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General CāH Arylation Strategy for the Synthesis of Tunable Visible Light-Emitting Benzo[<i>a</i>]imidazo[2,1,5ā<i>c</i>,<i>d</i>]indolizine Fluorophores
Herein
we report the discovery of the benzoĀ[<i>a</i>]ĀimidazoĀ[2,1,5-<i>c</i>,<i>d</i>]Āindolizine motif displaying tunable
emission covering most of the visible spectrum. The polycyclic core
is obtained from readily available amides via a chemoselective process
involving Tf<sub>2</sub>O-mediated amide cyclodehydration, followed
by intramolecular CāH arylation. Additionally, these fluorescent
heterocycles are easily functionalized using electrophilic reagents,
enabling divergent access to varied substitution. The effects of said
substitution on the compoundsā photophysical properties were
rationalized by density functional theory calculations. For some compounds,
emission wavelengths are directly correlated to the substituentās
Hammett constants. Easily introduced nonconjugated reactive functional
groups allow the labeling of biomolecules without modification of
emissive properties. This work provides a straightforward platform
for the synthesis of new moderately bright fluorescent dyes remarkable
for their chemical stability, predictability, and unusually high excitationāemission
differential