Mechanical force-induced luminescence enhancement and Chromism of donor-acceptor Tetraphenylethylene-naphthalene Chalcone isomers.

Two new donor-acceptor (D-A) tetraphenylethylene-naphthalene chalcone isomers, (E)-1-(naphthalen-2-yl)-3-(4-(1,2,2-triphenylvinyl)phenyl) prop-2-en-1-one (1N3T) and (E)-3-(naphthalen-2-yl)-1-(4-(1,2,2-triphenylvinyl)phenyl)prop-2-en-1-one (3N1T), were designed and synthesized to investigate their structure-dependent photophysical properties, aggregation-induced emission enhancement (AIEE), and mechanoresponsive behaviors. These two isomers feature tetraphenylethylene (TPE), a well-known aggregation-induced emission luminogen (AIEgen), coupled with a naphthalene chalcone moiety, where the positional isomerism arises from the distinct spatial arrangement of donor (naphthalene) and acceptor (chalcone) groups. Systematic characterization revealed intramolecular charge transfer (ICT) characteristics in solution, as evidenced by solvent-dependent fluorescence emission spectra. Density functional theory (DFT) calculations corroborated the ICT mechanism, demonstrating HOMO-LUMO localization patterns that align with the D-A configurations. Notably, both isomers exhibited exceptional mechanochromic sensitivity. Grinding-induced amorphization led to a remarkable enhancement in solid-state fluorescence quantum yields (QYs), increasing by 27-fold (1N3T) and 79-fold (3N1T). Powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FESEM) confirmed a reversible crystalline-to-amorphous phase transition, with the disordered amorphous state suppressing non-radiative decay pathways (e.g., π-π interactions) and unlocking enhanced emission. The superior mechanoresponsiveness of 3N1T was attributed to its optimized D-A geometry, which facilitates efficient structural disruption under mechanical stress. This work elucidates critical structure-property relationships governing AIEE and mechanochromism, emphasizing the role of positional isomerism in modulating solid-state packing and stimuli-responsive luminescence. The findings advance the rational design of adaptive optoelectronic materials for applications in pressure-sensitive sensors, smart coatings, and rewritable optical storage systems.