John Mondal

A cytochrome P450-mimetic monodispersed Fe-porphyrin-based porous framework is designed and synthesized via a FeCl3-assisted Friedel-Crafts reaction, to combine the advantages of heterogeneous systems with enzymatic reactivity. Specifically, the Fe-porphyrin site in this material mimics the heme-center in cytochrome P450, which efficiently catalyzes the aerobic oxidative cyclization of 2-aminophenols with isothiocyanates in water, affording a broad range of biologically relevant 2-aminobenzoxazoles in yields of up to 94% under mild conditions without the need for any external oxidants. Controlled experiments demonstrate the crucial role of molecular oxygen, indicating a radical-mediated reaction pathway. XAS provides insights into the local atomic structure, unravelling the key Fe(III)-active site influencing the reaction mechanism. Thermodynamically favorable formation of redox-active ligand and detailed mechanistic insights into the electron-transfer-mediated catalytic transformation are gained from quantum-chemical calculations. Oxygen activation forms peroxide-like species, followed by a sequence of radical steps ultimately leading to the product formation. Spin-density variation in these steps is well consistent with Fe(III)/Fe(II) redox-cycling. This work combining experiments and quantum simulations establishes a Fe-porphyrin-engineered porous organic polymer as an effective oxidative catalyst and highlights the potential of single-site bioinspired porous materials for sustainable aerobic oxidation chemistry.

Inspired by the electron‐transfer function of biological ferredoxins, we report a biomimetic iron–sulfur cluster‐functionalized porous organic polymer ( FeS‐POP ) for efficient oxygen evolution reaction (OER). FeS‐POP is constructed through polymerization‐induced restructuring of a diamagnetic diiron carbonyl precursor ( FeS‐Com ), wherein Fe─Fe bond cleavage and decarbonylation trigger a diamagnetic‐to‐paramagnetic transformation, generating atomically dispersed cubane [Fe ₄ S ₄ ] active centers within a conjugated porous framework. FeS‐POP exhibits excellent OER activity in alkaline media, delivering 10 mA cm ⁻² at an overpotential of 390 mV with a Tafel slope of 68 mV dec ⁻¹ , ∼89% Faradaic efficiency, and remarkable durability, positioning it among the leading polymer‐based OER electrocatalysts reported thus far. Importantly, synchrotron Fe K‐edge XAFS establishes a cubane [Fe ₄ S ₄ (OH) ₄ ] motif as the catalytically active center and reveals its structural resilience throughout prolonged electrolysis, thereby elucidating the atomic‐level structure–activity relationship governing OER. Complementary DFT calculations reveal the thermodynamic driving force for cluster reconstruction and show that cooperative multi‐metallic interactions within the [Fe ₄ S ₄ ] core facilitate O–O bond formation through a low‐barrier redox‐isomerization pathway. Our findings principally shed light on the molecular mechanism underlying this remarkable diamagnetic‐to‐paramagnetic transformation, establishing a synthetic blueprint for engineering biomimetic iron–sulfur active sites in porous electrocatalysts.

Achieving high selectivity in alkyne semi-hydrogenation without relying on toxic modifiers remains a major challenge in heterogeneous catalysis. In this work, we have explored the design of a series of heteroatom-functionalized porous organic polymer (POP)-supported Pd catalysts (S-Pd-POP, O-Pd-POP, and N-Pd-POP) to systematically tune catalytic behavior for semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY) through p-d orbital hybridization. These materials were synthesized via a scalable free-radical polymerization approach followed by Pd incorporation, yielding an amorphous porous network with a distinct electronic microenvironment. Notably, S-Pd-POP contains ultrasmall and well-dispersed Pd nanoparticles (∼2.5 nm), significantly smaller than those in O-Pd-POP (∼6.5 nm) and N-Pd-POP (∼8.5 nm), leading to greater exposure of active sites. Synchrotron X-ray absorption fine structure (XAFS) analysis confirms Pd exists predominantly in a metallic state, while EXAFS results reveal a clear decrease in Pd-Pd coordination numbers from O-Pd-POP to N-Pd-POP to S-Pd-POP, consistent with progressively smaller Pd clusters. We have achieved a good catalytic activity with S-Pd-POP with 95.3% conversion and 97.2% selectivity under mild conditions (60 °C, 5 bar H2), along with a lower activation energy (24.6 kcal mol-1) than its counterparts. Comprehensive density functional theory calculations validate experimental findings, which show strong overlap between S(p) and Pd(d) orbitals near the Fermi level, indicating pronounced p-d orbital hybridization, which is further supported by significant sulfur-to-Pd electron interaction donation from natural bond orbital analysis. In contrast, nitrogen- and oxygen-based systems show much weaker electronic interactions, corroborating their hydrogenation activity data. In situ ATR-IR spectroscopy studies reveal that the reaction proceeds via weakly bound π-intermediates, which promote rapid product desorption and effectively suppress over-hydrogenation. Overall, this work highlights p-d orbital hybridization as a key factor governing catalytic selectivity and provides a practical strategy for designing efficient, modifier-free hydrogenation catalysts.

Developing an efficient and robust photocatalyst for optimal C₂₊ product generation from carbon dioxide (CO₂) is a pressing need in advancing solar fuel production. In this study, we designed an ionic vinylene-bridged conjugated porous organic polymer (Py-POP) enriched with charged pyridine groups via a quaternization-promoted Knoevenagel condensation reaction. The resulting positively charged polymeric framework with shape-persistent nanochannels enabled the uniform assembly of SnS₂ units through ionic interactions mediated by amino and sulfhydryl groups. The hybrid porous photopolymer (SnS₂@Py-POP) converts CO₂ into ethylene with a rate of 34.7 μmol g^-1 h^-1 with a selectivity of ethylene around 78.7% under visible light photoirradiation, which outperforms all the C₂ selective Sn-based photocatalysts. Our findings principally sheds light on the mechanism of selectivity reversal (from C₁ to C₂ product) by hybrid catalyst framework engineering. In-depth investigations by synchrotron-based X-ray absorption spectroscopy (XAS) and morphological analysis via high-resolution transmission electron microscopy (HRTEM) reveal the nature of interaction for hybrid heterostructure formation within the porous network. Electron transfer pathways were mapped using time-resolved photoluminescence (TRPL) and transient absorption spectroscopy (TAS), which revealed a Z-scheme electron transfer mechanism. This mechanism facilitates enhanced electron accumulation on the SnS₂ layer, promoting efficient CO₂ activation and subsequent C-C coupling, ultimately leading to ethylene formation. Furthermore, the ethylene formation mechanism has been investigated in detail by time-resolved diffuse reflectance infrared spectroscopy (TR-DRIFTS), corroborated with density functional theory (DFT). This study opens a new avenue for achieving selectivity reversal in a C₁ selective photocatalyst through electronic modulation enabled by the formation of an inorganic-organic hybrid heterostructure.

Direct electrocatalytic co‐reduction of N ₂ and CO ₂ to urea remains constrained by sluggish kinetics and the absence of frameworks capable of concurrently activating both molecules. Herein, we present the first realization of a metalated porous organic polymer ( M‐POP )‐based electrocatalyst, Cu ₃ Fc‐Pyz‐POP , derived from in situ formed Cu ₃ (pyrazolate) triangular motif and 1,1′‐ferrocenedicarboxaldehyde through a template‐free Schiff base polymerization. The heterometallic Cu–Fe framework hosts atomically dispersed single‐site active centers that cooperatively activate and co‐reduce molecular N ₂ and CO ₂ , thereby promoting selective urea formation under ambient conditions. Operated in a 0.1 M KHCO ₃ electrolyte under ambient conditions, Cu ₃ Fc‐Pyz‐POP delivers an exceptional urea yield rate of 115.23 µgh ⁻¹ mg ⁻¹ and a Faradaic efficiency of 20.68% at –0.6 V vs RHE, surpassing its monometallic analogues. The catalyst exhibits excellent recyclability over 10 cycles and maintains stable performance during 45 h of continuous electrolysis. in situ FT‐IR spectroscopic investigation and DFT computational studies reveal that ferrocene (Fc) moieties facilitate enhanced conductivity with a dramatic decrease of HOMO‐LUMO energy gap and selective C‐N coupling between N ₂ and CO ₂ intermediates. Our finding establishes M‐POPs as promising platforms for ambient urea electrosynthesis, contributing to energy‐efficient fertilizer production and advancing low‐carbon chemistry.

This work reports the rational design of bio-inspired metal-functionalized POPs as robust platforms for sustainable catalysis and paves the way for the development of next-generation nanozyme-mimetic materials.

The conventional synthesis of acetophenone via the Friedel‐Crafts reaction is a highly waste‐intensive process. Consequently, the development of more sustainable and efficient alternatives is important. In this regard, radical oxidation represents a promising, environmentally benign route for acetophenone production. In this work, we designed a cobalt porphyrin‐based metalated porous organic polymer ( Co@POR‐POP ), a highly active catalytic system, offering a potentially viable and cleaner approach to acetophenone production, utilizing styrene as the starting material. The catalyst exhibits a high surface area (BET = 650 m ² g ⁻¹ ) with bimodal pores, and delivers more than 90% yield of acetophenone under ambient conditions with excellent selectivity. Synchrotron‐based XAFS spectroscopy study revealed a square‐planar Co‐N ₄ coordination environment with coordination number (CN) ≈4 and Co─N bond distance of ∼1.93 Å, with no evidence of Co–Co scattering, confirming the presence of isolated active sites. In situ EPR spectroscopy investigation displayed g _⊥ = 2.049 and g _∥ = 1.985 with hyperfine couplings A _⊥ = 49.8 MHz and A _∥ = 46.16 MHz, alongside an organic radical signal at g = 2.003. Spin‐trapping with DMPO detected both hydrogen (•H) and styrene (•C) radicals, validating a radical‐mediated mechanism. DFT calculations established a thermodynamically favourable pathway with an overall energy drop of −4.5 eV, supported by spin density localization at the Co centre and significant d‐π orbital overlap facilitating O ₂ activation. Overall, this work presents a new avenue of exploring novel organic transformation reactions using metalated porous organic polymer, opening scope for further investigations in this domain.

The development of efficient and sustainable heterogeneous catalysts remains central to the advancement of green oxidation chemistry. Herein, we report a Ni-salphen-derived metalated porous organic polymer (Ni@CAB), synthesized via a simple Friedel-Crafts alkylation strategy that integrates atomically dispersed Ni-N₂O₂ active sites into a robust carbazole-linked framework. A combination of 2D solid-state ¹³C-¹H double cross-polarization (CP) correlation NMR, XPS, synchrotron-based XAS, and electron microscopy techniques confirmed the structural integrity, amorphous porous architecture, and uniform dispersion of Ni centers. Electronic analyses revealed reduced surface electron density at the Ni sites, enhancing their Lewis acidity and catalytic reactivity. Ni@CAB demonstrated exceptional performance in the aerobic allylic oxidation of cyclohexene under ambient conditions, affording complete conversion with high selectivity and remarkable recyclability over multiple cycles without detectable Ni leaching. Complementary DFT calculations unveiled favorable charge transfer and energetically viable pathways consistent with experimental observations. This study establishes surface electron density as a powerful activity descriptor and underscores the promise of rationally engineered metalated porous polymers for sustainable oxidation catalysis.