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.

The donor–acceptor system 4 having pyrazine scaffold as an acceptor moiety coupled to donor amino groups through rotatable phenyl rings has been synthesized, which formed aggregates in aqueous media, exhibited copper induced restriction to intramolecular rotation, and served as a “not quenched” probe for the detection of copper­(II) ions. During this process, the aggregates of derivative 4 acted as reactors and stabilizers for the generation of CuO NPs and themselves became oxidized to form polyamine derivative 6. Interestingly, the oxidized species 6 in combination with copper oxide nanoparticles served as light-harvesting antennas and exhibited excellent photocatalytic efficiency in Sonogashira coupling under mild and eco-friendly conditions (room temperature, aqueous media, aerial conditions, and visible light irradiation).

In the present investigation, an intramolecular charge transfer (ICT) and aggregation induced emission enhancement (AIEE) active donor-acceptor-donor (D-A-D) system 5 having fumaronitrile as the acceptor and hexaphenylbenzene (HPB) as the donor moieties joined through rotatable phenyl rings has been designed and synthesized that is highly emissive in the solid state and exhibits stimuli-responsive reversible piezochromic behavior upon grinding and heating. Because of its AIEE characteristics, HPB derivative 5 undergoes aggregation to form fluorescent aggregates in mixed aqueous media that exhibit ratiometric fluorescence response toward aliphatic amines (primary/secondary/tertiary) and turn-off response toward aromatic amines and hence differentiates between them. Further, the solution-coated portable paper strips of derivative 5 showed pronounced and sensitive response toward aromatic and aliphatic amines with a detection limit in the range of picogram and nanogram level, respectively.

With an aim to achieve a balance between ground-state and excited-state reduction potential of donor acceptor systems for efficient C–N/C–C cross-coupling, a series of donor acceptor systems DA1–DA4 have been synthesized by varying the donor strength and connecting positions. With an increase in donor strength, systematic elevation in the ground-state reduction potential and decrease in the HOMO–LUMO gap was observed. Interestingly, all the derivatives DA1–DA4 could catalyze the C–N bond formation reaction between activated aryl halides and amines at low catalytic loading under metal-free conditions without the need of any external base upon irradiation with white LED. A balance was realized in the case of derivative DA2, which exhibits high efficiency in C–N couplings. Different control experiments support the validity of the energy as well as electron transfer pathways in the visible light-mediated C–N bond formation. This study further reveals the potential of derivative DA1 in “metal-free” Sonogashira coupling involving activated aryl halides which is attributed to its high excited-state reduction potential.

A supramolecular polymer of PBI derivative and ZnO NPs exhibits remarkable efficiency in direct dehydrogenative cross-coupling reaction for the synthesis of ynones under photocatalytic conditions.