研究方向

Metal-induced B-H activation and functionalization of dicarba-closo-dodecaboranes

Dicarba-closo-dodecaboranes have been used for decades as versatile building blocks for construction of functional materials and pharmaceuticals owing to their useful properties such as thermal stability, unique structures and electronic effects, enriched boron content and low bio-toxicity. However, substitution at boron atoms, in particular, selective boron-functionalization of carborane clusters is still a synthetic challenge because of the chemically close B−H bonds and limited functional groups. This situation seriously restricts further development of applications of carborane derivatives.

Figure 1

Recently we utilized metal-induction to have achieved selective B-H activation at ambient temperature through the introduction of substrates such as alkynes, azido species and azides. And unusual B-functionalized groups such as cyclopentadienyl (Cp), norbornyl and norbornadienyl (Figure 1) have been obtained that are unavailable by conventional methods. The mechanistic studies have been performed by combination of DFT calculations and experimental results.


Carborane tuning photophysical properties

Two-photon absorption (TPA) has attracted considerable attention for the promising applications in two-photon dynamic therapy, optical power limiting materials and bioimaging. We have introduced carboranes into dendritic or star-shaped π-conjugated organic fluorophores, as a result, fluorescence quantum yields were significantly improved and the largest two-photon absorption among the known carborane-based derivatives has been obtained thus the compound was successfully applied in two-photon fluorescence 2D & 3D bioimaging (Figure 2).

Figure 2

On the other hand, owing to the unique 3D pseudo-aromatic geometric structures and push-pull electronic properties, carboranes can considerably change luminescent efficiency and emission wavelengths of traditional iridium complexes. In addition, the effect of o-carborane derivatives on luminescence shows media-dependence both in solution and solid state that is converse to dielectric constant of media. This is attributed to the specific C–C bond of o-carborane in excited state which is strongly affected by its outer surroundings as DFT calculations has shown. The water-soluble nido-o-carborane-functionalized iridium(III) complex (nido-fac-o) has high phosphorescence efficiency and long emission lifetime in aqueous solution, thus has been successfully applied in bioimaging including fluorescence lifetime imaging (Figure 3).

Figure 3

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Prof. Yan's Group@Nanjing University