Bicarbazoles: Systematic Structure-Property Investigations on a Series of Conjugated Carbazole Dimers

A large series of conjugated carbazole dimers, namely bicarbazoles 1-12, were synthesized by Suzuki-Miyaura, Sonogashira, Hay, and McMurry coupling reactions. In 1-12, the two carbazole moieties are linked at the 1-, 2-, or 3-position directly or via an acetylenic or olefinic spacer. The structure property relationships, particularly the effects of the conjugation connectivity and the pi-conjugated spacers on the electronic, photophysical, and electrochemical properties of 1-12, were studied by extensive UV-vis and fluorescence spectroscopic measurements, cyclic voltammetry (CV), and theoretical calculations as well as X-ray crystallo-graphic analyses. The connection at the 1-position of carbazole ensures high extent of pi-conjugation, while that at the 3-position enhances the electron donating ability. Both acetylenic and olefinic spacers allow the extension of pi-conjugation, and the latter also causes the increase, of the donor ability. Moreover, the structural variations were found to affect the fluorescence quantum yields significantly, which are up to 0.84.