High-Boron-Content Porphyrin-Cored Aryl Ether Dendrimers: Controlled Synthesis, Characterization, and Photophysical Properties

The synthesis and characterization of a set of poly­(aryl ether) dendrimers with tetraphenylporphyrin as the core and 4, 8, 16, or 32 <i>closo</i>-carborane clusters are described. A regioselective hydrosilylation reaction on the allyl-terminated functions with carboranylsilanes in the presence of Karstedt’s catalyst leads to different generations of boron-enriched dendrimers. This versatile approach allows the incorporation of a large number of boron atoms in the dendrimers’ periphery. Translational diffusion coefficients (<i>D</i>) determined by DOSY NMR experiments permit estimation of the hydrodynamic radius (<i>R</i>_H) and molecular size for each dendrimer. Furthermore, a notable correlation between <i>D</i> and the molecular weight (MW) is found and can be used to predict their overall size and folding properties. The UV–vis and emission behavior are not largely affected by the functionalization, therefore implying that the presence of carboranes does not alter their photoluminescence properties

Fluorescent BODIPY-Anionic Boron Cluster Conjugates as Potential Agents for Cell Tracking

A series of novel fluorescent BODIPY-anionic boron cluster conjugates bearing [B₁₂H₁₂]^2– (<b>5</b>, <b>6</b>), [3,3′-Co­(1,2-C₂B₉H₁₁)₂]⁻ (<b>7</b>, <b>8</b>), and [3,3′-Fe­(1,2-C₂B₉H₁₁)₂]⁻ (<b>9</b>) anions have been readily synthesized from <i>meso</i>-(4-hydroxyphenyl)-4,4-difluoro-4-bora-3<i>a</i>,4<i>a</i>-diaza-<i>s</i>-indacene (BODIPY <b>4</b>), and their structure and photoluminescence properties have been assessed. Linking anionic boron clusters to the BODIPY (<b>4</b>) does not alter significantly the luminescent properties of the final fluorophores, showing all of them similar emission fluorescent quantum yields (3–6%). Moreover, the cytotoxicity and cellular uptake of compounds <b>5</b>–<b>9</b> have been analyzed <i>in vitro</i> at different concentrations of B (5, 50, and 100 μg B/mL) using HeLa cells. At the lowest concentration, none of the compounds shows cytotoxicity and they are successfully internalized by the cells, especially compounds <b>7</b> and <b>8</b>, which exhibit a strong cytoplasmic stain indicating an excellent internalization efficiency. To the best of our knowledge, these are the first BODIPY-anionic boron cluster conjugates developed as fluorescent dyes aiming at prospective biomedical applications. Furthermore, the cellular permeability of the starting BODIPY (<b>4</b>) was improved after the functionalization with boron clusters. The exceptional cellular uptake and intracellular boron release, together with the fluorescent and biocompatibility properties, make compounds <b>7</b> and <b>8</b> good candidates for <i>in vitro</i> cell tracking