Improving of molecular planarity via tailoring alkyl chain within the molecules to enhance memory device performance

Three conjugated small molecules with different planarity which were tailored by the alkyl chain (from methyl to cyclic alkyl chain) were designed and successfully synthesized. The memory devices based on each molecule exhibited similar write-once-read-many-times characteristics but different switch threshold voltages. Atomic force microscopy and X-ray diffraction results indicated that the film surface morphology became more planar and intermolecular packing more closer as improving the molecular planarity, which led to the lower switch threshold voltages and the higher ON/OFF current ratios. Mechanism analysis demonstrated that one charge trap arising from the benzoquinoline group in the molecular backbone was injected by charge carriers as the external bias increased, resulting in OFF and ON distinct current states. This work not only demonstrated a new memory device with low-power consumption but also offered fundamental insight for the rational design of small molecules for organic memory devices. •Three conjugated small molecules with different planarity were synthesized.•The three synthesized molecules exhibited different photoelectric properties.•The films based on three molecules exhibited different surface morphology.•Each of the devices showed write-once-read-many-times characteristics.•The methyl substituted benzoquinoline based device has the best performance.