Organic fluorescent molecules based on coumarin acylhydrazone with acidochromic luminescence and their application as anti-counterfeiting materials

Abstract

Stimuli-responsive organic luminescent materials have attracted much attention for their practical application in many fields. Acidochromic materials show color or fluorescence changes with the stimuli of external acid, and have wide applications in information encryption and anti-counterfeiting technology. In this work, two coumarin acylhydrazone derivatives were designed and synthesized. These compounds can emit strong blue fluorescence in weakly polar solvents with high fluorescence quantum yield, and show red-shifted fluorescence in highly polar solvents with low intensity, which is characterized as solvatochromism. The DFT calculations show that these molecules have a significant difference in HOMO and LUMO distributions, which suggests that they have the property of intramolecular charge transfer. Further studies showed that these compounds also possessed acidochromic properties. After encountering trifluoroacetic acid, the fluorescence intensity of these compounds could gradually decrease. The solutions of these compounds can be used as security inks. The fluorescent powders prepared from these compounds and montmorillonite showed a significantly different sensitivity to trifluoroacetic acid, and can be used as information encryption and anti-counterfeiting fluorescent materials.