Structurally twisted pyridyl π-conjugates as AIEgens: Acidochromism and responses against diverse amines

This study reports the metal-free synthesis of various anthracene-linked pyridyl fluorescent probes (Py-1, Py-2, and Py-3) in decent yields and establishes them as AIEgens/solid-state emitters to provide an efficient and sustainable approach for multiphase amine detection. These probes function as dual-state emitters, showing fluorescence responses in solution and solid states. The protonated forms of these probes Py-1H, Py-2H, and Py-3H) were mostly non-emissive and thus, used for amine sensing via turn-on response. Among the three, the Py-2H solution only showed a selective binding affinity for 1,3-diaminopropane (1,3-DAP) and 1,4-diaminobutane (1,4-DAB or PUT) due to the geometric complementarity of its binding site, enabling favorable hydrogen bonding and electrostatic interactions. In solid, isomeric Py-1H and Py-2H showed broad amine vapor sensitivity with substantial fluorescence shifts from red to green with Δλ(nm) as 116 and 65 respectively. The longer conjugated molecule Py-3H with a change in the pyridyl nitrogen atom exhibited slightly better selectivity, producing pronounced responses to a few amine vapors. Notably, Py-3H detected amine vapors from chicken samples, highlighting its practical utility for food freshness monitoring and on-site applications. These findings emphasize the importance of structural design in enhancing probe selectivity for amine sensing, which helps monitor the freshness of chicken samples.