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

Jierui Yu, Jaehong Park, Andrea Van Wyk, Garry Rumbles, Pravas Deria

Research output: Contribution to journalArticle

31 Citations (Scopus)

Abstract

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 (τ = 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.

Original languageEnglish
Pages (from-to)10488-10496
Number of pages9
JournalJournal of the American Chemical Society
Volume140
Issue number33
DOIs
Publication statusPublished - Aug 22 2018

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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