BITS Faculty Publications

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Author: search.filters.author.Ghosh, SarbaniSubject: search.filters.subject.Chemical engineering

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    Computational design of isomeric naphthalenediimide–naphthodithiophene (NDI–NDT) copolymers for organic electronics
    (ACS, 2025-09) Garg, Mohit; Ghosh, Sarbani
    This study presents a comprehensive investigation of conjugated donor–acceptor (D–A) copolymers based on naphthalenediimide (NDI) and two structural isomers of naphthodithiophene (NDT), i.e., linear (L-NDT) and angular (A-NDT), designated as NDI–L-NDT and NDI–A-NDT, respectively. By systematically analyzing their molecular structure, (opto)electronic properties, photovoltaic performance, morphological analysis, and mechanical stability, this study reveals the profound influence of donor isomerism on material properties, relevant to organic electronic applications. In particular, NDI–L-NDT exhibits a lower bandgap attributed to its extended donor π-conjugation and nearly coplanar D–A conformation compared to NDI–A-NDT. NDI–A-NDT demonstrates superior photovoltaic performance due to its higher power conversion efficiency compared to its linear counterpart. Morphological studies based on molecular dynamics simulations reveal that films of both copolymers exhibit similar levels of crystallinity. However, NDI–L-NDT possesses greater thermal stability and mechanical flexibility, capable of withstanding up to 100% strain without cracking, attributed to its dynamic conformational adaptability, making it a promising candidate for flexible electronic applications. This work reveals the potential of structural isomerism in fine-tuning D–A copolymers for multifunctional roles, as donors, acceptors, or single-component materials in next-generation organic electronic devices.
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    Electrochemical doping for absorption and conductivity tuning of p(NDI2OD-T2) films
    (ACS, 2025-04) Ghosh, Sarbani
    Electrochemical doping of thin films of poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)) is shown as straightforward method to achieve different degrees of doping both during in situ electrochemical experiments as well as in the solid state. Results obtained from cyclic voltammetry and absorption spectroscopy upon reduction can be explained by the presence of the neutral state as well as polaron and bipolaron species, including neutral/polaron and polaron/bipolaron mixed valence states. The UV-vis-NIR spectra are analyzed and explained based on the calculated electronic structure and the corresponding transitions between different states, this includes features such as numbers and positions of the peaks and their evolution during reduction. Most intruingly, doped films are stable after transfer in the solid state, as evidenced by absorption spectroscopy. Conductivity measurements of films with different degrees of doping show a bell-shaped conductivity profile, which underlines the classification of P(NDI2OD-T2) as a conjugated redox polymer with mixed valence transport. Maximum conductivities of up to 2 × 10−4 S cm−1 are obtained at intermediate doping levels under the coexistence of neutral state and polarons. Conductivity measurements of blade-coated films point to anisotropic charge transport with the highest charge transport along the blade /polymer chain direction and an anisotropic conductivity ratio of 4.1.
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    Theoretical investigation of electronic and optical properties of ndi-fused-bithiophene (NDI-f-BT) copolymer at different redox states for single-component ambipolar transistors
    (ACS, 2025-05) Ghosh, Sarbani; Garg, Mohit
    Naphthalene diimide (NDI) copolymerized with thiophene-based donor moieties has the potential to be used as an ambipolar conducting polymer to transport both charge carriers, viz, electrons and holes, at different redox states. The p-type conductivity in these copolymers is not up to the mark compared to the n-type conductivity, and there is scope for improvement by strategically modifying the donor moieties. So, replacing the nonfused thiophene donor moieties with fused thiophene moieties can lead to an increase in the π-conjugation length, which can improve the p-type electronic and optical properties. Here, we have studied the electronic and optical properties of the NDI-fused-bithiophene (NDI-f-BT) donor–acceptor polymer and their evolution at different redox states (up to 200% redox levels) using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The electron affinity and ionization potential of NDI-f-BT, considering the first redox states, are compared with the experimentally reported lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), respectively, measured through electrochemical switching, and they are in good agreement. We note that the TD-DFT calculated optical properties of NDI-f-BT are qualitatively in agreement with the experimental findings and can be used to understand the changes in optical properties during oxidation and reduction. The absorption spectra indicate a red shift up to the 100% redox state, indicating that NDI-f-BT has a good potential to be used in an ambipolar field effect transistor. We also observed the chemical alteration of the donor moieties beyond 100% oxidation level, which leads to an increase in the π-conjugation length to accommodate the bipolaron. This finding indicates that increasing the π-conjugation length can be a strategy to have a balanced p-type conductivity compared to that of the n-type, aiming for ambipolar conductivity of the donor–acceptor copolymer.
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    Recent trends in nanotechnology for sustainable living and environment:
    (Springer, 2023) Roy, Banasri; Ghosh, Sarbani; Etika, Krishna Chitanya
    This book presents the select proceedings of International Conference on Nanotechnology for Sustainable Living and Environment (ICON-NSLE 2022). It covers the latest trends in nanotechnology and its applications in various sectors such as energy, environment, food technology, and biomedicine. Various topics covered in this book are nanomaterial preparation and characterization, nanobiotechnology, nanodevices, waste to wealth, pollution abatement, renewable energy, advanced materials, sensors and portable electronics, biomedical applications, food preservation, etc. This book is useful for researchers and professionals working in the area of nanotechnology and environment sustainability.