Encoding isotopic watermarks in molecular electronic materials as an anti-counterfeiting strategy: Application to porphyrins for information storage

Abstract

An approach for information storage employs tetrapyrrole macrocycles as charge-storage elements attached to a (semi)conductor in hybrid chips. Anti-counterfeiting measures must cohere with the tiny amounts of such electroactive material and strict constraints on composition in chips; accordingly, the incorporation of typical anti-counterfeiting taggants or microcarriers is precluded. The provenance of the tetrapyrroles can be established through the use of isotopic substitution integral to the macrocycle. The isotopic substitution can be achieved by rational site-specific incorporation or by combinatorial procedures. The formation of a mixture of such macrocycles with various isotopic composition (isotopically unmodified, isotopologues, isotopomers) provides the molecular equivalent of an indelible printed watermark. Resonance Raman spectroscopic examination can reveal the watermark, but not the underlying molecular and isotopic composition; imaging mass spectrometry can reveal the presence of isotopologues but cannot discriminate among isotopomers. Hence, deciphering the code that encrypts the watermark in an attempt at forgery is expected to be prohibitive. A brief overview is provided of strategies for incorporating isotopes in meso-substituted tetrapyrrole macrocycles.