The photo‐induced phase transition in Et 2 Me 2 Sb[Pd(dmit) 2 ] 2

The large photo‐induced change of reflectivity has been observed in the unique charge separated phase of the Et 2 Me 2 Sb[Pd(dmit) 2 ] 2 crystal. We observe a clear spectral change due to the disappearance of the charge separated phase by femtosecond photo‐excitation in the [Pd(dmit) 2 ] dimer. The dynamics of the photo‐excited state depends on the excitation intensity. Obtained results strongly suggest that cooperative effect plays a key role in the photo‐excited state of this system. We tentatively classify the observed phenomena as a photo‐induced phase transition due to the melting of the charge separation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)