Revisiting Unsubstituted Ullazine: Concise Synthesis, Single Crystal
X-Ray Structure and Photophysical Properties
Abstract
We have developed an efficient synthetic route of parental ullazine in
three steps from commercially available synthons with overall yield of
53%. The single crystal X-ray structure of parental ullazine was
studied in detail. Parental ullazine core can be functionalized either
by late-stage Vilsmeier-Haack formylation/condensation sequence or by
C-N cross-coupling with a pre-installed bromine. Pre-liminary results
show that the condensation of CHO-substituted ullazine (U-CHO) gave a
novel imidazole substituted ullazine. The brominated ullazine (U-Br) can
undergo Buchwald-Hartwig cross-coupling smoothly, resulting a carbazole
substituted ullazine. In ad-dition, parental ullazine showed redshifted
absorption and emission spectra as compared to its isoelectronic isomer
pyrene, and no excimer formation in higher concentration.