Mechanochromism and aggregation-induced emission in a fluorene-fumaronitrile-based molecular system: The influence of supramolecular control on donor-acceptor interactions

Abstract

Effective control and reversible switching of solid-state luminescence in organic molecules are crucial for optoelectronic applications. This study presents a novel molecular system based on fluorene-diphenylfumaronitrile-fluorene (FDF), which exhibits mechanochromism and aggregation-induced emission (AIE). The design utilizes fluorene as the donor, leveraging its high photoluminescent quantum yield, thermal stability, and optimal solubility. The diphenylfumaronitrile moiety, used as the acceptor, is characterized by antiparallel dipoles, which align orthogonally with the chromophore's long axis, promoting effective self-assembly and supramolecular control of interchromophore interactions, in association with the cooperative hydrogen bonding of the amide end-functional groups. FDF demonstrates significant mechanochromic properties, in which mechanical stress induces a reversible shift from greenish-yellow to red emission due to alterations in molecular packing and hydrogen bonding. Additionally, FDF exhibits pronounced AIE behavior in DMF/water mixtures, transitioning from non-emissive in DMF to highly fluorescent upon nanoparticle formation. The investigation reveals that the control over donor-acceptor interactions is critical in modulating these luminescent properties, offering potential applications in stress sensing, bioimaging, and optoelectronic devices. These findings provide deeper insights into the molecular mechanisms underlying mechanochromism and AIE, highlighting the dual-functional nature of FDF and its applicability in advanced materials sciences.