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π‐expanded thioxanthones ‐ engineering the triplet level of thioxanthone sensitizers for lanthanide‐based luminescent probes with visible excitation.

Dansholm, Charlotte Nybro and Junker, Anne Kathrine R. and Nielsen, Lea G. and Kofod, Nicolaj and Pal, Robert and Sørensen, Thomas Just (2019) 'π‐expanded thioxanthones ‐ engineering the triplet level of thioxanthone sensitizers for lanthanide‐based luminescent probes with visible excitation.', ChemPlusChem, 84 (12). pp. 1778-1788.


Bright lanthanide based probes for optical bioimaging must rely on the antenna principle, where the lanthanide‐centred excited state is formed by a complex sensitization process. Efficient sensitization of lanthanide‐centred emission occurs via triplet states centred on the sensitizing chromophore. Here, the triplet state of thioxanthone chromophores is modulated by extending the π‐system. Three thioxanthone chromophores‐thioxanthone, benzo[c]thioxanthone, and naphtho[2,3‐c]thioxanthone were synthesised and characterised. The triplet state energies and lifetimes is found to change as expected, and two dyes are found to be suitable sensitizers for europium(iii) luminescence. Reactive derivatives of thioxanthone and benzo[c]thioxanthone were prepared and coupled to a 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (DO3A) lanthanide binding pocket. The photophysics and the performance in optical bioimaging of the resulting europium(iii) complexes were investigated. It is concluded that while the energetics favour efficient sensitization, the solution structure does not. While it was found that the complexes are too lipophilic to be efficient luminescent probes for optical bioimaging, we successfully demonstrated bioimaging using europium(iii) luminescence following 405 nm excitation.

Item Type:Article
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Publisher statement:This is the accepted version of the following article: Dansholm, Charlotte Nybro, Junker, Anne Kathrine R., Nielsen, Lea G., Kofod, Nicolaj, Pal, Robert & Sørensen, Thomas Just (2019). π‐Expanded Thioxanthones ‐ Engineering the Triplet Level of Thioxanthone Sensitizers for Lanthanide‐Based Luminescent Probes with Visible Excitation. ChemPlusChem 84(12): 1778-1788, which has been published in final form at This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for self-archiving.
Date accepted:No date available
Date deposited:15 August 2019
Date of first online publication:17 June 2019
Date first made open access:08 July 2020

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