An HLCT/HLCT–AIE-enabled donor–acceptor system through a locking and unlocking strategy and its versatile applications

Abstract

In this work, two donor–π–acceptor (D–π–A) fluorophores based on phenanthroimidazole cores were designed and synthesized to explore their photophysical behavior and multifunctional applications. Both systems were N1-substituted with diethylfluorene moieties to improve thermal stability, film-forming ability, and optical properties. The phenanthroimidazole–carbazole derivative (PI-FLCBZ) exhibited hybridized local and charge transfer (HLCT) emission, characterized by strong deep blue fluorescence and partially mixed LE/CT states. In contrast, the phenanthroimidazole–TPA analogue (PI-FLTPA) demonstrated combined HLCT and aggregation-induced emission (AIE) behavior, attributed to its twisted conformation and intramolecular charge transfer character. Both fluorophores showed high color purity and excellent photostability in the solid state. Their practical utility was validated through the successful fabrication of hybrid white light-emitting diodes (LEDs) with a high color rendering index of 87, selective fluorescence quenching-based picric acid detection, and reversible acidochromic response under acid–base addition.