Ajay Ugale

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).

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.

Two-dimensional metal-organic frameworks (2D MOFs) are emerging as a new class of multifunctional materials for diversified applications, although magnetic properties have not been widely explored. The metal ions and organic ligands in some of the 2D MOFs are arranged in the well-known Kagome lattice, leading to geometric spin frustration. Hence, such systems could be the potential candidates to exhibit an exotic quantum spin liquid (QSL) state, as was observed in Cu₃(HHTP)₂ (HHTP = hexahydroxytriphenylene), with no magnetic transition down to 38 mK. Hereto, we have investigated the spin intertwining in a bimetallic 2D MOF system, M₃(HHTP)₂ (M = Cu/Zn)_, arising from the localized (d-electron) and delocalized (π-electron) S = 1/2 spins from the Cu(II) ions and the HHTP radicals, respectively. The origin of the spin frustration (down to 5K) was critically examined by varying the metal composition in bimetallic systems, Cu_xZn_3-x(HHTP)₂ (x = 1, 1.5, 2), containing both S = 1/2 and S = 0 spins. Additionally, to gain a deeper understanding, we studied the spin interaction in the pristine Zn₃(HHTP)₂ system containing only S = 0 Zn(II) ions. In view of the quantitative estimate of the localized and delocalized spins, the d-π spin correlation appears essential in understanding the unusual magnetic and/or other physical properties of such hybrid organic-inorganic 2D crystalline solids.

Two-dimensional (2D) metal-organic frameworks (MOFs) are usually associated with higher electrical conductivity and charge carrier mobility when compared with 3D MOFs. However, attaining metallic conduction in such systems through synthetic or postsynthetic modifications is extremely challenging. Herein, we present the fabrication of thin films of a 2D MOF, Cu₃(HHTP)₂ (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), decorated with silver nanoparticles (AgNPs) exhibiting significant conductivity enhancement at room temperature. Variable-temperature electrical transport measurements across the low-temperature (200 K) to high-temperature (373 K) regime evidenced metallic conduction. Interestingly, thin films of a 3D MOF, CuTCNQ (TCNQ = 7,7,8,8-tetracyanoquinodimethane), upon decoration with AgNPs, disclosed a converse trend. The origin of such distinctive observations on AgNPs@Cu₃(HHTP)₂ and AgNPs@CuTCNQ systems was comprehended by using first-principles density functional theory (DFT) calculations and attributed to an interfacial electronic effect. Our work sheds new light on rationally designing synthetic modifications in thin films of MOFs to tune the electrical transport property.