Excited-State Electronic Properties in Zr-Based Metal–Organic Frameworks as a Function of a Topological Network

Journal Article · Tue Jul 24 04:00:00 EDT 2018 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.8b04980· OSTI ID:1467555

Yu, Jierui ^[1]; Park, JaeHong ^[2]; Van Wyk, Andrea ^[1]; Rumbles, Garry ^[3]; Deria, Pravas ^[1]

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1. Department of Chemistry and Biochemistry, Southern Illinois University, 1245 Lincoln Drive, Carbondale, Illinois 62901, United States
2. Department of Molecular Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
3. Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States; Department of Chemistry and Biochemistry and Renewable and Sustainable Energy Institute, University of Colorado at Boulder, Boulder, Colorado 80309, United States

Molecular assemblies in metal-organic frameworks (MOFs) are reminiscent of natural light-harvesting (LH) systems and considered as emerging materials for energy conversion. Such applications require understanding the correlation between their excited-state properties and underlying topological net. Two chemically identical but topologically different tetraphenylpyrene (1,3,6,8-tetrakis(p-benzoicacid)pyrene; H4TBAPy)-based ZrIV MOFs, NU-901 (scu) and NU-1000 (csq), are chosen to computationally and spectroscopically interrogate the impact of topological difference on their excited-state electronic structures. Time-dependent density functional theory-computed transition density matrices for selected model compounds reveal that the optically relevant S1, S2, and Sn states are delocalized over more than four TBAPy linkers with a maximum exciton size of ~1.7 nm (i.e., two neighboring TBAPy linkers). Computational data further suggests the evolution of polar excitons (hole and electron residing in two different linkers); their oscillator strengths vary with the extent of interchromophoric interaction depending on their topological network. Femtosecond transient absorption (fs-TA) spectroscopic data of NU-901 highlight instantaneous spectral evolution of an intense S1 -> Sn transition at 750 nm, which diminishes with the emergence of a broad (580-1100 nm) induced absorption originating from a fast excimer formation. Although these ultrafast spectroscopic data reveal the first direct spectral observation of fast excimer formation (t = 2 ps) in MOFs, the fs-TA features seen in NU-901 are clearly absent in NU-1000 and the free H4TBAPy linker. Furthermore, transient and steady-state fluorescence data collected as a function of solvent dielectrics reveal that the emissive states in both MOF samples are electronically nonpolar; however, low-lying polar excited states may get involved in the excited-state decay processes in polar solvents. The present work shows that the topological arrangement of the linkers critically controls the excited-state electronic structures.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22), Solar Photochemistry Program
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1467555
• Report Number(s): NREL/JA-5900-72258
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 33 Vol. 140; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
absorption spectroscopy
crystalline materials
electronic properties
electronic structure
energy conversion
excitons
organometallics
pyrene
tin
topology