Heterocyclic Units Research Articles

Sterically Tuned Ortho-Phenylene-Linked Donor-Acceptor Benzothiazole-Based Boron Difluoride Complexes as Thermally-Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes.

Two donor-acceptor dyes with an ortho-phenylene-linked carbazole electron donor and a benzothiazole-fused boron heterocyclic acceptor were designed, synthesized, and spectroscopically investigated. Due to the steric effects of boron heterocyclic units, the dyes demonstrate different conformations in the crystalline state. The presence of numerous hydrogen-bonding intermolecular interactions and the very weak π-π stacking in the molecular packing results in intense solid-state emission with photoluminescence quantum yields of 40 and 18% for crystals and 50 and 42% for host-based light-emitting layers. The compounds show aggregation-induced emission and thermally activated delayed fluorescence (TADF). The received ionization potential and electron affinity values suggested good charge-injecting ability and bipolar charge-transporting properties of the developed dyes. Transport of holes and electrons was detected in layers of one dye by the time-of-flight measurements. The benzothiazole-based boron difluoride complexes showed high electron mobility of 1.5 × 10-4 and 0.7 × 10-4 cm2 V-1 s-1 at an electric field of 1.35 × 106 V cm-1. Therefore, these dyes were successfully applied as emitters in organic light-emitting diodes with external quantum efficiencies of 15 and 13%, respectively. Our study marks a critical advancement in the area of solid-state emissive boron difluoride dyes, which can be applied as TADF emitters into organic light-emitting diodes. The obtained results reveal that the orientation of the acceptor unit in the ortho-phenylene-linked donor-acceptor dyes makes a significant impact on the TADF activity.

Current Progress in Visible Light-induced Synthesis and Functionalization of N- and S-Heterocycles: A Sustainable Perspective

Heterocycles are of much importance as the majority of the existing drugs contain one or more heterocyclic units in their structures. Among all the heterocycles, nitrogen, and sulphurcontaining ones occupy major space, and they have special properties which make them suitable for the textile, cosmetic, and paint industries other than pharmaceutical. Recently, visible light has emerged as a powerful tool for performing various reactions at ambient temperatures and mild conditions and thus it has been used for the key step in the synthesis of many molecules. In addition, visible light assisted methods are usually cost and time effective. Thus, this review highlighted the recent developments in visible light induced methods for the synthesis of some selected biologically active N- and S- containing heterocycles such as benzothiazoles, indoles and triazoles and their functionalization. The advantages, green aspects and limitations of these methods have also been discussed.

Asymmetric phthalocyanine-based hole-transporting materials: evaluating the role of heterocyclic units and PMMA additive.

Two novel asymmetric phthalocyanine derivatives, ZnPc-1 and ZnPc-2, are synthesized to enhance charge transfer properties and mitigate deep-level traps on the perovskite surface using electron-rich nitrogen atoms. PSCs with ZnPc-1 and ZnPc-2 as hole-transporting materials (HTMs) achieved power conversion efficiencies (PCEs) of 12.11% and 8.98%, respectively. Incorporating a small amount of PMMA into the HTM solution significantly improved performance, resulting in PCEs of 16.2% and 12.5% for ZnPc-1 and ZnPc-2, respectively. The addition of PMMA enhances conductivity and prevents moisture intrusion, boosting both the efficiency and stability of PSCs.

Pragmatic Access to Hybrid Quinoxaline Scaffold Mediated by Elemental Sulfur Enabling Actualization to π-Extended and Aza-Annulated Heterocyclic Units.

A metal-free approach for synthesizing hybrid quinoxaline derivatives from sulfoxonium ylide and a 1,5-bis-nucleophilic N-heterocycle mediated by elemental sulfur is presented to illuminate the [5+1] cascade cyclization sequence. Large-scale synthesis and postsynthetic functionalizations for the annulative π-extension and intramolecular aza-annulation reactions reveal the potential utility and actualize the fabricated approach.

Induced nematic phase with improved thermal characteristics for new maleic anhydride derivatives

A new group of liquid crystalline materials, denoted as (E)-4-(((4-(2,5-Dioxo-2,5-dihydro-1H-pyrrol-1-yl)phenyl)imino)methyl)phenyl 4-(alkoxy)benzoate (In), was synthesized from maleic anhydride and investigated for their mesomorphic and optical properties. This group includes four derivatives with different flexible chain lengths (6, 8, 10, and 12 carbons) attached to the phenyl ring near the ester bond. Polarized optical microscopy (POM) and differential scanning calorimetry (DSC) were carried out to examine their mesophase characteristics. The thermogravimetric analysis (TG) was employed to evaluate the thermal stability of the homolog set (I6). Molecular structures were characterized using NMR, FT-IR, and elemental analysis techniques. All the produced derivatives show enantiotropic nematic mesophases, according to the results. The range and stability of the produced nematic phase are affected by the introduction of the heterocyclic maleic anhydride unit into the molecular structure. Furthermore, comparison with short-size documented derivatives establishes that the addition of extra phenyl azomethine moiety in the molecular structure induces the formation of nematic phases.

NaBH4‐Induced Chemoselective Mechanochemical Neat Synthesis of Bio‐Active Dihydrofuran/ϵ‐Hydroxy‐α,β‐Unsaturated Esters and Synthetic Application to Isoindoles

AbstractThe synthesis of small heterocycles under neat mechanochemical conditions is of great interest in the field of drug design because most of the commercially available drugs contain at least one heterocyclic unit. The sodium borohydride (NaBH4) promoted reductive cyclization to fused dihydrofuran under grinding technique is one of the compendium additions for the clean future. The development of chemoselective reduction under silica‐gel supported conditions represents significant progress in organic synthesis, offering a versatile and efficient method for selective reduction of specific functional groups within complex molecules. Synthesis of isoindole derivatives from the chemoselective reduce product via a sustainable short synthetic pathway is another significant process of our newly developed protocol. Finally, antileishmanial investigations of our synthesized compounds establish a soft bridge between biology and chemistry.

Synthesis and crystal structure of 1,3-bis-(acet-oxymeth-yl)-5-{[(4,6-di-methyl-pyridin-2-yl)amino]-methyl}-2,4,6-tri-ethyl-benzene.

In the crystal structure of the title compound, C26H36N2O4, the tripodal mol-ecule exists in a conformation in which the substituents attached to the central arene ring are arranged in an alternating order above and below the ring plane. The heterocyclic unit is inclined at an angle of 79.6 (1)° with respect to the plane of the benzene ring. In the crystal, the mol-ecules are connected via N-H⋯O bonds, forming infinite supra-molecular strands. Inter-strand association involves weak C-H⋯O and C-H⋯π inter-actions, with the pyridine ring acting as an acceptor in the latter case.

Synthesis and properties of new metal complexes containing heterocyclic moieties and investigation of the role of the metal in carbon dioxide gas capture

The continuous release of carbon dioxide (CO2) into the atmosphere will inevitably lead to greater environmental damage. The capture and storage of CO2 is one strategy to mitigate the harm associated with its high concentrations in the atmosphere. The design and synthesis of new materials to act as storage media for CO2 is currently an important challenge for researchers. In this regard, the investigation into the synthesis of new organometallic materials and their potential as CO2 storage media is reported. Therefore, the current work aimed to produce new materials using a simple procedure and investigate their properties, including factors affecting their CO2 adsorption. Four metal complexes containing heterocyclic units were synthesized using a simple method, and their structures were confirmed using several techniques. The surface morphology of the materials was inspected by microscopy. The metal complexes exhibited tunable particle sizes with diameters that ranged from 16.77 to 97.62 nm and a Brunauer‒Emmett‒Teller surface area of 1.20–4.01 m2/g. The materials can capture CO2 at 323 K and 40 bars, with the manganese-containing complex showing the highest CO2 storage capacity (13.1 cm3/gm).

Synthesis and Photophysical Characterizations of Benzimidazole Functionalized BODIPY Dyes.

Herein, a series of new BODIPY dyes substituted by 2-phenyl benzimidazole units at the meso (C8) position including methyl/ethyl, phenyl, or p-methoxyphenyl moieties at the distal and proximal positions of the BODIPY core have been successfully synthesized and their photophysical characteristics were analyzed. Experimentally investigating absorption and fluorescence profiles in the THF media was followed by density functional theory (DFT) calculations to clarify photophysical features. Theoretical analyses have revealed that upon excitation, both electrons and holes are confined solely within the BODIPY core. The energy levels of the frontier molecular orbitals converge depending on the presence of the phenyl and p-methoxyphenyl substituents. The orbital distributions of both electron and hole were in the -3 and -5 positions, which demonstrates a continuous conjugation with the BODIPY core at these sites. However, the electron density present on the phenyl rings located at the -1, -7, and -8 (meso) positions was found to be negligible. The benzimidazole-BODIPYs exhibited photodynamic activity (Φ∆) ranging from ~ 7% to ~ 11%, determined by a comparative method. Moreover, the compounds have shown to maintain their stability thermally in a non-reactive/inert environment up to temperatures surpassing 300°C, exhibiting primarily a two-phase decomposition process. These compounds have the potential to function as antibacterial and anti-biofilm agents when used in concentrations ranging from 0.5 to 2.0mg/mL. The results provide a basis for evaluating heterocyclic benzimidazole units on photophysical processes containing BODIPY chromophores.

µSR studies for radical reactions of unsaturated organophosphorus compounds

In this paper, the µSR studies of some unsaturated organophosphorus compounds containing heavier congeners of cyclobutane-1,3-diyl and anthracene are reviewed by discussing the usefulness of µSR for main group chemistry. The regioselective addition of muonium (Mu = [µ+e–]) to one of the skeletal phosphorus atoms in an electron-donating air-stable crystalline 1,3-diphosphacyclobutane-2,4-diyl leading to the paramagnetic 4-membered P-heterocycle was characterized by the Δ1 (ΔM = ± 1) resonance signal observed by muon (avoided) level-crossing resonance (µLCR). Meanwhile, a crystalline 1,3-diphosphacyclobutane-2,4-diyl bearing an electron-deficient nitrogen heterocyclic unit was analyzed by transverse-field muon spin rotation (TF-µSR) to characterize predominant muoniation at the skeletal radical carbon centre. A 9-phosphaanthracene bearing the trifluoromethyl (CF3) stabilizing groups at the peri positions was also investigated from the views of radical reactivity, and the regioselective addition of muonium to the skeletal sp2-type phosphorus atom was characterized by the muon hyperfine coupling (hfc) constant observed by TF-µSR and the Δ0 (ΔM = 0) signal of µLCR. The light mass of muon (Mass = 0.1134 amu) causes the larger zero-point energy and promotes the high-energy molecular structure in which the fused aromatic rings are almost flat, although the CF3 groups would prefer the non-planar saddle-like 9-phosphaanthracene skeleton.

Rational Design of Selenophene‐infused BODIPY Molecules as Fluorogenic Probes for Lung Tumor Imaging – A Computational Approach

AbstractThe BODIPY based molecules show promising properties towards bioimaging applications due to its structural flexibility and versatile optoelectronic characteristic features. Among many strategies in the development of such molecules, fusion of heterocyclic units into the BODIPY core structure is vital in tuning the π‐delocalization and spectral properties. Recently reported Thieno [3,2b] Thiophene based BODIPY (TTB) attracts a lot of attention while the caliber of their Selenophene derivatives are interesting and yet to be explored. Therefore, a systematic replacement of Sulphur by Selenium has been done on TTB and seven new selenophene fused TTB molecules are computationally designed and evaluated for their optoelectronic properties towards bioimaging of CDK2 kinase tumor cells. The optimized geometries indicate that all these molecules are showing excellent π‐delocalization and further stabilized by a range of intra‐molecular C−H−F and B−F−S/Se interactions. Molecular docking studies show that these TTB molecules are potential inhibitors and can be used for lung tumor imaging in biomedical applications. Molecular Dynamics analysis confirms their preferential binding inside the active site up to 100 ns. In summary, this study highlights the importance of Se replacement in designing new BODIPY‐based bioimaging candidates with excellent near‐IR luminescence and photo sensitizers for future biomedical applications.

Proton exchange membrane deriving from sulfonated N-heterocyclic poly(aryl ether ketone)s containing ether-free proton conducting units and performing enhanced physicochemical stability and conduction properties

Sulfonated aromatic polymer proton exchange membranes suffer from the trade-off relationship between physicochemical stability and proton conductivity hampering the membrane application in fuel cells. To bridge the effect, the high-performance membranes exhibiting excellent proton conduction behavior and good stability are constructed from sulfonated N-heterocyclic poly(aryl ether)s designed elaborately, in which the hydrophilic units are constructed by combining the high-density pendant benzenesulfonic groups and biphthalazindione structures without the introduction of weak linkage units like ether bonds. The twisted heterocyclic structures and the multiple interactions between heterocyclic structures and sulfonic groups enhance the physical stability and proton-conduction behavior with the highest conductivity of 256 mS cm−1 for the membranes. The membranes perform rupture time between 3.9 and 7.1 h in high temperature Fenton's oxidation test, exhibiting good chemical stability. The cells loading the membranes perform the maximum power density between 1.08 and 2.30 W cm−2. The above results verify the benefits of constructing ether-free heterocyclic hydrophilic units with high-density proton-conducting groups for the improvement of comprehensive membrane performance.

Effect of heterocyclic and non-heterocyclic units on FDT-based hole transport materials for efficient perovskite solar cells: a DFT study.

The development of a new structure is one of the important approaches for the advancement of efficient hole-transporting materials (HTMs). In this work, novel and efficient HTMs are designed based on the experimentally reported fluorene-dithiophene (FDT) system which shows the effect of four different units phenyl, pyridine, thiane, and oxane in the FDT unit. The structural, optoelectronic, and charge transport properties of the newly developed HTMs are probed using density functional theory (DFT) and time-dependent DFT (TD-DFT) methodologies. The calculated highest occupied molecular orbital (HOMO) energies for all HTMs are higher compared to the valence band energy level of the perovskite which exhibits outstanding hole extraction ability of all HTMs at the charge buffer interface. In addition, the designed HTMs have red-shifted absorption spectra compared to FDT. The computed hole mobilities of newly designed HTMs are faster compared to that of FDT. Moreover, newly tailored HTMs demonstrate improved solubility. The results indicate that a one thiane and one phenyl unit-based system among all materials is the most suitable for HTM design.

Intramolecular chaperone-assisted dual-anchoring activation (ICDA): a suitable preorganization for electrophilic halocyclization.

The halocyclization reaction represents one of the most common methodologies for the synthesis of heterocyclic molecules. Many efforts have been made to balance the relationship between structure, reactivity and selectivity, including the design of new electrophilic halogenation reagents and the utilization of activating strategies. However, discovering universal reagents or activating strategies for electrophilic halocyclization remains challenging due to the case-by-case practice for different substrates or different cyclization models. Here we report an intramolecular chaperone-assisted dual-anchoring activation (ICDA) model for electrophilic halocyclization, taking advantage of the non-covalent dual-anchoring orientation as the driving force. This protocol allows a practical, catalyst-free and rapid approach to access seven types of small-sized, medium-sized, and large-sized heterocyclic units and to realize polyene-like domino halocyclizations, as exemplified by nearly 90 examples, including a risk-reducing flow protocol for gram-scale synthesis. DFT studies verify the crucial role of ICDA in affording a suitable preorganization for transition state stabilization and X+ transfer acceleration. The utilization of the ICDA model allows a spatiotemporal adjustment to straightforwardly obtain fast, selective and high-yielding synthetic transformations.

Photoinduced energy transfer in sulfur-based heterocyclic compounds and corrole dyads

We have designed and synthesized three donor-acceptor systems in which corrole macrocycle is an energy acceptor and sulfur-based heterocyclic compounds such as thianthrene (S1-Cor), dibenzothiophene (S2-Cor) and benzothiophene (S3-Cor) are the donors at its meso phenyl position. The molecular integrity of all three D-A systems has been characterized by various spectroscopic techniques that include elemental analysis, 1H NMR and MALDI-MS. Differential functional theory studies suggest that the electron density of the highest occupied molecular orbital (HOMO) spread on both corrole and sulfur-substituted heterocyclic units whereas the lowest occupied molecular orbital (LUMO) spreads on corrole macrocycle only. Singlet excited state properties indicate that there is an efficient intramolecular photoinduced energy transfer (PEnT) from donor heterocyclic unit to corrole, when excited at [Formula: see text]290 nm. Förster theory was adopted to explain the PEnT reaction in these dyads. The time-correlated singlet photon counting (TCSPC) studies suggest that energy transfer rates ([Formula: see text] are found to be in the range of 1.06 × 109 S[Formula: see text] to 6.67 × 109 S[Formula: see text] and are solvent-dependent.

Modified porphyrin chromophores: Synthesis and spectroscopic properties of nitronaphtho[1,2-b]porphyrins, benzothieno[2,3-b]porphyrins and their metalated derivatives

A series of c-annulated pyrroles were prepared by reacting isocyanoacetate esters with dinitronaphthalenes in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene. The resulting nitronaphthopyrroles esters condensed with an acetoxymethylpyrrole to afford dipyrrylmethanes and following cleavage of the ester groups, acid-catalyzed condensation with a dipyrrylmethane dialdehyde afforded four isomeric nitronaphthoporphyrins. Three of these isomers showed only minor differences in their electronic spectra compared to a known naphtho[1,2-b]porphyrin, although in two cases the intensities of the Soret band absorptions were reduced. However, when the nitro group was placed at a position one removed from the porphyrin nucleus, the UV–vis spectrum showed two very broad peaks in the Soret band region as well as distorted Q bands. This effect was also noted for the corresponding nickel(II), copper(II) and zinc complexes. An example of a benzo[b]thiophene-fused porphyrin was also prepared in three steps from 3-nitrothiophene, but the fused heterocyclic unit had virtually no effect on the porphyrin chromophore. This study demonstrates that while fused naphthalene and benzo[b]thiophene units do not significantly affect the electronic structure of porphyrins, the introduction of a suitably placed electron-withdrawing group can induce profound changes.

Synthesis and Characterization of Some Metal Complexes Prepared from Schiff Base Ligand having Heterocyclic Unit

Synthesis and Characterization of Some Metal Complexes Prepared from Schiff Base Ligand having Heterocyclic Unit

Synthesis, mesomorphic and fluorescent properties of 1,3,4-oxadiazoles/thiadiazoles with a terminal 3-fluoro-4-cyanophenyl group

A series of new liquid crystalline 1,3,4-oxa/thiadiazoles with a terminal 3-fluoro-4-cyanophenyloxy group were synthesized, and their structures were characterized by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS). The liquid crystal properties were studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). All of the 1,3,4-oxadizoles exhibited only Nematic mesophase, while the 1,3,4-thiadiazole analogues displayed Smectic A (SmA) and Smectic C (SmC) over a wide temperature range. The fluorescent properties were investigated using ultraviolet–visible spectrophotometer (UV–Vis) and fluorescence spectrometer. The solutions of all final compounds in CH2Cl2 individually displayed one absorption band with λabs-max values at 319–340 nm, and exhibited an intense emission with λem-max values at 432–448 nm, and the photoluminescence quantum yields reached 0.52–0.66. The effects of the heterocyclic structural units, the terminal alkoxy chain length and the lateral fluorine atom on liquid crystalline and fluorescent properties were comparatively discussed.

Environmentally-friendly synthesis, structural determination and antimicrobial activity of new class of spiropyrrolidine embedded with indenoquinoxaline and chromanone heterocyclic units

A regio- and stereoselective synthesis of hitherto unexplored novel class of dispiropyrrolidine embedded with indenoquinoxaline and chromanone hybrid heterocycle has been achieved employing an eco-friendly ionic liquid assisted multicomponent 1,3-dipolar cycloaddition cascade protocol. The dipolarophile, 3-(4-methoxybenzylidene)chroman-4-one reacts with non-stabilized 1,3-dipole component derived from indenoquinoxalinone and l-phenylalanine through decarboxylative cascade reaction pathway affording (2′S,4′S)-5′-benzyl-4′-(4-methoxyphenyl)dispiro[chromane-3,3′-pyrrolidine-2′,11′'-indeno[1,2-b]quinoxalin]-4-one (6) as the final product. The structure of 6 was confirmed through NMR and mass spectroscopic analyses. Further, stereochemistry of the spirocompound was undoubtedly determined through single crystal XRD analysis. In the crystal structure, the O…H and N…H interactions are the most common contacts and also have great importance in molecular packing. In addition, the C…H contacts are also important in the studied crystal structure. DFT and NBO calculations were performed on this system in order to discuss its electronic and reactivity parameters. The calculated dipole moment value is 2.9238 Debye indicating a polar compound. Compound 6 was assayed for antimicrobial efficacy and found to have potential activity against eight tested microbial pathogens. Among them, E. coli ML_KSUB22 and C. albicans ML_KSUF05 were found to be highly susceptible than the other pathogens.

Benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole)-4-carbonitrile

Electron-withdrawing heterocyclic units are found in most organic optoelectronic materials. Benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) is an interesting new heterocyclic system, the chemical properties of which are much less studied than other fused thiadiazoles. Cyano derivatives of electron-accepting heterocycles are known as potential components of photoluminescent materials. In this communication, benzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole)-4-carbonitrile was successfully obtained via the cyanation of 4-bromobenzo[1,2-d:4,5-d′]bis([1,2,3]thiadiazole) with copper(I) cyanide in DMF. The structure of the newly synthesized compound was established by means of elemental analysis, high-resolution mass spectrometry, 1H and 13C NMR, and IR spectroscopy.