Tuning the Molecular Rotor Dynamics of Pyrrolo[3,4‐b]Pyridin‐5‐Ones: Steric and Electronic Control of Environmental Sensing

Abstract

A series of seven pyrrolo[3,4‐b]pyridin‐5‐ones were synthesized via a one‐pot process involving an Ugi‐Zhu reaction followed by a cascade sequence (N‐acylation/aza Diels–Alder cycloaddition/decarboxylation/dehydration) incorporating different substituents no aromatic and aromatic such as furan, tetrahydrofuran, and pyridine. The pyrrolo[3,4‐b]pyridin‐5‐ones were optically characterized through their photoluminescence spectra, quantum yields, and fluorescence lifetimes. By combining spectroscopic measurements with DFT/TDDFT calculations, photophysical behavior was elucidated, specifically addressing solvent effects on transition magnitudes and the electronic nature of absorption and emission states. Structure–property relationship analyses revealed that steric and electronic substituent effects govern the interplay between charge‐transfer (CT) and locally excited (LE) states. Finally, the most promising candidates were successfully evaluated as fluorogenic microviscosity and polarity sensors, demonstrating their potential for advanced sensing applications.