Two novel styrene-containing meta-carborane derivatives substituted at the second carbon cluster atom (C_c) with either a methyl (Me) or a phenyl (Ph) group are introduced herein along with a new set of stilbene-containing ortho- (o-) and meta- (m-) carborane dyads. The latter set of compounds have been prepared from styrene-containing carborane derivatives via a Heck coupling reaction. High regioselectivity has been achieved for these compounds by using a combination of palladium complexes [Pd₂(dba)₃]/[Pd(t-Bu₃P)₂] as a catalytic system, yielding exclusively E isomers. All compounds have been fully characterised and the crystal structures of seven of them were analysed by X-ray diffraction. The absorption spectra of these compounds are similar to those of their respective fluorophore groups (styrene or stilbene), showing a very small influence of the substituent (Me or Ph) linked to the second C_c atom or the cluster isomer (o- or m-). On the other hand, fluorescence spectroscopy revealed high emission intensities for Me-o-carborane derivatives, whereas their Ph-o-carborane analogues evidenced an almost total lack of fluorescence, confirming the significant role of the substituent bound to the adjacent C_c in o-carboranes. In contrast, all the m-carborane derivatives display similar photoluminescence (PL) behavior regardless of the substituent attached to the second C_c, demonstrating its small influence on emission properties. Additionally, m-carborane derivatives are significantly more fluorescent than their o-counterparts, reaching quantum yield values as high as 30.2%. Regarding solid state emission, only stilbene-containing Ph-o-carborane derivatives, which showed very low fluorescence in solution, exhibited notable PL emission in films attributed to aggregation-induced emission. DFT calculations were performed to successfully complement the photoluminescence studies, supporting the experimentally observed photophysical behavior of the styrene and stilbene-containing carborane derivatives. In conclusion, in this work it is proved that it is possible to tailor the PL properties of carborane–stilbene dyads by changing the C_c substituent and the carborane isomer.

A new set of four different fluorescent boron-rich hybrids based on an octasilsesquioxane core (T₈) are presented herein. The syntheses have been carried out starting from styrene-containing ortho- and meta-carboranes and an adequately substituted octasilsesquixane derivative (p-BrStyrenylOS) via Heck coupling reaction. The carborane clusters are attached to the T₈ core through para-substituted stilbene spacers, which act as the main electronic donor of the molecule and as a result are responsible for the photoluminescence properties of the hybrids. These have been assessed in DCM solution, concluding that the presence of the carborane clusters plays a key role in the increase of the fluorescence emission displayed by the hybrids. A comparative study of different substituents (H, Me or Ph) linked to the adjacent carbon atom of the ortho-cluster revealed that the unsubstituted o-carborane derivative (POSS-H) has a much higher quantum yield in solution (Φ_F = 59%) than its two counterparts. Besides, a comparison between two hybrids containing phenyl-substituted ortho- (POSS-Ph) and meta-carborane (POSS-mPh), demonstrated a significantly higher emission enhancement by the latter, backing the results we have previously reported for similar systems. In the solid state, the emission is largely quenched in all cases (Φ_F = 4 to 7%) as well as bathochromically shifted due to considerable intermolecular interactions. Finally, the thermal resistances of these hybrids were tested by TGA under an inert atmosphere, unveiling weight losses as low as 15.8% and proving that the attachment of the carborane moieties to the T₈ core outstandingly improves the thermal stability of the final POSS.