Browsing by Author "Grover, Nitika"

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1O2 Mediated Conversion of β-Enaminonitriles to α-Keto Amides Photosensitized by Recyclable H2TPP in Visible Light
(ACS, 2024-03) Grover, Nitika
We report a one-step approach for the conversion of β-enaminonitriles to synthetically versatile α-keto amides in moderate to high yields under visible light irradiation photosensitized by porphyrins. The method is mild, cost-effective, and sustainable and requires air as the sole reagent/oxidant. The reaction is believed to proceed via an ene-type pathway initiated by 1O2, followed by dehydration, imine hydrolysis, and subsequent nucleophilic substitution of the cyanide group by amine. The method offers a broad substrate scope and has also been extended for synthesis of α-keto esters with aliphatic alcohols as nucleophiles. The porphyrin recovered after the reaction can be reused multiple times.
Asymmetrically Crowded “Push–Pull” Octaphenylporphyrins with Modulated Frontier Orbitals: Syntheses, Photophysical, and Electrochemical Redox Properties
(ACS, 2015-12) Grover, Nitika
A new series of β-substituted octaphenylporphyrins were synthesized and the influence of unsymmetrical substitution on the photophysical and electrochemical properties of the compounds is elucidated. The examined compounds are represented as MOPP(R)X2 where OPP = the dianion of octaphenylporphyrin, R = NO2, CHO, or CH2OH, X = Br or CN, and M is Co(II), Cu(II), Ni(II), or Zn(II). Routes to the trifunctionalized β-octaphenylporphyrins begin with the synthesis of MOPP(R) (R = NO2, CHO, and CH2OH) and the conversion of MOPP(NO2) to MOPP(NO2)X2 (X = Br and CN). These “push–pull” octaphenylporphyrins exhibit high dipole moments, tunable redox properties, and red-shifted electronic spectral features due to asymmetric β-substitution. Photophysical data on the series of MOPP(R)X2 compounds also reflect the nonplanar conformation of these porphyrins. Quantum yield and lifetime data are invariably lower than what has been reported in the literature for related β-substituted porphyrins. The spectroscopic properties and electrochemical redox potentials of the porphyrins are influenced by both the peripheral substituents and nature of the core metal ion. A decrease in the HOMO–LUMO gap and increase in Δb1 is observed as the number of electron withdrawing groups on the molecule was increased. In addition, a tuning of the redox potentials could be achieved by introducing both electron donating (CH2OH) and withdrawing (CN, NO2, CHO, and Br) substituents into the MOPP skeleton which led to a “cross-polarized push–pull effect” of the β-substituents and a nonplanarity of the molecule. Metal-centered oxidations were exhibited for all of the Co(II) porphyrins and an M(II)/M(III) process was also observed to occur for NiOPP(R) (R = CH2OH, H, CHO, and NO2) and CuOPP(NO2)(CN)2. These electrode reactions for the latter two series of compounds occur after an initial conversion of the neutral porphyrin to its dicationic form under the electrochemical conditions. Evidence for the site of electron transfer is given in part by comparison with data in the literature for related compounds and in part by theoretical calculations and thin-layer spectroelectrochemical data carried out in the current study.
Asymmetrically β-Substituted Porphyrins and Chlorins: Synthesis, Spectroscopic, and Electrochemical Redox Properties
(IOP, 2015) Grover, Nitika
Asymmetrically β-substituted chlorins, viz. 2,3-bis(dicyanomethyl)-meso-tetraphenylchlorin (1), diethoxycarbonylcyclopropano-meso-tetraphenylchlorin (2) and 2-ethylacetoacetanato-meso-tetraphenylporphyrin (3), and their metal (Ni(II), Cu(II) and Zn(II)) complexes have been synthesized and characterized by various spectroscopic techniques. Cyclic voltammetric (CV) studies were carried out for these porphyriniods in CH2Cl2 containing TBAPF6 as supporting electrolyte. The first ring redox potentials of 1, 2 and their metal complexes are anodically shifted (0.58 - 0.30 V) as compared to meso-tetraphenylchlorin (H2TPC) due to electron withdrawing nature of malononitrile and diethyl malonate substituents. Notably, Ni(II) complex of 3 exhibited metal centered oxidation (NiII/NiIII) due to extended conjugation and electronic nature of β-subtituent.
Bicyclo[1.1.1]pentane Embedded in Porphyrinoids
(Wiley, 2023-03) Grover, Nitika
We report a two-step approach to obtain synthetically versatile bicyclo[1.1.1]pentane (BCP) derivatives using Grignard reagents. This method allows the incorporation of BCP units in tetrapyrrolic macrocycles and the synthesis of a new class of calix[4]pyrrole analogues by replacing two bridging methylene groups with two BCP units. In addition, a doubly N-confused system was also formed in the presence of electron-withdrawing substituents at the BCP bridgeheads. The pyrrole rings in BCP containing macrocycles exist in 1,3-alternate or αβαβ conformations, as observed from single-crystal X-ray diffraction analyses and 2D NMR spectroscopy. Bioisosteres are chemical moieties that can be substituted for common functional groups or linkages; for example, bicyclo[1.1.1]pentane offers a linear connection similar to para-phenylene, and this replacement can inhibit usual aggregation and metabolic inactivation in drugs.1 BCP derivatives are also used as liquid crystals, molecular rotors, and as spacer unit in chromophoric arrays.2 To meet the increased demand for BCPs in pharmaceutical and material sciences several research groups are developing synthetic protocols for novel BCP building blocks. Most BCP derivatives have been synthesized via ring opening of [1.1.1]propellane followed by multi-step chemical transformation to append functional groups at bridgehead positions.
Bridging and Conformational Control of Porphyrin Units through Non-Traditional Rigid Scaffolds
(Wiley, 2019-11) Grover, Nitika
Connecting two porphyrin units in a rigid linear fashion, without any undesired electron delocalization or communication between the chromophores, remains a synthetic challenge. Herein, a broad library of functionally diverse multi-porphyrin arrays that incorporate the non-traditional rigid linker groups cubane and bicyclo[1.1.1]pentane (BCP) is described. A robust, reliable, and versatile synthetic procedure was employed to access porphyrin-cubane/BCP-porphyrin arrays, representing the largest non-polymeric structures available for cubane/BCP derivatives. These reactions demonstrate considerable substrate scope, from utilization of small phenyl moieties to large porphyrin rings, with varying lengths and different angles. To control conformational flexibility, amide bonds were introduced between the bridgehead carbon of BCP/cubane and the porphyrin rings. Through varying the orientation of the substituents around the amide bond of cubane/BCP, different intermolecular interactions were identified through single crystal X-ray analysis. These studies revealed non-covalent interactions that are the first-of-their-kind including a unique iodine-oxygen interaction between cubane units. These supramolecular architectures indicate the possibility to mimic a protein structure due to the sp3 rigid scaffolds (BCP or cubane) that exhibit the essential conformational space for protein function while simultaneously providing amide bonds for molecular recognition.
Chirality induction to porphyrin derivatives co-confined at the air–water interface with silica nano-helices: towards enantioselective thin solid film surfaces
(RSC, 2024) Grover, Nitika
A supramolecular approach based on self-assembled structures allows the formation of large structured co-assemblies based on chiral and achiral compounds with original physicochemical features. In this contribution, an achiral and hydrophobic porphyrin was co-assembled at the air–water interface with mesoscopic silica nano-helices dispersed in the water subphase of a Langmuir trough without covalent bond formation. This procedure allowed transferring the porphyrin/nano-helix co-assemblies on a solid support within a thin hybrid layer. The interaction between the two species was characterized using spectroscopic techniques and atomic force microscopy. As evidenced by the circular dichroism measurements performed directly on solid films, tunable chirality was induced to the porphyrin aggregates according to the chirality of the silica nano-helices. When the co-assemblies were transferred on surface plasmon resonance (SPR) slides and exposed to aqueous solutions of histidine enantiomers, selective chiral discrimination was observed which was determined by the matching/mismatching between the chirality of the analyte and the helicity of the nano-helical structure.
Cover Feature: An Insight into Non-Covalent Interactions on the Bicyclo[1.1.1]pentane Scaffold
(Wiley, 2021-02) Grover, Nitika
The Cover Feature shows artist Ella Marushenko′s view of the docking between an iodinated bicyclo(1.1.1)pentane (BCP) derivative and 1,4-diazabicyclo[2.2.2]octane (DABCO). It illustrates noncovalent interactions of the BCP scaffold and how they can be used for the precise assembly of molecular components in chemical space. More information on BCP interactions – studied by crystallographic and theoretical methods
Emerging devices and materials
(Springer, 2026-01) Grover, Nitika
This chapter surveys the fast-moving landscape of emerging devices and materials that are reshaping electronics, photonics, energy, and biomedicine. We begin with the motivations beyond silicon limits and outline advances in flexible and wearable platforms—displays, skin-like sensors, and body-conformal systems—that enable continuous health and environment monitoring. We then profile quantum materials (topological insulators, 2D semiconductors, and quantum dots) alongside next-generation energy technologies, including solid-state batteries, supercapacitors, and perovskite solar cells, highlighting the performance gains and stability/sustainability challenges that steer current research. At the device level, we discuss advanced semiconductors (GaN power devices, silicon photonics, and organic semiconductors) that deliver higher speed, power density, and integration. Bridging biology and electronics, we review biocompatible implants, self-healing materials, and biohybrid systems that promise personalized therapies and regenerative interfaces. Finally, we examine nanotechnology-driven catalysts and medicines, as well as smart and sustainable materials (piezoelectrics, metamaterials, biodegradable polymers) that enable self-powered sensing, wave engineering, and circular-economy pathways. Across these domains, the chapter emphasizes cross-disciplinary design, scalable fabrication, low-toxicity alternatives, and life-cycle thinking as the keys to translating laboratory breakthroughs into human-centered, eco-conscious systems.
Enantioselective Discrimination of Histidine by Means of an Achiral Cubane-Bridged Bis-Porphyrin
(ACS, 2021-11) Grover, Nitika
A Langmuir film of cubane-bridged bisporphyrin (H2por-cubane-H2por) at the air/water interface was developed and characterized. The floating film was successfully employed for the chiral discrimination between l- and d-histidine. The enantioselective behavior persisted after the deposition of the film on a solid support using the Langmuir–Schaefer method. Distinct absorption and reflection spectra were observed in the presence of l- or d-histidine, revealing that conformational switching was governed by the interaction between H2por-cubane-H2por and the histidine enantiomer. The mechanism of chiral selection was investigated using an ad hoc modified nulling ellipsometer, indicating the anti-conformation was dominant in the presence of l-histidine, whereas the presence of d-histidine promoted the formation of tweezer conformation.
Engineering dielectric and metallic metasurfaces for sensing applications in the near-infrared region
(SPIE, 2024) Grover, Nitika; Arora, Pankaj
Dielectric and metallic metasurfaces are proposed to demonstrate the sensing applications in the near-infrared region under normal incidence light. The geometrical parameters of the proposed metasurfaces are designed using Rigorous coupled analysis under wavelength interrogation, and the results are verified using Comsol Multiphysics software. A layer of 2D nanomaterial (MoS2) is considered to increase the adsorption on the sensing surface. Aluminum-based metallic metasurfaces offer a sensitivity of 1100nm/RIU with a figure of merit of 250 RIU-1. The proposed metasurfaces are further used for the detection of cancer cells in human blood, and a red shift in the wavelength spectra is observed due to the increase in the refractive index.
Facile Conversion of Ni(II) Cyclopropylchlorins into Novel β-Substituted Porphyrins through Acid-Catalyzed Ring-Opening Reaction
(ACS, 2016-12) Grover, Nitika
The conversion of cyclopropylchlorins into porphyrins represents a key step in the synthetic manipulation of macrocycles with tunable physical and chemical properties. Herein, we report a facile method for the synthesis of novel β-substituted porphyrins from cyclopropylchlorins. A series of Ni(II) cyclopropylchlorins was converted into the corresponding Ni(II) and free base porphyrins using TFA and H2SO4 under mild reaction conditions in good yields (75–86%). The new chlorins and porphyrins were characterized by various spectroscopic techniques and the single-crystal X-ray diffraction method. The reaction proceeds very fast (<5 min.) with complete conversion of chlorin into porphyrin with distinct color change. Facile conversion, shorter reaction time scale, and good yield (75–86%) without any side products are the significant features of this new protocol. These porphyrinoids exhibited red-shifted electronic spectral features with varying degrees nonplanar conformation, tunable redox properties, and porphyrin core basicity.
Facile synthesis of porphyrin-conjugates as amphiphilic modified photosensitizer structures of m-THPP bearing carbamate, carboxylate and sulfonate linkers
(World Scientific, 2022) Grover, Nitika
5,10,15,20-Tetrakis(3-hydroxyphenyl)porphyrin (m-THPP) bearing various nitrogen and sulfur containing heterocycles, aromatic, aliphatic and alicyclic residues covalently linked to the oxygen atom of the meta-hydroxy group of the porphyrin unit were synthesized in good yields as potential photosensitizers for photodynamic therapy (PDT). These new amphiphilic conjugates were designed to use three different polar linkers (carboxylate, sulfonate, and carbamate linker units)via the reaction of m-THPP with nicotinoyl chloride hydrochloride (carboxylate linker), 5-bromothiophene-2-sulfonyl chloride (sulfonate linker), phenyl isocyanate, 3,5-bis(trifluoromethyl)phenyl isocyanate, hexyl isocyanate and cyclohexyl isocyanate (carbamate linker). The heterocycles employed are 5- and 6-membered rings with different solubility characteristics
Fundamental electronic changes upon intersystem crossing in large aromatic photosensitizers: free base 5,10,15,20-tetrakis(4-carboxylatophenyl)porphyrin
(RSC, 2022) Grover, Nitika
Free base 5,10,15,20-tetrakis(4-carboxylatophenyl)porphyrin stands for the class of powerful porphyrin photosensitizers for singlet oxygen generation and light-harvesting. The atomic level selectivity of dynamic UV pump – N K-edge probe X-ray absorption spectroscopy in combination with time-dependent density functional theory (TD-DFT) gives direct access to the crucial excited molecular states within the unusual relaxation pathway. The efficient intersystem crossing, that is El-Sayed forbidden and not facilitated by a heavy atom is confirmed to be the result of the long singlet excited state lifetime (Qx 4.9 ns) and thermal effects. Overall, the interplay of stabilization by conservation of angular momenta and vibronic relaxation drive the de-excitation in these chromophores.
I(III)-promoted facile and rapid synthesis of imidazo-azepino-fused porphyrins with enhanced absorption as singlet oxygen generators
(Wiley, 2026-01) Grover, Nitika
A facile, high-yielding synthetic protocol has been developed to access azepino-fused porphyrins via iodine(III)-mediated oxidative intramolecular cyclization of β-imidazole or benzimidazole substituted porphyrins. The absorption of the synthesized compounds showed the characteristic features of meso-β-fused porphyrins, with intense Soret bands centered between 440 and 460 nm and two weak bands ranging from 550 to 750 nm (Q-bands) Among the synthesized compounds, the free-base imidazo-azepino-fused porphyrin was found to be an efficient 1O2 producer with a higher singlet oxygen quantum yield (ΦΔ ∼0.78 in DMF) as compared to H2TPP (ΦΔ = 0.64 in DMF). It was observed that the protonated form of 4aH2 exhibits a significant red shift of ∼24 nm in Soret and ∼150 nm in Q-bands. Fitting of the titration data of 4aH2 with TFA yielded an apparent pKa of ∼3.58, demonstrating that imidazole fusion enhances the basicity of the porphyrin system.
Incremental Introduction of Organocatalytic Activity into Conformationally Engineered Porphyrins
(Wiley, 2019-01) Grover, Nitika
To study the correlation of macrocycle nonplanarity and catalytic activity of free base porphyrins in detail, a series of six tetraphenylporphyrins with graded degree of β-ethyl substitution (“H2EtxTPPs” 1–6; x = 0, 2, 4, 6, 8) was applied in organocatalyzed reactions. The macrocycles display incrementally increasing nonplanarity due to repulsive peri-interactions. This creates an out-of-plane vector and better accessibility of the core amine and imine groups as the number of alkyl substituents increases. Following such a molecular engineering approach, the inner core system could be used to activate small molecules as a result of significant saddle distortion. The potential organocatalyst “H2EtxTPPs” were used in benchmark sulfa-Michael reactions and we found a distinct relationship between nonplanarity and conversion. These observations were attributed to the combined effect of enhanced basicity and increased H-bonding potential that could facilitate bifunctional organocatalysis. Ultimately, density functional theory (DFT) calculations were performed on 1–6 to monitor some electronic properties of the title compounds.
Investigation of aluminum-based plasmonic devices for sensing applications in the near-infrared region
(SPIE, 2024-03) Arora, Pankaj; Grover, Nitika
We present surface plasmon resonance-based sensing devices with Aluminum (Al) as the plasmonic metal in the near-infrared region and analyze the output performances in terms of higher sensitivity and the Figure of Merit (FOM). The optical characteristics of Al-based plasmonic sensors are explored using different interrogation modes (angle and wavelength). Biorecognition elements help to enhance the sensor’s performance, for which 2D nanomaterials are explored for the biofunctionalization of the top surface. In the end, we also present an Al-based plasmonic device that utilizes both prism and nanostructure-based configurations, and the same designed parameters for the device offer high sensitivity and FOM in both angle and wavelength interrogation.
Investigation of the Reactivity of 1-Azido-3-iodobicyclo[1.1.1]pentane under “Click” Reaction Conditions
(ACS, 2020-12) Grover, Nitika
The bicyclo[1.1.1]pentane (BCP) unit is under scrutiny as a bioisostere in drug molecules. We employed methodologies for the synthesis of different BCP triazole building blocks from one precursor, 1-azido-3-iodobicyclo[1.1.1]pentane, by “click” reactions and integrated cycloaddition–Sonogashira coupling reactions. Thereby, we accessed 1,4-disubstituted triazoles, 5-iodo-1,4,5-trisubstituted triazoles, and 5-alkynylated 1,4,5-trisubstituted triazoles. This gives entry to the synthesis of multiply substituted BCP triazoles on either a modular or a one-pot basis. These methodologies were further utilized for appending porphyrin moieties onto the BCP core.
Iodine(III)-induced cascade annulation of β-cyanoporphyrins for the efficient synthesis of n-aryliminonaphtho-fused and n-aryl-carboxamide porphyrins
(Wiley, 2025-12) Grover, Nitika; Kumar, Dalip
Meso-β fused porphyrins with tunable optoelectronic properties are attractive candidates for applications in light-harvesting, sensing, and catalysis, yet their synthesis often requires harsh conditions or tedious synthetic routes. Herein, a mild, operationally simple, and Cu(OTf)2-catalyzed protocol is reported to access meso-N-aryliminonaphtho-fused and N-arylcarboxamide porphyrins from readily available β-cyanoporphyrins and diaryliodonium salts. Reaction selectivity is controlled by the water content present in the reaction mixture, affording either fused imines or carboxamides in high yields. The protocol tolerates different symmetrical diaryliodonium salts and enables the preparation of free-base, Zn (II), and Cu (II) porphyrin derivatives, all fully characterized by NMR, UV–visible spectroscopy, high resolution mass spectrometry, electrochemistry, and single crystal X-ray diffraction. The π-extended systems exhibit distinct bathochromic shifts (≈42 nm in Soret and ≈80–90 nm in Q-bands) and narrowed highest molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps up to 1.54 eV. Electrochemical studies reveal that fused porphyrins exhibited anodically shifted reduction potentials, while Density functional theory calculations attribute the gap reduction to LUMO stabilization and HOMO destabilization induced by fusion. Overall, this strategy provides rapid access to structurally diverse π-extended porphyrins with tailored photophysical and redox properties.
Meso-substitution controlled synthesis of bodipy–dpm conjugates: a pathway to tailored photophysical properties
(2026) Roy, Aniruddha; Arora, Pankaj; Grover, Nitika
We show that the electronic nature of the meso-aryl substituent in 1,3,5,7-tetramethyl BODIPYs governs the reactivity of the 1,7-methyl (α-methyl) groups toward the Knoevenagel condensation. Reaction of pyrrole-2-aldehyde with electron-deficient 1,3,5,7-tetramethyl-meso-pentafluorophenyl and 1,3,5,7-tetramethyl-meso-4-nitrophenyl BODIPYs yields double condensation at the 1,7-methyl positions to give the corresponding bis(pyrrole) derivatives, whereas the electron-rich meso-tolyl analogue selectively undergoes single condensation at only one of the α-methyl groups under identical conditions. This substituent-dependent divergence extends to reactions with 1,9-diformyl-meso-aryl dipyrromethanes, enabling access to structurally distinct BODIPY–DPM conjugates. Reaction of 1,9-diformyl-DPM with meso-tolyl BODIPY selectively yields acyclic monosubstituted BODIPY–DPM conjugates, whereas the higher reactivity of meso-pentafluorophenyl BODIPY enables condensation between both 1,7-methyl groups and the two aldehyde functionalities of the diformyl-DPM scaffold, affording cyclic, porphyrin-like BODIPY–DPM frameworks. Notably, meso-pentafluorophenyl BODIPYs also undergo nucleophilic aromatic substitution of the para-fluorine atom by piperidine under the condensation conditions, as confirmed unambiguously by single-crystal X-ray diffraction. The resulting BODIPY–DPM and BODIPY–pyrrole conjugates exhibit pronounced bathochromic shifts (90–180 nm relative to parent BODIPYs), deep-red to near-infrared absorption (~670 nm) and emission (~750 nm), enlarged Stokes shifts, and strong intramolecular charge-transfer character. These features translate into efficient heavy-atom-free triplet formation, with singlet-oxygen quantum yields reaching up to 0.45. A representative conjugate (10) exhibits potent photodynamic activity in B16F10 melanoma cells with minimal dark toxicity (IC₅₀ = 0.95 μM). TD-DFT analysis indicates that excited-state twisting reduces ΔEST, thereby facilitating heavy-atom-independent intersystem crossing. Collectively, these results establish a robust molecular design framework for next-generation heavy-atom-free photosensitizers.
N-Confused Porphyrin – A Unique “Turn-On” Chemosensor for CN− and F− ions and “Turn-Off” Sensor for ClO4− ions
(Wiley, 2020-05) Grover, Nitika
N-Confused meso-tetrakis(4-carbomethoxyphenyl)porphyrin (1) and its Ni(II) complex (1 a) have been synthesized and utilized for anion sensing studies, and the results are compared with N-confused meso-tetraphenylporphyrin (NCTPP). Anion susceptibilities of 1 and 1 a were investigated using spectroscopic, electrochemical, and DFT studies. Porphyrins 1 and 1 a were able to detect CN−, F−, and ClO4− ions selectively over the tested set of anions even at ppm level. Interestingly, the addition of ClO4− ions resulted in fluorescence quenching (turn off) whereas the addition of F− or CN− resulted in fluorescence enhancement (turn on). Notably, the TFA addition resulted in fluorescence quenching, whereas the fluorescence enhancement was observed while adding TBAOH. The higher association constant (Ka) values with anions, lower detection limit, and shifts in redox potentials are due to the electron-withdrawing effect of the −COOCH3 group at the para-position of the meso-phenyl ring. This electron-withdrawing nature is crucial for the higher affinity towards anions. The anion sensing description in this article may not only unveil the built-in nature of N-confused porphyrins, but may also provide a general proposal for the development of novel anion sensors based on porphyrinoids. The electron-deficient porphyrin framework, large polarisable π-system, and anion binding through the outer NH or a combination of the above factors serve as a foundation for N-confused porphyrin to act as an anion sensor.