Vandana Tiwari

All Publications

• Intermolecular Interactions in Crystals Modulate Intramolecular Excited State Proton Transfer Reactions. The journal of physical chemistry. B Hwang, H., Mackenzie, A., Kochman, M. A., Gallagher-Jones, M., Tiwari, V., Bittmann, S. F., Tellkamp, F., Botchway, S., Kirkland, A. I., Duan, H., Miller, R. J., Jha, A. 2025

  Abstract

  Proton transfer is a fundamental process underlying chemical and biological phenomena, and its dynamics are significantly influenced by the surrounding environment. This paper studies the excited state intramolecular proton transfer (ESIPT) process, which is crucial to the photostability of hydroxyanthraquinone-based pigments through efficient energy dissipation, by investigating how crystalline packing influences photoinduced proton transfer dynamics in single crystals of dihydroxyanthraquinone (DHAQ) constitutional isomers. Comparing the proton transfer dynamics in crystalline and solution phases, we show substantial differences due to the crystalline environment, particularly in the 1,4- and 1,5-DHAQ isomers. These isomers show intermolecular hydrogen bonding within the crystal lattice, resulting in larger excitonic couplings, which significantly alters their reaction pathways compared to their behavior in solution. We show that 1,8-DHAQ, which does not form intermolecular hydrogen bonds in the crystal, shows minimal changes in dynamics between the phases. In contrast, in the case of 1,4-DHAQ, intermolecular interactions within the molecular crystal phase open up an ESIPT relaxation channel, which is not observed in the solution phase. These findings highlight the critical role of crystal packing in modulating proton transfer dynamics and offer insights into how molecular packing can be strategically manipulated to control and optimize reaction pathways in solid-state environments.

  View details for DOI 10.1021/acs.jpcb.5c03855

  View details for PubMedID 40717365

• Crystal Lattice-Induced Stress modulates Photoinduced Jahn-Teller Distortion Dynamics ACS PHYSICAL CHEMISTRY AU Tiwari, V., Gallagher-Jones, M., Hwang, H., Duan, H., Kirkland, A. I., Miller, R., Jha, A. 2024

  View details for DOI 10.1021/acsphyschemau.4c00047

  View details for Web of Science ID 001327117700001

• Intermolecular vibrations mediate ultrafast singlet fission. Science advances Duan, H. G., Jha, A. n., Li, X. n., Tiwari, V. n., Ye, H. n., Nayak, P. K., Zhu, X. L., Li, Z. n., Martinez, T. J., Thorwart, M. n., Miller, R. J. 2020; 6 (38)

  Abstract

  Singlet fission is a spin-allowed exciton multiplication process in organic semiconductors that converts one spin-singlet exciton to two triplet excitons. It offers the potential to enhance solar energy conversion by circumventing the Shockley-Queisser limit on efficiency. We study the primary steps of singlet fission in a pentacene film by using a combination of TG and 2D electronic spectroscopy complemented by quantum chemical and nonadiabatic dynamics calculations. We show that the coherent vibrational dynamics induces the ultrafast transition from the singlet excited electronic state to the triplet-pair state via a degeneracy of potential energy surfaces, i.e., a multidimensional conical intersection. Significant vibronic coupling of the electronic wave packet to a few key intermolecular rocking modes in the low-frequency region connect the excited singlet and triplet-pair states. Along with high-frequency local vibrations acting as tuning modes, they open a new channel for the ultrafast exciton transfer through the resulting conical intersection.

  View details for DOI 10.1126/sciadv.abb0052

  View details for PubMedID 32948583