[2+2] Cycloaddition Sensitized by CsPbX₃ Nanocrystals: Cooperative Effects of Driving Force and Exciton Confinement

Energy-transfer-induced reactions enable efficient photochemical synthesis by harnessing long-lived triplet states that enhance stereoselectivity and suppress side reactions under mild excitation. Semiconductor nanocrystals (NCs), with rapid intersystem crossing and mild photoredox potentials, serve as highly effective triplet sensitizers. In NC-sensitized systems, energy transfer efficiency is primarily governed by the driving force and exciton confinement. To probe their individual and combined effects, we conducted a systematic study using CsPbX₃ and 4-vinylbenzoic acid (4VBc) as a model system: (I) tuning both confinement and driving force through size-controlled CsPbBr₃ NCs, (II) varying driving force at a fixed size via Br-to-Cl substitution, and (III) modulating confinement with Br/I mixed NCs in the low-bandgap regime. Our results show that stronger exciton confinement steeply increases the energy transfer rate, which is amplified by a more favorable driving force. Tuning the driving force alone for non-confined NCs provides only incremental increases in the reaction rate. These findings highlight a cooperative design strategy-maximizing coupling via exciton confinement and fine-tuning the driving force (ΔG°)-thereby leveraging structure-energetics synergy to advance NC-sensitized energy-transfer chemistry.