Rhodamine-benzothiazole dyad: AIE-active probe with solid-state optoelectronic properties, selective sensing of 1,3-diaminopropane and hydrazine detection guided by DFT and machine learning.

The widespread release of organic amines from industrial waste and food spoilage poses a significant environmental and food safety concern. Herein, to address this challenge, a new rhodamine-benzothiazole (RHB) dyad was synthesized for selective and sensitive detection of 1,3-diaminopropane (DAP) and hydrazine. RHB exhibited remarkable optoelectronic performance featuring an indirect band gap of 1.72 eV and a direct band gap of 2.25 eV, as well as solvent-dependent optical band gaps ranging from 2 to 4 eV. In solvent-water binary mixtures, RHB exhibited Aggregation Induced Emission (AIE) behavior, which was further validated by Dynamic Light Scattering (DLS) measurement, confirming formation of the nano-aggregates of different sizes. The probe's low detection limits allowed it to detect DAP preferentially in DMSO (0.007 ppm), DMF (0.006 ppm), MeOH (0.026 ppm), EtOH (0.068 ppm), and MeCN (0.202 ppm). The cyclized RHB + DAP adduct exhibits a "turn-on" response in comparison to other diamines due to suppression of Photoinduced Electron Transfer (PET) and Intramolecular Charge Transfer (ICT) processes. The RHB + DAP adduct system effectively identified hazardous hydrazine by restoring PET from the -NH2 group, 94% quenching efficiency. An Artificial Neural Network (ANN) model achieved the highest accuracy in predicting the quenching intensity. The Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT) calculations reveal that the DAP adduct formation increases the HOMO-LUMO energy gap, confirming the suppression of non-radiative pathways. Lastly, real-time, on-site DAP detection was demonstrated by a smartphone-based platform, validating the probe's usefulness in food safety monitoring.