Stochastic Model Analysis of Luminescence Switching in Hybrid Systems of CdSe/CdS Quantum Dots − Spiropyran Molecular Photoswitches

Hybrid systems (HSs) of quantum dots (QDs) and molecular photoswitches exhibit luminescence switching of QDs based on energy transfer, and have garnered attention for their potential applications in sensors and optical memories. In HSs, the chemical composition, such as the number of attached ligands, is inherently distributed, posing challenges for extracting the energy transfer process from the QD to a single acceptor molecule. The stochastic model, assuming a Poisson distribution for the number of acceptors, proves to be an effective approach for extracting the process. In this study, we synthesized HSs comprising CdSe/CdS QDs and spiropyran molecular photoswitches. The luminescence switching of QDs by energy transfer from QDs to merocyanine formed by the UV irradiation of spiropyran was analyzed using a stochastic model. The estimated donor-acceptor distances obtained from the model showed significant concordance with other experimental findings, highlighting the utility of the model. In addition, trap states were reversibly formed on the surface of QDs by a photochromic reaction. One of the advantages of this model is its ability to analyze elementary processes and provide insights into microscopic structural details, such as the mean number of acceptors and trap states.