Single-Molecule Level Study and Control of Collective Photoresponse in Molecular Complexes and Related Systems

We studied nanoscale photosynergetic response of molecular complexes and related inorganic and hybrid materials using single-molecule detection and spectroscopy. As examples, we report simultaneous electroluminescence and photoluminescence study of single CsPbBr3 perovskite nanocrystals which revealed the origin of blinking and of reduced quantum efficiency of electroluminescence devices. In addition, we observed linear and quadratic Stark shift on individual nanocrystals in different matrices. For novel I-III-IV semiconductor quantum dots, defect emission was found to originate from multiple sites in one particle, and the phenomenon of blinking was suppressed by multi-color excitation. In hybrid metal nanoparticle-organic dye systems, selective excitation of a localized plasmon in single gold nanorods by the polarization of light was found to enhance Forster energy transfer efficiency by two orders of magnitude. Localized plasmon was also found to cause previously unknown phenomenon of enhancement of triplet Dexter transfer in photon upconversion materials. Nanoscale study of triplet exciton diffusion in molecular solids by visualization of upconversion emission helped to uncover heterogeneity and the role of molecular orientation in the diffusion process.