Kefu Wang1,Nguyen Nhien2,Joseph Schwan3,Minglee Tang4,Lorenzo Mangolini3,Timothy Su3
University of Utah1,University of california, Riverside2,University of California, Riverside3,The University of Utah4
Kefu Wang1,Nguyen Nhien2,Joseph Schwan3,Minglee Tang4,Lorenzo Mangolini3,Timothy Su3
University of Utah1,University of california, Riverside2,University of California, Riverside3,The University of Utah4
Si quantum dots (QDs) holds great applicative potential in optoelectronic devices and bio-fluorescent agents due to their biocompatibility compared to conventional toxic Group II-VI and III-V metal-based quantum dots.<sup> [1]</sup> Recently, Si QDs have shown excellent photon upconversion property and a high photon upconversion efficiency of 7% was obtained for Si QD - 9-ethylanthracene (Si:9EA) system.<sup> [2]</sup> In addition, it has been reported that sigma Si-Si bonds exhibited comparable electron/ hole conductivity compared to C=C bonds. <sup>[3]</sup> This motivated us to investigate the binding group between Si QDs and molecular transmitters to facilitate triplet energy transfer so as to improve photon upconversion efficiency. In this work, we successfully attached silyl anthracene transmitter to Si QD surface with Si-Si bond employing di-tert-butyl peroxide as the radical initiator. Si-anthracene system with three different binding group (-CH<sub>2</sub>-CH<sub>2</sub>-; -Si(Me)<sub>2</sub>-Si(Me)<sub>2</sub>-; -Si(Me)<sub>2</sub>-Si(TMS)<sub>2</sub>-) between Si QDs and anthracene molecules were compared to investigate how they affect triplet energy transfer and photon upconversion. We found all three Si-anthracene systems showed high photon upconversion exceeding 5%, indicating the efficient triplet energy transfer between Si QD and anthracene transmitter for these binding bridges. Compared to Si-anthracene system with C-C binding bridge, Si-anthracene system with Si-Si binding bridge exhibited a red-shift and broader triplet excited states absorption. Overall, this work shows efficient triplet energy transfer and photon upconversion efficiency in silicon quantum dot-molecular hybrid system for both C-C or Si-Si binding bridges, which might shed light on controlling energy or charge transfer at nanoscale interfaces for optoelectronic applications.<br/><br/>[1] Cheng, X., Lowe, S. B., Peter J. Reece, P. J., Gooding, J. J. Colloidal silicon quantum dots: from preparation to the modification of self-assembled monolayers (SAMs) for bio-applications. <i>Chem. Soc. Rev.</i> 2014, 43, 2680–2700.<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.<br/>[3] Grozema, F. C., Siebbeles, L. D. A., Warman, J. M. Seki, S. Tagawa, S. Scherf, U. Hole conduction along molecular wires: sigma-bonded silicon versus π-bond-conjugated carbon. <i>Adv. Mater.</i> 2002, 14, 228–230.