BEGIN:VCALENDAR VERSION:2.0 PRODID:-//132.216.98.100//NONSGML kigkonsult.se iCalcreator 2.20.4// BEGIN:VEVENT UID:20260828T040410EDT-6049PkJnbV@132.216.98.100 DTSTAMP:20260828T080410Z DESCRIPTION:Zoom link: https://mcgill.zoom.us/j/86201000272?pwd=QUl4U3F6and 6M2VVai9OYzJLUWljUT09\n\nAbstract:\n\nThe ability to efficiently up-conver t broadband\, low-intensity light would be an enabling technology for volu metric 3D printing\, background-free biomedical imaging\, and sensitizing silicon focal plane arrays to the short-wave infrared. Our approach uses c olloidal quantum dots to absorb low-energy photons and sensitize the spin- triplet excitonic states of nearby conjugated molecules.1‒3 Once there\, p airs of these long-lived excitations can combine via triplet fusion to gen erate shorter-wavelength fluorescence.\n\nI will discuss how we are advanc ing triplet-fusion upconversion by using optical spectroscopy to deepen ou r understanding of nanocrystal synthesis\, and probe the movement of energ y and charge within and between organic and inorganic semiconductors. For instance\, we uncovered that a pre-nucleation cluster intermediate had his torically frustrated efforts to synthesize low-dispersity ensembles of sma ll (d<4 nm) PbS nanocrystals\, and showed that basic additives can restore one-step growth and yield markedly narrower heterogeneous linewidths in r eactions that run to completion.4 We are expanding from this insight to bu ild mechanistic understanding of the synthesis5 and surface6\,7 of metal-c halcogenide nanocrystals.\n\n\n I will focus on how we harnessed this refin ed synthesis and used ultra-small (d~1.9 nm\, hνpeak\,abs=2.0 eV) PbS quan tum dots to sensitize ‘red-to-blue’ triplet-fusion upconversion in solutio n.8 We showed that the long (>µs) photoluminescence lifetimes help to over come a mildly endothermic sensitization scheme that maximizes the anti-Sto kes shift (ΔE=1.04 eV) and minimizes non-specific excitation. This archite cture facilitated the photo-initiated polymerization of methylmethacrylate using only long-wavelength light (λ: 637 nm)\; a demonstration of nanocry stal-sensitized upconversion photochemistry.8 However\, this performance m ay have been unanticipated\, because steady-state spectroscopy of these (a nd other9\,10) ultra-small nanocrystals implies an unacceptable loss of in cident photon energy through excited-state relaxation and/or structural re organization. However\, from the quasi-equilibrium dynamics of triplet ene rgy transfer that we measure\, we infer that the chemical potential of pho toexcited\, ultra-small PbS quantum dots is surprisingly high—completing a n advantageous suite of properties for upconversion photochemistry\, while reinforcing questions regarding the emissive state.\n\n References:\n\n 1. Wu\, Congreve\, MWBW et al. (Bulovic\, Bawendi\, Baldo) Nature Photon. 10: 31 (2016)\n\n 2. Huang et al. (Bardeen\, Tang) Nano Lett. 15:5552 (2015)\n \n 3. Mongin\, et al. (Castellano) Science 351(6271):369-372 (2016\n\n 4. Gr een\, et al. (MWBW) Chem. Mater. 32(9):4803–4094 (2020)\n\n 5. Yarur Villan ueva\, et al. (MWBW) ACS Nano (2021) 15(11):18085-18099\n\n 6. Green\, et a l. (MWBW) ACS Appl. Nano. Mater. 4(6):5655–5664 (2021)\n\n 7. Green\, et al . (MWBW) Chem. Mater. 33(23): 9270-9284\n\n 8. Imperiale\, et al. (MWBW) Ch emical Science. 12(42):14111-14120 (2021)\n\n 9. Mooney\, et al. (Kambhampa ti)\, Phys. Rev. B 87(8):1‒5 (2013)\n\n 10. Hasham\, et al. (MWBW) Submitte d\n\n\nBio:\n\nMark W.B. Wilson (he/him) is an Assistant Professor in the Department of Chemistry at the University of Toronto\, where his team uses optical spectroscopy to explore\, understand\, and develop excitonic and nanostructured materials for optoelectronic applications. His first degree s were in Engineering Physics and History at Queen’s University (Kingston\ , Canada). He next received a PhD in Physics (2012) from the University of Cambridge for his studies of singlet exciton fission under the supervisio n of Prof. Sir Richard Friend. Then\, as a member of the Centre for Excito nics at the Massachusetts Institute of Technology\, he pursued postdoctora l studies (2012-2016) into triplet energy transfer between organic molecul es and semiconductor nanocrystals with Prof. Moungi Bawendi (Chemistry) an d Prof. Marc Baldo (Electrical Engineering)\, before starting his independ ent career.\n DTSTART:20220222T180000Z DTEND:20220222T193000Z SUMMARY:Chemical Society Seminar: Mark Wilson - Nanocrystal-sensitized trip let fusion upconversion photochemistry URL:https://www.mcgill.ca/chemistry/channels/event/chemical-society-seminar -mark-wilson-nanocrystal-sensitized-triplet-fusion-upconversion-333777 END:VEVENT END:VCALENDAR