE SPECTROSCOPY OF AMYLOSE-IODINE

Single-wavelength picosecond polarized pump-probe spectroscopy has bee n used to study the excited state dynamics of aqueous suspensions of t he amylose-iodine complex at wavelengths within the broad absorption b and centered at about 635 nm. A single-exponential fit of the magic an gle signal at 600 nm gave an average ground state recovery time of 870 +/- 50 ps. For excitation at 570 nm a bi-exponential decay with a sho rt component of about 160 ps and a long component of 870 ps gave the b est fit of the magic angle signal. The non-exponential decay is attrib uted to overlapping absorption and relaxation processes due to differe nt polyiodide chains. Since no fluorescence is observed from the compl ex, the pump-probe signals must be due to relaxation from a long-lived excited state which is not part of the singlet manifold of states. No excitation intensity dependence was observed in the decay kinetics. T he anisotropy was constant over the time range of our experiment. The value of the anisotropy was about 0.35 +/- 0.04, which is less than th e maximum theoretical value of the initial anisotropy, r(o) = 0.4. The se results are shown to be consistent with a five-level model.