Three organic small molecules with alkyl chains of different lengths based on an azobenzene scaffold were designed and synthesized. The indium-tin oxide (ITO)–Azo–Al sandwich memory devices showed write-once-read-many-times (WORM) characteristics. The switch threshold voltage of Azo-based memory devices significantly decreased as the end-capping alkyl chain extends, which is totally consistent with the AFM and X-ray diffraction results that the thin films showed smoother morphologies and closer intermolecular packing with the molecular alkyl-chain length prolonging. These results demonstrated that variation in the alkyl-chain length at the end of the conjugated molecules is a powerful strategy for tuning film microstructure and intermolecular packing to enable high performance of the fabricated sandwiched devices.