Halogenated dibenzoylmethane Eu3+ complexes as spectroscopic markers: a pioneering photobleaching strategy for counterfeit applications and controlling luminescence efficiency†

Abstract

A novel method for identifying counterfeit goods based on the difference between photobleaching rates of spectroscopic marker components is proposed. Controlled photobleaching of the dye is achieved via introduction of halogens (I, Cl, Br, and F) into the aromatic moiety of the dibenzoylmethane (DBM) ligand in coordination compounds of Eu³⁺. A spectroscopic marker model that consists of two coordination compounds with different halogens is developed. These compounds exhibit indistinguishable luminescence spectra and emission intensities at low irradiation power. However, exceeding the threshold irradiation power results in rapid photobleaching of the marker fragment derived from the complex with the highest charge number of halogen atoms. This approach introduces new possibilities for quality control of goods that require storage in light-protected environments. The results obtained during the research have both practical and fundamental significance. For the first time, it is established that the halogenation of the DBM ligand leads to the intersystem crossing process termination. Energy of electronic excitation transfers from the singlet excited state to the ion through a charge transfer state instead of the triplet excited state. Such energy transfer pathways sensitize luminescence of Eu³⁺ more effectively, resulting in an increase in quantum yield up to 64% upon the introduction of chlorine atoms.