Pyrazine derivatives
DIPY
,
TETPY
and
CNDIPY
have been designed and synthesized which form fluorescent supramolecular assemblies in mixed aqueous media due to their AIEE and ICT characteristics. Among all the derivatives, the assemblies of
TETPY
and
CNDIPY
show strong absorption in the visible region with high absorption coefficients, low HOMO-LUMO gap, and high photostability. Further, the supramolecular nanoassemblies of
TETPY
and
CNDIPY
show excellent potential to generate reactive oxygen species (ROS) under the visible light irradiation. Owing to their strong absorption in the visible region and ROS generation ability, the supramolecular nanoassemblies of
TETPY
and
CNDIPY
act as efficient photoredox catalytic systems for carrying out (a) oxidative amidation of aromatic aldehydes (b) hydroxylation of boronic acid and (c) oxidative homocoupling of benzylamines under mild conditions such as aqueous media, aerial environment, and natural sunlight as a source of irradiation. All the mechanistic investigations suggest the participation of
in-situ
generated ROS in the organic transformations upon light irradiation.
Supramolecular nanoassemblies of
an AIEE-ICT-active pyrazine derivative
(TETPY) having strong absorption in the visible region and excellent
transportability have been utilized as an efficient photoredox catalytic
system for the synthesis of a variety of benzimidazoles having electron-withdrawing/electron-releasing/aliphatic
groups under “metal-free” conditions. The reaction protocol
involves the successful harvesting of visible light by TETPY assemblies
to catalyze the coupling of o-phenylenediamine/substituted
diamines and substituted aromatic/heterocyclic/aliphatic aldehydes
under aerial conditions using mixed aqueous media as the reaction
solvent. TETPY assemblies could activate aerial oxygen to generate
superoxide for completing the vital proton abstraction step without
the need for any external metal/base/oxidant. Moreover, all the products
are purified by recrystallization from organic solvents. The TETPY
assemblies also exhibited high efficiency in catalyzing the synthesis
of 2-substituted benzothiazoles and quinazolines in excellent yields.
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