Sequence‐Defined Oligourethane Isomeric Mixtures for Irreversible Encryption

Sequence‐defined polymers (SDPs) offer a promising molecular medium for information storage and encryption, yet current strategies for enhancing security typically depend on extending chain length or increasing monomer diversity—approaches that impose substantial synthetic complexity. Here, we introduce a fundamentally different encryption mechanism based on isomeric mixtures of sequence‐defined oligourethanes (SDOs). Because isomeric SDOs share identical molecular weights, their mixtures collapse into a single peak in primary MALDI‐TOF MS, concealing compositional identity. More critically, tandem MS fragmentation generates multiple degenerate decoding paths, preventing reconstruction of the original mixture and establishing an intrinsically one‐way, irreversible molecular encryption process. Using four octameric isomers as a proof‐of‐concept system, we further integrate these mixtures into CMYK molecular digital inks that enable direct printing and secure information transmission. Encrypted messages can be retrieved only through a bespoke MS/MS decoding algorithm coupled with a predefined ASCII‐mapping scheme. This work introduces isomeric oligomer mixtures as a new class of molecular cryptographic media, bridging chemical design with information theory and offering a scalable platform for next‐generation data security and anti‐counterfeiting technologies.