Dynamics of photoinduced gap states and self-trapped excitons in the MX chain compounds with degenerate and non-degenerate CDW ground states

We have characterized the photoinduced gap states from the photoinduced absorption (PA) spectroscopy in the halogen (X)-bridged metal (M) complexes having degenerate CDW state, ([Pt(en)2][Pt(en)2X2](ClO4)4 : XCl, Br) and those having non-degenerate CDW state, ([Pd(en)2][Pt(en)2X2](ClO4)4 : XBr, I). In the former complexes, observed are the two midgap bands named as A and B, which have been assigned to spin-solitons, while in the latter complexes, photogenerations of solitons are suppressed. Photogenerations of polarons have been detected in both types of complexes. We have also investigated the excitation profiles of the luminescence from the self-trapped excitons, which are compared with those of the PA signals due to the gap states. The results demonstrate that the luminescence process strongly competes with the dissociation process to spin-soliton pairs followed by nonradiative recombinations.