A green plant-derived fluorescent polyphenol: Investigating the fluorescence properties of ellagic acid in diverse solvents

Abstract

Ellagic acid (EA), a natural and environmentally friendly polyphenol, positively impacts human health and is widely used in the food and medical industries. It features a well-organized planar structure with an extensive sp2 carbon-conjugated area and four phenolic hydroxyl groups, making it favorable for light energy absorption and fluorescent emission. This positions EA as a promising candidate for advanced fluorescence applications. To date, the fluorescence properties of EA have not been thoroughly investigated. In this research, we comprehensively examined the fluorescence properties of EA in various solvents—including alkaline aqueous, alcoholic, nitrogenous, other organic solvents, and polyethylene glycols (PEGs)—using transient/steady-state fluorescence spectroscopy, ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and density functional theory calculations. Additionally, the relationship between structural changes of EA in these solvents and its fluorescence properties was deeply investigated. It was discovered that general solvation effects (solvent polarity effects), hydrogen bonding effects, and viscosity effects are the main ways that solvents alter the optical characteristics of EA. EA exhibits outstanding fluorescence characteristics in PEG400, creating a bright green fluorescence with the highest Stokes shift at 170 nm among the 32 organic solvents and alkaline aqueous solutions examined. This study is both foundational and essential, setting the stage for advancing the research on EA-based fluorescent materials in future endeavors.