Application of the time-resolved spectroscopy on the photo-dissociation dynamics of disulfide compounds in supercritical fluids

Photo-dissociation dynamics of two disulfide compounds [bis(p-aminophenyl) disulfide (BADS) and bis(p-dimethylaminophenyl) disulfide (BDMADS)] in supercritical carbon dioxide and trifluoromethane were studied by transient absorption spectroscopy. For bis(p-aminophenyl) disulfide in carbon dioxide, we found that the absorption bandshape of the p-aminophenylthiyl (APT) radical generated by the photo-dissociation shows an asymmetrical change with a time constant of about 40 ps, as was reported in the case of nonpolar solvents (Y. Hirata, Y. Niga, S. Makita, T. Okada, J. Phys. Chem. A. 101 (1997) 561). For (bis(p-dimethylaminophenyl) disulfide in carbon dioxide, we did not observe an evident change of the absorption bandshape of the p-dimethylaminophenylthiyl radical. On the other hand, we found that the absorption peak position of the radical in trifluoromethane shows a red-shift in the initial 40 ps. The bandshape change and the peak shift were discussed in terms of the radical pair dynamics and the solvation dynamics.