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Issue 26, 2018
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Exploiting the benefit of S0 → T1 excitation in triplet–triplet annihilation upconversion to attain large anti-stokes shifts: tuning the triplet state lifetime of a tris(2,2′-bipyridine) osmium(II) complex

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Abstract

Os(II) complexes are particularly interesting for triplet–triplet annihilation (TTA) upconversion, due to the strong direct S0 → T1 photoexcitation, as in this way, energy loss is minimized and large anti-Stokes shift can be achieved for TTA upconversion. However, Os(bpy)3 has an intrinsic short T1 state lifetime (56 ns), which is detrimental for the intermolecular triplet–triplet energy transfer (TTET), one of the crucial steps in TTA upconversion. In order to prolong the triplet state lifetime, we prepared an Os(II) tris(bpy) complex with a Bodipy moiety attached, so that an extended T1 state lifetime is achieved by excited state electronic configuration mixing or triplet state equilibrium between the coordination center-localized state (3MLCT state) and Bodipy ligand-localized state (3IL state). With steady-state and time-resolved transient absorption/emission spectroscopy, we proved that the 3MLCT is slightly above the 3IL state (by 0.05 eV), and the triplet state lifetime was prolonged by 31-fold (from 56 ns to 1.73 μs). The TTA upconversion quantum yield was increased by 4-fold as compared to that of the unsubstituted Os(II) complex.

Graphical abstract: Exploiting the benefit of S0 → T1 excitation in triplet–triplet annihilation upconversion to attain large anti-stokes shifts: tuning the triplet state lifetime of a tris(2,2′-bipyridine) osmium(ii) complex

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Publication details

The article was received on 20 Dec 2017, accepted on 19 Feb 2018 and first published on 19 Feb 2018


Article type: Paper
DOI: 10.1039/C7DT04803C
Citation: Dalton Trans., 2018,47, 8619-8628
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    Exploiting the benefit of S0 → T1 excitation in triplet–triplet annihilation upconversion to attain large anti-stokes shifts: tuning the triplet state lifetime of a tris(2,2′-bipyridine) osmium(II) complex

    D. Liu, Y. Zhao, Z. Wang, K. Xu and J. Zhao, Dalton Trans., 2018, 47, 8619
    DOI: 10.1039/C7DT04803C

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