Highly uniform supramolecular nano-films derived from carbazole-containing perylene diimide via surface-supported self-assembly and their electrically bistable memory behavior

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For electrical memory applications, two perylenetetracarboxylic diimide (PDI) derivatives, N,N′-(6-carbazole hexyl)-1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-tetracarboxylic diimide (PDI-6Cz) and N,N′-(2-carbazole ethyl)-1,7-di(4-tert-butylphenoxy)perylene-3,4,9,10-tetracarboxylic diimide (PDI-2Cz), were synthesized and their surface-supported self-assembly behaviors were investigated. PDI-2Cz tends to self-organize into regular rods, which are proved to be hexagonal lattices with single crystal nature, based on which memory device fabrication and electrically bistable behavior evaluation are technically infeasible. Whereas PDI-6Cz readily self-assembles into highly uniform nano-films with a considerably smooth surface, in which the X-ray diffraction study indicates strong π–π stacking between the aromatic skeletons. Further characterization indicates that sandwich memory devices using a PDI-6Cz nano-film as the active layer exhibit reprogrammable flash-type memory behavior with a switching-on voltage of ca. 0.8 V and an ON/OFF current ratio of 104. Besides, the devices exhibit excellent long-term operation stability, enduring up to 108 reading cycles without obvious current variation and an ultrafast switching response period of less than 20 ns. Photophysical and electrochemical measurements and DFT molecular simulations were conducted to determine the electronic transition occurring in the supramolecular self-assembled nano-film. Compared with organic storage materials based on polymers, the current memory device exhibits lower threshold voltage and more rapid response speed, which provides a new way for developing high-performance organic data storage materials.

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