Surface States Mediate Triplet Energy Transfer in Nanocrystal-Acene Composite Systems

Jon A. Bender, Emily K. Raulerson, Xin Li, Tamar Goldzak, Pan Xia, Troy Van Voorhis, Ming Lee Tang, Sean T. Roberts

Research output: Contribution to journalArticlepeer-review

89 Scopus citations

Abstract

Hybrid organic:inorganic materials composed of semiconductor nanocrystals functionalized with acene ligands have recently emerged as a promising platform for photon upconversion. Infrared light absorbed by a nanocrystal excites charge carriers that can pass to surface-bound acenes, forming triplet excitons capable of fusing to produce visible radiation. To fully realize this scheme, energy transfer between nanocrystals and acenes must occur with high efficiency, yet the mechanism of this process remains poorly understood. To improve our knowledge of the fundamental steps involved in nanoparticle:acene energy transfer, we used ultrafast transient absorption to investigate excited electronic dynamics of PbS nanocrystals chemically functionalized with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) ligands. We find photoexcitation of PbS does not lead to direct triplet energy transfer to surface-bound TIPS-pentacene molecules but rather to the formation of an intermediate state within 40 ps. This intermediate persists for ∼100 ns before evolving to produce TIPS-pentacene triplet excitons. Analysis of transient absorption lineshapes suggests this intermediate corresponds to charge carriers localized at the PbS nanocrystal surface. This hypothesis is supported by constrained DFT calculations that find a large number of spin-triplet states at PbS NC surfaces. Though some of these states can facilitate triplet transfer, others serve as traps that hinder it. Our results highlight that nanocrystal surfaces play an active role in mediating energy transfer to bound acene ligands and must be considered when optimizing composite NC-based materials for photon upconversion, photocatalysis, and other optoelectronic applications.

Original languageEnglish
Pages (from-to)7543-7553
Number of pages11
JournalJournal of the American Chemical Society
Volume140
Issue number24
StatePublished - 20 Jun 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2018 American Chemical Society.

Funding

Work performed at the University of Texas at Austin was supported by the Robert A. Welch Foundation (Grant F-1885) and the National Science Foundation (CHE-1610412). M.L.T. acknowledges support by the Alfred P. Sloan foundation and the National Science Foundation (CHE-1351663).

FundersFunder number
Robert A. Welch FoundationF-1885
National Science Foundation1610412, CHE-1610412
Alfred P. Sloan FoundationCHE-1351663
University of Texas at Austin

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