AIE−Active BODIHYs Based on Benzothiazole–Hydrazone Chelates and Their Artificial Light Harvesting and Reversible Mechanochromic Behavior

Efficient artificial light-harvesting systems (ALH) involving energy transfer via FRET in an aqueous environment has been reported. Hydrazone ligands L1−L3 and -BF₂ complexes (BODIHYs; B1−B3) derived from these have been synthesized and meticulously characterized by various techniques like¹H, ¹³C, ¹¹B, ¹⁹F NMR, ESI–MS, UV–vis, fluorescence spectroscopy, and structures of B1 and B2 unequivocally determined by X−ray single crystal analyses. Applicability of the B1−B3 have been examined as a LHS platform and categorically shown that these in combination with rhodamine B (RhB) display efficient light harvesting activity under aqueous conditions via aggregation−induced emission (AIE). Calculated energy transfer efficiency and antenna effect for the BODIHYs are significantly high (B1 = 22%, 5.04; B2 = 18%, 4.07) at a donor/acceptor ratio of 23:1. Furthermore, hypsochromic shift shown by B1 and B2 after grinding completely reverses upon exposure to dichloromethane vapors. Powder X−ray diffraction (PXRD) analyses before and after grinding revealed that the external forces modify crystal packing by disrupting weak intra− and intermolecular interactions within the molecules.