Effects of gradual oxidation of aromatic sulphur-heterocycle derivatives on multilevel memory data storage performanceElectronic supplementary information (ESI) available: The compositions of the small molecules, the memory device, TGA, energy levels for the three functional moieties, DFT molecular simulation results, stability tests of the devices, I-V curve. See DOI: 10.1039/c4tc02087a

Three symmetrical conjugated small molecules derived from phenothiazine (PTZ), PTZ-CN, PTZO-CN and PTZDO-CN, were designed and successfully synthesized for multilevel memory data storage. By reserving the terminal electron-accepting cyano moiety, the sulphur atom in phenothiazine (PTZ) was adjusted to different oxidation states, such as sulfide, sulfoxide, and sulfone, to tune the electron-accepting ability ( J. Liu et al. , Chem. Mater. , 2008, 20 , 4499 ). Therefore, a differentiated trap depth was achieved between the central sulphur-containing group and the terminal cyano groups when the molecules were charged. Devices based on PTZO-CN exhibited excellent ternary memory behaviour, while those based on PTZ-CN or PTZDO-CN only showed binary memory characteristics. Therefore, it is a viable approach to easily obtain multilevel memory organic materials by adjusting the difference between two electron-withdrawing groups in the conjugated molecular backbone through gradual oxidation of the central sulphur atom to achieve ternary memory performance. Three symmetrical conjugated small molecules derived from phenothiazine (PTZ), PTZ-CN, PTZO-CN and PTZDO-CN, were designed and successfully synthesized for multilevel memory data storage.