Green Synthesis of Novel Diorganotin Heterocycles From PET Waste Under Ultrasound Irradiation for Reversible Turn‐off Fluorescence Sensing of Cu 2+ Ions in Water

Herein, we report two novel diorganotin compounds derived from poly (ethylene terephthalate) waste that exhibit reversible turn‐off fluorescence sensing properties. The compounds were synthesized in good yields through an ultrasound‐assisted one‐pot reaction completed within 30 min. Both organotin compounds were comprehensively characterized using NMR ( 1 H, 13 C, and 119 Sn) spectroscopy, vibrational analysis, molecular absorption, fluorescence emission, and high‐resolution mass spectrometry. The 119 Sn resonance, along with the characteristic tin satellites 3 J ( 1 H‐ 119 Sn) of the new organotin derivatives, indicates the high molecular symmetry and the formation of pentacoordinate diorganotin species, as supported by high‐resolution mass spectrometry. The diorganotin derivatives displayed intense fluorescence emission in freshly prepared solutions at room temperature, achieving quantum yields of approximately 37% and 44%. Notably, the n ‐butyl‐substituted organotin heterocycle exhibited enhanced photostability relative to the dimethyl analogue. Theoretical calculations provided insight into the role of steric effects in governing the chemical and optical stability of these diorganotin derivatives. Compound 3a demonstrated highly sensitive spectrofluorometric recognition of Cu 2+ ions in water, leading to complete quenching of the fluorescence emission band at 465 nm. The corresponding LOD and LOQ were 7.0 and 22.0 μM, respectively. The sensing mechanism was elucidated through a combination of vibrational spectroscopy, surface analysis, and theoretical calculations.