Protonation-driven structural deformation in a conformationally twisted pyridyl-linked AIEgen: a platform to detect polyamines and nicotine

Abstract

Stimuli-responsive fluorescent probes have emerged as key tools in chemical sensing and environmental monitoring due to their high sensitivity and real-time detection capabilities. However, conventional probes often rely on limited mechanisms, restricting their adaptability and scope. Addressing this challenge, this study introduces a bis-pyridyl anthracene-based fluorophore, TB4Py, as an AIEgen that exhibits reversible acidofluorochromic behavior in both solution and solid states through a rare structural deformation event. Upon protonation, TB4Py undergoes a significant and reversible distortion from planarity within its anthracene core, distinguishing it from conventional fluorescent probes. Such a structural deformation with an anthracene ring bend angle of ∼40.5° drives a redshift in emission and pronounced fluorescence (FL) quenching. This weakly emissive platform offers a visually distinct and reliable turn-on response for detecting aliphatic polyamines/biogenic amines (PAs/BAs) and nicotine (NIC) through a pronounced blueshift in color change (∼73 nm), enabling detection in both solution and solid states. The solution state detection was relatively more selective towards putrescine. While multiple mono/polyamine vapors responded to the solid state, the emission was relatively more intense for PAs. Incorporating distant, dual pyridine units significantly amplifies the sensitivity and selectivity of TB4Py. This advancement is exemplified through practical applications, such as detecting fish spoilage, highlighting its utility in food safety and quality monitoring. This study emphasizes the largely untapped potential of structural deformation in stimuli-responsive fluorescent probes, offering novel approaches to enhance chemical sensing technologies.