Keto–enol tautomerism modulates the photoluminescent sensing of ketones by terpyridine derivatives

Ketones are versatile organic compounds involved in various natural and industrial processes. Therefore, developing practical methods for their detection is essential for applications in industrial safety, food quality control, and environmental monitoring. This work reports a novel and fundamental method for the photoluminescent sensing of ketones with terpyridine derivatives. Firstly, 4′-(4- N -aminoethylenephenyl)-2,2′:6′,2″-terpyridine (TpyPhEDA) was synthesized, and a comprehensive study of its structural and photoluminescent properties was conducted, emphasizing its application as a sensor. The luminescent response was evaluated in various organic solvents and ketones of different chemical nature, revealing a highly selective reaction with acetylacetone (AcAc). The analytical response was characterized by rapid reaction kinetics, enhanced emission intensity, band broadening, emission lifetime shortening, and a shift in the emission wavelengths as AcAc concentration increased. The underlying sensing mechanism involves a Schiff base formation between TpyPhEDA and AcAc, governed by a keto-enamine tautomeric form. The resulting Schiff base is stabilized in its keto-enamine form, enabling molecular polarization, as demonstrated by molecular electrostatic potential surface (MEPS) diagrams. This polarization triggers intramolecular charge transfer (ICT) processes, leading to turn-on luminescence and wavelength-shifting dual-mode detection of AcAc. Those results demonstrate that keto-enol tautomerism plays a crucial role in modulating the sensor's photoluminescent response, explaining variations in reaction kinetics and providing the basis for selective sensing of ketones. • A novel photoluminescent sensor was developed for the selective detection of acetylacetone. • Keto-enol tautomerism was identified as a key factor modulating the sensor's response. • The sensor enables dual-mode detection via turn-on emission and wavelength shifting. • Spectroscopic techniques, NMR, and DFT calculations elucidate the sensing mechanism. • A detection limit of 45.6 μg/mL was achieved, highlighting its potential for safety monitoring. • The reported mechanism provides the basis for the selective detection of other ketones.