TD-DFT Calculations Research Articles

Solvent effect, DFT and NLO studies of A–π–D–π–A and A–π–D–π–D push–pull chromophore of 1,2-diazepin-4-ol based derivatives with optical limiting application

The nonlinear optical properties of push–pull chromophores, namely (E)-7-(4-bromophenyl)-2,5-bis(4-nitrophenyl)-3,4,5,6-tetrahydro-2H-1,2-diazepin-4-ol (A–π–D–π–A) and (E)-7-(4-bromophenyl)-5-(4-nitrophenyl)-2-phenyl-3,4,5,6-tetrahydro-2H-1,2-diazepin-4-ol (A–π–D–π–D), have been investigated using the z-scan technique. NMR, FT-IR, and UV–visible spectral analysis have been performed. The results were compared with density functional theory calculations employing the B3LYP/6-311++G (d, p) basis set. Geometry optimization, frontier molecular analysis, and TD-DFT calculations were conducted in various solvent environments to elucidate solute–solvent interactions. Gaussian 09 software was employed for natural bond orbital analysis, natural population analysis, and molecular electrostatic potential exploration. This comprehensive approach provides insights into the molecular structure and electronic properties of the investigated chromophores, shedding light on their potential applications in nonlinear optics. Normal coordinate analysis using the MOLVIB software has been used to assign the vibrational mode unambiguously. Theoretical second-order hyperpolarizability was computed, and NLO investigations have been employed to determine the second-order hyperpolarizability in both the polar and non-polar solvents. Further, the optical limiting capability was also examined.

Molecular engineering of BODIPY-bridged fluorescent probes for lysosome imaging - a computational study.

Lysosome imaging plays an important role in diagnosing many diseases and understanding various intracellular processes. Recently, B0 was reported as a fluorescent probe capable of detecting lysosomal viscosity changes. BODIPY is fused into the molecule as a bridge between the acceptor and donor components of B0, yielding nine new B molecules. Computational design and analysis of their optoelectronic properties were conducted to evaluate their effectiveness as fluorescent probes for lysosome imaging, with a specific target of HSA inside lysosomes. Optimized geometries reveal excellent π electron delocalization, resulting in nearly planar molecular structures. Frontier molecular orbital analysis suggests intramolecular charge transfer, along with π-π* transitions, from donor to bridge. TD-DFT calculations were performed to study absorption properties in the solvent phase, with B3PW91 showing good agreement with experiments. Molecular docking studies indicate that B derivatives can bind with HSA, and molecular dynamics simulations confirm their HSA targeting ability. This investigation highlights the introduction of BODIPY as a bridge for developing new probes capable of producing NIR fluorescence for bio-imaging, aiding in disease diagnosis.

High quantum yield blue fluorescent molecule of hydroxybenzo[c]chromen-6-ones: Synthesis and fluorescence characteristics

Hydroxybenzo[c]chromen-6-ones had been synthesized by the reaction of hydroxy‑substituted chalcone and ethyl acetoacetate in the presence of Cs2CO3 and their optical properties were then investigated. We found it particularly that dimethylamino-substituted hydroxybenzocoumarin 4e had extremely high quantum yield blue fluorescence (λem = 487 nm, ФF = 0.83) in dichloromethane and the fluorescence red shifted with the increase of solvent polarity, which had a good solvatochromic effect on the polarity of the solvent. Additionally, DFT and TD-DFT calculations were applied to explain and verify the good fluorescence properties of hydroxybenzo[c]chromen-6-one 4e.

Synthesis and photophysical properties of 3-aryl-2-cyanoacrylamides: Design of a turn-on fluorescent probe for cyanide ion detection

Three 3-aryl-2-cyanoacrylamide derivatives were synthesised in 71−79 % yields from cheap reagents and mild reaction conditions using the Et3N-mediated Knoevenagel condensation of fluorescent arylaldehydes (e.g., triphenylamine and anthracene) with cyanoacetamide. These dyes' photophysical properties and anions-recognizing behaviour were studied, revealing that the 9-anthracenyl derivative can "turn on" fluorescence in cyanide presence, with high selectivity and a detection limit (LOD) of 710 nM. Initially, there is fluorescence quenching by the energy transfer (ET) from the anthracene ring to the 2-cyanoacrylamide moiety due to the non-coplanarity of these fragments and, upon the cyanide addition to Cβ of the receptor unit, the intrinsic fluorescence of anthracene is restored. HRMS and NMR experiments and TD-DFT calculations were performed to confirm the detection mechanism and fluorescence properties of the design chemodosimeter; fluorescent test paper was also used to detect cyanide in an aqueous medium.

A theoretical approach to study oxide-based perovskite materials XTiO3 (X = Be, Mg, Ca, Sr and Ba) for photovoltaic applications

Oxide-based perovskite materials have a large application in fuel and hydrogen sensors, non-volatile random access memory devices, semiconductor fabrications, optoelectronic, thermoelectric and photovoltaic devices. In this report, equilibrium geometries, and optoelectronic properties of oxide-perovskite materials XTiO3 (X = Be, Mg, Ca, Sr and Ba) are investigated through Conceptual Density Functional Theory (CDFT) technique. The HOMO–LUMO energy gap obtained from functional B3LYP/LANL2DZ and B3PW91/LANL2DZ are observed in the range of 1.201 eV–4.647 eV and 1.519 eV–4.903 eV respectively, which justifies their applications in solar cells and optoelectronic devices. HOMO–LUMO energy gap shows a downward trend when materials travel from Be to Mg to Ca to Sr to Ba, except for BaTiO3 in B3PW91/LANL2DZ. BeTiO3 displays the maximum value of HOMO–LUMO gap, hardness and electronegativity value. Hardness and softness of these substances are found between 0.600–2.452 eV and 0.204–0.788 eV respectively whereas refractive index and dielectric constant of XTiO3 are observed in the range of 2.017–3.684 and 4.067–13.574 respectively. Across all relationships, XTiO3’s dielectric constant and refractive index show a rising pattern from Be to Mg to Ca to Sr to Ba, except for BaTiO3 computed using B3PW91/LANL2DZ. The lowest refractive index and dielectric constant are displayed by the BeTiO3. TD-DFT calculation is performed to understand the absorption spectra of these materials. Optical transition energy and wavelength of XTiO3 are found between 0.339–3.535 eV and 350.68–3656.15 nm respectively. An interesting relationship is established between HOMO–LUMO energy gap, optical transition energy and wavelength of XTiO3 materials. The investigated compounds exhibit a linear pattern between HOMO–LUMO energy gap and optical transition energy whereas wavelength shows an inverse trend. MEP of these compounds are also discussed.

The indenyl effect on d0 organotransition metal complex LMCT luminescence: Synthesis, structural characterization, cyclic voltammetry, spectroscopic studies, and TD-DFT computations on (η5-permethylindenyl)tetrachlorotantalum(V), and comparison to (η5-pentamethylcyclopentadienyl)tetrachlorotantalum(V)

The new organotantalum(V) chloride (η5-permethylindenyl)tetrachlorotantalum, Ind*TaCl4, was prepared by addition of previously-unreported Ind*SnBu3 to TaCl5 in toluene at 70° in 53 % isolated yield. The solid-state four-legged piano-stool structure, consistent with solution multinuclear NMR spectroscopies, demonstrated that tantalum is bonded to all carbons of the five-membered ring of the permethylindenyl ligand, with little deviation in the Ta-C distances. The permethylindenyl ring torsional angles for the three independent molecules in the unit cell vary from 2.46(17)° to 5.10(17)°. The cyclic voltammogram of Ind*TaCl4 in tetrahydrofuran showed one reversible reduction feature at −1.24 V [Ta(V)/Ta(IV)] and one quasi-reversible reduction feature at −1.65 V [Ta(IV)/Ta(III)] vs. Fc/Fc+. The UV/vis LMCT absorption λmax at 593 nm (ε = 2000 M−1 cm−1) in toluene is remarkably red-shifted from that of the known η5-pentamethylcyclopentadienyl analog, luminescent-yellow Cp*TaCl4. TD-DFT calculations were used to explain the comparative UV/vis absorption spectra.

Structural and Electronic Factors Controlling the Efficiency and Rate of Intersystem Crossing to the Triplet State in Thiophene Polycyclic Derivatives.

Thiophene polycyclic derivatives are widely used in organic light-emitting diodes, photovoltaics, and medicinal chemistry applications. Understanding the electronic and structural factors controlling their intersystem crossing rates is paramount for these applications to be successful. This study investigates the photophysical, electronic structure, and excited state dynamics of 1,2-benzodiphenylene sulfide, benzo[b]naphtho[1,2-d]thiophene, and benzo[b]naphtho[2,3-d]thiophene in polar aprotic and non-polar solvents. Steady-state absorption and emission spectroscopy, femtosecond transient absorption spectroscopy, and DFT and TD-DFT calculations are employed. Low fluorescence quantum yields of 1.2 to 2.7% are measured in acetonitrile and cyclohexene, evidencing that the primary relaxation pathways in these thiophene derivatives are nonradiative. Linear interpolation of internal coordinates calculations predict that an S-C bond elongation reaction coordinate facilitates the efficient intersystem crossing to the T1 state. Excitation of 1,2-benzodiphenylene sulfide and benzo[b]naphtho[1,2-d]thiophene at 350 nm or benzo[b]naphtho[2,3-d]thiophene at 365 nm, populates the lowest-energy 1ππ* state, which relaxes to the 1ππ* minimum in tens of picoseconds or intersystem crosses to the triplet manifold in ca. 500 ps to 1.1 ns depending on the position at which the benzene rings are added. Excitation at 266 nm does not affect the intersystem crossing rates. Laser photodegradation experiments demonstrate that the thiophene polycyclic derivatives are highly photostable.

Benzothiazole-based Schiff base for sensing Ca2+ ions: Synthesis, DFT studies, toxicity evaluation in zebrafish embryo and in silico analysis of MMP-9 inhibition

A new heterocyclic Schiff base, 2-(2-benzo(d)thiazol-2yl)hydrazono)methyl)phenol (BTAZ) synthesized from 2-hydrazinobenzothaizole and salicyclaldehyde was characterized by spectral, mass and single crystal XRD data and subjected to sense Ca2+ ions in methanol–water mixture (1:1, v/v) using UV–visible absorption and fluorescence emission spectral studies. The probe BTAZ showed specific detection of Ca2+ ions in a solution containing various metal ions with a detection limit as low as 5.1 × 10−6 M via photo-induced electron transfer (PET) pathway. The binding stoichiometry between BTAZ and Ca2+ was determined to be 2:1 by Job’s plot method. The stoichiometry and optical properties of both BTAZ and BTAZ-Ca2+ complex showed good correlation with theoretical results based on DFT and TD-DFT calculations. The pharmacological evaluation of the probe BTAZ against bacterial and fungal stains also demonstrated its notable efficacy to control their growth in vitro along with anti-oxidant capabilities. Further, toxicity assay of the probe BTAZ against zebrafish embryo did demonstrate that it is non-toxic to the test model in vivo. Ability of the probe BTAZ to inhibit matrix metalloproteinase-9 (MMP-9) enzyme was analyzed in detail using in silico experiments.

Probing the Local Environment in Potassium Salts and Potassium-Promoted Catalysts by Potassium Valence-to-Core X-ray Emission Spectroscopy.

Potassium plays an important role in biology as well as a promoter in heterogeneous catalysis. There are, however, limited characterization techniques for potassium available in the literature. This study elucidates the potential of element-selective X-ray emission spectroscopy (XES) for characterizing the coordination environment and the electronic properties of potassium. A series of XES measurements were conducted, primarily focusing on the VtC transition (Kβ2,5) of potassium halides (KCl, KBr, and KI) and oxide-bound potassium salts, including potassium nitrate (KNO3) and potassium carbonate (K2CO3). Across the series of potassium halides, the VtC transition energy is observed to increase, as accurately reproduced by TDDFT calculations. Molecular orbital analysis suggests that the Kβ2,5 transition is primarily derived from halide np contributions, with the primary factor influencing the energy shift being the metal-ligand distances. For oxide ligands, an additional Kβ″ transition appears alongside the Kβ2,5, which is attributed to a low-energy ligand ns, as elucidated by theoretical calculations. Finally, the XES spectra of two potassium-promoted catalysts for ammonia decomposition/synthesis were measured. These spectra show that potassium within the catalyst is distinct from other K salts in the VtC region, which could be promising for understanding the role of potassium as an electronic promoter.

In-silico antibacterial activity of piperazinyl-based copper(II) metallo-organic pharmacophores

The piperazinyl-based Cu(II)-Schiff base complex {[Cu(HL1′)(N3)]2∙(ClO4)2·4H2O} (1) [HL1′ is the Zwitter ionic form of (E)-2-((2-piperazin-1-ylethylimino)methyl)phenol] was synthesized and characterized by spectroscopic and single crystal X-ray diffraction studies. The X-ray single crystal structure analysis shows that the asymmetric unit of 1 contains a four-coordinate discrete complex cation, [Cu(HL1′)(N3)]+ (1a), with a perchlorate anion and a lattice water molecule. Two square planar units of 1a are dimerized by weak Cu···N intermolecular interaction, forming [Cu(HL1′)(N3)]2 2+ (1′a). DFT and TD-DFT calculations of the monomeric cationic unit, [Cu(HL1′)(N3)]+ (1a) were performed. In-silico antibacterial activities of HL1 as well as monomeric and dimeric cationic units 1a and 1'a, respectively, were performed and study shows that 1a (EC50 0.30 μM) and 1′a (EC50 0.06 μM) may be treated as antibacterial drugs after in-vivo analysis and clinical testing.

Ru-terpyridine complexes containing clotrimazole as potent photoactivatable selective antifungal agents

The overuse of antimicrobial agents in medical and veterinary applications has led to the development of antimicrobial resistance in some microorganisms and this is now one of the major concerns in modern society. In this context, the use of transition metal complexes with photoactivatable properties, which can act as drug delivery systems triggered by light, could become a potent strategy to overcome the problem of resistance. In this work several Ru complexes with terpyridine ligands and the clotrimazole fragment, which is a potent antimycotic drug, were synthesized. The main goal was to explore the potential photoactivated activity of the complexes as antifungal agents and evaluate the effect of introducing different substituents on the terpyridine ligand. The complexes were capable of delivering the clotrimazole unit upon irradiation with visible light in a short period of time. The influence of the substituents on the photodissociation rate was explained by means of TD-DFT calculations. The complexes were tested against three different yeasts, which were selected based on their prevalence in fungal infections. The complex in which a carboxybenzene unit was attached to the terpyridine ligand showed the best activity against the three species under light, with minimal inhibitory concentration values of 0.88 μM and a phototoxicity index of 50 achieved. The activity of this complex was markedly higher than that of free clotrimazole, especially upon irradiation with visible light (141 times higher). The complexes were more active on yeast species than on cancer cell lines.

Tripodal BODIPY-Tagged and Functional Molecular Probes: Synthesis, Computational Investigations and Explorations by Multiphoton Fluorescence Lifetime Imaging Microscopy.

A range of novel BODIPY derivatives with a tripodal aromatic core was synthesized and characterized spectroscopically. These new fluorophores showed promising features as probes for in vitro assays in live cells and offer strategic routes for further functionalization towards hybrid nanomaterials. Incorporation of biotin tags facilitated proof-of-concept access to targeted bioconjugates as molecular probes. Computational explorations using DFT and TD-DFT calculations identified the most stable tripodal linker conformations and predicted their absorption and emission behavior. The uptake and speciation of these molecules in living prostate cancer cells was imaged by single- and two-photon excitation techniques coupled with two-photon fluorescence lifetime imaging (2P FLIM).

Aromaticity in the Spectroscopic Spotlight of Hexaphyrins.

Spectroscopic properties are commonly used in the experimental evaluation of ground- and excited-state aromaticity in expanded porphyrins. Herein, we investigate if the defining photophysical properties still hold for a diverse set of hexaphyrins with varying redox states, topologies, peripheral substitutions, and core-modifications. By combining TD-DFT calculations with several aromaticity descriptors and chemical compound space maps, the intricate interplay between structural planarity, aromaticity, and absorption spectra is elucidated. Our results emphasize that the general assumption that antiaromatic porphyrinoids exhibit significantly attenuated absorption bands as compared to aromatic counterparts does not hold even for the unsubstituted hexaphyrin macrocycles. To connect the spectroscopic properties to the hexaphyrins' aromaticity behaviour, we analyzed chemical compound space maps defined by the various aromaticity indices. The intensity of the Q-band is not well described by the macrocyclic aromaticity. Instead, the degeneracy of the frontier molecular orbitals, the HOMO-LUMO gap, and the |ΔHOMO-ΔLUMO|2 values appear to be better indicators to identify hexaphyrins with enhanced light-absorbing abilities in the near-infrared region. Regions with highly planar hexaphyrin structures, both aromatic and antiaromatic, are characterized by an intense B-band. Hence, we advise using a combination of global and local aromaticity descriptors rooted in different criteria to assess the aromaticity of expanded porphyrins instead of solely relying on the absorption spectra.

Synthesis, crystal Structure, theoretical calculation and luminescence properties of Cu(Ⅱ), Co(Ⅱ), Ni(Ⅱ) and Zn(Ⅱ) quinolinyl benzimidazole complexes with multiple coordination number induced by proton

The innovative ligand H2L, featuring a benzimidazole structure substituted with 8-hydroxyquinoline and equipped with N,O donor sites, underwent successful synthesis and meticulous characterization. Notably, this ligand was exclusively synthesized through catalysis under protonated conditions, accompanied by an in-depth exploration of the catalytic mechanism. Employing single-crystal X-ray diffraction, we acquired and authenticated four distinct asymmetric double-decker sandwich mononuclear transition metal complexes: [Cu(HL)2]·2H2O, [Co(HL)2]·CH3OH, [Ni(HL)2] and [Zn(HL)2]·CH2Cl2. Among these, complex 1 revealed an intriguing five-coordinate Cu(II) center adopting a distorted square pyramidal geometry, whereas the central metal ions in complexes 2–4 exhibited a six-coordinate configuration, characterized by a distorted octahedral geometry. Noteworthy is the observation that the dihedral angles within the crystal structures of complexes 2–4 approached approximately 90° to a significant extent. To delve deeper into the electronic properties and transitions, meticulous DFT and TD-DFT calculations were performed on both the ligand H2L and complexes 1–4. Furthermore, a comprehensive investigation into the luminescence properties of both H2L and its complexes was conducted, revealing a pronounced luminescence quenching effect in the complexes compared to the ligand. Through thorough analysis utilizing Hirshfeld surface examination and IRI analysis, various weak intermolecular interactions within the system were elucidated.

Aggregation-Induced Emissive Feringa-Type Motor: Toward the Dual-Functional Motor in a Single Molecular Aggregation System.

Aggregation-induced emission (AIE)allows tunable photoluminescence via the simple regulation of molecular aggregation. The research spurt along this vein has also offered tremendous opportunities for light-responsive artificial molecular machines that are to be fully explored for performing versatile functions. Herein, the study reports a light-driven Feringa-type motor, when in the appropriate aggregation state, not only demonstrates the light-activated rotary motion but emits photons with good quantum yield. A semi-quantitative TD-DFT calculation is also conducted to aid the understanding of the competitive photoluminescence and photoisomerization processes of the motor. Cytotoxicity test shows this motor possesses good biocompatibility, laying a solid foundation for applying it in the bio-environment. The results demonstrated that the engagement of the aggregation-induced emission concept and light-driven Feringa-motor can lead to the discovery of the novel motorized AIEgen, which will further stimulate the rise of more advanced molecular motors capable of executing multi-functionalities.

An inclusive comparison regarding aggregation of surface active ionic liquid and conventional surfactant with a cationic dye Acridine Red exposed in view of spectroscopic and theoretical study

The investigation was conducted on the interaction of acridine red (AR) with sodium dodecyl sulfate (SDS) and 1-butyl-3-methyl imidazolium octyl sulfate (BMImOS) in both premicellar and post micellar concentrations. The interaction between AR and room temperature ionic liquid (RTIL) 1-butyl-3-methyl imidazolium bromide (BMImBr) was studied to understand the effect of imidazolium cation on micellization. Spectroscopic experiments, such as UV–visible absorption spectroscopy, steady-state fluorescence spectroscopy, time-resolved fluorescence spectroscopy, and dynamic light scattering, have been introduced. Various important parameters like spectral shifts, anisotropy, and aggregation number have been determined spectroscopically. However, a fresh insight into density functional theory calculations has also been provided. The observed results have been explained in terms of the aggregation behavior of the amphiphiles. A prominent redshift accompanied by a change in intensity is observed in the presence of surfactant and SAIL. However, in the case of BMImBr, no such spectral shift has been observed; only a decrease in spectral intensity highlights the quenching ability of the imidazolium cation. Average lifetime also provides some additional information regarding the difference in the formation of aggregates by SDS and BMImOS, which is further established from particle size density obtained from DLS. The salt like role of 1-butyl-3-methyl imidazolium cation also has been logically explained by anisotropy measurement and the determination of aggregation number. Using Gauss View 5.0 and Gaussian 09 package, the energy of optimization of each set of amphiphiles along with dye has been determined to follow the interaction at the molecular level. TDDFT calculations have also been performed to determine the structure of HOMO and LUMO.

Reversible Optical Switching of Polyoxovanadates and Their Communication via Photoexcited States.

The 2-bit Lindqvist-type polyoxometalate (POM) [V6O13((OCH2)3CCH2N3)2]2- with a diamagnetic {V6O19} core and azide termini shows six fully oxidized VV centers in solution as well as the solid state, according to 51V NMR spectroscopy. Under UV irradiation, it exhibits reversible switching between its ground S0 state and the energetically higher lying states in acetonitrile and water solutions. TD-DFT calculations demonstrate that this process is mainly initialized by excitation from the S0 to S9 state. Pulse radiolysis transient absorption spectroscopy experiments with a solvated electron point out photochemically induced charge disproportionation of VV into VIV and electron communication between the POM molecules via their excited states. The existence of this unique POM-to-POM electron communication is also indicated by X-ray photoelectron spectroscopy (XPS) studies on gold-metalized silicon wafers (Au//SiO2//Si) under ambient conditions. The amount of reduced vanadium centers in the "confined" environment increases substantially after beam irradiation with soft X-rays compared to non-irradiated samples. The excited state of one POM anion seems to give rise to subsequent electron transfer from another POM anion. However, this reaction is prohibited as soon as the relaxed T1 state of the POM is reached.

Investigation of substituent effects on the electronic structure and antiviral activity of favipiravir derivatives for Covid-19 treatment using DFT and molecular docking

In this study, Density-functional theory/Time-dependent density-functional theory (DFT/TDDFT) and Molecular docking method was used to investigate the effect of methyl acetate, tetrahydrofuran and cyanobenzylidene substituents on the electronic structure and antiviral activity of favipiravir for treating COVID-19. The DFT and TDDFT computations were employed using the Gaussian 09 software package. The values were calculated using the 6-311++G(d, p) basis set and the hybrid B3LYP functional method. Autodock vina software was used for simulations to better predictions and to validate the modified compounds' binding affinities and poses. Results of the study indicate that compounds 1 to 6 all displayed a planar structure, where the pyrazine ring, carboxamide, hydroxyl groups, and other substituents are all situated within the same plane. In addition, the energy gaps (Egap) of these six compounds (Cpd 1, 2, 3, 4, 5, and 6) were compared. The significant dipole moment and binding affinity achieved implies a particular orientation for binding within the target protein, signaling the anticipated strength of the binding interaction. In all six compounds, the electrophilic domain is situated in the vicinity of the amine functional group within the carboxamide compound, whereas the nucleophilic domain encompasses both the carbonyl and hydroxyl groups. The most negatively charged sites are susceptible to electrophilic interactions. In conclusion, compounds 5 and 6 exhibit a high binding affinity of the target protein, while compound 6 has a high energy gap, which could enhance its antiviral activity against the COVID-19 virus.

CPL of Mellein and Related Natural Compounds: Analysis of the ESIPT Phenomenon.

(R)-(-)-Mellein, (3R,4R)-4-hydroxymellein and (3R,4S)-4-hydroxymellein obtained from fungi, i. e. from Diplodia globulosa, were investigated as a class of natural products presenting ESIPT (excited state intramolecular proton transfer) phenomenon, through fluorescence and CPL (circularly polarized luminescence). The study was preceded by the assessment of the absolute configuration through ECD and VCD (electronic and vibrational circular dichroism) spectroscopies in addition to NMR spectra. It is found that ESIPT takes place in these systems very rapidly, and no dual fluorescence has been observed. The experimental study is backed up by TD-DFT calculations of ECD and CPL spectra, plus MD calculations to follow proton transfer in the excited state and careful analysis of the puckering dynamics of the lactone ring. Deprotonated forms of the three compounds were also investigated by the same chiroptical experimental and theoretical methods, showing how one can find in natural compounds not only biological activity but also biologically compatible sensing probes.

Synthesis, crystal structure, and DFT studies of NHC mediated Pd-PEPPSI complex: Application for Suzuki reaction

A novel air and moisture resistant Pd-PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) complex was synthesized via the reaction of benzimidazolium salt, PdCl2, KBr, K2CO3, and pyridine. The structure was characterized by spectroscopic methods such as 1H and 13C NMR, FT-IR, UV–vis. and single X-ray diffraction techniques. In order to evaluate the synthesized Pd complex in a detailed manner in terms of structural, bonding, electronic, and thermodynamic characteristics, DFT-based calculations were carried out at the B3LYP/6-311++G (d, p)/LANL2TZ theory level. Natural bond orbital (NBO) analysis was implemented to provide more insights about the possible donor-acceptor interactions and types of hybridization. Also, TD-DFT calculations were performed to rationalize the nature of the observed electronic transitions. The complex showed high catalytic activity in the Suzuki–Miyaura cross coupling of aryl chlorides with phenylboronic acid. Aryl chlorides bearing either electron- donating or withdrawing substituents afforded a wide range of biaryl derivatives that were isolated in the range of 55–97 % yields (7 examples). The reactions were carried out at very low catalyst loading (0.25 mol%) in the presence of air using a green water-based solvent (ipr:H2O/ 1:3). The palladium complex was found to be efficient for the coupling of aryl chlorides with arylboronic acids under aerobic conditions, affording the corresponding biaryls in high yields.