Kefu Wang1,Robert Cline2,Joseph Schwan3,Jacob Strain4,MingLee Tang5,Lorenzo Mangolini3,Sean Roberts4,Joel Eaves2
University of Utah1,University of Colorado Boulder2,University of California, Riverside3,The University of Texas at Austin4,The University of Utah5
Kefu Wang1,Robert Cline2,Joseph Schwan3,Jacob Strain4,MingLee Tang5,Lorenzo Mangolini3,Sean Roberts4,Joel Eaves2
University of Utah1,University of Colorado Boulder2,University of California, Riverside3,The University of Texas at Austin4,The University of Utah5
Photon upconversion enables the conversion of low-energy photons into high-energy photons. It has potential applications in many fields, such as solar cells, bioimaging and photodynamic therapy.<sup>[1]</sup> Among photon upconverting systems, silicon quantum dot (Si QD) -molecular structures emerged recently due to non-toxic and bio-compatible properties. A high photon upconversion efficiency of 7% has been reported for the Si QD - 9-ethylanthracene (Si:9EA) system that is potentially biocompatibility.<sup>[2]</sup> This initial demonstration of triplet energy transfer between Si QDs and molecular transmitters motivated us to investigate various physical parameters to improve the photon upconversion efficiency. In this work, we explore factors like Si QD size, molecular transmitter loading, the length of surface-passivating ligand and investigate how they affect triplet energy transfer and photon upconversion. In addition, we designed a new molecular transmitter (9-vinylanthracene) with a double-bond bridge. This conjugated carbon bridge introduces strong electronic coupling between the Si QD and anthracene transmitter. We found a much shorter triplet transfer time constant (3ns) for the Si:9VA system compared with the Si:9EA system (15ns) that has less electronic coupling. A high photon upconversion efficiency exceeding 10% was achieved for Si:9VA system. Overall, this work demonstrates that the triplet energy transfer in silicon quantum dot-molecular hybrid system could be mediated and improved by promoting electronic coupling. This is a new strategy for controlling energy or charge transfer at nanoscale interfaces.<br/> <br/>[1] Yanai, N.; Kimizuka, N. New triplet sensitization routes for photon upconversion: thermally activated delayed fluorescence molecules, inorganic nanocrystals, and singlet-to-triplet absorption. <i>Acc. Chem. Res.</i> 2017, 50, 2487–2495.<br/>[2] Xia, P., Raulerson, E.K., Coleman, D., Gerke, C.S., Mangolini, L., Tang, M.L., Roberts, S.T. Achieving spin-triplet exciton transfer between silicon and molecular acceptors for photon upconversion. <i>Nature Chem.</i> 2020, 12, 137–144.