Browsing by Author "Biswajit Maiti"

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A useful scaffold based on acenaphthene exhibiting Cu 2+ induced excimer fluorescence and sensing cyanide via Cu 2+ displacement approach
(2012) Mohammad Shahid; Syed S. Razi; Priyanka Srivastava; Rashid Ali; Biswajit Maiti; Arvind Misra
A new simple organic scaffold based on acenaphthene 4 was designed and synthesized. The chromogenic and fluorogenic properties of 4 toward different metal ions and anions were investigated in H 2O/MeCN (8:2, v/v) solution. The probe 4 in the presence of Cu 2+ exhibited strong static excimer emission at 507 nm along with a decrease in monomer emission at ∼400 nm ratiometrically, attributed to a complexation through aldimine and amide groups of 4. Additionally, 4 upon interaction with different anions illustrated significant fluorescence enhancement with cyanide. However, interaction of complex, 4-Cu 2+ with CN - revealed fluorescence quenching attributed to formation of stable [Cu(CN) x] 1-x species in the medium. A naked-eye sensitive fluorescent green color of solution was changed to blue. The mechanism of interaction between 4 and Cu 2+ and sensing of cyanide through Cu 2+ displacement approach was confirmed by the change in optical behaviors and 1H NMR and ESI-MS spectral data analysis. © 2012 Elsevier Ltd. All rights reserved.
Biocompatible thermoresponsive N-isopropyl-N-(3-(isopropylamino)-3-oxopropyl)acrylamide-based random copolymer: synthesis and studies of its composition dependent properties and anticancer drug delivery efficiency
(Royal Society of Chemistry, 2022) Sourov Mondal; Archana Kumari; Kheyanath Mitra; Abhineet Verma; Satyen Saha; Biswajit Maiti; Ranjeet Singh; Partha Pratim Manna; Pralay Maiti; Hironobu Watanabe; Masami Kamigaito; Biswajit Ray
A new acrylamide monomer, N-isopropyl-N-(3-(isopropylamino)-3-oxopropyl)acrylamide (M3i), consisting of both isopropyl and isopropylamidopropyl moieties, has been synthesized from isopropylamine and N-isopropylacrylamide via an aza-Michael addition reaction followed by amidation with acryloyl chloride. The homopolymer of M3i (polyM3i) and a series of random copolymers of M3i and poly(ethylene glycol)methyl ether acrylate (PEGA: CH2 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 CHCO2(CH2CH2O)nMe, Mn = 480, n = 9 on average) with varying compositions have been synthesized via reversible addition-fragmentation chain transfer polymerization using 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) as well as 1-phenylethyl phenyl dithioacetate (PEPD) as a RAFT agent. These polymers have been characterized by 1H NMR, FTIR, GPC, UV-Vis, fluorescence, TGDTA, DSC, DLS, and TEM techniques. A lower critical solution temperature (LCST) and glass transition temperature (Tg) for polyM3i prepared using DDMAT were observed at 17 and 133 °C, respectively, while for a polymer formed using PEPD, no LCST was observed until 0 °C and its observed Tg was found at 127.3 °C. The polymers are thermally stable up to 300 °C. Upon an increase in the M3i content in the copolymers, LCST decreases, Tg increases, and the apparent hydrodynamic diameter decreases. Moreover, the effects of concentration and the addition of urea and sodium chloride on the LCST of the copolymer with an LCST close to body temperature were studied. Owing to the incorporation of PEGA, a higher critical micellar concentration and larger TEM particle size of this copolymer were observed with respect to those of polyM3i. The usefulness of the micelles of the copolymers as nano-carriers for the drug doxorubicin was explored. The in vitro tumoricidal activity of the micelles of the doxorubicin-loaded copolymers was also assessed against Dalton's lymphoma cells. © 2022 The Royal Society of Chemistry.
Communications: Direct dynamics study of the O (3P) + C 2 H2 reaction: Contribution from spin nonconserving route
(2010) Karunamoy Rajak; Biswajit Maiti
The importance of intersystem crossing dynamics for the O (3P) + C2 H2 reaction is demonstrated in this work. A direct dynamics trajectory surface hopping method has been employed to study the intersystem crossing effects. Our study reveals that there is a significant contribution from the spin nonconserving route to the chemical dynamics of the O (3P) + C2 H2 reaction, despite small spin-orbit coupling constant values (<70 cm-1P). © 2010 American Institute of Physics.
Dual Fluorophore Containing Efficient Photoinduced Electron Transfer Based Molecular Probe for Selective Detection of Cr3+ and PO4 3- Ions through Fluorescence " Turn-On-Off" Response in Partial Aqueous and Biological Medium: Live Cell Imaging and Logic Application
(American Chemical Society, 2018) Sushil K. Dwivedi; Ramesh C. Gupta; Priyanka Srivastava; Priya Singh; Biplob Koch; Biswajit Maiti; Arvind Misra
The present work describes a new photoinduced electron transfer (PET) based molecular probe in which naphthalimide (NPI) and anthracene (AN) chromophores are linked through a molecular bridge of piperazine and triazole units by the Click reaction. A typical meaningful structural variation has made the present probe highly selective for Cr3+ ion (limit of detection (LOD), 5.567 × 10-8 M) that displayed enhanced, "turn-On" emission (due to the PET-Off photophysical mechanism) and naked-eye sensitive bright green color fluorescence in the environment of interfering and competitive ions, in Tris-HCl buffer. The minimum energy structure obtained through theoretical calculations (density functional theory (DFT) and time-dependent (TD)-DFT) revealed a "tub" shape structure for probe 10. Upon complexation, the conformation of piperazine fragment changes from chair to boat in which the triazole and piperazine units create a cavity to tether Cr3+. Moreover, the probe showed excellent biocompatibility and cell permeability to sense Cr3+ sensitively in live cells and, thus, holds great promise for application in biological and environmental sciences. Additionally, the sensitive "Off-On-Off" sensing behavior of probe 10 providing two chemical inputs (Cr3+ and PO4 3-) helps to construct an INHIBIT logic gate. Also the probe has been utilized as printing material to decode secret information through the Cr3+ ion containing "marker ink" under UV light. © 2018 American Chemical Society.
Dynamics of the C(3P) + Ethylene Reaction: A Trajectory Surface Hopping Study
(American Chemical Society, 2018) Mrinmoy Mandal; Subhendu Ghosh; Biswajit Maiti
The direct dynamics trajectory surface hopping (DDTSH) method has been employed to study the reaction of C(3P) with ethylene (C2H4). Our trajectory simulations show that at a reagent collision energy of 7.36 kcal/mol, there are two possible product channels: propargyl (H2CCCH) + H and carbene (CH2) + acetylene (HCCH). Estimated branching ratios based on trajectory propagations indicate that propargyl radical formation is the dominant channel contributing (94.1 ± 5.2) % of the overall products formation with (5.9 ± 1.7)% contribution from the minor CH2 + HCCH channel. These findings are consistent with earlier experimental observations and theoretical predictions that propargyl (H2CCCH) formation is the dominant channel for the C(3P) + C2H4 collision reaction. Our trajectory simulations, however, unravel five distinctly different dynamical pathways, unlike earlier experimental and theoretical predictions of only two pathways proposed for the formation of propargyl radical, and three different dynamics are followed for the CH2 + HCCH channel (this channel was not detected experimentally). The computed translational energy distribution for the propargyl + H channel is narrower and showed peak maximum at a lower energy compared to the experimental one. While the center of mass product angular distribution based on our trajectory propagation is nearly isotropic in nature indicating formation of long-lived intermediate complexes, the experimental one was reported to be backward-forward distributed with more intensity in the forward direction indicating the formation of an osculating complex. Our trajectory surface hopping calculations confirm that the effect of intersystem crossing (ISC) is not important for the title reaction presumably because of weak spin-orbit coupling values (<10 cm-1) for the (C + C2H4) system. No trace of cyclic products formation was obtained from our trajectory simulations, which however was predicted to be a minor (2%) product channel, experimentally. © 2018 American Chemical Society.
Dynamics of the O(3P,1D) + SiH4 reaction: A trajectory surface hopping study
(Elsevier B.V., 2017) Subhendu Ghosh; Mrinmoy Mandal; Biswajit Maiti
A quasiclassical trajectory surface hopping (TSH) method is employed to study the O(3P,1D) + SiH4 reaction with special emphasis on the contribution of nonadiabatic path in the formation of various products. Tully's fewest switches algorithm is used to compute nonadiabatic transitions. Our calculation showed that while the H formation is the most important channel for the O(3P) reaction with SiH4, the OH formation is the dominating channel for the O(1D) reaction, at an initial collision energy of 8 kcal/mol. Comparison with a recent crossed molecular beam experiment shows qualitative agreement so as to primary product branching ratios, except for the formation of H2O from the O(1D) reaction that was not detected experimentally. In addition our calculation revealed a major contribution (∼50%) of the H3SiO + H channel from the O(3P) + SiH4 reaction through an addition complex H4SiO intermediate which was also not explored, experimentally. © 2017 Elsevier B.V.
Effect of Isotacticity of Linear Poly(N-isopropylacrylamide) on its Gelation in Benzyl Alcohol
(Springer India, 2016) Chandra Sekhar Biswas; Kheyanath Mitra; Shikha Singh; Dinesh K Patel; Biswajit Maiti; Pralay Maiti; Biswajit Ray
Thermoreversible gelation of three different isotactic linear poly(N-isopropylacrylamide) (PNIPAM)s having meso dyad (m) values 62, 68 and 81% has been observed in benzyl alcohol. All the gels were transparent in nature. SEM image of the dried gels showed fibrillar network morphology. Melting temperature of the gels gradually increased with the increase in the concentration. XRD data of dry polymers and their corresponding dry gels showed shifting in the peak positions. Rheological study showed that stronger gels were formed with increasing isotacticity of PNIPAM while lower isotactic sample exhibited typical polymer melt rheology. The formation of a plunge in the storage modulus as well as in the viscosity plot at the same frequency range indicates the reversible nature of the structure breaking/reformation under frequency sweep. Moreover, the mechanical strength of the gel decreased with increase in temperature. UV-Vis kinetic study also indicated the change in the conformation and aggregation of PNIPAM chains during gelation. Molecular modelling calculation showed that the number of solvent molecules involved in forming gel (polymer-solvent compound) decreased with the increase in the isotacticity of the polymer. Gelation rate of these gels was studied as a function of temperature, concentration and isotacticity using test-tube tilting method. It increased with the increase in the concentration and isoacticity of the polymer, and with the decrease in the temperature. Critical gelation concentration of the gel gradually increased with the decrease in the isotacticity and with the increase in the temperature. All these experimental results indicated that gelation occurs presumably through polymer-solvent compound formation. [Figure not available: see fulltext.] © 2016, Indian Academy of Sciences.
Effect of n-Alkyl Side Chain Length on the Thermal and Rheological Properties of PolyN-(3-(alkylamino)-N-(3-(isopropylamino)-3-oxopropyl)acrylamide) Homopolymers
(John Wiley and Sons Inc, 2021) Archana Kumari; Sambhav Vishwakarma; Kheyanath Mitra; Chuangbi Chen; Shuming Cui; Biswajit Maiti; Sourov Mondal; Chandra Sekhar Biswas; Pralay Maiti; Florian J. Stadler; Biswajit Ray
Four new N-isopropylacrylamide- and N-n-alkyl amine-based acrylamide monomers, N-(3-(alkylamino)-N-(3-(isopropylamino)-3-oxopropyl) acrylamide (Mn) (n = 4, 8, 10, 12) are successfully synthesized and polymerized via reversible addition-fragmentation chain-transfer polymerization (polyMn, n = 4, 8, 10, and 12), which are characterized by gel permeation chromatography, 1H NMR, Fourier transform infra red spectroscopy, thermo-gravimetry-differential thermal analysis, differential scanning calorimetry (DSC), and rheology. All polymers are thermally stable and undergo a two-step degradation process at ≈280 and ≈375 °C. Glass transition temperature (Tg)s of these polymers decrease gradually from 99.6 to 52.5 °C with increasing n-alkyl side chain length. The rheology of these polymers in melt state agrees to a typical Rouse-melt behavior and allows for confirming the Tg determined from DSC. Benzyl alcohol solution rheology proves a weak structural build-up, in particular for polyM12. Comparison of the quantum chemical calculations of polyMns with n = 4–8 reveals increase in backbone helicity with increasing n-alkyl side chain length. © 2021 Wiley-VCH GmbH.
Effects of tacticity and molecular weight of poly(N -isopropylacrylamide) on its glass transition temperature
(2011) Chandra Sekhar Biswas; Vijay Kumar Patel; Niraj Kumar Vishwakarma; Vimal K. Tiwari; Biswajit Maiti; Pralay Maiti; Masami Kamigaito; Yoshio Okamoto; Biswajit Ray
A series of high molecular weight poly(N-isopropylacrylamide) (PNIPAM)s with low polydispersity (Mn = 7.0 × - 104 to 10.2× - 104 g mol-1, PDI = 1.23-1.35) having different isotacticity [meso diad (m) = 47-88%]] was successfully synthesized using the reversible addition-fragmentation chain transfer (RAFT) polymerization method in the presence of different concentrations of Y(OTf)3 Lewis acid. Measurement of the glass transition temperature (Tg) of this high molecular weight isotactic PNIPAM series and the low molecular weight PNIPAM series (Mn = 3.5 × - 104 to 4.0 × - 104 g mol-1, PDI = 1.2-1.3) having different isotacticity [meso diad (m) = 45-72%)] reported earlier by us (Ray et al. Polym. J. 2005, 37, 234) showed that Tg of PNIPAM decreases with increase in its meso diad content (m %) and decrease in its molecular weight. © 2011 American Chemical Society.
Electron beam-induced piezoelectric phase in poly(vinylidene fluoride) nanohybrid: EFFECT at the molecular level
(John Wiley and Sons Ltd, 2015) Vimal K Tiwari; Madhab C Rath; Sisir K Sarkar; Vijay K Patel; Biswajit Ray; Biswajit Maiti; Pralay Maiti
A nanohybrid has been synthesized by incorporating organically modified layered silicate in a poly(vinylidene fluoride) (PVDF) matrix. Molecular-level phenomena have been explored after exposing PVDF and its nanohybrid to an electron beam of varying doses. The electron beam interacts with polymer chains and thereby generates different free radicals, the number of which is quite high in nanohybrid as compared to pure PVDF. The stability of free radicals has been confirmed through density functional theory energy minimization, predicting stable β-phase free radicals in the nanohybrid. Quantitative analyses of chain scission, crosslinking and double bond formation are reported and compared after irradiation for both PVDF and its nanohybrid using UV-visible and Fourier transform infrared spectroscopies, sol-gel analyses and gel permeation chromatography, revealing both chain scission and crosslinking phenomena in irradiated PVDF and its nanohybrid, but at higher dose (>90Mrad) crosslinking dominates in the nanohybrid due to more free radicals and proximity of radical chains on top of templated system in the nanohybrid as compared to pure PVDF. The enhanced crosslinking alters the nanostructure causing disappearance of the peak at 2θ ≈ 3°. Moreover, the electron beam induces significant piezoelectric β-phase in the nanohybrid against only α-phase in pure PVDF at a similar dose and raises the possibility for the use of electron-irradiated nanohybrid as an electromechanical device. β-Phase formation is also supported through solid-state NMR, scanning electron microscopy and differential scanning calorimetry studies. The thermal properties in terms of heat of fusion and degradation temperature have been verified indicating steady decrease of melting point and heat of fusion for pure PVDF while considerably less effect is observed for the nanohybrid. The combined effect of chain scission and crosslinking makes both PVDF and its nanohybrid brittle, but with greater stiffness with respect to unirradiated specimens. © 2014 Society of Chemical Industry.
Facile Metal-Free Synthesis of Phenanthridines by SN2′ Reaction/C–H Functionalization/Aromatization through the Reaction of Morita–Baylis–Hillman Acetates with Nitroalkanes
(Wiley-VCH Verlag, 2018) Tanu Gupta; Jay Bahadur Singh; Kalpana Mishra; Biswajit Maiti; Radhey M. Singh
A simple, highly efficient, and regioselective synthesis of functionalized phenanthridines by the reaction of MBH acetates of 2-chloroquinoline-3-carbaldehydes with nitroalkanes is described. The reaction involves an SN2′ reaction/C–H functionalization/aromatization process. The method is simple and proceeds under mild conditions under an air atomosphere to give phenanthridines in good to excellent yields. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Fluorene and Triazine-Based Conjugated Polymer Networks with Tuned Frontier Orbital Energy Levels for Improving Organic Photocatalysis
(American Chemical Society, 2024) Raj Laxmi; Anshuman; Neelam Gupta; None Anamika; Arpita Maurya; Ravi Prakash Behere; Rahul Sharma; Biswajit Maiti; Biplab K. Kuila
Here, we describe a method for fine-tuning the frontier orbital energy levels or redox potential of a conjugated polymer network (CPN) consisting of triazine and fluorene by systematically introducing electron-withdrawing groups at the fluorene moiety through simple structural modification. The band gap of CPN decreases with an increase in the strength of the electron-withdrawing group, and the relative position of the frontier orbital energy becomes more favorable for reactions like photocatalytic aerobic oxidation, which has been further confirmed by theoretical and experimental studies. The CPN with a CN group at the 9 position of fluorene (CPN3) shows the maximum photocatalytic activity (32% higher) compared to CPN1 (hydrogen at the 9 position) in white light. The best-performing catalyst CPN3 was further employed for photocatalytic reactions under white light, like the oxidation of alcohols to carbonyl and boronic acid to the corresponding alcohol, which show noteworthy characteristics like low catalyst loading, high yield, and selectivity with broad substrate scope (aliphatic, aromatic, biphenyl, and heterocyclic). CPN3 exhibited turnover frequencies of 13.33 and 10.9 mmol g-1 h-1 in 3 W blue and white LED lights, respectively, which are much higher than those of state-of-art photocatalysts. The recyclability of the catalyst was tested for up to 5 cycles without much change in the catalytic activity. The practical usefulness of the suggested method was further demonstrated by the CPN3-photocatalyzed gram-scale synthesis of high-value chemicals such as acetophenone from 1-phenylethanol and phenol from phenylboronic acid. © 2024 American Chemical Society.
Heteroleptic arene ruthenium complexes based on meso-substituted dipyrrins: Synthesis, structure, reactivity, and electrochemical studies
(2009) Mahendra Yadav; Ashish Kumar Singh; Biswajit Maiti; Daya Shankar Pandey
First examples of heteroleptic arene ruthenium complexes containing dipyrrin ligands with the general formulations [(η6-arene)RuCI(L) ] [(arene = C6H6, C10H14; L = 5-(4-cyanophenyl)-dipyrromethene, cydpm; 5-(4-nitrophenyl)-dipyrromethene, ndpm and 5-(4-benzyloxyphenyl)-dipyrromethene, bdpm] have been synthesized. The complexes [η6 -C10H14)RuCI(L)] (L = ndpm and cydpm) reacted with NaN3 and NH4SCN to afford neutral mononuclear complexes [(η6-C10H14)Ru(N 3)(L)] and [η6 -C10H14)Ru(SCN) (L)]. Their reactions with EPh3 (E = P, As) and exobidentate ditopic P-P and N-N donor ligands, namely, bis-(diphenylphosphino)methane (dppm) and 4,4′-bipyridine (bpy) in the presence of AgSO3CF3 afforded cationic mono- and binuclear complexes [(η6 -C 10-H14)Ru(L)(EPh3)]SO3CF 3, [{(η6-C10H14)Ru(L)} 2(μ-dppm)](SO3CF3)2, and [{(η6-C10H14)Ru(L)}2(μ-bpy)] (S03-CF3)2, respectively. The reaction products have been characterized by analytical and spectral studies. Molecular structures of the representative complexes [η6-C 10H14)RuCI(cydpm)], [(η6-C 6H6)RuCI(cydpm)], [η6-C10H 14)RuCI-(ndpm)], [(η6-C10H 14)Ru(N3)(ndpm)], and [η6-C 10H14)Ru(PPh3)(ndpm)]SO3CF 3 have been determined crystal-lographically. Redox behavior of the complexes has been investigated by electrochemical studies. Emission spectral studies at room temperature suggested that the complexes under study are non-emissive. © 2009 American Chemical Society.
Heteroleptic dipyrrinato complexes containing 5-ferrocenyldipyrromethene and dithiocarbamates as coligands: Selective chromogenic and redox probes
(2012) Rakesh Kumar Gupta; Rampal Pandey; Roopshikha Singh; Nitin Srivastava; Biswajit Maiti; Satyen Saha; Peizhou Li; Qiang Xu; Daya Shankar Pandey
Six heteroleptic dipyrrinato complexes [Ni(fcdpm)(dedtc)] (1), [Ni(fcdpm)(dipdtc)] (2), [Ni(fcdpm)(dbdtc)] (3), [Pd(fcdpm)(dedtc)] (4), [Pd(fcdpm)(dipdtc)] (5), and [Pd(fcdpm)(dbdtc)] (6) (fcdpm = 5-ferrocenyldipyrromethene; dedtc = diethyldithiocarbamate; dipdtc = diisopropyldithiocarbamate; dbdtc = dibutyldithiocarbamate) have been synthesized and characterized by elemental analyses and spectral (ESI-MS, IR, 1H, 13C NMR, UV-vis) and electrochemical studies. Crystal structures of 1, 2, 4, and 5 have been authenticated by X-ray single-crystal analyses. Nickel-based complexes 1-3 display selective chromogenic and redox sensing for Hg2+ and Pb2+ ions, while palladium complexes 4-6 display selective chromogenic and redox sensing only for Hg2+. Electronic absorption, ESI-MS, and electrochemical studies indicated that sensing arises from interaction between 1-3 and Hg2+/Pb2+ through sulfur of the coordinated dithiocarbamates, while it arises from the pyrrolic nitrogen of fcdpm and dithiocarbamate sulfur from 4-6 and Hg 2+. Different modes of binding between Ni and Pd complexes have further been supported by theoretical studies. The receptor-cation binding constants (Ka) and stoichiometry between probes and Hg 2+/Pb2+ have been estimated by the Benesi-Hildebrand method and Job's plot analysis. Detection limits for 1-3 toward Hg 2+/Pb2+ and 4-6 for Hg2+ have been found to be reasonably high. © 2012 American Chemical Society.
Highly efficient polyurethane ionomer corrosion inhibitor: The effect of chain structure
(2011) Sitashree Banerjee; Abhinay Mishra; Madan M. Singh; Biswajit Maiti; Biswajit Ray; Pralay Maiti
A series of polyurethane (PU) ionomers with different degree of sulfonation (DS) have been synthesized and successfully used as corrosion inhibitor for mild steel (MS) in acidic medium. Nuclear magnetic resonance (NMR) and Fourier transform infra red (FTIR) spectra of the sulfonated PUs confirmed the sulfonation on the >NH group of the urethane linkage and DS increases with the increase in the ratio of the sulfonating agent and PU. More than 90% inhibition efficiency (IE) of sulfonated polyurethanes (SPU) has been reported using only 20 ppm of the ionomers. These ionomers inhibited the corrosion of MS through adsorption following the Langmuir adsorption isotherm. Surface coverage has been scaled using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The effect of sulfonation on the electronic and chemical structure of PU molecules has also been investigated. Electronic structure calculations have been performed to predict the adsorption behavior of ionomers on the metal surface, and thereby, the relative inhibition has been quantitatively correlated with DS. © The Royal Society of Chemistry 2011.
Hydrogen bonding patterns and DFT studies of (4-Acetylphenyl)amino 2,2-Dimethylpropanoate and (E)-1-(4-aminophenyl)-3-[4-(dimethylamino)phenyl] prop-2-en-1-one
(Springer New York LLC, 2014) Rama Kant; Biswajit Maiti; Satish Kumar Awasthi; Alka Agarwal
The (4-acetylphenyl)amino 2,2-dimethylpropanoate (1) and (E)-1-(4-aminophenyl)-3-[4-(dimethylamino)phenyl]prop-2-en-1-one (2), were synthesized and characterized by elemental analysis, FT-IR, 1H NMR, 13CNMR and single crystal X-ray diffraction techniques. Both compounds 1 and 2 crystallized in orthorhombic crystal system with Pbca and P212121 space group respectively, having the unit cell parameters: a = 11.7220(12) Å, b = 14.4580(13) Å, c = 15.7853(12) Å, β = 90°, Volume = 2675.2(4) Å3, Z = 8 for 1 and a = 6.1146(5) Å, b = 9.0567(8) Å, c = 26.079(3) Å, β = 90°, Volume = 1444.2(2) Å3, Z = 4 for compound 2. The crystal structures of both compounds (1 and 2) are stabilized by N-H···O strong intermolecular hydrogen bonding forming C 1 1 (8) motifs. In compound 1, the molecules are linked by three C-H···O intramolecular H-bond forming S(6) motifs. In compound 2, the molecules are linked by C-H···N intermolecular H-bond exhibiting C 1 1 (12) motif and C-H···O intramolecular H-bond leading to S(5) motif. Crystallographic and vibrational data are compared with the results of density functional theory (DFT) method at the B3LYP/6-31G(d,p) level. The electronic (UV-vis) spectra was calculated by using the TD-DFT method and correlated with experimental spectra. © 2014 Springer Science+Business Media New York.
Importance of intersystem crossing in the C(3P) + SiH4reaction
(Royal Society of Chemistry, 2020) Mrinmoy Mandal; Prabhash Mahata; Biswajit Maiti
The contribution of intersystem crossing (ISC) in the C(3P) + SiH4reaction that leads to products formation in the singlet electronic state is investigated using a direct dynamics trajectory surface hopping (TSH) method with Tully's fewest switches algorithm. Interestingly, in contrast to the O(3P) + SiH4reaction with no ISC effect, for the title reaction we observed ∼7% product formation through ISC despite weak spin-orbit coupling interactions (less than 25 cm−1) between the ground singlet and triplet states. This is presumably because of the topological differences in the potential energy surfaces of the two reactions at the entrance channel. The O(3P) + SiH4reaction follows either an addition reaction (with shallow attractive potential and a late singlet-triplet crossing) or a direct abstraction pathway with singlet-triplet crossing at near or after the top of the barrier making ISC ineffective. On the other hand, an insertion mechanism is exclusively followed by the C(3P) + SiH4reaction with no entrance barrier to the reaction in the triplet state. The triplet insertion complex initially formed (3H3SiCH) can go to the singlet state through ISC due to the fact that the triplet-singlet crossing is accessed several times during the course of the reaction. Our computed overall product angular distributions for H and H2elimination channels are found to be broad and flat or nearly isotropic in nature indicating the formation of stable intermediate complexes, which corroborates the most recent crossed molecular-beam study. © the Owner Societies 2020.
Improved DSSC performance with acidic extract of Euphorbia milii red flower, the effect of pH variation and DFT analysis of phytoconstituents
(Elsevier B.V., 2025) Nikhil Srivastav; Kalpajyoti Dihingia; Himanshu Patel; Yoganand Singh; Ananya Rai; Biswajit Maiti; Pankaj Kumar Srivastava
Dye-sensitized solar cells (DSSCs) have garnered significant attention in recent years, surpassing traditional solar cells in terms of cost-effectiveness, ease of fabrication, and operation in low-light conditions. However, the synthesis of dyes, crucial for DSSCs, is often complex and involves hazardous or trace metals, prompting the exploration of natural dyes as an alternative. Euphorbia milii (E.milii) plants have already been recognized for their medicinal uses and application as a natural acid-base indicator. In this study, an acid-mediated extract of E. milii red flowers was prepared and effect of post-extraction pH variation was studied. The modified extracts were subsequently utilized as a sensitizer in TiO2 based DSSCs. Phytochemical studies were carried out to ensure the presence of constituents in the obtained extract. The UV-Vis spectra indicated a widening of the absorption range with variation in the pH. The Cyclic Voltammogram showed the redox nature of the acidic extract obtained at different pH. The UV-Vis and FTIR analysis revealed potential functional groups belonging to phytoconstituents that interact with the TiO2 surface effectively. PL and TRPL studies were also carried out to analyse the excited state dynamics. DFT (Density Functional Theory) and TD-DFT (Time-dependent DFT) were carried out using B3LYP and CAM-B3LYP functional respectively at 6–311++G(d, p) basis set and solvent effect was studied in ethanol over SMD model to validate the experimental environment and corresponding results. The HOMO-LUMO position and the band-gap were determined for the various phytoconstituents. Further, the ΔGinj, ΔGreg and the LHE (light harvesting efficiency) values were estimated. These analyses led to the viability of the extract as a sensitizer-dye. The photovoltaic parameters i.e., Jsc, Voc, photo conversion efficiency (η), and fill factor (FF) were investigated for the fabricated cell. Additionally, stability and electrochemical impedance spectroscopy (EIS) studies for the charge transfer characteristics, were also performed. Among all pH levels, relatively high absorption intensity, photocurrent (Jsc=0.7mAcm−2) and electron lifetime (τe=7ms) were recorded for pH 3.1 extract-based cell. © 2025 The Authors
Lighting the Path: A Sustainable Catalyst Free Approach Toward Trifluoromethylation of Indoles
(John Wiley and Sons Inc, 2025) Nikita Gupta; Imtiaz Ahmed; Ajit Kumar Gupta; Kalpajyoti Dihingia; Biswajit Maiti; Vijay Kumar Das
In this study, we report an innovative development of a visible light-induced synthesis of trifluoromethyl indoles. This novel methodology not only obviates the need for traditional catalysts but also harnesses the energy of photons to selectively introduce trifluoromethyl groups into indole substrates. Leveraging the inexpensive, easily handled, and non-toxic Langlois reagent (CF3SO2Na) as the CF3 source, in conjunction with visible light and tert-butyl hydrogen peroxide (TBHP), facilitates the direct C─H trifluoromethylation of indoles. The mechanistic pathway of the reaction is predicted with the help of density functional theory (DFT) calculations at the (U)B3LYP/6–31++G(d,p)/SMD/acetonitrile level of theory. © 2025 Wiley-VCH GmbH.
Mechanistic Insight and Intersystem Crossing Dynamics of the C(3P) + H2CO/D2CO Reaction
(American Chemical Society, 2023) Mrinmoy Mandal; Karunamoy Rajak; Biswajit Maiti
The reaction of atomic carbon, C(3P), with H2CO has been investigated using the direct dynamics trajectory surface hopping (DDTSH) method with Tully's fewest switches algorithm. The lowest lying ground triplet and single states are considered for the dynamics study at a reagent collision energy of 8.0 kcal/mol. From the trajectory calculations, we observed that CH2+ CO and H + HCCO are the two major product channels for the title reaction. The insertion mechanism of the C(3P) + H2CO reaction is rather complex and is followed by three distinct intermediates with no entrance channel barrier to the reaction on the B3LYP/6-31G(d,p) potential energy surfaces. The triplet insertion complexes are formed by three different approaches; "Sideways", "End-on" and "Head-on" attack of the triplet carbon atom toward H2CO molecule. Our dynamics calculations predict a new product channel (H + HCCO(X 2A′′)) with a contribution of ∼46% of the overall products formation via ketocarbene intermediate through "Head-on" approach. Despite the weak spin-orbit coupling (SOC) interactions, intersystem crossing (ISC) via a ketocarbene intermediate has a small but significant contribution, about 2.3%, for the CH2+ CO channel. To understand the kinetic isotope effects on the reaction dynamics, we have extended our study for the C(3P) + D2CO reaction. It is seen that isotopic substitution of both the H atoms has a small reduction in the extent of ISC dynamics for the carbene formation. Our results, certainly, reveal the importance of the ketocarbene intermediate and the H + HCCO products channel as one of the major product formation channels in the title reaction, which was not reported earlier. © 2023 American Chemical Society. All rights reserved.