Two polymer-Hemin composites, AB type block copolymer (PStCH-b-P4VP): Hemin and homopolymer of poly(4-vinylpyridine) (P4VP): Hemin, can be fabricated into sandwich memory devices. The memory device characteristics of the PStCH-b-P4VP: Hemin blends can show Flash memory behavior, while the P4VP polymer with Hemin only shows write-once-read-many-times (WORM) performance. Charge transfer and nanocomposite redox are probably responsible for the conductance-switching behavior. The results of cyclic voltammogram (CV) measurement indicate that the reversible Fe-III/Fe-II redox reaction is preserved well in the composite PStCH-b-P4VP: Hemin, while only polymer oxidation is observed in the P4VP: Hemin system. Due to the hindrance of StCH moiety, the coordination of pyridine and Fe-II can keep the FeII active. The P4VP has a more flexible chain that saturates the Fe-II center and results in stable coordination; Fe-III/Fe-II redox reaction is therefore an obstacle. By tuning the coordination surroundings of the metal ion, different memory types can be obtained. (C) 2015 Elsevier Ltd. All rights reserved.