1-Carbazolyl Spirobifluorene: Synthesis, Structural, Electrochemical, and Photophysical Properties

The present work reports one of the rare examples of a new emerging family of spirobifluorene derivatives, namely, 1-substituted spirobifluorenes. We report the synthesis and the structural, electrochemical, and photophysical properties of 9-(9,9'-spirobi[fluorene]-1-yl)-9H-carbazole 1-Cbz-SBF, constructed from the connection of the widely known electron-rich carbazole fragment at the C1 position of spirobifluorene. We show with 1-Cbz-SBF that the substitution at C1 induces two important characteristics which drive the electronic properties. First, there is a complete pi-conjugation breaking between the pending substituent, herein, carbazole, and the substituted fluorene. Second, there is a through-space interaction between the carbazole and its cofacial fluorene. Thanks to a structure-property relationship approach with its constituting building blocks 9,9'-spirobifluorene SBF and carbazole Cbz, we show how some electronic properties are driven by the carbazole unit such as the highest occupied molecular orbital energy level, whereas others are driven by the fluorene unit such as the triplet-state energy level. As 1-substituted spirobifluorenyl represents a new and promising molecular scaffold for phosphorescent organic light-emitting diode applications and more generally for organic electronics, such a study provides fundamental knowledge to design future organic materials for specific applications.