Multistimuli-Responsive\nTriphenylphosphine Anils:\nDevelopment of a High-Contrast Wearable Ammonia Sensor

Stimuli-responsive organic materials with configurable\nluminescence\nare an important class of materials with potential use in sensing,\ndata security, and display devices. Emergent vapofluorochromic materials,\nwith the ability to sense and detect, are significant for real-time\napplications across the sectors. Specific market demand varies based\non technological advancements, regulatory changes, and industry trends,\nmaking the discovery of such advanced materials essential. Aiming\nthe design and engineering of solid-state emission, we report the\nsynthesis and characterization of three simple Schiff bases <b>1–3</b>, with nonplanar propeller triphenylphosphine functionality\non the one end and functional group variation on the other end. Contrarily,\nthe molecular solids <b>1</b> and <b>2</b> undergo emission\nquenching, while feeble emission in <b>3</b> (λ<sub>max</sub> 573 nm, ϕ 16%, and τ 3.118 ns) arises due to H-aggregate\nformation. Solid-state emission of <b>3</b> is further validated\nby aggregation-induced emission and thin-film studies. Existing as\nzwitterionic solids, due to intramolecular proton transfer of acidic\nproton, the solid forms respond to base exposures as observed during\nthin film studies, and further detailed vapochromic studies establish\nreversible emission switching in <b>2</b> and tuning in <b>3</b>. Working of a simple demonstrative wearable sensor for the\ndetection of ammonia fumes is reported. Electrochemical, crystallographic,\ncomputational, and mechanochromic studies have been carried out to\nunderstand the structure–function relationship.