Experimental and computational study of naphthalimide derivatives: Synthesis, optical, nonlinear optical and antiviral properties.

The nonlinear optical (NLO) and antiviral properties of naphthalimide Schiff base compounds (5a-c) were experimentally and computationally investigated. The synthesized compounds (5a-c) were successfully characterized via UV-Vis, FTIR, 1H NMR, fluorescence spectroscopy, and elemental analysis. The calculated average third-order NLO polarizabilities (˂γ˃) of 5a, 5b, and 5c were found to be 5, 9, and 21 times greater than the ˂γ˃ amplitude of p-NA, respectively. The computed results revealed the potential of the synthesized compounds for NLO applications. Additionally, molecular docking studies of the synthesized compounds with two crucial SARS-CoV-2 proteins were performed to examine their biochemical properties. Compound 5c exhibited a higher binding affinity with the spike protein compared to that with Mᴾᴿᴼ. The results obtained herein indicate the potential of the synthesized naphthalimide derivatives for optoelectronic and drug design applications.

Yolk-shell smart polymer microgels and their hybrids: fundamentals and applications.

Yolk-shell microgels and their hybrids have attained great importance in modern-day research owing to their captivating features and potential uses. This manuscript provides the strategies for preparation, classification, properties and current applications of yolk-shell microgels and their hybrids. Some of the yolk-shell microgels and their hybrids are identified as smart polymer yolk-shell microgels and smart hybrid microgels, respectively, as they react to changes in particular environmental stimuli such as pH, temperature and ionic strength of the medium. This unique behavior makes them a perfect candidate for utilization in drug delivery, selective catalysis, adsorption of metal ions, nanoreactors and many other fields. This review demonstrates the contemporary progress along with suggestions and future perspectives for further research in this specific field.

Computational prediction for designing novel ketonic derivatives as potential inhibitors for breast cancer: A trade-off between drug likeness and inhibition potency.

Unlike simple molecular screening, a combined hybrid computational methodology has been applied which includes quantum chemical methods, molecular docking, and molecular dynamics simulations to design some novel ketonic derivatives. The current study contains the derivatives of an experimental ligand which are designed as a trade-off between drug likeness and inhibition strength. We investigate the interaction of various newly designed ketonic compounds with the breast cancer receptor known as the Estrogen Receptor Alpha (ERα). The molecular structures of all newly designed ligands were studied quantum chemically in terms of their fully optimized structures, 3-D molecular orbital distributions, global chemical descriptors, molecular electrostatic potentials and energies of frontier molecular orbitals (FMOs). All ligands under study show good binding affinities with the ERα protein. The ligands CMR2 and CMR4 exhibit improved molecular docking interactions. The intermolecular interactions indicate that CMR4 demonstrates better hydrophobic and hydrogen bonding interactions with protein (ERα). Furthermore, molecular dynamics simulations were conducted on ligands and reference drugs interacting with the ERα protein over a time span of 120 nanoseconds. The molecular dynamics results are interpreted in terms of ligand-protein stability and flexible behaviour based on their respective values of RMSD, RMSF, H-bonds, the radius of gyration, and SASA graphs. To analyse ligand-protein interactions throughout the entire 120 ns trajectory, a more advanced MM/PBSA method is utilized, where six selected ligands (CMR1, CMR2, CMR3, CMR4, CMR5 and CMR9) illustrate promising results for inhibition of the ERα receptor as assessed through MM/BBSA analysis. The CMR9 has the highest MM/BBSA binding free energy (-14.46 kcal/mol). The ADMET analysis reveals that CMR4 has maximum intestinal absorption (6.68) and clearance rate (0.1). All the compounds are non-toxic and safe to use. These findings indicate the potential of involving different computational techniques to design the ligand structures and to study the ligand-protein interactions for better understanding and achieving more potent synthetic inhibitors for breast cancer.

Recent developments in chitosan based microgels and their hybrids.

Chitosan based microgels have gained great attention because of their chemical stability, biocompatibility, easy functionalization and potential uses in numerous fields. Production, properties, characterization and applications of chitosan based microgels have been systematically reviewed in this article. Some of these systems exhibit responsive behavior towards external stimuli like pH, light, temperature, glucose, etc. in terms of swelling/deswelling in an aqueous medium depending upon the functionalities present in the network which makes them a potential candidate for various applications in the fields of biomedicine, agriculture, catalysis, sensing and nanotechnology. Current research development and critical overview in this field accompanying by future possibilities is presented. The discussion is concluded with recommended possible future works for further progress in this field.

Exploring the synthetic potential of epoxide ring opening reactions toward the synthesis of alkaloids and terpenoids: a review.

Epoxides are oxygen containing heterocycles which are significantly employed as crucial intermediates in various organic transformations. They are considered highly reactive three-membered heterocycles due to ring strain and they undergo epoxide ring opening reactions with diverse range of nucleophiles. Epoxide ring-opening reactions have gained prominence as flexible and effective means to obtain various functionalized molecules. These reactions have garnered substantial attention in organic synthesis, driven by the need to comprehend the synthesis of biologically and structurally important organic compounds. They have also found applications in the synthesis of complex natural products. In this review article, we have summarized the implementation of epoxide ring opening reactions in the synthesis of alkaloids and terpenoids based natural products reported within the last decade (2014-2023).

A novel investigation of pressure-induced semiconducting to metallic transition of lead free novel Ba3SbI3 perovskite with exceptional optoelectronic properties.

The structural, electronic, mechanical, and optical characteristics of barium-based halide perovskite Ba3SbI3 under the influence of pressures ranging from 0 to 10 GPa have been analyzed using first-principles calculations for the first time. The new perovskite Ba3SbI3 material was shown to be a direct band gap semiconductor at 0 GPa, but the band gap diminished when the applied pressure increased from 0 to 10 GPa. So the Ba3SbI3 material undergoes a transition from semiconductor to metallic due to high pressure at 10 GPa. The Ba3SbI3 material also exhibits an increase in optical absorption and conductivity with applied pressure due to the change in band gap, which is more suitable for solar absorbers, surgical instruments, and optoelectronic devices. The charge density maps confirm the presence of both ionic and covalent bonding characteristics. Exploration into the mechanical characteristics indicates that the Ba3SbI3 perovskite is mechanically stable. Additionally, the Ba3SbI3 compound becomes strongly anisotropic at high pressure. The insightful results of our simulations will all be helpful for the experimental structure of a new effective Ba3SbI3-based inorganic perovskite solar cell in the near future.

Quantum chemical framework for tailoring N/B doped phenalene derivatives to achieve high performance nonlinear optical materials.

Nonlinear optical (NLO) response materials are among the smartest materials of the era and are employed to modulate the phase and frequency of the laser. The present study presents a quantum chemical framework for tailoring nitrogen/boron doped derivatives of Dihydrodibenzo [de,op]pentacene through terminal and central core modifications. The derivatives of these compounds have been designed by introducing various π-conjugated connectors as well as B/N heteroatoms in the phenalene rings. Density functional theory (DFT) methods are used to optimize the ground state molecular geometries of designed compounds, represented as 1 to 4 (phenalene derivatives) and 1-BN to 4-BN (B/N doped phenalene derivatives) at the M06-2X/6-311G* level of theory. The highest value of 116.9 × 10-24 esu and 240.2 × 10-24 esu for isotropic and anisotropic linear polarizability is shown by compound 4. Among the designed compounds, 4-BN has achieved the highest γ amplitude of 1858 × 10-36 esu owing to its unique molecular structural design. Further analysis of electronic parameters, such as electron density difference (EDD) maps, the density of states, electrostatic potentials, transition density matrix (TDM) analysis, and frontier molecular orbitals analysis (FMOs), demonstrated the more effective intramolecular charge transfer (ICT) for the best compounds, resulting in a good NLO response. The compounds were also analyzed for their potential in photovoltaic applications based on factors such as open circuit voltage values determined to be between (0.14 eV and 1.82 eV), and light harvesting efficiency (0.425-0.909).

Development of novel transition metal-catalyzed synthetic approaches for the synthesis of a dihydrobenzofuran nucleus: a review.

The synthesis of dihydrobenzofuran scaffolds bears pivotal significance in the field of medicinal chemistry and organic synthesis. These heterocyclic scaffolds hold immense prospects owing to their significant pharmaceutical applications as they are extensively employed as essential precursors for constructing complex organic frameworks. Their versatility and importance make them an interesting subject of study for researchers in the scientific community. While exploring their synthesis, researchers have unveiled various novel and efficient pathways for assembling the dihydrobenzofuran core. In the wake of extensive data being continuously reported each year, we have outlined the recent updates (post 2020) on novel methodological accomplishments employing the efficient catalytic role of several transition metals to forge dihydrobenzofuran functionalities.

Improving the efficiency of a CIGS solar cell to above 31% with Sb2S3 as a new BSF: a numerical simulation approach by SCAPS-1D.

The remarkable performance of copper indium gallium selenide (CIGS)-based double heterojunction (DH) photovoltaic cells is presented in this work. To increase all photovoltaic performance parameters, in this investigation, a novel solar cell structure (FTO/SnS2/CIGS/Sb2S3/Ni) is explored by utilizing the SCAPS-1D simulation software. Thicknesses of the buffer, absorber and back surface field (BSF) layers, acceptor density, defect density, capacitance-voltage (C-V), interface defect density, rates of generation and recombination, operating temperature, current density, and quantum efficiency have been investigated for the proposed solar devices with and without BSF. The presence of the BSF layer significantly influences the device's performance parameters including short-circuit current (Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE). After optimization, the simulation results of a conventional CIGS cell (FTO/SnS2/CIGS/Ni) have shown a PCE of 22.14% with Voc of 0.91 V, Jsc of 28.21 mA cm-2, and FF of 86.31. Conversely, the PCE is improved to 31.15% with Voc of 1.08 V, Jsc of 33.75 mA cm-2, and FF of 88.50 by introducing the Sb2S3 BSF in the structure of FTO/SnS2/CIGS/Sb2S3/Ni. These findings of the proposed CIGS-based double heterojunction (DH) solar cells offer an innovative method for realization of high-efficiency solar cells that are more promising than the previously reported traditional designs.

2D Materials in Advanced Electronic Biosensors for Point-of-Care Devices.

Since two-dimensionalal (2D) materials have distinct chemical and physical properties, they are widely used in various sectors of modern technologies. In the domain of diagnostic biodevices, particularly for point-of-care (PoC) biomedical diagnostics, 2D-based field-effect transistor biosensors (bio-FETs) demonstrate substantial potential. Here, in this review article, the operational mechanisms and detection capabilities of biosensing devices utilizing graphene, transition metal dichalcogenides (TMDCs), black phosphorus, and other 2D materials are addressed in detail. The incorporation of these materials into FET-based biosensors offers significant advantages, including low detection limits (LOD), real-time monitoring, label-free diagnosis, and exceptional selectivity. The review also highlights the diverse applications of these biosensors, ranging from conventional to wearable devices, underscoring the versatility of 2D material-based FET devices. Additionally, the review provides a comprehensive assessment of the limitations and challenges faced by these devices, along with insights into future prospects and advancements. Notably, a detailed comparison of FET-based biosensors is tabulated along with various other biosensing platforms and their working mechanisms. Ultimately, this review aims to stimulate further research and innovation in this field while educating the scientific community about the latest advancements in 2D materials-based biosensors.

Baeyer-Villiger oxidation: a promising tool for the synthesis of natural products: a review.

Baeyer-Villiger oxidation is a well-known reaction utilized for the synthesis of lactones and ester functionalities from ketones. Chiral lactones can be synthesized from chiral or racemic ketones by employing asymmetric Baeyer-Villiger oxidation. These lactones act as key intermediates in the synthesis of most of the biologically active natural products, their analogues, and derivatives. Various monooxygenases and oxidizing agents facilitate BV oxidation, providing a broad range of synthetic applications in organic chemistry. The variety of enzymatic and chemoselective Baeyer-Villiger oxidations and their substantial role in the synthesis of natural products i.e., alkaloids, polyketides, fatty acids, terpenoids, etc. (reported since 2018) have been summarized in this review article.

Investigating the synergetic effect of tungsten oxide doping into the 1,3-dicarbonyl moiety grafted chitosan and phytic acid impregnated sodium alginate for efficient U(VI) adsorption.

In this work, chemical modification of the chitosan with ethyl acetoacetate was performed through a base-catalyzed reaction in which epichlorohydrin facilitated the insertion as well as nucleophilic substitution reaction to graft the 1,3-dioxo moiety across the linear chains of the base biopolymer to establish specificity and selectivity for U(VI) removal. The modified chitosan (EAA-CS) was intercalated into phosphate rich alginate matrix (PASA). Later on, the WO3-doped composites with different WO3 to PASA mass ratio were prepared and characterized using FTIR, XPS, SEM-EDS, XRD, and elemental mapping analysis. WO3 significantly contributed to chemically stable inorganic-organic composites with improved porous texture. Among the prepared composites, MCPS-3 microspherical beads, having mass ratio of 30.0 % w/w, exhibited excellent sorption capacity for U(VI) at an optimal pH 4.5. The successful U(VI) sorption was validated by the existence of two U4f peaks at 392.25 and 381.36 eV due to U4f5/2 and U4f7/2 sub-peaks with an intensity ratio of 3:4, respectively. Batch mode sorption kinetics followed pseudo-second-order rate equation (R2 ≈ 0.99, qe,th ≈ 116.88 mg/g, k2 = 0.86 × 10-4 g/mg.min-1) and equilibrium sorption data aligns with Langmuir (R2 = 0.99, qm = 343.85 mg/g at 310 K and pH = 4.5, KL = 2.00 × 10-2 L/mg) and Temkin models (R2 ≈ 0.99). Thermodynamic parameters ΔHo (30.51 kJ/mol), ΔSo (0.19 kJ/mol.K) and ΔGo (-25.64, -26.89, and - 27.91 kJ/mol) at 298, 305, and 310 K, respectively, suggested that the uptake process is feasible, endothermic and spontaneous. Based on these findings, it is reasonable to conclude that MCPS-3 could be a better hydrogel-based biomaterial for appreciable uranium recovery.

Tungsten oxide encapsulated phosphate-rich porous alginate composites for efficient U(VI) capture: Insights into synthesis, adsorption kinetics and thermodynamics.

In this work, novel monoclinic tungsten oxide (WO3)-encapsulated phosphate-rich porous sodium alginate (PASA) microspherical hydrogel beads were prepared for efficient U(VI) capture. These macroporous and hollow beads were systematically characterized through XRD, FTIR, EDX-mapping, and SEM-EDS techniques. The O and P atoms in the PO and monoclinic WO3 offered inner-spherical complexation with U(VI). The in situ growth of WO3 played a significant role inside the phosphate-rich biopolymeric network to improve its chemical stability, specific surface area, adsorption capacity, and sorption rate. The phytic acid (PA) served for heteroatom doping and crosslinking. The encapsulated WO3 mass ratio was optimized in different composites, and WO3/PASA3 (the microspherical beads with a mass ratio of 30.0 % w/w) exhibited remarkable maximum sorption capacity qm (336.42 mg/g) computed through the best-fit Langmuir model (R2 ≈ 0.99) and rapid sorption equilibrium, teq (150 min). The isothermal sorption studies were conducted at different temperatures (298, 303, and 308 K) and thermodynamic parameters concluded that the process of U(VI) sorption using WO3/PASA3 is endothermic and feasible having ΔHo (8.19 kJ/mol), ΔGo (-20.75, -21.38, and - 21.86 kJ/mol) and proceeds with a minute increase in randomness ΔSo (0.09 kJ/mol.K). Tungsten oxide (WO3)-encapsulated phosphate-rich porous microspherical beads could be promising material for uranium removal.

Free energy landscape and thermodynamics properties of novel mutations in PncA of pyrazinamide resistance isolates of Mycobacterium tuberculosis.

Pyrazinamide (PZA) is one of the first-line antituberculosis therapy, active against non-replicating Mycobacterium tuberculosis (Mtb). The conversion of PZA into pyrazinoic acid (POA), the active form, required the activity of pncA gene product pyrazinamidase (PZase) activity. Mutations occurred in pncA are the primary cause behind the PZA resistance. However, the resistance mechanism is important to explore using high throughput computational approaches. Here we aimed to explore the mechanism of PZA resistance behind novel P62T, L120R, and V130M mutations in PZase using 200 ns molecular dynamics (MD) simulations. MD simulations were performed to observe the structural changes for these three mutants (MTs) compared to the wild types (WT). Root means square fluctuation, the radius of gyration, free energy landscape, root means square deviation, dynamic cross-correlation motion, and pocket volume were found in variation between WT and MTs, revealing the effects of P62T, L120R, and V130M. The free energy conformational landscape of MTs differs significantly from the WT system, lowering the binding of PZA. The geometric shape complementarity of the drug (PZA) and target protein (PZase) further confirmed that P62T, L120R, and V130M affect the protein structure. These effects on PZase may cause vulnerability to convert PZA into POA.Communicated by Ramaswamy H. Sarma.

Exploration of violet-to-blue thermally activated delayed fluorescence emitters based on "CH/N" and "H/CN" substitutions at diphenylsulphone acceptor. A DFT study.

The violet-to-blue thermally activated delayed fluorescence (TADF) emitters were created employing several substituents based on 5,5-dimethyl-5,10-dihydropyrido [2,3-b][1,8] naphthyridine-diphenylsulphone (DMDHPN-DPS) called 1a via "CH/N" and "H/CN" substitutions at the diphenylsulphone acceptor (DPS) moiety. The parent compound 1a was selected from our former work after extensive research employing "CH/N" substitution on Dimethyl-acridine (DMAC) donor moiety. There is a little overlap amid the highest occupied molecular orbitals (HOMOs) and lowest un-occupied molecular orbitals (LUMOs) due to the distribution of HOMOs and LUMOs primarily on the DMDHPN donor and the DPS acceptor moieties, respectively. It resulted in a narrower energy gap (∆E ST) between the lowest singlet (S1) and triplet (T1) excited state. In nearly all derivatives, the steric hindrance results in a larger torsional angle (85°-98°) between the plane of the DMDHPN and the DPS moieties. The predicted ΔE ST values of the compounds with "H/CN" substitution were lower than those of the comparable "CH/N" substituents, demonstrating the superiority of the reversible inter-system crossing (RISC) from the T1 → S1 state. All derivatives have emission wavelengths (λ em) in the range of 357-449 nm. The LUMO → HOMO transition energies in the S1 states are lowered by the presence of -CN groups or -N = atoms at the ortho or meta sites of a DPS acceptor unit, causing the λ em values to red-shift. Furthermore, the λ em showed a greater red-shift as there were more-CN groups or -N = atoms. Three of the derivatives named 1b, 1g, and 1h, emit violet (394 nm, 399 nm, and 398 nm, respectively), while two others, 1f and 1i, emit blue shade (449 nm each) with reasonable emission intensity peak demonstrating that these derivatives are effective violet-to-blue TADF nominees. The lower ΔE ST value for derivative 1i (0.01 eV) with λ em values of 449 nm make this molecule the finest choice for blue TADF emitter amongst all the studied derivatives. We believe our research might lead to the development of more proficient blue TADF-OLEDs in the future.

An innovative approach to synthesize graft copolymerized acetylacetone chitosan/surface functionalized alginate/rutile for efficient Ni(II) uptake from aqueous medium.

In this study, an innovative approach is followed to synthesize graft copolymerized chitosan with acetylacetone (AA-g-CS) through free-radical induced grafting. Afterwards, AA-g-CS and rutile have been intercalated uniformly into amino carbamate alginate matrix to prepare its biocomposite hydrogel beads of improved mechanical strength having different mass ratio i.e., 5.0 %, 10.0 % 15.0 % and 20.0 % w/w. Biocomposites have been thoroughly characterized through FTIR, SEM and EDX analysis. Isothermal sorption data showed good fit with Freundlich model as conferred from regression coefficient (R2 ≈ 0.99). Kinetic parameters were evaluated through non-linear (NL) fitting of different kinetic models. Experimental kinetic data exhibited close agreement to quasi-second order kinetic model (R2 ≈ 0.99) which reveals that chelation between heterogeneous grafted ligands and Ni(II) is occurring through complexation. Thermodynamic parameters were evaluated at different temperatures to observe the sorption mechanism. The negative values of ΔG° (-22.94, -23.56, -24.35 and - 24.94 kJ/mol), positive ΔH° (11.87 kJ/mol) and ΔS° (0.12 kJ/molK-1) values indicated that the removal process is spontaneous and endothermic. The maximum monolayer sorption capacity (qm) was figured as 246.41 mg/g at 298 K and pH = 6.0. Hence, 3AA-g-CS/TiO2 could be better candidate for economic recovery of Ni(II) ions from waste effluents.

Exploration of high-performance triptycene-based thermally activated delayed fluorescence materials via structural alteration of donor fragment.

The utilization of thermally activated delayed fluorescence (TADF) materials in highly proficient organic light-emitting diodes (OLEDs) has attracted much attention. Based on TADF material TPA-QNX(CN)2, a series of three-dimensional donor-acceptor (D-A) triptycenes have been designed via structural modification of D-fragment. The influences of different D-fragments with various electron-donating strengths on the singlet-triplet energy gap (ΔEST), emission wavelength (λem), and electron/hole reorganization energy (λe/λh) are extensively studied by applying density functional theory (DFT) coupled with time-dependent density functional theory (TD-DFT). The computed results imply that as the electron-donating strength of the D-fragments increases, the ΔEST value decreases and λem is red-shifted for the molecules using the same acceptor units. Analogously, the 1CT‒3CT state splitting (ΔEST (CT)) is also decreased by enlarging the twist angle (ß) between the phenyl ring and alternative D-fragment. Therefore, efficient color tuning within a broad emission range (434-610 nm), as well as small ΔEST (CT) values (0.01-0.05 eV), has been accomplished by structural modification of the D-fragments. The greater electron-donating strength, the smaller ΔEST, and the smaller λh for PPXZ-QNX(CN)2 make it the best candidate among all the designed molecules.

Insighting the optoelectronic, charge transfer and biological potential of benzo-thiadiazole and its derivatives.

The current investigation applies the dual approach containing quantum chemical and molecular docking techniques to explore the potential of benzothiadiazole (BTz) and its derivatives as efficient electronic and bioactive materials. The charge transport, electronic and optical properties of BTz derivatives are explored by quantum chemical techniques. The density functional theory (DFT) and time dependent DFT (TD-DFT) at B3LYP/6-31G** level of theory utilized to optimize BTz and newly designed ligands at the ground and first excited states, respectively. The heteroatoms substitution effects on different properties of 4,7-bis(4-methylthiophene-2yl) benzo[c] [1,2,5]thiadiazole (BTz2T) as initial compound are studied at molecular level. Additionally, we also study the possible inhibition potential of COVID-19 from benzothiadiazole (BTz) containing derivatives by implementing the grid based molecular docking methods. All the newly designed ligands docked with the main protease (MPRO:PDB ID 6LU7) protein of COVID-19 through molecular docking methods. The studied compounds showed strong binding affinities with the binding site of MPRO ranging from -6.9 to -7.4 kcal/mol. Furthermore, the pharmacokinetic properties of the ligands are also studied. The analysis of these results indicates that the studied ligands might be promising drug candidates as well as suitable for photovoltaic applications.

A systematic study of the effects of thionation in naphthalene dimide derivatives to tune their nonlinear optical properties.

In the present study, the number and position of sulfur atoms on naphthalene diimide (NDI) is systematically investigated to tune its nonlinear optical (NLO) response properties. Our DFT calculations for third-order polarizability (γ) show that the thionation significantly influences the nonlinear optical property of NDI as it is seen among its several designed derivatives (NDI-1 to NDI-10). The smallest and the largest γzzzz amplitudes are 503.49 × 10-36 and 1299.5 × 10-36 esu for NDI-1 (having tetraone group) and NDI-10 (having tetrathione group), respectively. The increase in γzzzz amplitude for NDI-10 is 796 × 10-36 esu, which is ∼150% from the γzzzz amplitude of NDI-1. A comparison of the γzzzz amplitudes of our designed derivatives are made with para-nitroaniline i.e. a prototype NLO molecule. The γzzzz amplitude of pNA is found to be 42.64 × 10-36 esu at the same B3LYP/DZVP2 level of theory. Using two-level model, the origin of larger γzzzz amplitudes is traced in lower transition energy of NDI-10. Furthermore, the calculation of vertical ionization potentials (VIPs) shows that the thionation does not affect the stability of designed derivatives, where a slight difference of 0.06 eV is seen between the VIPs of NDI-1 (6.63 eV) and NDI-10 (6.57 eV). Thus, a systematic comparison of the third-order polarizability and other electro-optical properties of our designed derivatives shows that our derivative systems possess good potential for their practical realization in the field of optical and NLO materials.

Exploring the novel donor-nanotube archetype as an efficient third-order nonlinear optical material: asymmetric open-shell carbon nanotubes.

Contrary to the enormous number of previous studies on carbon nanotubes (CNTs), herein, we realized the origin of the intrinsic open-shell diradical character and second hyperpolarizability γ using a broken symmetry approach. This study was inspired by our recent findings (S. Muhammad, et al., Nanoscale, 2016, 8, 17998 and Nakano, et al., J. Phys. Chem. C, 2016, 120, 1193). We performed structural modifications through a unique asymmetric donor-nanotube framework, which led to a novel paradigm of modified CNTs with tunable open-shell diradical character and remarkably superior NLO response properties. Interestingly, asymmetry and diradical character were found to be the crucial factors to modulate the second hyperpolarizability γ. We initially performed a comparative analysis of the diradical characters and γ amplitudes of boron nitride nanotubes (BNNTs) and CNTs possessing significant ionic characters and covalent characters, respectively. The basic findings for these simple configurations were further extended to the donor-acceptor CNT paradigm, which finally led to excellent asymmetric donor-CNT configurations with remarkably larger γ amplitudes. Furthermore, among the CNTs, finite length zigzag CNT(6,0)3 were modified with different donor-acceptor configurations. Interestingly, for the first time, unique donor-nanotube configurations [1,4-(NH2)2CNT-(6,0)3 and 1,4-(NH2)2CNT-(6,0)5] were found; they showed significantly robust γ amplitudes as large as 2519 × 103 and 4090 × 103 a.u. at the LC-UBLYP(µ = 0.33)/6-31G* level of theory. Additionally, several molecular level insights have been obtained for these novel donor-nanotube configurations using their odd electron densities, molecular electrostatic maps, densities of states and γ density analyses to highlight the realization of these novel materials for highly efficient optical and NLO applications.