Carbon Quantum Dots as a Luminescent Platform for Photoswitchable Bioactive Hybrids: Tuning Butyrylcholinesterase Inhibition Through Functional Group Engineering

Light-responsive materials enabling external modulation of bioactivity and spatial control are highly requested for photopharmacology—a booming research area of modern medicine. We present organo-inorganic hybrids of photoswitchable, bioactive symmetric diamine-phosphine oxides conjugated with luminescent carbon quantum dots (CQDs). The phosphonate compound was found to undergo Z-E isomerization upon 266 nm laser irradiation and exhibit butyrylcholinesterase (BChE) inhibition that increases twofold (15–30%) after photoconversion. Hybrids were fabricated via physical adsorption and chemisorption using different CQD surface groups, and characterized by UV-Vis, luminescence, and FTIR spectroscopy, confirming hybrid formation and retention of functional properties. In both binding modes, the molecules retained photoswitching capability despite steric constraints. All hybrids displayed orthogonal functions: luminescence (excitation at 350 nm) and photomodulation of BChE inhibition (at 266 nm). Remarkably, the binding mode dictated the bioactivity window—chemisorbed hybrids showed narrow 1.5-fold modulation, whereas physisorbed hybrids exhibited ultra-wide >10-fold modulation. This tunable responsiveness, achieved simply by altering the binding mode, demonstrates the exceptional potential of this hybrid design strategy for developing photoswitchable materials with tailored photopharmacological performance.