| Autor: |
Bender JA; Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States., Raulerson EK; Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States., Li X; Department of Chemistry , University of California Riverside , Riverside , California 92521 , United States., Goldzak T; Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States., Xia P; Materials Science & Engineering Program , University of California Riverside , Riverside , California 92521 , United States., Van Voorhis T; Department of Chemistry , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States., Tang ML; Department of Chemistry , University of California Riverside , Riverside , California 92521 , United States.; Materials Science & Engineering Program , University of California Riverside , Riverside , California 92521 , United States., Roberts ST; Department of Chemistry , The University of Texas at Austin , Austin , Texas 78712 , United States. |
| Abstrakt: |
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. |
