Colloidal CuInS2 quantum dots as versatile platforms for light-driven systems

This thesis explores the synthesis, surface chemistry, and photophysical behavior of Copper Indium Sulfide Quantum Dots (CIS-QDs), with the aim of evaluating their potential in light-driven applications. CIS-QDs represent an environmentally compatible alternative to cadmium- or lead-based nanocrystals, offering highly tunable electronic and optical characteristics derived from quantum confinement. Comprehensive studies on CIS-QDs synthesized via the heating-up method revealed a dynamic and labile surface ligand environment dominated by metal–thiolate adducts in rapid equilibrium with free ligands in solution. Photoluminescence quantum yield and lifetime were significantly enhanced (up to 3.5-fold) through passivation with Zn²⁺ salts, particularly in the presence of halide anions. In photochemical applications, CIS-QDs enabled complete (E)→(Z) photoisomerization of azobenzene derivatives under visible light, a rare achievement attributed to the interaction of the metastable (Z) isomer with the QD surface. Synthesis of Cu-In-Zn-S (CIZS) QDs directly in water yielded highly emissive (∼20% PLQY) and colloidally stable materials when thiolated ligands were employed. Mechanistic insights indicated the early formation of copper clusters, possibly acting as luminescent precursors. Furthermore, Mn(II)-doped CIZS QDs were developed as dual-emissive, luminescent thermometers, exhibiting a linear and reversible lifetime-based thermal response in the physiological range (25–45 °C), stable against pH changes, oxygen, and ionic interferences (e.g., HCO3- or Cl-). Finally, CIS-QDs were applied as sensitizers in photoelectrochemical cells (QDSPECs). Substantial photocurrents were achieved using sacrificial donors; however, charge recombination severely limited performance with reversible redox mediators such as TEMPO. Surface association of substrates was identified as a prerequisite for efficient oxidation, and surface engineering strategies (silanization, annealing, ligand exchange) could not overcome recombination losses. Overall, this work establishes CIS-QDs as a versatile and tunable platform for optoelectronic and photochemical applications, while highlighting the pivotal role of surface chemistry in dictating both their fundamental photophysics and device-level performance.