AIEE Active Nanoassemblies of Pyrazine Based Organic Photosensitizers as Efficient Metal-Free Supramolecular Photoredox Catalytic Systems

Abstract

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.

Visible Light-Induced Aerobic Oxidative Dehydrogenation of C–N/C–O to C=N/C=O Bonds Using Metal-Free Photocatalysts: Recent Developments

“…Sunlight is a sustainable alternative source of energy that can be employed in photocatalysis. Thus, the aerobic oxidative coupling of benzylamines to render 2 under sunlight irradiation has been carried out using very low loadings of the xanthene-based photocatalyst Eosin Y (3) [73] and a terpyridine-based supramolecular nanoassembly of pyrazinebased donor-acceptor systems, (TETPY, 4) [74], both catalysts showing excellent activity (Figure 1). In the first case, the fact that it could be possible to mimic the solar light environment with a sunlight simulator lamp makes the system very attractive, while in the second case carried out under direct real sunlight irradiation, the nanoassemblies have excellent aggregation-induced emission enhancement (AIEE) and intramolecular charge transfer (ICT), characteristics added to their potential to generate ROS.…”

Photocatalytic Homocoupling Transformations

“…It is well-known that the benzylamine homocoupling reaction giving 84 has been implemented in many contributions using metallic photocatalysts such as cobalt(II) 60 and ruthenium(II), 61 or even in the presence of some pyrazine-based donor-acceptor photosensitizers (e.g., TETPY) (Scheme 27). 62 This is not a true dimerization process, although in some cases such reactions have been classified using this term.…”

‘Light‐Up’ AIE‐Active Materials: Self‐Assembly, Molecular Recognition and Catalytic Applications

“…Building on our efforts in developing ecofriendly catalytic systems, we are recently focusing on preparation of ‘metal‐free’ photocatalytic systems. In this context, we synthesized AEE‐ICT active nanoassemblies of pyrazine based derivative 37 which exhibit high potential to transport the electron from donor to acceptor which is highly desirable for the derivative to act as a photocatalyst and hence generate reactive oxygen species (ROS) [44] . This ability was utilized to perform various reactions which includes amidation of aldehydes, hydroxylation of boronic acids and homocoupling of benzylamines.…”