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.