Photoinduced phase separation with local structural ordering in organic molecular conductors

In this work, polarized pump-probe spectroscopy was carried out to investigate the effects of a structural ordering of molecules on photoinduced phase separation (PIPS) in the organic conductors k-(BEDT-TTF)(2)X [X = Cu[N(CN)(2)]Br (k-Br) and Cu(NCS)(2) (k-NCS)]. We found that the anisotropic response for the probe polarization appeared at around T-g, where the glasslike structural transition occurs. The anisotropy can be a result of a transient destruction of the local ordering of molecules, indicating a connection between the glasslike transition and PIPS. Moreover, we found that the PIPS response gradually develops with decreasing temperature in k-Br, whereas it steeply increases in k-NCS. This qualitative difference suggests that the structural ordering caused by a PIPS is more crucial in k-NCS than in k-Br.