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 π-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 crystallographic
analyses. The connection at the 1-position of carbazole ensures high
extent of π-conjugation, while that at the 3-position enhances
the electron-donating ability. Both acetylenic and olefinic spacers
allow the extension of π-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.