TIFR
Department of Chemical Sciences
School of Natural Sciences

Calender

June 17, 2021 at 4.00 pm (Via Zoom)

Title :

Modulating Mechanical Properties of β-Rich Proteins

June 14, 2021 at 4.00 pm (Via Zoom)

Title :

Transient Raman Spectroscopy for Probing Charge Transfer States

Abstract :

Charge transfer (CT) states form the basis for multitude of chemical reactions, and has become relevant due to its ubiquity in all light energy conversion paradigms.[1] In order to discover new materials with optimized charge transfer rates at molecular interfaces for energy conversion technologies, it is imperative to diagnose the structure-function corrleations “in operando”. Tracking the non-equilibrium nuclear dynamics leading up to the charge transfer states and probing the subsequent separation of charges requires time-resolved spectroscopy with structural sensitivity. In this talk, I will discuss the utility of transient Raman spectroscopy as a tool to structurally probe the formation of CT states in molecular dyes with large Stokes shift,[2] and uncover the hidden lengthscale of the photochemistry inside the active site of metalloproteins.[3] Both frequency domain and time-domain methods will be elaborated with emphasis on challenges of real-time Raman detection during chemical reactions.

References

1. Sajjad Dadashi-Silab, Sean Doran and Yusuf Yagci; Chem. Rev. 2016, 116, 17, 10212–10275; Alexey V. Akimov, Amanda J. Neukirch and Oleg V. Prezhdo; Chem. Rev. 2013, 113, 6, 4496–4565.

2. Shreetama Karmakar, Abhinandan Ambastha, Ajay Jha, Aditya Dharmadhikari, Jayashree Dharmadhikari, Ravindra Venkatramani, and Jyotishman Dasgupta; J. Phys. Chem. Lett. 2020, 11, 12, 4842–4848.

 

3. Soumyajit Mitra, ASR Koti, and Jyotishman Dasgupta; to be submitted.

June 10, 2021 at 4.00 pm (Via Zoom)

Title :

Overcoming resistance in cancer cells – Exploring new metal compounds for broader spectrum of anticancer activity

June 7, 2021 at 4.00 pm (Via Zoom)

Title :

Optical Properties and Applications of Novel Stimuli-Responsive Organic Smart Materials

Abstract :

Prediction of multi-stimuli responsive behaviour in newly developed luminogen is an appealing yet challenging puzzle, since no concrete design strategy has been developed so far. In this talk, I will discuss about our unique strategy to establish structure-property relationship for designing of multi-stimuli responsive mechanoluminiscent material. First time we have reported that synergistic effect between twisting, conformational flexibility of donor moieties along with numerous non-covalent interactions endow the multi-stimuli responsive behaviours1.

In the second part of my talk, I will be talking about a unique strategy to sensitize centrosymmetrically packed organic luminogens,2 which generally do not respond to external stimuli owing to their zero gross dipole moment and degenerate electronic energy states in solid-state packing.

In the last part of my talk, I will be talking about the next generation fluorophores exhibiting “all in one” type applications potentiality. Our work provides the important concept of “all in one” type luminogens possessing the following features comprising optical, biological and materials applications: 1) single source white light emission, 3) stimuli-responsive mechanoluminiscent feature, 2) selective mitochondria tracking.3

1. Bibhisan Roy, M. Chenna Reddy, Partha Hazra. Chemical Science, 2018, 9, 3592-3606.

2. Bibhisan Roy, M. Chenna Reddy, Soumendra Nath Panja, Partha Hazra. J. Phys. Chem. C, 2019, 123, 3848-3854.

 

3. Bibhisan Roy, M. Chenna Reddy, Gregor P. Jose, Felix C. Niemeyer, Jens Voskuhl, and Partha Hazra. J. Phys. Chem. Lett. 2021, 12, 1162-1168.

June 3, 2021 at 4.00 pm (Via Zoom)

Title :

Towards Understanding the Photodynamics of Tris(pentafluronyl)Borane-doped P3HT

June 1, 2021 at 2.30 pm (Via Zoom)

Title :

Evaluating the Role of an Electrolyte in Photocatalytic  Water Splitting

 

May 31, 2021 at 4.00 pm (Via Zoom)

Title :

Assessment of response theory based methods for open shell systems

May 27, 2021 at 5.00 pm (Via Zoom)

Title :

Photogeneration of Carbene and its Reactivity inside Supramolecular Cavity

May 20, 2021 at 4.00 pm (Via Zoom)

Title :

Assessing GKS - RPA approach for predicting Core Electron Binding Energies (CEBEs)

May 6, 2021 at 4.00 pm (Via Zoom)

Title :

TT Pair in Singlet Fission

Abstract :

Singlet fission1-2 (SF) is a process in which a molecular chromophore in its singlet excited state shares its excitation energy with an unexcited neighbour leading to formation of two triplet excitons through a spin-allowed process. Due to the high singlet-to-triplet conversion quantum efficiencies up to 200%, SF chromophores have potential application in boosting solar cell efficiencies3. However molecular triplet excitons produced through SF usually have shorter triplet lifetimes due to exciton-exciton recombination and relaxation pathways, thereby resulting in complex device architectures for SF-boosted solar cells. In order to elucidate the fundamental mechanism of SF and the triplet-triplet recombination pathways it is highly important to understand the intrinsic nature of the intermediate correlated T-T pair states. Here, using femtosecond transient absorption and femtosecond stimulated Raman spectroscopy, we demonstrate optical as well as vibrational signature of TT pair state in SF across different kinds of SF chromophores namely carotenoids and diketopyrrolopyrrole derivatives. These spectroscopic signatures will help us to understand the origin of the TT pair and fate of it in SF, importance of the morphology of the aggregates to get distinct signatures of the TT pair compared to the free triplets and enhancement of the free triplet lifetime.4 A complete fundamental understanding of the T-T pair state will enable us to draw the proper structure-function relationship to get the next generation SF chromophores for the application in solar cell devises.

 

1)     Smith, M. B.; Michl, J., Singlet fission. Chemical reviews 2010, 110, 6891-6936.

2)     Smith, M. B.; Michl, J., Recent advances in singlet fission. Annual review of physical chemistry 2013, 64, 361-386.

3)     Rao, A.; Friend, R. H., Harnessing singlet exciton fission to break the Shockley-Queisser limit. Nature reviews materials 2017, 2, 1-12.

4)     Kundu, A.; Dasgupta, J., Photogeneration of Long-Lived Triplet States through Singlet Fission in Lycopene H-Aggregates. J. Phys. Chem. Lett. 2021, 12, 5, 1468–1474

May 3, 2021 at 4.00 pm (Via Zoom)

Title :

Fluorescent Chemo-sensors for Biomolecules and Ions

April 29, 2021 at 5.00 pm (Via Zoom)

Title :

Effect of circular permutation on a metalloprotein azurin

April 26, 2021 at 4.00 pm (Via Zoom)

Title :

Black Gold Based “Antenna-Reactor” of Nickel: Concept of Forced Plasmon to Activate Non-plasmonic Metal Catalysts

Abstract :

Localized surface plasmon resonance (LSPR) allows metal nanoparticles (NPs) to harvest light and concentrate it near the nanoparticle surface. Light energy is then utilized in the generation of excited charge carriers as well as heat. Plasmonic catalysts used these energetic charge carriers (and the heat) to drive chemical transformations on their surface and allowed the discovery of novel and selective reaction pathways that were not possible in thermal catalysis1-3. However, since the number of metals that show plasmon absorption in the visible range is limited, the reactions that can be catalyzed by these metals are also limited. Using the concept of multicomponent plasmonic catalysis, one can design a hybrid catalyst by combining plasmonic metals with non-plasmonic but active catalytic metals in close proximity to each other, named as “antenna-reactor”4.           

   In this work, we have designed and synthesized dendritic plasmonic colloidosomes (DPCs), known as Black Gold5 based “Antena Reactor” of Nickel (DPC-Ni).When DPC-Ni was illuminated with visible light, the plasmonic metal antenna of Au undergo LSPR and non-radiative Landau damping induces an optical polarization in non-plasmonic Ni metal (reactor) by creating a flow of plasmon energy from the antenna (Au) to the reactor (Ni). This created plasmon on non-plasmonic Ni metal (forced plasmon), which then undergo decay to generate hot charge carriers (electrons and holes). The forced plasmon made the reactor Ni catalytically active and it was able to catalyze several challenging reactions (H2 dissociation, propene reduction, and C-Cl bond activation) using visible light at room temperature, which generally need high temperature and pressure. In this talk, I will present the synthesis of DPC-Ni, their characterizations, application in catalysis and preliminary insights into the reaction mechanism and electron dynamics of DPC-Ni catalyst.

 

References:

1. Aslam, U.; Rao, V. G.; Chavez, S.; Linic, S. Catalytic conversion of solar to chemical energy on plasmonic metal nanostructures. Nat. Catal. 2018, 1, 656−665

2. Gelle, A.; Jin, T.; de la Garza, L.; Price, G. D.; Besteiro, L. V.; Moores, A. Applications of Plasmon-Enhanced Nanocatalysis to Organic Transformations. Chem. Rev. 2020, 120, 986−1041

3.  Zhan, C.; Chen, J. X.; Yi, J.; Li, F. J.; Wu, D. Y.; Tian, Z. Q. From Plasmon-Enhanced Molecular Spectroscopy to Plasmon Mediated Chemical Reactions. Nat. Rev. Chem. 2018, 2, 216−230.

4. Halas, J. N. et al. Heterometallic Antenna−Reactor Complexes for Photocatalysis. Proc. Natl. Acad. Sci. U.S.A. 2016, 113, 8916–8920.

5. Polshettiwar etl al. Plasmonic Colloidosomes of Black Gold for Solar Energy Harvesting and Hotspots Directed Catalysis for CO2 to Fuel Conversion. Chemical Science, 2019, 10, 6594-6603.

April 22, 2021 at 4.00 pm (Via Zoom)

Title :

Exploring high valent rhenium complexes for antiproliferative activities

Abstract :

Chemotherapy is the cutting-edge method for treatment of both metastatic and localized cancers. Traditionally, platinum based drugs like cisplatin, oxaliplatin, carboplatin are used to treat a variety of cancer. Despite the clinical success, emergence of resistance and lack of cancer selectivity leading to severe side effects like nephrotoxicity, neurotoxicity, anaemia, etc are the major drawbacks of these class of drugs. Altering the metal centre could alter the accumulation, biomolecular interaction leading to an altered cell death. Hence, we plan to explore the non-platinum-based drug candidates for its anticancer properties. Low valent Re-complexes are routinely used for in vitro and in vivo imaging purposes. In recent decade, despite only a few  low valent Re complexes were reported to show excellent anticancer and antibacterial properties, a Re(V) complex was reported to induce necroptosis mode of cell death. Thus, we are interested in high valent Rhenium complexes, hypothesising that the complex will be activated by reduction only under reducing cellular environment and thereby reducing the side effects.

 

With the aim of finding structurally new class of compounds with superior potency than cisplatin, we have succeeded to synthesise to new class of Re(VII) and Re(V) coordination complexes. Both of these classes were designed to have labile and non-labile similar to cisplatin.

 

April 20, 2021 at 5.00 pm (Via Zoom)

Title :

Ultrastable organic fluorophores for single-molecule research: part II

Abstract :

Single-molecule Förster resonance energy transfer (smFRET) imaging is an integral tool for examining conformational and compositional processes critical to the functions of biological systems. Robustness of smFRET imaging and reproducibility of smFRET efficiencies are increased through photostabilization of fluorophores, state-of-the-art instrumentation, data analysis, and stringent data correction procedures [1,2]. Here, we report that small molecule photostabilizing agents in imaging buffers are although important for photostabilization of fluorophores, they can be bottlenecks for quantitative smFRET imaging due to their varied photophysical and photochemical impacts on fluorophores. To mitigate these problems, we provide a simple strategy of using ‘self-healing’ organic fluorophores that are intramolecularly photostabilized by cyclooctatetraene (COT) as a triplet state quencher. COT-mediated self-healing mechanism enables robust determination of true smFRET efficiency of organic fluorophores on both nucleic acids and proteins in oxygenated as well as in deoxygenated imaging buffers. These findings conceptually advance our understanding of smFRET and provide strategies for robust, quantitative smFRET imaging [3].

[1] Hellenkamp et al., Nat. Methods, 15, 669–676 (2018).

[2] Lerner et al., eLife, 10:e60416 (2021).

 

[3] Pati et al., manuscript to be submitted.