<p>The present investigation reports an interesting observation wherein full complementary resistive switching (CRS) characteristics of a memory device were obtained when the active layer was used as the mixed film of two individual materials, namely phenol red sodium salt (PRSS) and toluidine blue O (TBO). What is interesting is that when these two materials were used individually as the active layers in the resistive memory devices, in both cases, write-once read-many (WORM) resistive memory characteristics were observed. This paradigm shift from WORM to CRS characteristics in the memory device is explained based on the relative positions of HOMO–LUMO energy levels of both the PRSS and TBO. Charge recombination in the HOMO–LUMO energy levels is proposed as the reason for this shift from WORM to CRS behaviour in the memory device.</p> Graphical Abstract <p></p>