Abstract
Large singlet exciton diffusion lengths are a hallmark of high performance in organic-based devices such as photovoltaics, chemical sensors, and photodetectors. In this study, exciton dynamics of a two-dimensional covalent organic framework, 2D COF-5, is investigated using ultrafast spectroscopic techniques. After photoexcitation, the COF-5 exciton decays via three pathways: (1) excimer formation (4 ± 2 ps), (2) excimer relaxation (160 ± 40 ps), and (3) excimer decay (>3 ns). Excitation fluence-dependent transient absorption studies suggest that COF-5 has a relatively large diffusion coefficient (0.08 cm2/s). Furthermore, exciton-exciton annihilation processes are characterized as a function of COF-5 crystallite domain size in four different samples, which reveal domain-size-dependent exciton diffusion kinetics. These results reveal that exciton diffusion in COF-5 is constrained by its crystalline domain size. These insights indicate the outstanding promise of delocalized excitonic processes available in 2D COFs, which motivate their continued design and implementation into optoelectronic devices.
Original language | English (US) |
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Pages (from-to) | 14957-14965 |
Number of pages | 9 |
Journal | Journal of the American Chemical Society |
Volume | 142 |
Issue number | 35 |
DOIs | |
State | Published - Sep 2 2020 |
Funding
We acknowledge the Army Research Office for a Multidisciplinary University Research Initiatives (MURI) award under Grant No. W911NF-15-1-0447. Parts of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and the Dow Chemical Company. This research used resources of the Advanced Photon Source and Center for Nanoscale Materials, both U.S. Department of Energy (DOE) Office of Science User Facilities operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE- AC0206CH11357. A.M.E. is supported by the National Science Foundation Graduate Research Fellowship under Grant No. (DGE-1324585), the Ryan Fellowship, and the Northwestern University International Institute for Nanotechnology. This work has also made use of the IMSERC, EPIC, and Keck II facility of NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the MRSEC program (NSF DMR-1720139) at the Materials Research Center, the Keck Foundation, the State of Illinois, and International Institute for Nanotechnology (IIN). N.C.F and L.X.C. are partially supported by Basic Energy Science, CBG Division, U.S. Department of Energy through Argonne National Laboratory under Contract No. DE-AC02-06CH11357. I.C. is partially supported by the Army Research Office under Grant No. W911NF-18-1-0359.
ASJC Scopus subject areas
- Catalysis
- General Chemistry
- Biochemistry
- Colloid and Surface Chemistry