Optimizing the light trapping process and subsequent charge separation chemistry is at the heart of engineering efficient photon-conversion devices and discovering new photocatalysts. We have taken a two-pronged approach towards this problem:
1) New Materials for Charge Generation: Using time-resolved spectroscopy we have established that anthraquinones are potent materials for carrying out barrierless ultrafast charge transfer reactions, and tailored them in correct geometry to host long-lived charge separated states through delocalization.
2) Probing Interfaces in Organic Solar Cells: We have used charge transfer (CT) reactivity to probe the functional donor-acceptor (D-A) interfaces in polymer-based organic solar cells. Through the analysis of the CT reaction rates, we have selectively identified reactive polymer domains in bulk solution and at the nanoparticle surface for the first time. Our work motivates chemical tailoring of D-A interfaces within solution state for device optimization of organic solar cells.
A. Jha, D. Chakraborty, V. Srinivasan*, and J. Dasgupta*, “Photoinduced Charge Transfer in Solvated Anthraquinones is Facilitated by Low-frequency Ring Deformations”, J. Phys. Chem. B, (2013) 117, 12276–12285.
A. Jha, V. Benyamin, H. Jasbeer, C. Kanimozhi, S. Patil and J. Dasgupta*, “Heterogeneity in Dye-TiO2 Interactions Dictate Charge Transfer Efficiencies for Diketopyrrolopyrrole-Based Polymer Sensitized Solar Cells”; J. Phys. Chem. C (2014), 118, 29650−29662.
P. Roy, A. Jha, and J. Dasgupta*, “Photoinduced Charge Generation Rates in Soluble P3HT:PCBM Nano-aggregates Predict the Solvent-Dependent Film Morphology ”; Nanoscale (2016),8, 2768-2777.
Visible Light Photochemistry inside Nanocages
Host-Guest CT mediated Reactions: Combining the idea of generating optically allowed delocalized hot-guest CT states with the reactive confinement provided by molecular cages, we have pioneered a new photochemical strategy to execute visible light mediated organic photochemistry. Using a well-defined metal-organic nanocage as a delocalized electron acceptor, we have formulated an efficient chemical scheme to carry out ultrafast hydrogen abstraction reactions from organic substrates in water. The method highlights the first use of singlet excited states to trigger efficient atom transfer reactions.
R. Gera, A. Das, A. Jha and J. Dasgupta*, “Light-Induced Proton-Coupled Electron Transfer Inside a Nanocage”; J. Am. Chem. Soc. (2014), 136, 15909–15912 *corresponding author
A. Das, A. Jha, R. Gera and J. Dasgupta*, “Photoinduced Charge Transfer State Probes the Dynamic Water Interaction around Metal-Organic Nanocages”; J. Phys. Chem. C (2015), ASAP.
A. Das, I. Mandal, R. Venkatramani and J. Dasgupta*; “Ultrafast Photoactivation of C-H Bonds inside Water-Soluble Nanocages”, Science Advances (2019) in press *corresponding author
Enzyme Driven Chemistry of Large pi-conjugated Molecules
Carotenoid Metabolism: Enzymes can remodel the ground state reactivity of large conjugated organic substrates by controlling the local protein-substrate interactions and slow conformational fluctuations. We are currently working to understand the metabolic regulation of carotenoid lycopene in photosynthetic organisms by the enzyme CRTISO. We recently demonstrated the existence of a competing light-dependent pathway for efficient generation of lycopene through triplet sensitization.
K. Vijayalakshmi, A. Jha and J. Dasgupta*, “Ultrafast Triplet Generation and its Sensitization Drives Efficient Photoisomerization of tetra-cis-lycopene to all-trans-lycopene” J. Phys. Chem. B (2015), 119, 8669–8678.
M Johny, K Vijayalakshmi, A Das, P Roy, A Mishra and J. Dasgupta*,"Modulating the Phe-Phe dipeptide aggregation landscape via covalent attachment of an azobenzene photoswitch", Chemical Communications (2017) 53, 9348-9351. *corresponding author