Bithiophene-naphthalene chalcone as a fluorescent pigment in eco-friendly security ink formulation

Approaches to prevent document/product forgery using eco-friendly printing inks and security printing techniques on flexible substrates are two vital areas of research that demand coherent advancements. In this context, a new bithiophene-naphthalene chalcone (BTNP) was synthesized and characterized as a fluorescent pigment for use in security ink. BTNP exhibited good solid-state and solution phase fluorescence with intramolecular charge transfer confirmed using theoretical studies and emission spectra collected in THF/THF–hexane mixtures. The aggregation-induced emission of BTNP was established using solution phase studies in THF/THF–water mixtures. The strong solid-state yellow emission of BTNP prompted its use as a pigment in the preparation of an environment-friendly UV fluorescent formulation, devoid of any volatile organic compounds or hazardous air pollutants. The screen prints obtained on a UV dull paper substrate utilizing BTNP ink revealed good fluorescence, photostability, colorimetric, densitometric, and rub resistance characteristics, which showcase the potential applicability of the BTNP formulation in security printing. The low cytotoxic nature of the chalcone as observed in the MTT assay could also be exploited for the use of formulation in inkpads. Graphical abstract: [Figure not available: see fulltext.]