About

Raja Ghosh is an Assistant Professor in the Department of Chemistry at NC State University. His research focuses on areas including computational and theoretical chemistry, with particular interest in the design and investigation of organic frameworks, charge transport in conjugated systems, and the electronic properties of functionalized materials. His work involves the use of advanced computational techniques to explore defect-driven polaron localization, intermolecular interactions, and the tuning of stacking and electronic properties in two-dimensional covalent organic frameworks. Ghosh has contributed to the understanding of paramagnetic spin centers in metal-free organic frameworks and the role of molecular structure in charge transport, advancing the field of materials chemistry through his research.

Research topics

• Chemistry
• Physics
• Chemical physics
• Thermodynamics
• Materials science
• Condensed matter physics
• Nanotechnology
• Composite material
• Quantum mechanics
• Optoelectronics
• Biological system
• Organic chemistry
• Computational chemistry

Selected publications

• Defect-Driven Polaron Localization in π-Conjugated Systems: The Role of Spatial Correlation and Coulomb Binding

  Journal of Chemical Theory and Computation · 2025-10-23

  articleSenior authorCorresponding

  Defect engineering offers a powerful strategy to modulate polaron delocalization in π-conjugated materials; however, the complex interplay between different types of defects and dopant-induced Coulomb binding remains insufficiently understood. Here, we present a comprehensive theoretical investigation of hole-polaron transport using a Holstein-style Hamiltonian applied to π-conjugated lattices such as polymers and covalent organic frameworks (COFs) that incorporate vacancy and linker defects, a disorder framework encompassing distributions of disordered sites, and dopant-induced Coulomb binding effects. Simulated mid-infrared signatures and polaron coherence numbers uncover distinct and nuanced behaviors, revealing how the spatial correlation (random vs correlated) of different defect types governs polaron delocalization pathways. While dopant counterions strongly localize polarons, their precise positioning relative to crystalline versus disordered domains critically modulates transport efficiency. To establish experimental relevance, we compare our simulations with polarized intrachain and interchain mid-infrared spectra of doped P3HT films, providing fundamental insights into how specific dopant-polymer configurations give rise to anisotropic spectroscopic signatures and their direct correlation with anisotropic polaron transport. The strong agreement between theory and experiment validates our predictions and establishes guiding principles for optimizing polaron transport in disordered π-conjugated materials.

  PublisherDOI

• AI-guided high-throughput investigation of conjugated polymer doping reveals importance of local polymer order and dopant-polymer separation

  Matter · 2025-10-09 · 1 citations

  article
  PublisherDOI

• Engineering Paramagnetic Spin Centers in Metal-Free Organic Frameworks

  ChemRxiv · 2025-08-25

  articleOpen accessSenior author

  Tuning the density of paramagnetic spin centers (PSCs) in π-conjugated systems en- ables coherent quantum dynamics, controllable magnetism, and molecular spin qubits, thereby opening new frontiers in molecular-scale quantum technologies. We investi- gate the fundamental mechanisms governing spin pairing and PSC concentration in sp2-carbon-conjugated polymeric systems using a Hubbard-style Hamiltonian, mod- ified to incorporate electrostatic interactions and static defects, in combination with combinatorial analysis and Monte Carlo simulations. By analyzing linear polymers, 2D Lieb-type monolayers, and π-stacked Lieb structures, we elucidate how the interplay of various quantum-mechanical interactions such as spin–spin repulsion, spin–anion attraction, and anion–anion repulsion along with structural features such as 2D π- connectivity, building-block design, and pore size, collectively influence the propensity for spin-paired bipolaron formation and, consequently, the concentration of PSCs. Our results reveal that π-stacked 2D organic frameworks intrinsically suppress spin pairing, thereby facilitating enhanced PSC densities compared to monolayers and linear poly- mers consistent with experimental observations. Building upon good agreement with experiments, we identify key design principles that provide experimentally actionable guidelines for engineering high-spin-density organic materials and lay the foundation for the rational design of metal-free magnets and spin-active semiconductors for next- generation organic spintronics and quantum information technologies.

  PublisherOA PDFDOI

• Engineering Paramagnetic Spin Centers in Metal-Free Organic Frameworks

  ChemRxiv · 2025-07-21

  preprintOpen accessSenior author

  We investigate the fundamental mechanisms governing spin pairing and the formation of paramagnetic spin centers (PSCs) in fully carbon-conjugated 1D and 2D polymeric systems using a modified Hubbard Hamiltonian combined with combinatorial analysis and Monte Carlo simulations. By analyzing 1D polymer chains, single-layer Lieb lattices, and pi-stacked Lieb structures, we reveal how specific quantum-mechanical interactions and structural factors dictate the propensity for spin-paired bipolaron formation. Our results show that pi-stacked architectures intrinsically suppress spin pairing, leading to enhanced PSC concentrations, in excellent agreement with recent experimental observations. Furthermore, we identify key design parameters—including counterion proximity, pore size, building-block chemistry, and disorder tolerance—that collectively control PSC densities in organic frameworks. These insights provide experimentally relevant guidelines for engineering high-spin-density organic systems and pave the way for the rational design of metal-free magnets and spin-active semiconductors for next-generation spintronic and quantum information technologies.

  PublisherOA PDFDOI

• Defect-Driven Polaron Localization in π-Conjugated Systems: The Role of Spatial Correlation and Coulomb Binding

  ChemRxiv · 2025-07-22

  preprintOpen accessSenior author

  Defect engineering is a powerful strategy to tune polaron delocalization in π-conjugated materials; however, the intricate interplay between spatially correlated defects, amorphous–crystalline heterogeneity, and dopant-induced Coulomb binding needs a more detailed analysis. Here, we present a comprehensive theoretical investigation of hole-polaron transport using a Holstein-style Hamiltonian in two-dimensional π-conjugated lattices incorporating vacancy and linker defects, binary disorder, and Coulomb binding. Simulated mid-infrared signatures and polaron coherence numbers reveal that correlated vacancies preserve extended polaron delocalization, whereas random vacancies strongly localize polarons. In contrast, correlated linker defects form extended barriers, inducing stronger localization than randomly distributed linkers. For binary disorder, the energetic trap depth dominates over spatial arrangement, with negligible correlation effects at high trap densities. Dopant counterions strongly localize polarons, but their positioning relative to disordered domains critically modulates transport. Comparison with recent experimental polarized mid-infrared spectra of doped P3HT validates these predictions, providing important design principles for optimizing polaron transport through vacancy clustering, reduced energetic disorder, and controlled dopant distribution in polymer matrices.

  PublisherOA PDFDOI

• Defect-Driven Polaron Localization in π-Conjugated Systems: The Role of Spatial Correlation and Coulomb Binding

  ChemRxiv · 2025-08-28

  preprintOpen accessSenior author

  Defect engineering offers a powerful strategy to modulate polaron delocalization in π-conjugated materials; however, the complex interplay between different types of defects and dopant-induced Coulomb binding remains insufficiently understood. Here, we present a comprehensive theoretical investigation of hole-polaron transport using a Holstein-style Hamiltonian applied to π-conjugated lattices such as polymers and COFs that incorporate vacancy and linker defects, a disorder framework encompassing distributions of shallow and deep traps, and dopant-induced Coulomb binding effects. Simulated mid-infrared signatures and polaron coherence numbers uncover distinct and nuanced behaviors, revealing how the spatial correlation (random vs. correlated) of dif- ferent defect types governs polaron delocalization pathways. While dopant counterions strongly localize polarons, their precise positioning relative to crystalline versus dis- ordered domains critically modulates transport efficiency. To establish experimental relevance, we compare our simulations with polarized intrachain and interchain mid- infrared spectra of doped P3HT films, providing fundamental insights into how spe- cific dopant–polymer configurations give rise to anisotropic spectroscopic signatures and their direct correlation with anisotropic polaron transport. The strong agreement between theory and experiment validates our predictions and establishes guiding prin- ciples for optimizing polaron transport in disordered π-conjugated materials.

  PublisherOA PDFDOI

• Intermolecular Interactions Override Chemical Intuition in Tuning Stacking and Electronic Properties of Functionalized Two-Dimensional Covalent Organic Frameworks

  Chemistry of Materials · 2025-08-22 · 2 citations

  articleCorresponding

  Rising energy demands underscore the need for renewable energy solutions such as solar energy. Covalent organic frameworks (COFs), with their tunable compositions, structures, and photophysical properties, are promising candidates; however, a comprehensive understanding of their composition-structure–property relationships remains limited. Here, combining all-electron quantum chemistry with coarse-grained Holstein Hamiltonians, we show that although slipped-stacked configurations are generally most stable, the degree of slipping is strongly influenced by the nature of the functional groups and does not follow simple electron-donating or -withdrawing trends. While van der Waals interactions primarily drive the stacking behavior, electrostatic contributions unique to each substituent modulate its extent. Furthermore, we find that in highly symmetric lattice backbones, small substituent changes have minimal effect on electronic structure, whereas symmetry-breaking functionalization offers a robust and effective route to tune electronic, transport, and photophysical properties. While the stacking arrangement primarily governs interlayer electron coherence, its influence diminishes in the high-disorder regime. Our findings provide fundamental insights and design principles to guide the development of high-performance COFs for photocatalytic applications.

  PublisherDOI

• Prunella vulgaris-phytosynthesized platinum nanoparticles: Insights into nanozymatic activity for H2O2 and glutamate detection and antioxidant capacity

  Talanta · 2024-04-03 · 15 citations

  articleOpen access

  Artificial nanozymes (enzyme-mimics), specifically metallic nanomaterials, have garnered significant attention recently due to their reduced preparation cost and enhanced stability in a wide range of environments. The present investigation highlights, for the first time, a straightforward green synthesis of biogenic platinum nanoparticles (PtNPs) from a natural resource, namely Prunella vulgaris (Pr). To demonstrate the effectiveness of the phytochemical extract as an effective reducing agent, the PtNPs were characterized by various techniques such as UV–vis spectroscopy, High-resolution Transmission electron microscopy (HR-TEM), zeta-potential analysis, Fourier-transform infrared spectroscopy (FTIR), and Energy dispersive spectroscopy (EDS). The formation of PtNPs with narrow size distribution was verified. Surface decoration of PtNPs was demonstrated with multitudinous functional groups springing from the herbal extract. To demonstrate their use as viable nanozymes, the peroxidase-like activity of Pr/PtNPs was evaluated through a colorimetric assay. Highly sensitive visual detection of H2O2 with discrete linear ranges and a low detection limit of 3.43 μM was demonstrated. Additionally, peroxidase-like catalytic activity was leveraged to develop a colorimetric platform to quantify glutamate biomarker levels with a high degree of selectivity, the limit of detection (LOD) being 7.00 μM. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) test was used to explore the scavenging nature of the PtNPs via the degradation of DPPH. Overall, the colorimetric assay developed using the Pr/PtNP nanozymes in this work could be used in a broad spectrum of applications, ranging from biomedicine and food science to environmental monitoring.

  PublisherDOI

• Using Molecular Structure to Tune Intrachain and Interchain Charge Transport in Indacenodithiophene-Based Copolymers

  Journal of the American Chemical Society · 2024-07-26 · 27 citations

  articleOpen access

  -benzopyrollodione), p(IDT-BPD)─with orders of magnitude different mobilities to understand the effect charge carrier intrachain delocalization has on electronic transport. Quantum chemical calculations show that p(IDT-BPD) has a barrier to torsion that is significantly lower than that of p(IDT-BT) and is thus more likely to have reduced conjugation lengths. We utilize absorption and photoluminescence spectroscopy to characterize energetic disorder and show that p(IDT-BPD) has higher energetic disorder. Charge modulation spectroscopy (CMS) and model calculations are used to show that charge carriers are substantially delocalized in p(IDT-BT) and occupy near-uniform energetic environments. We find that mobility activated hopping barriers are similar in these two materials. Electronic structure calculations show that both intrachain and interchain couplings of monomer units are poor enough in p(IDT-BPD) that charge carriers collapse to single IDT units and transport via a through-space tunneling mechanism. This work highlights the remarkable charge transport properties of p(IDT-BT) by showing that high mobilities are achievable on device-relevant length scales with only 1D carrier delocalization.

  PublisherOA PDFDOI

• Engineering flat and dispersive bands in 2D layered COFs via interlayer stacking and donor-acceptor strategy

  ChemRxiv · 2023-03-06

  preprintOpen accessSenior author

  Covalent organic frameworks (COFs) are an emergent class of two-dimensional (2D) crystalline organic materials that exhibit unique electronic, optical, and transport properties. In this study, we employ density functional theory (DFT) and the multiparticle Holstein formalism (MHF) to investigate the electronic structure and two-dimensional coherence of polarons in donor-acceptor COFs as a function of interlayer stacking arrangement. We show that simple modifications in the interlayer stacking arrangement have a profound impact on the transport properties, which can range from metallic behavior with vanishing band gap to highly localized states having completely flat bands. The extent of charge delocalization is found to be sensitive to the type of stacking arrangement and the precise arrangement of the donor and acceptor fragments within the COF structure. The results from the DFT calculations are consistent with MHF-based simulations, demonstrating that stacking-induced interlayer interac- tions facilitate better in-plane charge delocalization. As a consequence, we find that interlayer interactions help circumvent defect-induced trap states to enhance overall charge delocalization. Based on these analyses, we conclude that interlayer stacking can be exploited to guide the design of new 2D layered COF structures with potential applications in organic electronics.

  PublisherOA PDFDOI

Frequent coauthors

• Francesco Paesani

  University of California, San Diego

  32 shared

• Frank C. Spano

  Temple University

  16 shared

• Marc Riera

  10 shared

• Alberto Salleo

  9 shared

• Christine K. Luscombe

  Okinawa Institute of Science and Technology Graduate University

  8 shared

• Sukhendu Mandal

  Indian Institute of Science Education and Research Thiruvananthapuram

  6 shared

• K. S. Asha

  National Aerospace Laboratories

  6 shared

• Alan Hirales

  San Diego Supercomputer Center

  5 shared

Labs

• Raja Ghosh LabPI