The Dasgupta Research Group @ TIFR

Ultrafast Biophysics and Photomaterials Group

Chemistry with a "Non-local" Perspective!

We are a young and dynamic group interested in deciphering chemical reaction mechanisms of photoinduced reactions specifically at the interface of chemistry and biology with emphasis on the "Energy Problem". Half of the group designs novel ultrafast and structure-sensitive experiments with the aim of understanding collective motions in variety of molecular/biomolecular systems, while the other half is involved in designing novel molecular photomaterials with high fault-tolerence and robustness.

 

NEWS FLASH!!

 

New Mechanism invoked for Intramolecular Singlet Fission in Pentacene Dimers

 

 

Singlet Fission is a process by which two triplets are generated upon one photon absorption event. Using a specifically designed pentacene dimer pair which is covalently linked with a diketopyrrolopyrrole (DPP) chromophore, we demonstrate that spin density localization governs the intramolecular Singlet Fission rates. The multiexcitonic nature of the Singlet state in such a bepentacene system could be tuned via electronic delocalization through the variation in DPP-bridges. The iSF process was blocked in both thiophene and Selenophene derivatives while a less delocalized phenyl system optimally provided an access to the T-T pair state.

The paper has appeared in Nature Communications on 3rd January 2019!

Nature Communications 2019

Congratulations to Krishnapriya, Palas Roy, Boregowda Puttaraju, Ulrike, Andrew Musser and Satish Patil. This work was acollaborative effort with IISc colleagues (Satish Patil and group), Bilkent University (Ulrike Salzner) and University of Sheffield (Andrew Musser) 

 

 Transient Raman snapshots of the exciton in donor-pi-acceptor polymers: pi-Bridge torsion gates the formation of ICT state! 

 

 

 

Exciton dynamics in donor-pi-acceptor polymers is critical to charge generation in organic photovoltaics. Here we probed the structural elements that lead to generation of the intramolecular charge transfer (ICT) state within the backbone. Femtosecond stimulated Raman spectroscopy provided a glimpse of the pi-bridge torsion which gates the formation of the CT state. Clear Raman signatures of the high frequency C=C stretch features were elucidated which could be interpreted as hot ICT formation in ~400 fs and localized ICT in few picoseconds!

The paper came out in Nature Communications in November 2017. 

Nature Communications 2017

Congratulations to Palas Roy, Ajay Jha, Vineeth Benyamin...especially since all your hardwork in setting up the FSRS system in TIFR paid off! We would also like to thank our material collaborators Boregowda Puttaraju and Satish Patil from IISc Bangalore. 

 

 

Modulating the Aggregation Landscape of a Phe-Phe dipeptide using a Azobenzene Photoswitch!

 

 

 

Synthetic control of peptide-based supramolecular assemblies can provide molecular cues to understand protein aggregation while also inspiring the development of novel chemical biology tools to deliver cargoes inside cells. Here we show that the trans-to-cis photoisomerization of a pendant azo-group covalently attached to a Phe–Phe dipeptide can comprehensively ‘turn-off’ its native fibrillation propensity as well as provide an optical handle to reversibly switch the aggregate morphology from fibril to vesicle.

This work appeared in Chemical Communications in June 2017!

 ChemComm 2017

Congratulations to Melby Johny, K. Vijayalakshmi, Aseem Mishra, Ankita Das and Palas Roy! This was a wonderful collaboration with Aseem! And also special mention to Vijayalakshmi for making SERS a tool in the lab. 

 

 

 Experimental Evidence for Solvent-dependent Ternary Phase in Polymer:Fullerene mixtures of BHJ solar cells

 

 

 

We have now provided an elegant demonstration of the hypothesized solvent dependent ternary phase responsible for controlling the nano-morphology of spin-casted films for BHJ solar cells. Nanoscopy through the perspective of exciton diffusion and polaron generation timescales, provide us an unequivocal evidence for nanometric sized seed domains that are solvent dependent during the spin casting process. CONGRATULATIONS to Palas Roy and Ajay Jha!

The paper was accepted in Nanoscale, an RSC journal. The link for the paper is here:

 

 Nanoscale2016

 This paper was selected in the New Frontiers in Indian Research Issue in 2016!

 

 Dynamic Water Interaction Timescales around Nanocages Deciphered

 

 

 

 We elucidate the timescale of water interaction and dynamics around the metal-organic nanocages. Our work provides the basis for optimizing confined organic photochemistry within supramoleular nanocavities. Our new paper came out in Journal of Physical Chemistry C for the month of June 2015. Please read the full article here:

 http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b06628

Congratulations to Ankita, Ajay and Rahul!! Way to go!

 

Ultrafast Triplet Generation for Prolycopene in solution

 

 Abstract Image

 

We demonstrate the generation of reactive triplets in prolycopene on an ultrafast timescale. This state forms the basis for lycopene formation with high quantum yield of 0.58 if triplet sensitization is carried out through porphyrin sensitizer. Our new paper came out yesterday and is already in Top 20 most downloaded in Journal of Physical Chemistry B for June 2015. Please read the full article here:

http://pubs.acs.org/doi/abs/10.1021/acs.jpcb.5b02086

Congrats Vijayalakshmi and Ajay!

 

Heterogeneity in Polymer-TiO2 interactions

 

 Abstract Image

 

A detailed excited state description of the electron transfer process in DPP-based polymer-TiO2  films reveals instrument response function (IRF) limited (<110 fs) charge injection from a minor polymer fraction followed by a picosecond recombination. The major fraction of photoexcited polymers, however, does not show injection indicating pronounced ground state heterogeneity induced due to nonspecific polymer–TiO2 interactions. Our work therefore underscores the importance of gathering molecular-level insight into the competitive pathways of ultrafast charge generation along with probing the chemical heterogeneity at the nanoscale within the polymer–TiO2 films for optimizing photovoltaic device efficiencies. Our paper was in the TOP 20 downloaded papers in Journal of Physical Chemistry B for the month of November-Decemeber 2014.

Read our paper at: http://pubs.acs.org/doi/abs/10.1021/jp510733k

 Congrats to Ajay, Vineeth, Hadiya, Satish and Catherine!

 

Light-induced PCET inside a Nanocage

 

 Abstract Image

 

We demonstrate the fastest H-abstraction step using the sequential proton-coupled electron transfer (PCET) event using host-guest CT excitations. Our work lays the basic ground work for envisioning photodriven catalysis in the visible in confined systems and through energy efficient Singlet states. To read this communication that got published in the Journal of the American Chemical Society, follow this llink:

http://pubs.acs.org/doi/abs/10.1021/ja509761a

Congrats to Rahul, Ankita and Ajay!

 

 Normal mode engineering

 

Our first research paper stressing the importance of low-frequency dynamics in molecular structures got accepted in Journal of Physical Chemistry B and can be found through this link: Our paper

Congrats to Ajay Jha and Debayan Chakraborty for putting together a solid piece of work!!! In future we plan to extend our work to incorporate the "Normal Mode Engineering" concept in many new supramolecular structures.

Our paper is currently the TOP 20 downloaded papers in Journal of Physical Chemistry B for the month of September-October. See the link: Top 20 in JPCB


POSITIONS AVAILABLE

We currently looking for a highly motivated and talented POSTDOC with background in either Physics, Chemistry or Biology willing to take up challenging problems and participating in a highly interdisciplinary work. Background in optics and electronics will be a plus. If you think you are a good fit, send your CV, 3 letters of recommendation and your proposed area of work to Dr. Jyotishman Dasgupta (dasgupta-AT-tifr.res.in)

Interested PhD students should come through the regular TIFR entrance examination held annually in December. For further information see:

TIFR Entrance Examination

Positions are available for Junior Research Fellows (JRF) to join our group. These are usually based on departmental vacancy. At this time we are looking for one JRF to join the group.

If you are an undergraduate student with an interest in our program call us or email Dr. Dasgupta.

 

OUR Contact Address:

Dr. Jyotishman Dasgupta

Room: B-127, B-block 1st Floor

Department of Chemical Sciences,

Tata Institute of Fundamental Research,

 Mumbai, 400005, INDIA

Phone: 91-22-2278-2383

Email: dasgupta-AT-tifr.res.in