Cationic and Betaine-Type Boronated Acridinium Dyes: Synthesis, Characterization, and Photocatalytic Activity

A series
of isomeric boronated acridinium dyes were obtained by
reactions of 10-(4′-octyloxyphenyl) functionalized 9­(10H)-acridanone derivative with lithiated phenylboronic azaesters
followed by aromatization with perchloric acid. The effect of the
position of boronic group attached at ortho, meta, and para positions
of the 9-phenyl ring on the photophysical properties was investigated.
Conversion to related betaine trifluoroborato-substituted compounds
was successfully performed, and the effect of this structural change
on UV–vis absorption and fluorescence spectroscopy characteristics
was established. Furthermore, cyclic voltammetry studies revealed
that electrochemical behavior of cationic versus betaine structures
is different in terms of redox potential values as well as stability.
The theoretical calculations revealed a different scheme for molecular
excitation processes in B­(OH)2 versus BF3–-substituted compounds as charge transfer to acridinium
core is observed from N-aryl or B-aryl moiety, respectively. Obtained compounds were active as photocatalysts
in selected visible-light-promoted addition reactions to unsaturated
substrates.