Condensed Phase Dynamics Group
Experimental work
Illustrations
Key Questions
Effect of local environment on motion of molecular aggregates:
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Effect of local environment on motion of molecular aggregates:
In recent years, excitonic energy transfer and dynamics within molecular aggregates have gained high interest as they mimic pigment assemblies within photosynthetic complexes. In molecular aggregates, excitonic interaction results from electronic coupling between monomers which depends on the arrangement of transition dipole moments leading to formation of J- and H-aggregates.
How one can control the rate of energy transfer within these aggregates by controlling external parameters, like, pH or viscosity of the medium?
Coherent effects in solvation:
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In condensed phase the solvent, without being just a mere spectator, dynamically controls the rates of many fundamental reactions (for example, electron transfer) at ultrafast time scale. The coordinated motion of solvents leads to population relaxation of the probe solute at various time scales. For solvation in bulk water, a substantial part of early time (<1 ps) solvation dynamics completes within <200 fs and hence is un-accessed by fluorescence-based techniques with hundreds of picoseconds resolution. This <200 fs component accounts for more than 50% of early time solvation and mediated via inertial solvent response. In recent times, focus has been made to explore the specific energy relaxation pathways associated with this component and the need of defining spectrum at time zero.
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Can we probe early time ultrafast solvation dynamics using femtosecond pump-probe and two-dimensional electronic spectroscopy?
See our recent work on solvation dynamics probed by xanthenes dyes:
Chemical Physics Letters (Frontiers Article)
Ultrafast energy transfer dynamics within photovoltaic materials:
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Following the introduction of expensive silicon-based solar cells utilized in spacecrafts in 1960's, low-cost dye-sensitized solar cells and organic/inorganic thin-film/bulk hetero-junction solar cells have been developed for past few decades. However the sensitivity of these inexpensive solar cells has so far been quite low (~10%) compared with natural light-harvesting systems. Using ultrafast two-dimensional coherent spectroscopy, we are interested in understanding energy and charge transfer dynamics within these novel synthetic complexes.
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What are the dynamical bottle-necks in solar cells? and Does (quantum) coherence has any role in artificial analogs?
Stable trapping of single molecules in solution:
Recent experiments on electrostatically trapped single pigment-protein complex in solution have revealed the role of slow conformational motion on ultrafast energy transfer. In single molecule manipulation, a micron sized spherical plastic bead is tethered to the (macro)molecule and this bead is trapped so that the forces exerted on the bead can be measured and the process be observed in bright-field video microscopy. The challenge for directly trapping a single (macro)molecule or a dielectric nanoparticle is due to erractic Brownian motion as well as low polarizability. It was speculated that using femtosecond laser excitation smaller particles may be trapped more efficiently.
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By harnessing optical nonlinearity, can we directly trap individual single macromolecules in solution without attaching them to a bead?
Structural dynamics in photoswitchable fluorescent proteins:
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Light harvesting in photosynthetic systems involves excitation energy transfer on ultrafast timescales. Any photosynthetic system adapts to varying sunlight conditions through photoswitching. Photoswitching involves photoinduced slow (micro- to milli-seconds) conformational changes that result in switching between bright and dark states. Such light induced conformational changes were shown to occur within photosynthetic pigment-protein complexes as well as within fluorescent proteins. We wish to map the potential energy surface (PES) across the family of fluorescent proteins and study structural dynamics in photoswitchable/photoactivable fluorescent proteins.
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How slow processes (conformational changes) affect the ultrafast processes ?
What is the molecular-level mechanism of photosynthetic (or rather, photoprotective) role of FPs?
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See our recent work on excited state dynamics of a yellow fluorescent protein variant:
Spatial beam shaping of femtosecond pulsed laser using Spatial Light Modulator:
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In recent years, the laser beam shaping has been of great interest due to its applications in the industries and different fields of research. Nowadays, the spatial beam shaping of a pulsed laser is the most concerned topic of study in the field of photonics.
•We wish to study the spatial beam shaping of femtosecond pulsed laser using a Spatial Light Modulator (SLM).
•We will also study the optical force/potential in an optical trap by coupling the beam shaping setup with the optical tweezer setup.
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Can the propagation of the pulsed Bessel/Laguerre Gaussian beam differ from a pulsed Gaussian beam?
Will the spatial properties change on the beam shaping of pulsed laser?
How the force/potential will behave in optical tweezer on using a shaped pulse beam?
Controlling chemical reactions using pulse shaper:
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In recent years coherent control has earned high scientific interest as it has applications far beyond chemistry (high harmonic generation etc.). In the case of manipulating chemical reactions, the question arises whether certain chemical products can be generated with high efficiency simultaneously reducing unwanted side products. Pulse shaping aids most to explore such controlling events. It is an important technology used as an experimental tool with computer controlled feedback (adaptive) algorithm to generate preferred (tailored) laser pulses in femtoseconds time scale.
We are interested in coherent control of different molecular systems in condensed phase in both the high (strong field) and low (weak field) intensity regimes. We use externally controlled pulse shaper (Dazzler) combined with our pump-probe or 2DES setup.
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