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UID:20250819T080443EDT-4148EWSIGj@132.216.98.100
DTSTAMP:20250819T120443Z
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:/chemistry/channels/event/chemical-society-seminar
 -mark-wilson-nanocrystal-sensitized-triplet-fusion-upconversion-333777
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