Synthesis of functionalized disiloxanes with nonconventional fluorescence via oxa-Michael addition reaction

Developing a new organosilicon synthetic methodology is significant because it enables the design and synthesis of organosilicon materials with novel structures and functionality, thereby expanding their potential applications. Herein, we introduce the classical oxa-Michael addition reaction to prepare functionalized disiloxanes by reacting 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane with various commercial vinyl compounds containing electron-withdrawing groups, while employing a phosphazene base as the catalyst. The impact of various factors, including catalytic systems, reaction solvent, and reaction temperature, on the efficiency of the process was investigated. It was found that functionalized disiloxanes can be obtained under mild conditions with moderate-to-high yields. Remarkably, these compounds exhibit nonconventional fluorescence due to the cluster-triggered emission of chromophores, such as cyano and sulfone. Moreover, the fluorescence performance of these compounds surpasses that of the analogs lacking Si–O–Si units. This observation is distinct from previous reports suggesting that the enhancement is commonly achieved by the formation of coordination bonds between the heteroatoms and the Si–O units. This implies that the introduction of a Si–O unit can efficiently enhance the fluorescence emission by weak interactions between a Si atom and an O atom from ether groups. These findings demonstrate the efficiency of the oxa-Michael addition reaction as an organosilicon synthetic methodology, thus opening up the possibilities for the development of more organosilicon materials with unique structures and enhanced functionality.