Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 142, Issue 35, Pages 14957-14965Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.0c05404
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Funding
- Army Research Office [W911NF-15-1-0447, W911NF-18-1-0359]
- Northwestern University
- Dow Chemical Company
- DOE Office of Science [DE-AC0206CH11357]
- National Science Foundation Graduate Research Fellowship [DGE-1324585]
- Ryan Fellowship
- Northwestern University International Institute for Nanotechnology
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource [NSF ECCS-1542205]
- MRSEC program at the Materials Research Center [NSF DMR-1720139]
- Keck Foundation
- State of Illinois
- International Institute for Nanotechnology (IIN)
- Basic Energy Science, CBG Division, U.S. Department of Energy through Argonne National Laboratory [DE-AC02-06CH11357]
- E.I. DuPont de Nemours Co.
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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-S, is investigated using ultrafast spectroscopic techniques. After photoexcitation, the COF-S 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 cm(2)/s). Furthermore, exciton-exciton annihilation processes are characterized as a function of COF-S crystallite domain size in four different samples, which reveal domain-size-dependent exciton diffusion kinetics. These results reveal that exciton diffusion in COF-S 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.
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