The development of photoluminescent boron cluster-based organic p-conjugated systems has attracted huge interest as active materials in (opto)electronic devices, solar cells, biological sensors and fluorescence bioimaging. Anthracene derivatives are molecules with excellent luminescence properties, whereas carborane clusters (C2B10H12) are fascinating chemical species with unique structural and electronic properties, as well as low toxicity in biological systmes. In carborane-containing fluorophores, the fluorescence efficiency can be tailored by the cluster isomer and the substituent at the cluster atom (Cc).
We have synthesized three m-carborane-anthracenyl dyads, containing 0, 1 or 2 iodo groups at Bc atoms. They exhibit exceptional blue emission properties with high quantum yields (around 100 %) in solution, confirming that linking m-carborane to a fluorophore produces a significant enhancement of the emission efficiency in the target compounds. Notably, these dyads exhibit moderate fluorescence in aggregate state (between 19–23 %), pointing out that they are extremely good emitters in solution, while maintaining the emission properties in solid state. None of them shows cytotoxicity for HeLa cells. Confocal microscopy studies confirm that all compounds are internalised by cells via endocytosis, being the di-iodinated compound the best-internalised by cells. This suggest that the presence of iodo lead to a higher lipophilicity facilitating an efficient transport across the plasma membrane and a better cellular uptake. This di-iodinated dyad is an excellent fluorescent dye for bioimaging studies in fixed cells, and due to the high boron content and exceptional cellular uptake, a potential anticancer agent for Boron Neutron Cancer Therapy (BNCT).
Efficient blue light emitting materials based on m-carborane-anthracene dyads. Structure, photophysics and bioimaging studies
Mahdi Chaari, Zsolt Kelemen, Duane Choquesillo-Lazarte, Nerea Gaztelumendi, Francesc Teixidor, Clara Viñas, Carme Nogués,* Rosario Núñez*. Biomaterials Science, 7, 5324, 2019
Figure: Fluorescence intensity emitted by cells incubated for 4 h with 10 µM of diiodinated antracene-m-carborane. Image obtained with the confocal laser scanning microscope.