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Ultrafast IR spectroscopy of photo-induced electron transfer in self-assembled donor–acceptor coordination cages

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Abstract

Photo-induced processes in self-assembled coordination cages were studied by femtosecond infrared pump–probe spectroscopy. Densely packed, interpenetrated double cages were constructed from eight bis-monodentate redoxactive ligands bound to four Pd(II) nodes. Two types of ligands consisting of electron rich phenothiazine (PTZ) or electron deficient anthraquinone (ANQ) chromophores were used to assemble either homo-octameric or mixed-ligand cages. Upon photoexcitation the homo-octameric acceptor cage undergoes intersystem crossing to a long-lived triplet state, similar to the free acceptor ligand. Excitation of the free donor ligand leads to a fluorescent state with intramolecular charge transfer character. This fluorescence is completely quenched in the homo-octameric donor double cage due to a ligand-to-metal charge transfer followed by back electron transfer on a ps timescale. Only for the mixed-ligand cage irradiation produces a charge separated state with an oxidized PTZ radical cation and a reduced ANQ radical anion as proven by their vibrational fingerprints in the transient IR spectra. In dichloromethane the lifetime of this charge separated state extends from tens of ps to >1.5 ns which is attributed to the broad distribution of mixed-ligand cages with different stoichiometry and/or stereo configurations.

Graphical abstract: Ultrafast IR spectroscopy of photo-induced electron transfer in self-assembled donor–acceptor coordination cages

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Publication details

The article was received on 07 Apr 2017, accepted on 11 May 2017 and first published on 12 May 2017


Article type: Paper
DOI: 10.1039/C7CP02253K
Citation: Phys. Chem. Chem. Phys., 2017, Advance Article
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    Ultrafast IR spectroscopy of photo-induced electron transfer in self-assembled donor–acceptor coordination cages

    J. Ahrens, M. Frank, G. H. Clever and D. Schwarzer, Phys. Chem. Chem. Phys., 2017, Advance Article , DOI: 10.1039/C7CP02253K

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