Nirmalya Ballav

Interfacial electrostatics are central to charge separation, catalysis, sensing, energy conversion, and electronic transport, but the built-in potential of heterojunctions is generally considered fixed by the constituent materials. Here we show that redox-active metal–organic framework (MOF) heterointerfaces enable reversible optical control over the junction electrostatics. A heterostructured thin film assembled from n-type Cu-BHT (BHT = benzenehexathiol) and p-type Cu-ADA (ADA = azobenzenedicarboxylate) exhibits pronounced current rectification together with a light-induced increase in the cut-in voltage by ∼0.9 V. Spectroscopic measurements identify Cu(I) centers and sulfur radical anions as photoactive redox sites. Combined electrical measurements and density functional theory calculations reveal substantial interfacial charge reconstruction and a Type-I band alignment that confines photogenerated holes near the junction. This charge accumulation expands the depletion region and increases the built-in potential, as corroborated by the capacitance–voltage measurements. Our findings establish MOF heterojunctions as chemically programmable platforms for dynamic control of interfacial electrostatics and adaptive optoelectronic functionality.

Covalent organic frameworks (COFs) are crystalline porous polymers with tunable structures, high surface area, and chemical stability, making them promising electrode materials for rechargeable Li-ion batteries (LIBs) and Na-ion batteries (SIBs).

This work examines graphene and MXene electrodes integrated with three imidazolium-based ionic liquid electrolytes for supercapacitor applications. Quantum capacitance and electric double-layer capacitance were systematically analyzed to evaluate electrode-electrolyte performance. MXenes exhibited nearly an order of magnitude higher quantum capacitance than multilayer graphene, highlighting their superior suitability. Among the electrolytes, EMIM-TCB showed limited applicability with peak capacitance confined to zero potential. In contrast, BMIM-PF 6 and BMIM-BF 4 displayed strong compatibility, particularly with MXenes, delivering enhanced capacitance across a wide potential range due to favorable structural and electrostatic interactions. Overall, the MXene-BMIM-PF 6 combination emerges as a promising candidate among the investigated materials for high-performance supercapacitors, while the study emphasizes the critical role of interfacial engineering in the design of next-generation energy storage systems.

Cu-based 2D MOFs (p-Cu-THQ and d-Cu-THQ) reveal how porosity affects Li-ion storage, with dense d-Cu-THQ showing higher capacity and rate due to pseudocapacitive behaviour while porous p-Cu THQ offers better cycling stability via improved diffusion.

Bimetallic 2D MOF CuCo-THQ demonstrates efficient HER activity in alkaline media with low overpotential, favourable kinetics, and strong durability. Synergistic Cu–Co interactions enhance the catalytic performance beyond that of Cu-THQ and Co-THQ.

Solid-state photophysical properties of [Ru(bpy)₃]²⁺ are well-studied, whereas those of [Ru(bpy)₃]³⁺ remain elusive. Here, we report ambient-conditions stabilization of [Ru(bpy)₃]³⁺ in an organic-inorganic hybrid crystal, [Ru(bpy)₃]₂Ag₆Br₁₂. Utilizing two-dimensional hexagonal anionic network, (Ag₆Br₁₁)_n^5n-, featuring strong argentophilic interactions, this system stabilizes the spin-bearing low-spin d⁵ Ru(III) exhibiting unusual room-temperature photoluminescence with three emission peaks (~586, ~612, and ~686 nm), a behavior rarely seen in ruthenium tris(bipyridine) systems. Temperature-dependent and time-resolved photoluminescence measurements reveal average lifetimes of ~10 ns at 300 K across all peaks. The origin of the three emission peaks is identified by time-dependent density functional theory calculations, revealing three doublet ligand-to-metal charge-transfer states to a doublet ground state transitions. The extracted spin-density plot suggests near spin-degeneracy of the d_z², d_x²_-y² and d_xy orbitals, corroborating trigonal antiprismatic (D_3d) microsymmetry. The organic-inorganic hybrid also displays ultralow thermal conductivity (~0.21 W·m^-1·K^-1 at 480 K), qualifying it as a promising multifunctional material.

Organic–inorganic hybrid halides (OIHHs) have gained attention as potential ferroelectric materials due to structure‐property synergy of the organic and inorganic constituents. This study introduces an unusual Ag(I)‐based ternary OIHH, (4,4′‐bpy)Ag ₂ Br ₄ , featuring rotational flexibility in the organic dication to induce asymmetry into the structure. The compound crystallizes in a monoclinic crystal system with a non‐centrosymmetric polar P 2 ₁ space group at room‐temperature and undergoes a structural phase transition to a centrosymmetric phase ( P 2 ₁ / c ) at Curie temperature ( T _c ) of 330 K which was further supported by differential scanning calorimetry (DSC), second harmonic generation (SHG) signals, dielectric anomaly, current‐voltage ( I–V ) profiles, and X‐ray photoelectron spectroscopy (XPS) data. Ferroelectricity is confirmed through polarization–electric field ( P – E ) hysteresis loops and piezoresponse force microscopy (PFM), exhibiting switchable polar domains. Density functional theory (DFT) calculations revealed electronic structures of the ferroelectric and paraelectric phases, identified the ( β ‐AgBr ₂ ) _n ⁿ⁻ inorganic anionic chain contributing to the net polarization, and in general, complemented the experimental results. Comparative studies with structurally analogous Ag(I)‐based OIHHs lacking dication rotational freedom endorse the critical role of organic flexibility in driving ferroelectricity. This study provides insights into the role of organic dications in controlling ferroelectric behavior and offers a promising pathway for developing coinage metal‐based OIHH ferroelectric materials.

Organic–inorganic hybrid halides (OIHHs) have gained attention as potential ferroelectric materials due to structure‐property synergy of the organic and inorganic constituents. This study introduces an unusual Ag(I)‐based ternary OIHH, (4,4′‐bpy)Ag ₂ Br ₄ , featuring rotational flexibility in the organic dication to induce asymmetry into the structure. The compound crystallizes in a monoclinic crystal system with a non‐centrosymmetric polar P 2 ₁ space group at room‐temperature and undergoes a structural phase transition to a centrosymmetric phase ( P 2 ₁ / c ) at Curie temperature ( T _c ) of 330 K which was further supported by differential scanning calorimetry (DSC), second harmonic generation (SHG) signals, dielectric anomaly, current‐voltage ( I–V ) profiles, and X‐ray photoelectron spectroscopy (XPS) data. Ferroelectricity is confirmed through polarization–electric field ( P – E ) hysteresis loops and piezoresponse force microscopy (PFM), exhibiting switchable polar domains. Density functional theory (DFT) calculations revealed electronic structures of the ferroelectric and paraelectric phases, identified the ( β ‐AgBr ₂ ) _n ⁿ⁻ inorganic anionic chain contributing to the net polarization, and in general, complemented the experimental results. Comparative studies with structurally analogous Ag(I)‐based OIHHs lacking dication rotational freedom endorse the critical role of organic flexibility in driving ferroelectricity. This study provides insights into the role of organic dications in controlling ferroelectric behavior and offers a promising pathway for developing coinage metal‐based OIHH ferroelectric materials.

Azobenzene-based lanthanide MOF thin films fabricated via electrodeposition exhibited a unique thermally-driven conformational twist, distinct from trans – cis isomerization, significantly enhancing electrical conductivity upon molecular doping.