Multistimuli-responsive fluorescent molecules (PF-B and PF-N) with logically programmable states are synthesized, which utilize a phenyl ring and a nitrogen atom, respectively, as the center connected with three isolated electron-accepting phenanthridine units. Both PF-B and PF-N exhibit fluorescence color changes to trifluoroacetic acid, Al 3+ , Fe 2+ , rigidifying polymer matrix, and heat, resulting in five write-in modes. Meanwhile, PF-N presents a larger bathochromic shift than that of PF-B upon applying an identical stimulus, beneficial from its intramolecular charge transfer (CT) character. The multiple stimulus-responsive feature endows PF-B and PF-N with flexible and diverse applications, including rewritable and security printing, and multiple optical outputs for anti-counterfeiting. More importantly, the response of the fluorophores depends not only on the present stimulus but also on the sequence of past stimuli. Additionally, the build-in reversibility and irreversibility of their responses to different stimuli remarkably diversify the outputs, leading to a well-programmed anti-counterfeiting scheme based on "sequential + OR" logic gates for the first time. This work not only provides a feasible strategy to develop multiple stimuli-responsive luminescence materials at the molecular level but also offers a general design principle of logic schemes for advanced anti-counterfeiting and data protection.
Traditional security inks relying on fluorescent/phosphorescent molecules are facing increasing risks of forgery or tampering due to their simple readout scheme (i.e., UV‐light irradiation) and the advancement of counterfeiting technologies. In this work, a multidimensional data‐encryption method based on non‐fluorescent polymers via a “lock–key” mechanism is developed. The non‐fluorescent invisible polymer inks serve as the “lock” for data‐encryption, while the anti‐rigidochromic fluorophores that can distinctively light up the polymer inks with programed emissions are “keys” for decryption. The emission of decrypted data is prescribed by polymer chemical structure, molecular weight, topology, copolymer sequence, and phase structure, and shows distinct intensity, wavelength, and chirality compared with the intrinsic emission of fluorophores. Therefore, the data is triply encrypted and naturally gains a high‐security level, e.g., only one out of 20 000 keys can access the only correct readout from 40 000 000 possible outputs in a three‐polymers‐based data‐encryption matrix. Note that fluorophores lacking anti‐rigidochrimism cannot selectively light up the inks and fail in data‐decryption. Further, the diverse topologies, less well‐defined structures, and random‐coiled shapes of polymers make it impossible for them to be imitated. This work offers a new design for security inks and boosts data security levels beyond the reach of conventional fluorescent inks.
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