RESUMO
Aromatic polycyclic systems have been extensively utilized as structural subunits for the preparation of various functional molecules. Currently, aromatics-based polycyclic systems are predominantly generated from the extension of two-dimensional (2D) aromatic rings. In contrast, polycyclic compounds based on the extension of three-dimensional (3D) aromatics such as boron clusters are less studied. Here, we report three types of boron cluster-cored tricyclic molecular systems, which are constructed from a 2D aromatic ring, a 3D aromatic nido-carborane, and an alkyne. These new tricyclic compounds can be facilely accessed by Pd-catalyzed B-H activation and the subsequent cascade heteroannulation of carborane and pyridine with an alkyne in an isolated yield of up to 85% under mild conditions without any additives. Computational results indicate that the newly generated ring from the fusion of the 3D carborane, the 2D pyridyl ring, and an alkyne is non-aromatic. However, such fusion not only leads to a 1H chemical shift considerably downfield shifted owing to the strong diatropic ring current of the embedded carborane but also devotes to new/improved physicochemical properties including increased thermal stability, the emergence of a new absorption band, and a largely red-shifted emission band and enhanced emission efficiency. Besides, a number of bright, color-tunable solid emitters spanning over all visible light are obtained with absolute luminescence efficiency of up to 61%, in contrast to aggregation-caused emission quenching of, e.g., Rhodamine B containing a 2D-aromatics-fused structure. This work demonstrates that the new hybrid conjugated tricyclic systems might be promising structural scaffolds for the construction of functional molecules.
RESUMO
The classical aggregation-induced emission (AIE)-active luminogens (AIEgens) usually include two-dimensional aromatic systems such as tetraphenylethenes, which are synthesized in several steps by using toxic additives. Here, we proposed a new molecular design strategy for the realization of AIE properties by combining three-dimensional aromatic boron clusters of carboranes with vinyl group(s). To obtain a library of the boron cluster-based AIEgens, a Pd-catalyzed hydroboration of alkynes with carboranes is reported. This reaction protocol proceeds in one step under mild conditions with rapid reaction rate, excellent yields and regioselectivity. Photophysical property studies demonstrate that the facile molecular motions in solution can be inhibited in the solid state for these molecules, which leads to interesting AIE properties. This work provides not only a general design principle for AIEgens but also an efficient methodology to synthesize boron cluster-based photo-functional molecules.
