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Issue 10, 2014
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Energy and charge transfer by donor–acceptor pairs confined in a metal–organic framework: a spectroscopic and computational investigation

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Abstract

Molecular organization of donor–acceptor pairs within a metal–organic framework (MOF) offers a new approach to improving energy and charge transfer at donor–acceptor interfaces. Here, the photo-physical effects of infiltrating MOF-177 (ZnO4(BTB)2; BTB = 1,3,5-benzenetribenzoate) with α,ω-dihexylsexithiophene (DH6T) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), representing well-established polymeric and molecular materials used in organic photovoltaics, were probed using UV-visible absorption and luminescence spectroscopies combined with first-principles electronic structure calculations. The energetics of guest molecule infiltration were determined by constructing potential energy curves from self-consistent charge density-functional tight-binding (SCC-DFTB) calculations. These reveal that infiltration is energetically favored and that DH6T and PCBM are strongly bound to MOF-177 by 55 kcal mol−1 and 57 kcal mol−1, respectively. Solution-phase infiltration with PCBM achieved a 22 wt% loading, comparable to those in bulk heterojunction solar cells, but without evidence of phase segregation. DH6T loadings were very light (maximum of ∼1 molecule per 11 unit cells), but this was sufficient to produce significant quenching of the MOF-177 photoluminescence (PL). The coincident appearance of DH6T PL demonstrates that efficient Förster resonance energy transfer (FRET) from the MOF-177 linkers to DH6T occurs. These results show that the MOF is a multifunctional host that not only confines and stabilizes guest molecules, but also plays an active role, serving as a photon antenna that harvests light not efficiently absorbed by a donor molecule (DH6T in this case) and transferring it to guest acceptor molecules. Finally, time-dependent density functional theory (TDDFT) predicts the existence of linker-to-PCBM charge transfer states, suggesting that photoconductivity might be achievable in an appropriately designed guest@MOF system.

Graphical abstract: Energy and charge transfer by donor–acceptor pairs confined in a metal–organic framework: a spectroscopic and computational investigation

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Publication details

The article was received on 24 Oct 2013, accepted on 14 Jan 2014 and first published on 24 Jan 2014


Article type: Paper
DOI: 10.1039/C3TA14328G
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J. Mater. Chem. A, 2014,2, 3389-3398

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    Energy and charge transfer by donor–acceptor pairs confined in a metal–organic framework: a spectroscopic and computational investigation

    K. Leong, M. E. Foster, B. M. Wong, E. D. Spoerke, D. Van Gough, J. C. Deaton and M. D. Allendorf, J. Mater. Chem. A, 2014, 2, 3389
    DOI: 10.1039/C3TA14328G

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