Research highlights

Part I:

Reactions involving Fischer carbene-chromium complexes and alkynes have emerged as a powerful tool for synthetic organic chemists, allowing for the direct synthesis of a variety of natural molecules. Our Group worked on Fischer carbene-chromium complexes and alkynes chemistry and has developed a novel and interesting method for the generation of heteroaromatic isobenzofurans e.g. azaisobenzofuran intermediates by a one-pot three-component coupling of appropriate o-alkynylheteroaryl carbonyl derivatives with Fischer carbene complexes. We have generated azaisobenzofuran intermediates e.g. furo[3,4-b]quinoxaline, furo[3,4-b]pyrazine, furo[3,4-d]pyrimidine, conformationally flexible dienylazaisobenzofurans etc intermediates in situ. These in situ generated azaisobenzofuran intermediates were trapped with suitable dienophiles leading to the synthesis of series of complex azaheterocycles, namely, heterolignanes, phenazines, quinoxaline derivatives,  quinazolines, furo[2,3-h]quinolines, furo[2,3-h]isoquinoline derivatives, azafuranophane derivatives, azahomosteroids etc.

Part II

Recently our Group is working on the design, synthesis, characterization and studies on the optoelectronic properties of highly branched molecular architectures, now commonly known as p-conjugate oligomers, which have emerged to become a key element in the research efforts of scientist worldwide. Many applications have been claimed for this new type of compounds, namely, bio-sensing materials i.e. potential vehicles for delivery of druges and immunogens, biomimetic catalysts and optoelectrical properties. These molecules are also useful for applications in organic electronics e.g. light emitting diodes (OLEDs).  We have designed and synthesized some of the p-conjugate oligomers and studied their photophysical properties. We have shown that:

(i) A fluorescent “switch on” probe for the reliable detection and monitoring of amyloid fibrils was studied. The probe consists of a peptide component for binding with amyloid structure and a color component with an aggregation-induced green emission property. This probe isnonfluorescent in the presence of amyloid forming monomer protein/peptide, but fluorescence “switch-on” occurs after binding with amyloid fibrils. Compared to conventionally used thioflavin T, this probe offers a high signal-to-noise ratio, which is unaffected by the quencher ion/nanoparticle. The proposed new probe has been used for the detection and monitoring of amyloid fibrils produced by a wide variety of amyloid protein/peptides and can be extended for in vitro diagnostic applications.

(ii) Aggregation induced emission (AIE) active molecules are widely used for fluorescence “turn-on” detection applications with the unique advantages over conventional fluorescent probes. Transformation of AIE molecule into functional nanoparticle can greatly expand their biomedical application potential. We have synthesized TPE-based nanoparticle functionalized with polyethylene glycol, primary amine, aspartic acid, glucose, and arginine. Compared to reported methods of making AIE-based nanoparticles, presented nanoparticles have distinct advantages that they are composed of AIE molecules only (without any non-AIE molecule/polymer) and wide variety of surface functionalization can be achieved by this approach. Nanoparticles have good colloidal stability with fluorescence quantum yield of 12−15% and fluorescence remains intact in the presence of conventional quenchers.

(iii) Luminescent materials with mechanoluminescence and high electroluminescence efficiencies are the quest for sensing and optoelectronic applications. We have synthesized a new tailor-made luminogen, 1,2-bis(4-(1-([1,1ʹ-biphenyl]-4-yl)-2,2-diphenylvinyl)phenyl)-1,2-diphenylethene which  forms supramolecular spherical aggregates at the air-water interface of a Langmuir trough J-aggregation.  As a consequence, a large enhancement of luminescence is obtained from the mono and multilayer LB films of this compound displaying the phenomenon of aggregation induced emission. The luminogens exhibit reversible mechanoluminescence response displaying photoluminescence switching owing to the change in crystalline states under external stimuli. The unique feature of luminescence enhancement is utilized for the fabrication of light emitting diodes with low threshold voltage using supramolecular aggregates as active layer. This work not only demonstrates an efficient strategy for obtaining controlled supramolecular aggregates of AIE-gens but also demonstrate the potential of the synthesized compound in the dual application of mechanoluminescence and electroluminescence.