Synthesis, Structure, Electrochemistry, and Electrochemiluminescence of Thienyltriazoles

Four blue-emitting thienyltriazoles with desired N and
O coordination
atoms were prepared in high yield via click chemistry for potential
incorporation into metal complexes. Three of their crystal structures
were determined by X-ray crystallography. The electrochemical properties,
electronic structures of these thienyltriazoles, 1–4, and their correlations were studied using cyclic voltammetry
and differential pulse voltammetry techniques along with density function
theory (DFT) calculations. All of the compounds underwent irreversible
redox reactions, leading to unstable electrogenerated radical cations
and anions. Electrochemical gaps determined from the differences between
first formal reduction and oxidation reactions were correlated to
HOMO–LUMO energy gaps obtained from UV–vis spectroscopy
and the DFT calculations as well as energies of excited states measured
from photoluminescence spectroscopy. We observed weak electrochemiluminescence
(ECL) from annihilation of these thienyltriazole radicals in acetonitrile
containing 0.1 M tetra-n-butylammonium perchlorate
as electrolyte. An enhancement in ECL efficiency ranging from 0.16
to 0.50% was observed upon addition of benzoyl peroxide as a coreactant
in the above electrolyte solutions. The generation of excimers in
solutions of 1–4 was observed as
seen by the red-shift in ECL maxima relative to their corresponding
photoluminescence peak wavelengths. Our work is of importance for
the development of efficient blue-emitting fluorophores via click
chemistry that could be potential luminophores in metal complexes.