Aggregation can be regarded as a force of nature that drives similar entities to assemble and function as a broader dynamic organism. However, even until very recent times, a much broader opportunity of this phenomenon towards the developments of luminescent materials was hidden from our sight. It was generally considered (and observed) that the aggregation of luminescent dyes can only result in quenching of luminescence. In a breakthrough discovery in 2001, Tang et al. demonstrated that aggregation of flexible molecular systems can significantly improve their luminescence efficiency. This phenomenon of Aggregation-Induced Emission (AIE) is largely contributed to the restricted molecular motions of the luminescent units in their aggregated states. Following this report, a significant number of systems have been identified, developed and applied as versatile AIE active materials finding applications in various aspects of material sciences e.g. biological evaluations, security, sensing etc.  In recent years, we have been interested in the developments of AIE active based on NPIs. [2-3] NPIs are well known as p - synthons due to their strong intermolecular p-p interactions which also often lead to their emission quenching in aggregated or condensed-states. In our trials, systematic alterations of the NPI based molecular backbone in order to fine-tune their extended solid-state structures. It was found that a balance of intermolecular forces and molecular environment can be an effective recipe to impart AIE features in NPIs. Following these observations, we also noticed that incorporation of NPI with boron containing dyes can result in broad emissive AIES (Aggregation-Induced Emission Switching) active materials.  Apart from these efforts, our group is also exploring the possibilities of D-A systems based on organometallic boron compounds.
(1) S. Mukherjee, P. Thilagar, J. Mater. Chem. C, 2016, DOI: 10.1039/c5tc02406d. (2) S. Mukherjee, P. Thilagar, Chem. Commun., 2013, 49, 7292-7294. (3) S. Mukherjee, P. Thilagar, Chem. Eur. J., 2014, 20, 8012-8023. (4) S. Mukherjee, P. Thilagar, Chem. Eur. J., 2014, 20, 9052-9062.
Conventional knowledge and understanding of luminescent dyes have been restricted to the realms of solution-state for a rather long period of time.  However, practical applications of any given material greatly rely on its compatibility in solid-state. In most instances, commonly encountered luminescent dyes show very poor or no emissive features in their condensed or solid-state resulting from the effects of strong intermolecular forces which lead to self-quenching of luminescence. Thus, considerable scientific interests are being drawn towards the developments of solid-state emissive organic emitters owing to their potential applications in OLEDs, security, Lighting and sensing etc. In general, design of a solid-state emitter might not be straightforward and often successes are met only through hit-and-trail methods or brute-force synthetic strategies. However, if one wants to gain insights into the structure-property relationships of solid-state emitters, systematic design strategies can be of significant interests. In recent years, our research group has been involved in imparting solid-state emissive properties in boron based dyes and NPIs. [2-4] These classes of compounds were well-known for their versatile photophysical properties in solution-state, photo-stability and tunable emission features. However, these dyes suffer from significant quenching of luminescence in their solid-state due to considerable p-p stacking interactions and related strong intermolecular forces. In our efforts, we were able to systematically fine-tune the substitution pattern in these classes of compounds, resulting in alteration of their molecular flexibility as well as nature of intermolecular interactions. Furthermore, the systematic alterations of the molecular structures of the compounds also provided significant insights into the controlling parameters which affect the bulk emissive features of such compounds. The correlation between the color, quantum yields and structural patterns of the compounds reflect that small changes at molecular level can result in significant alteration of emissive properties in bulk-state. Also, it is unveiled that p-p interactions can be either detrimental or beneficial depending on the relative arrangements of neighboring luminescent units. These understanding of luminescent materials are of significant and fundamental interest in order to gain a broader understanding of structure-property relationships in luminescent materials.
(1) S. Mukherjee, P. Thilagar, Chem. Commun., 2015, 51, 10988-11003. (2) S. Mukherjee, P. Thilagar, Phys. Chem. Chem. Phys., 2014, 16, 20866-20877. (3) C. A. Swamy, S. Mukherjee, P. Thilagar, J. Mater. Chem. C, 2013, 1, 4691-4698. (4) P. Sudhakar, S. Mukherjee, P. Thilagar, Organometallics, 2013, 32, 3129-3133.
Identification of chemical species is always an indispensible part and goal of chemical research. In recent times, detection of toxic ionic species is finding significant attention owing to their relevance to human health. In general, colorimetric and fluorescent sensors are finding significant interests in this regard due to their easy operational procedures. Especially in India, contamination of toxic ionic species in water sources is a huge concern wing to their detrimental effects in human health. In southern parts of India, contamination of fluoride ions has drawn considerable attention. In our research group, for past few years, we have been engaged in understanding the chemistry of fluoride ions and to develop fluorescent molecules which can specifically recognize fluoride ions without any interference from other anions. Conventional fluorescent sensors for fluoride ions often utilize the hydrogen bonding interactions. However, such weak interactions can lead to very less selectivity or specificity. We have been interested in the developments of triarylborane (TAB) based luminescent sensors in this regard. TAB based molecules can reversibly bind to fluoride anions via Lewis acid-base adduct formations often accompanied with observable changes of their optical properties. [1-10] However, they also experience interference from small anions like cyanide etc. which often complicates the recognition process. In our trials, we have been successful in development of specifically fluoride selective sensors as well as Lab-on-a-molecule systems which can effectively distinguish fluoride and cyanide anions via different optical channels or processes. [5-6] Apart from this, we have been also successful in the developments of far-red and NIR sensors based on TAB moieties. 
(1) C. A. Swamy, S. Mukherjee, P. Thilagar, Chem. Commun., 2013, 49, 993-995. (2) S. K. Sarkar, P. Thilagar, Chem. Commun., 2013, 49, 8558-8560. (3) C. A. Swamy, S. Mukherjee, P. Thilagar, Inorg. Chem., 2014, 53, 4813-4823. (4) C. A. Swamy, S. Mukherjee, P. Thilagar, Anal. Chem., 2014, 86, 3616-3624. (5) Kumar, G. R.; Thilagar, P. Dalton Trans. 2014, 43, 3871. (6) Kumar, G. R.; Thilagar, P. Dalton Trans. 2014, 43, 7200. (7) G. R. Kumar, P. Thilagar, Phys. Chem. Chem. Phys., 2015, 17, 30424-30432. (8) S. K. Sarkar, S. Mukherjee, P. Thilagar, Inorg. Chem., 2014, 53, 2343-2345. (9) C. A. Swamy, S. Mukherjee, P. Thilagar, Eur. J. Inorg. Chem., 2015, 53, 2338-2344. (10) C. A. Swamy, P. Thilagar, Inorg. Chem., 2014, 53, 2776-2786.
Formation follows function. In most cases, properties of bulk materials are greatly affected by small alterations at the molecular level as well as their physical states or phase. [1-2] In case of solid-state emissive materials, stimuli-responsive alterations of their bulk properties of great interest to researchers as it allows development of different functional luminescent materials which can be applied in solid-state sensing, security, information coding and decoding, forensic analysis etc. In recent times, significant attention has been drawn to the developments and understanding of such materials.
Concentrating on the chemistry of boron, our lab has been involved in the development of stimuli responsive solid-state emitters based on organoboron compounds. Although a large number of borate-dyes are known for their intriguing and flexible emission properties in condensed-states, TAB (triarylborane) based systems are yet to be explored in these frontiers.  The inherent Lewis acidity coupled with the unique electronic structure of three-coordinate boron centre can provide several opportunities to develop smart sensor materials as well as colour-tunable OLED systems. Utilising the chemistry of simple D-A (donor-acceptor) molecules,  our group has successfully developed libraries of molecules with intriguing properties [5, 6].
(1) Z. Chi,X. Zhang,B. Xu,X. Zhou,C. Ma,Y. Zhang,S. Liu, J. Xu, Chem. Soc. Rev., 2012, 41, 3878-3896. (2) Y. Sagara and T. Kato, Nat. Chem., 2009, 1, 605-607. (3) S. Mukherjee, P. Thilagar,J. Mater. Chem. C, 2016,4, 2647-2662. (4) P. Sudhakar, S. Mukherjee, P. Thilagar, Organometallics, 2013, 32, 3129-3133. (5) Kalluvettukuzhy K. Neena and Pakkirisamy Thilagar, Aggregation Induced Emission, Mechanoluminescence and Nitroaromatic Sensing Characteristics of Tetra-arylaminoboranes, J. Mater. Chem. C, 2016, 4, 11465-11473. (6) Kalluvettukuzhy K. Neena, Pagidi Sudhakar, Kumbhar Dipak and Pakkirisamy Thilagar, Diarylboryl-phenothiazine based multifunctional molecular siblings, Chem. Commun., 2017,53, 3641-3644.
Since the discovery of lysosome it was believed that cellular proteins are degraded by this organelle. However, several independent researchers showed strong evidence for non-lysosomal intracellular protein degradation, but the mechanisms for this process were unclear until the discovery of proteasome. The ubiquitin-proteasome pathway is a major avenue for degradation of proteins in the cytosol and nucleus of eukaryotic cells. Proteins are marked for degradation via the attachment of an ubiquitin group whereby the proteasome recognize, unfold, and digests these proteins. The 26S proteasome is cylindrical shaped proteolytic complex (Figure 1 (left)) incorporates the ATP-dependent 19S caps, which recognize the proteins marked for degradation and unfold substrates, which are in turn fed to the 20S proteasome, where proteolysis occurs. 20S core particle is a four stacked heptameric ring composed of a and B units (a 7, B 7, B 7, a 7). a subunits guard the entrance to the active site by allowing access to only unfolded proteins.
The catalytic activities are confined to the B subunits that are responsible for mediating the enzymatic activity of the proteasome. Three of the B-subunits in B-ring are catalytically active and have an N-terminal threonine (side-chain hydroxyl group activated by the N-terminal amine moiety) acts as the proteolytic nucleophile (Figure 1 (right)). The proteasome has at least three distinct peptidase activities and, by comparison with substrate specificities of known proteases, they are designated as chymotrypsin-like (B5-subunit), trypsin-like (B2-subunit), and caspase-like activities (B1- subunit).
Figure: Protolytically active B units (left). Active sites located within the 20S core particles hydrolyze these unfolded polypeptides into small peptides and amino acids (Right). Proteins that are synthesized in the cell (direct presentation) or are released from endosomes (cross-presentation) are polyubiquitylated in the cytoplasm and degraded by hybrid proteasomes consisting of the 20S proteasome core, the 19S regulator. The peptides that are produced are either of the ideal length for binding to MHC class I molecules or are amino-terminally extended precursors that can be further cleaved by aminopeptidases in the cytoplasm.
Not only does it remove abnormal proteins that may be misfolded, aged, or damaged by oxidation, it also regulates the half-life of the short-lived regulatory proteins such as cyclins that are involved in the control of cell cycle and transcription regulators such as p53, NF-kB. Through its destruction function, the proteasome is thus involved in a variety of cellular processes such as protein quality control, cell cycle, antigen presentation, apoptosis, and cell signaling. Proteasomes are also found in several bacterial species of the order Actinomycetales. Numerous studies demonstrated that mycobacterium tuberculosis (Mtb), an Actinomycete pathogenic to humans, involves proteasome function to root infections. Thus, the understanding of proteasome function in Mtb would help in getting new insight into how the host combats infections. Thus, proteasome become an attractive therapeutic target for controlling various diseases including cancer.
The active site of proteasome is nothing but Lewis basic hydroxyl groups. Obviously a simple Lewis acid can be employed to control the activity of proteasome. Our research group has been actively involved in exploiting the Lewis acidity of tricoordinated boron for the development of boron based proteasome inhibitors (BPI) and understanding the differences in the catalytic activity of multiple proteolytic sites in both eukaryotic and bacteria proteasomes. Our long range goals to utilise the acquired knowledge to design novel BPIs to control proteasome activities in specific diseases. We are also actively pursuing design and development of boronopeptides and their role as antibacterial and diabetes wound healing drug molecules.