Postdoctoral work
My primary research interest is to illustrate the excited-state properties of organic chromophores using theoretical and computational approaches, where I mainly focused on multireference methodologies. My interests include the characterization and tuning of excited-state energies using chemical modifications to singlet exciton fission, thermally activated delayed fluorescent (TADF), as well as symmetry-breaking charge separation (SBCS) chromophores. Some highlights are:
In this collaborative work with Prof. Apurba L. Koner, we intend to provide a theoretical explanation for the symmetry-breaking charge separation (SBCS) in regioisomers of perylene monoimide. The Kasha-like Coulombic coupling between the monomers is where we have begun, and it is mostly reliant on the transition electric dipole moment. The complexes under study exhibit non-traditional behavior for the Kasha model, meaning that when the transition dipole moment increases, the Coulombic coupling diminishes. Frenkel-CT mixing provided an explanation for the unusual behavior. When the torsional angle drops, there is a noticeable shift in the CT coupling. The solvent polarity breaks down the adiabaticity of the state and simplifies the Frenkel-CT mixing in the excited state. As a result, the fluorescence lifespan decreases, leading to an ultrafast SBCS [Chem. Sci., 2024, 15, 6363-6377].
The linear polarizabilities (α) and second hyperpolarizabilities (γ) of unsubstituted azobenzenes and push-pull azobenzene derivatives are calculated using a variety of standard exchange–correlation functionals and a non-empirically tuned long-range corrected (LC) functional with range-separated exchange. The improvements of the CT excitation energies do not clearly correlate with improvements of γ toward the CC reference data because the dynamic electron correlation is important for this property. To describe a charge transfer state, computational approaches—more especially, methods for optimal tuning of an LC functional with regard to a particular chromophore—are crucial [Phys. Chem. Chem. Phys., 2018, 20, 7303-7316].
By chemical modification of pentacene dimers, it is possible to adjust the pathway of multiexciton (ME) state generation in singlet fission [J. Chem. Theory Comput. 2019, 15, 9, 5014–5023 (Link)] as well as to the push-pull naphthalenediimide dimer, as shown in a collaborative work with Professors Jotishman Dasgupta and Pritam Mukhopadhyay [Chem. Sci., 2022, 13, 11506-11512 (Link)].
Intermolecular stacking modulates reverse intersystem crossing (RISC) in the TADF of 10-anthryl-9-phosphoanthracene chromophore [J. Phys. Chem. A 2020, 124, 11025–11037 (Link)] and conformational tuning of the donor part modulates RISC in phenothiazine-quinoline conjugate, as discussed in collaboration work with Prof. Debdas Ray [J. Phys. Chem. B 2023, 127, 9833–9840 (Link)].
The arcus inverted region plays an important role in singlet-oxygen photosensitizers because it suppresses the RISC and helps to harvest the energy of triplet excitons [J. Chem. Phys. 2024, 160, 164720 (Link)]. Furthermore, in collaborative work with Prof. Suhrit Ghosh, a strategy for a redox-activatable heavy-atom-free photosensitizer (PS) was proposed based on thiolated naphthalimide [ACS Macro Lett. 2023, 12, 928−934 (Link)], and pH-triggered activable phototoxicity was also discussed for a thionated acceptor–donor–acceptor conjugated photosensitizer [Angew. Chem. Int. Ed., 2026, e25481 (Link)].
Ph.D.
A correct description of the magnetic exchange coupling constant (J) in organic radicals was taken as a problem in my PhD thesis.
For example, we have shown that the Heisenberg coupling constants are modest enough to create a ferrimagnetically coupled linkage in Calix[4]arene-based organic spinglass [J. Phys. Chem. C 2014, 118, 27599–27610].