Structural Effects on the Electronic Properties of Extended Fused-Ring Thieno[3,4-b]pyrazine Analogues

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Enzyme-/metal-free quinoxaline assemblies: direct light-up detection of cholesterol in human serum

Supramolecular assemblies of quinoxaline derivative (QxPyA) have been developed for turn-on detection of cholesterol in human serum and in aqueous media with a detection limit of 4 nM.

Design and Characterization of Naphthalene Ionic Liquids

Surfactants have a great number of applications. Among these chemicals, petroleum sulfonates have been widely used due to their effectiveness in reducing interfacial tension. This is the case of sodium octylnaphthalene sulfonate which is a solid with a very low solubility in water. To overcome these drawbacks, this work aimed to synthesize new surface active ionic liquids based on a naphthalene sulfonate anion and traditional cations of these salts (imidazolium, pyrrolidinium, and pyridinium). The new chemicals showed high thermal stability, ionic liquid nature, and a stronger surfactant character than the original naphthalene. Moreover, they were found to be water soluble which greatly facilitates their application in the form of aqueous formulations. 1-Hexyl-3-methylimidazolium 4-(n-octyl)naphthalene-1-sulfonate showed the best capacity to reduce water-air and water-oil interfacial tension.

Elaboration of low-band-gap π-conjugated systems based on thieno[3,4-b]pyrazines

In order to understand the electronic contribution of the thienopyrazine building block on the electronic properties of π-conjugated systems, small molecules containing thiophene and thienopyrazine moieties are synthesized and jointly studied by theoretical (DFT) and experimental methods (UV-Vis, UPS). Taking advantages of these preliminar attractive results, four low band gap extended structures have been elaborated on the base of Donor-Acceptor-Donor sequences (DAD); these elongated π-conjugated molecules exhibit noticeable electronic and absorption properties spreading from the near UV to NIR regions.

Novel Riboflavin-Inspired Conjugated Bio-Organic Semiconductors

Flavins are known to be extremely versatile, thus enabling routes to innumerable modifications in order to obtain desired properties. Thus, in the present paper, the group of bio-inspired conjugated materials based on the alloxazine core is synthetized using two efficient novel synthetic approaches providing relatively high reaction yields. The comprehensive characterization of the materials, in order to evaluate the properties and application potential, has shown that the modification of the initial alloxazine core with aromatic substituents allows fine tuning of the optical bandgap, position of electronic orbitals, absorption and emission properties. Interestingly, the compounds possess multichromophoric behavior, which is assumed to be the results of an intramolecular proton transfer.

The effect of the fused-ring substituent on anthracene chalcones: crystal structural and DFT studies of 1-(anthracen-9-yl)-3-(naphthalen-2-yl)prop-2-en-1-one and 1-(anthracen-9-yl)-3-(pyren-1-yl)prop-2-en-1-one

The title chalcone compounds, C27H18O (I) and C33H20O (II), were synthesized using a Claisen-Schmidt condensation. Both compounds display an s-trans configuration of the enone moiety. The crystal structures feature inter-molecular C-H⋯O and C-H⋯π inter-actions. Quantum chemical analysis of density functional theory (DFT) with a B3LYP/6-311++G(d,p) basis set has been employed to study the structural properties of the compound. The effect of the inter-molecular inter-actions in the solid state are responsible for the differences between the experimental and theoretical optimized geometrical parameters. The small HOMO-LUMO energy gap in (I) (exp : 3.18 eV and DFT: 3.15 eV) and (II) (exp : 2.76 eV and DFT: 2.95 eV) indicates the suitability of these compounds for optoelectronic applications. The inter-molecular contacts and weak contributions to the supra-molecular stabilization are analysed using Hirshfeld surface analysis.

(E)-1,3-Bis(anthracen-9-yl)prop-2-en-1-one: crystal structure and DFT study

The title compound, C31H20O, was synthesized using a Claisen-Schmidt condensation. The enone group adopts an s-trans conformation and the anthracene ring systems are twisted at angles of 85.21 (19) and 83.98 (19)° from the enone plane. In the crystal, mol-ecules are connected into chains along [100] via weak C-H⋯π inter-actions. The observed band gap of 3.03 eV is in excellent agreement with that (3.07 eV) calculated using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. The Hirshfeld surface analysis indicates a high percentage of C⋯H/H⋯C (41.2%) contacts in the crystal.

Substituent influence in phenanthroline-derived ancillary ligands on the excited state nature of novel cationic Ir(iii) complexes

Influence of ancillary ligands derived from phenanthroline on the nature of the deactivation pathways of novel cationic Ir(iii) cyclometalated complexes.

Bulky 4,6-disubstituted tetraphenylethene–naphthalimide dyad: synthesis, copolymerization, stimuli-responsive fluorescence and cellular imaging

We report the design and synthesis of a tetraphenylethene substituted with naphthalimide at the 4, 6 positions, named NI-2TPE. NI-2TPE exhibits strong solvent-dependent emission properties with combined ICT and AIE characteristics in THF–H₂O systems. This probe was used directly on test papers to distinguish normal organic solvents using their emission colours under UV light based on its AIE and ICT nature. Thanks to the vinyl group in NI-2TPE, we synthesized a copolymer of NIPAM and NI-2TPE, termed P(NIPAM-co-NI-2TPE). The resulting polymer is highly soluble and fluorescent in water (Φ_F = 15.4%). Due to the well-known thermo-responsive character of NIPAM, P(NIPAM-co-NI-2TPE) exhibits an interesting fluorescence change in response to various temperatures. Due to the thermo-induced shrinking of the PNIPAM chain, the fluorescence intensity gradually increased from 20 to 34 °C. As the temperature further increased from 34 to 90 °C, the fluorescence intensity decreased sharply, which was caused by the well-known thermal effects. Furthermore, we synthesized a P(HEA-co-NI-2TPE–TPP acrylate) copolymer, in which HEA is a hydrophilic unit, TPP is a mitochondria label and NI-2TPE a fluorescent probe. The corresponding polymer probe is highly soluble in water with FLQY = 7% and we have further applied this probe as a mitochondria targeted imaging tracker in HeLa cells successfully.

A study of fused-ring thieno[3,4-e]pyrazine polymers as n-type materials for organic supercapacitors

Conjugated polymer pseudocapacitors achieve high capacitances because they store charge through fast, reversible redox reactions.

The optoelectronic properties of organic materials based on triphenylamine that are relevant to organic solar photovoltaic cells

A triphenylamine compound bridged with a pyrazine derivative was characterized theoretically using DFT and TD-DFT as a promising acceptor in BHJs.

DFT and TD-DFT calculation of new thienopyrazine-based small molecules for organic solar cells

BACKGROUND

Novel six organic donor-π-acceptor molecules (D-π-A) used for Bulk Heterojunction organic solar cells (BHJ), based on thienopyrazine were studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, to shed light on how the π-conjugation order influence the performance of the solar cells. The electron acceptor group was 2-cyanoacrylic for all compounds, whereas the electron donor unit was varied and the influence was investigated.

METHODS

The TD-DFT method, combined with a hybrid exchange-correlation functional using the Coulomb-attenuating method (CAM-B3LYP) in conjunction with a polarizable continuum model of salvation (PCM) together with a 6-31G(d,p) basis set, was used to predict the excitation energies, the absorption and the emission spectra of all molecules.

RESULTS

The trend of the calculated HOMO-LUMO gaps nicely compares with the spectral data. In addition, the estimated values of the open-circuit photovoltage (V_oc) for these compounds were presented in two cases/PC₆₀BM and/PC₇₁BM.

CONCLUSION

The study of structural, electronics and optical properties for these compounds could help to design more efficient functional photovoltaic organic materials.

Synthesis, Characterization, and Electropolymerization of Extended Fused-Ring Thieno[3,4-b]pyrazine-Based Terthienyls

The synthesis, characterization, and electropolymerization of a series of extended fused-ring thieno[3,4-b]pyrazine-based terthienyls are reported. The target terthienyls contain a central extended thieno[3,4-b]pyrazine analogue containing 2-thienyl units at the reactive α-positions of the central thiophene. The extended fused-ring thieno[3,4-b]pyrazine analogues studied include acenaphtho[1,2-b]thieno[3,4-e]pyrazine, dibenzo[f,h]thieno[3,4-b]quinoxaline, and thieno[3′,4′:5,6]-pyrazino[2,3-f][1,10]phenanthroline. Comparison of the electrochemical and photophysical properties to simple thieno[3,4-b]pyrazine-based terthienyls and their polymeric analogues are reported in order to provide structure-function relationships within this series of compounds and materials.

Thieno[3,4-b]pyrazine as an Electron Deficient π-Bridge in D-A-π-A DSCs

Thieno[3,4-b]pyrazine (TPz) is examined as an electron deficient π-bridge enabling near-infrared (NIR) spectral access in dye-sensitized solar cells (DSCs). Seven dissymmetric dyes for DSCs were synthesized (NL2-NL8) with TPz as the π-bridge utilizing palladium catalyzed C-H activation methodology. C-H bond cross-coupling was uniquely effective among the cross-couplings and electrophilic aromatic substitution reactions analyzed in monofunctionalizing the TPz building block. The TPz-based NL2-NL8 dyes examine the effects of various donors, π-spacers, and acceptors within the donor-π bridge-acceptor (D-π-A) dye design. Proaromatic TPz stabilizes the excited-state oxidation potential (E(s+/s*)) of the dyes by maintaining aromaticity upon excitation of the dye molecule. This leads to concise conjugated systems capable of accessing the NIR region. Through judicious structural modifications, dye band gaps were reduced to 1.48 eV, and power conversion efficiencies (PCEs) reached 7.1% in this first generation TPz-dye series.

Donor-Acceptor-Donor Thienopyrazines via Pd-Catalyzed C-H Activation as NIR Fluorescent Materials

A series of thienopyrazine-based donor-acceptor-donor (D-A-D) near-infrared (NIR) fluorescent compounds were synthesized through a rapid, palladium-catalyzed C-H activation route. The dyes were studied through computational analysis, electrochemical properties analysis, and characterization of their photophysical properties. Large Stokes shifts of approximately 175 nm were observed, which led to near-infrared emission. Computational evaluation shows that the origin of this large Stokes shift is a significant molecular reorganization particularly about the D-A bond. The series exhibits quantum yields of up to φ = >4%, with emission maxima ranging from 725 to 820 nm. The emission is strong in solution, in thin films, and also in isolation at the single-molecule level. Their stable emission at the single-molecule level makes these compounds good candidates for single-molecule photon sources in the near-infrared.

Design and Synthesis of Mixed Oligomers with Thiophenes, Dithienothiophene S,S-Dioxides, Thieno[3,4]pyrazines and 2,1,3-Benzothiadiazoles: Flipper Screening for Mechanosensitive Systems

Monomers with large surface area and high quantum yield, that is fluorescent flippers, have been engineered into twisted push–pull oligomers to create membrane probes with high mechanosensitivity and long fluorescence lifetime. Here, the synthesis and characterization of thieno[3,4]pyrazines and 2,1,3-benzothiadiazoles are described in comparison with the original dithienothiophene S,S-dioxides. Dithienothiophene S,S-dioxide flippers are confirmed as the best reported so far, and poor results with single flipper probes support that two flippers are needed for the probe to really “swim”, that is, for high mechanosensitivity.

Strengthening the acceptor properties of thiadiazoloquinoxalines via planarization

Fused aromatic ring extension strongly enhances the acceptor strength.

A concise method to prepare novel fused heteroaromatic diones through double Friedel–Crafts acylation

Different types of fused heteroaromatic diones have been successfully prepared through the concise intramolecular double Friedel–Crafts acylation strategy.

Thieno[3,4-b]pyrazines and their applications to low band gap organic materials

The application of fused-ring thieno[3,4-b]pyrazines in conjugated organic polymers has been found to be a powerful approach to the production of low band gap materials. While thieno[3,4-b]pyrazine-based materials date back to the early 1990s, significant advances in the preparation and scope of thieno[3,4-b]pyrazine-based materials have been reported in recent years, primarily in response to the increasing demand for reduced band gap materials in photovoltaic devices. In this review, we provide an overview of thieno[3,4-b]pyrazines and their application to conjugated materials, highlighting in particular the recent advances in the breadth of thieno[3,4-b]pyrazine building blocks and the promise of tuning materials to achieve optimal properties for specific applications.