Chirality or the handeness is ubiquitous in Nature. Almost all biomolecules are chiral, and biomolecular functions such as protein-drug binding and enzymatic catalysis are strongly influenced by molecular chirality. Several modern emerging research thrusts in materials chemistry engage chiral nanomaterials and chiral plasmonics for efficient solar light harvesting, enantioselective photocatalysis, and spin-based devices. The overarching aim of our research group is to probe femtosecond chiral-optical and related magneto-optical dynamics in the excited-state and leverage it to address pressing challenges related to solar harvesting, quantum spintronics, and biomolecular functions.
Our work is primarily motivated by two simple questions: (i) How does excited state chirality influence ultrafast photochemistry and photophysics? (ii) Can we take advantage of ultrafast chirality to improve functional property of a system?
Chiral Photochemistry and Photophysics: Femtosecond Circular Dichroism spectroscopy
Among different types of spectroscopic methods, circular dichroism spectroscopy (CD) stands out for its unique sensitivity to chiral-optical and magneto-optical interactions through light polarization. This makes femtosecond circular dichroism spectroscopy an ideal technique to probe ultrafast electronic structural dynamics and spin depolarization dynamics in excited states. We are currently developing and employing novel techniques for highly sensitive measurements of broadband time-resolved circular dichroism in excited electronic states of molecules and materials. The application of ultrafast CD spectroscopy, we envision, will open new vistas in the area of chiral femtochemistry, femtosecond structural biology and understanding chiroptical dynamics in advanced materials.
Quantum Spintronics: Ultrafast Magneto-Optical and Spin Dynamics in Advanced Materials
Due to strong spin-orbit coupling, advanced materials such as perovskites, transition metal dichalcogenides and their heterostructures exhibit the potential to store quantum information in individual electrons that may hold the key to the next generation of quantum computers and quantum communication. Understanding the spin or valley-dependent photophysics of different photoexcited species like carriers and excitons in these materials is important to optimize their function. To this goal, we employ ultrafast CD spectroscopy and related polarization-resolved ultrafast spectroscopy to study their spin, valley and magnetization dynamics. These studies aim to shed new light on their spin or valley-dependent photophysics and will provide the necessary design principles to develop spintronics materials with long spin lifetimes.
Instrumentation: Development of Novel Chiroptical Spectroscopy Techniques
A complete understanding of structure-dynamics-property correlations would require following the structural dynamics of (bio)-molecules and materials from the shortest time onwards, ideally with femtosecond time-resolution. This is hindered, however, by the structural-temporal gap that exists in the field of optical spectroscopy. An important part of our research effort is directed towards diminishing the gap through the development of novel chiroptical techniques which simultaneously provide high temporal resolution and structural sensitivity. This involves pushing the current chiroptical techniques such as time-resolved Circular Dichroism (CD), Circularly Polarized Luminescence (CPL), Raman Optical Activity (ROA) beyond state-of-the-art.