New pyrimidine- and fluorene-containing oligo(arylene)s: synthesis, crystal structures, optoelectronic properties and a theoretical study

New pyrimidine containing oligo(arylene)s, notably the pyrimidine-fluorene hybrid systems 13-16, have been synthesised by Suzuki cross-coupling methodology. An efficient synthesis of the key reagent 9,9-dihexylfluorene-2,7-diboronic acid 10 from 2,7-dibromo-9,9-dihexylfluorene 9 is reported. Cross-coupling of 10 with two equivalents of 2-bromopyrimidine, 5-bromopyrimidine and 2,5-dibromopyrimidine gave 2,7-bis(2-pyrimidyl)-9,9-dihexylfluorene 13. 2,7-bis(5-pyrimidyl)-9,9-dihexylfluorene 14 and 2,7-bis(5-bromo-2-pyrimidyl)-9,9-dihexylfluorene 15 in 23-34% yields. A further two-fold Suzuki reaction of benzeneboronic acid with compound 15 gave 2,7-bis(5-phenyl-2-pyrimidyl)-9,9-dihexylfluorene 16 (35% yield). Ab initio calculations of the geometries and electronic structures at the Hartree Fock (HF) and density functional theory (DFT) levels of theory are reported for compounds 13, 14 and 16 (with ethyl substituents replacing hexyl) and for their dipyrazinyl and bistetraazenyl analogues, 17, 18, 20 and 21. The heterocyclic nitrogen atoms of 13 and 16 facilitate planarisation of the system, compared to 14, which is in agreement with X-ray structural data obtained for 5-bromo-2-phenylpyrimidine 6, 2,5-diphenylpyrimidine 7 and compound 15. Bistetrazenyl derivative 21 is calculated to be a fully planar system. The cyclic voltammogram (CV) of compound 16 in dichloromethane solution shows a quasi-reversible oxidation wave at E(1/2)0 = +1.36 V (vs. Ag/Ag+). Compound 13 is a poorer donor with an oxidation observed at Epa = +1.50 V which is in good agreement with the difference in the energies of their HOMO orbitals calculated at both HF and DFT levels of theory (0.11-0.12 eV). For compound 14 we were not able to measure an Eox potential which should lie at much more positive potentials. Compounds 15 and 16 are blue emitters in solution, with photoluminescence quantum yields (PLQY) of 25% and 85%, respectively. For thin films of 16 the PLQY is reduced to 21%. An OLED using compound 16 as the emissive layer has been fabricated in the configuration ITO/PEDOT/16/Ca/Al: blue-green light (lambda max 500 nm) most likely emanating primarily from excimer states is emitted at a high turn-on voltage.     

Synthesis, self-assembly, and photophysical properties of cationic oligo(p-phenyleneethynylene)s

Three series of cationic oligo p-phenyleneethynylenes (OPEs) have been synthesized to study their structure-property relationships and gain insights into the transition from molecular to macromolecular properties. The absorbance maxima and molar extinction coefficients in all three sets increase with increasing number of repeat units; however, the increase in λ(max) between the oligomers having 2 and 3 repeat units is very small, and the oligomer having 3 repeat units shows virtually the same spectra as a p-phenyleneethynylene polymer having 49 repeat units. A computational study of the oligomers using density functional theory calculations indicates that while the simplest oligomers (OPE-1) are fully conjugated, the larger oligomers are nonplanar and the limiting "segment chromophore" may be confined to a near-planar segment extending over three or four phenyl rings. Several of the OPEs self-assemble on anionic "scaffolds", with pronounced changes in absorption and fluorescence. Both experimental and computational results suggest that the planarization of discrete conjugated segments along the phenylene-ethynylene backbone is predominantly responsible for the photophysical characteristics of the assemblies formed from the larger oligomers. The striking differences in fluorescence between methanol and water are attributed to reversible nucleophilic attack of structured interfacial water on the excited singlet state.     

Sulfonyl-bridged oligo(benzoic acid)s: synthesis, X-ray structures, and properties as metal extractants

Sulfonyl-bridged oligo(benzoic acid)s 7 _n (n = 2–4) are prepared from the corresponding triflate esters (8 _n ) of sulfur-bridged oligophenols by palladium-catalyzed methoxycarbonylation of the triflate moieties, followed by hydrolysis of the resulting methyl esters, and subsequent oxidation of the sulfur bridges. X-ray analysis reveals that dimer 7 ₂ forms supramolecular zig-zag chains through intermolecular hydrogen bonds between the carboxy groups. As for the crystal of trimer 7 ₃ , two molecules are associated through two couples of intermolecular hydrogen bonds between terminal and central carboxy groups to form a cyclic dimer, which connects with two adjacent dimers with the remaining carboxy groups to construct an infinite columnar structure. Tetramer 7 ₄ adopts a monomolecular cyclic structure through intramolecular hydrogen bonds between the terminal carboxy groups, and a molecule connects with each of two adjacent molecules through two couples of intermolecular hydrogen bonds between inner carboxy and sulfonyl groups. Solvent extraction experiments reveal that the oligo(benzoic acid)s exhibit high extractability toward lanthanoid ions (Ln³⁺); the performance follows the order 7 ₄  ≈ 7 ₃  > 7 ₂ . Moderate extraction selectivity is observed for the extraction of Pr³⁺, Gd³⁺, and Yb³⁺ with 7 ₂ . X-ray crystallographic analysis of cluster [Tb₄L₄(H₂O)₆](Et₃NH)₄, which was prepared from 7 ₄ (H₄L) and Tb(NO₃)₃·6H₂O in the presence of Et₃N, reveals that no sulfonyl oxygens coordinate to the metal centers. This indicates that the high extractability of 7 ₄ originates from the electron-withdrawing nature of the sulfonyl function, which increases the acidity of two adjacent carboxy groups.     

Combinatorial synthesis of oligo(phenylene ethynylene)s

The combinatorial synthesis of oligo(phenylene ethynylene) tetramers, both in solution and on solid support, is described. These products are of interest for molecular electronics applications. An iterative sequence, coupling of aryl halides to alkynes under Sonogashira conditions, was used. Five monomers functionalized with electron-donating or electron-withdrawing groups were synthesized, and used to generate a library of 25 trimers in a solution-phase based process. A library of 24 tetramers was prepared by subsequent protodesilylation and coupling with the alligator clip 4-iodo-1-thioacetylbenzene. The solution-phase based sequence was successfully adapted to a higher yielding directed split-and-pool solid-phase process, with average yields of 78–86% for each step over seven steps. A triazene linker group was used to attach the starting monomer to the polymer beads. At the completion of the solid-phase-based process, traceless cleavage of trimers from the resin was achieved by sonication of the resin in 10% HCl/THF solution. The released products were then poised for the final step in the sequence, attachment of the alligator clip.     

m-Phenylene-linked aromatic poly(aminium cationic radical)s: persistent high-spin organic polyradicals

[structure: see text] High molecular weight and networked aromatic polyamines prepared by palladium-catalyzed polycondensation were oxidized to yield the corresponding poly(aminium cationic radical)s, which displayed a substantial stability and an intramolecular ferromagnetic interaction of eight or nine spins.     

New poly(phenyleneethynylene)s with cationic,facially amphiphilic structures

Polymers based on meta substituted phenylene ethylene are prepared with patterned polar and nonpolar groups to favor an extended conformation. These polymers were characterized at the air-water interface by Langmuir techniques and found to form stable monolayers with an extended conformation based on molecular models. In addition, these polymers show phospholipid membrane activity as measured by induced leakage of calcein from large unilamellar vesicles. These polymers represent new facially amphiphilic structures which are cationic in nature and surface active.     

Iterative synthesis of heterotelechelic oligo(phenylene-vinylene)s by olefin cross-metathesis

A novel iterative synthesis of heterotelechelic oligo(phenylene-vinylene)s using olefin cross-metathesis is reported. The metathesis homologation proceeds in good yields and allows for further functionalization, including the facile formation of donor-acceptor complexes and repeating sequence copolymers.     

Preparative fluorous mixture synthesis of diazonium-functionalized oligo(phenylene vinylene)s

[structure: see text] A series of building blocks for the synthesis of oligo(phenylene vinylene)s (OPVs) and hybrid oligomers were prepared, and alternating Heck coupling and Horner-Wadswoth-Emmons (HWE) reactions were used to couple the building blocks. Model studies were carried out to optimize the reaction strategies. The products were made to bear aryl diazonium functionalities that allow them to be used as surface grafting moieties in hybrid silicon/molecule assemblies. A library of OPV and hybrid oligomer tetramers was synthesized using fluorous mixture synthesis (FMS). The fluorous tags, which are secondary amines bearing different numbers of fluorine atoms, were synthesized and used as phase tags in mixture synthesis. The tags and substrates were anchored together by triazene linkages. The mixture synthesis was monitored by analytical HPLC on a fluorous column, and isolation of final OPV and hybrid oligomer tetramers was achieved by preparative HPLC. At the end of the FMS, after demixing, the tagged products were detagged by cleaving the triazene linkage and generating a series of aryl diazonium compounds. The fluorous tags could be recovered and reused. The NMR spectra of the 1-aryl-3,3-dialkyltriazenes are discussed.     

Fast and solvent-free microwave-assisted synthesis of thermoresponsive oligo(glycidyl ether)s

Low-molecular weight linear poly(glycidyl ether)s are typically synthesized via the “classical,” oxy-anionic ring-opening polymerization (ROP) of glycidyl ether monomers at elevated temperatures. To reduce reaction times, a fast process was developed to synthesize oligo(glycidyl ether)s (OGEs) in bulk at a gram-scale utilizing microwave heating. Well-defined thermoresponsive copolymers comprising glycidyl methyl ether and ethyl glycidyl ether with molecular weights of up to 3 kDa were synthesized via microwave-assisted ROP with reaction times of approximately 10 min. The fast reaction kinetics were attributed to the rapid and uniform heating and high temperatures reached during the reaction. Consequently, no significant microwave-specific acceleration of the oxy-anionic ROP was observed. The temperature-triggered phase transition of the OGEs in aqueous solution revealed cloud point temperatures that are highly dependent on the OGE molecular weight, concentration, and comonomer composition, which extends previously reported data. Furthermore, oligo(glycidyl ether) acrylates (OGEAs) with reactive, functional end groups were directly accessible via in situ quenching of the anionic, microwave-assisted ROP with acrylic acid chloride. The obtained thermoresponsive OGEA macromonomers represent a promising material for the functionalization of surfaces via radical grafting methods to obtain functional, thermoresponsive coatings with potential application in cell culture. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2496–2504     

Novel synthesis of protected thiol end-capped stilbenes and oligo(phenylenevinylene)s (OPVs)

The first general procedures for preparation of thiol end-capped stilbenes and oligo(phenylenevinylene)s (OPVs) with tert-butyl- and acetyl-protected thiol termini have been developed. These reactions proceed via Br/Li exchange, McMurry, and Wittig-type reactions. The thiol functionality is protected against strong basic and acidic reaction conditions as a t-Bu sulfide. As a key point in the method, reprotection of the thiol group is accomplished by means of acetyl chloride and boron tribromide. The novel strategy forms the basis for stepwise introduction of 4-mercaptostyryl units in OPVs. The new mono-, di-, and trimercapto OPVs have potential applications as one, two, and three terminal molecular devices in gold nanoparticle clusters, self-assembled monolayers, and optoelectronic devices.     

Organoantimony(V) cyanoximates: synthesis,spectra and crystal structures

A series of 25 new organoantimony(V) cyanoximates has been synthesized and studied using IR, visible, and NMR spectroscopy and X-ray analysis. Crystal structures were determined for compounds (C6H5)4Sb[ONC(CN)C(O)NH2] (1) and (C6H5)4Sb[ONC(CN)C(O)N(CH3)2] (2). Both complexes crystallized in the monoclinic space group P2(1)/c (Z = 4) with unit cell parameters (A, grad) of a = 14.921(3), b = 10.165(2), c = 17.571(7), beta = 113.26(6) for compound 1, and a = 16.415(4), b = 10.406(3), c = 17.152(3), beta = 17.152(3), beta = 117.79(2) for compound 2. For 5438 and 5056 independent reflections the refinement yielded R-factors 0.022 and 0.037 for the structures of 1 and 2, respectively. Cyanoxime anions are bound to the antimony(V) atoms in a monodentate fashion via the oxygen atoms of the oxime groups. The ligands adopt trans-anti configuration in these compounds. The coordination polyhedron in both complexes is a distorted trigonal bipyramid with the axial location of the cyanoxime ligand. A similar binding mode of other anions in synthesized organoantimony(V) complexes has been offered on the basis of the similarity of their IR spectra to those of the compounds whose structures were determined crystallographically. The exact assignment of vibrations involving the oxime group was carried out using synthesized 15N(53%), isotopomers.     

Carbodithioate-terminated oligo(phenyleneethynylene)s: synthesis and surface functionalization of gold nanoparticles

Carbodithioate-terminated bis(phenylene)ethynylenes and oligo(phenyleneethynylene)s have been synthesized from TMSE-protected 4-iododithiobenzoic acid ester (1) and 4-ethynyldithiobenzoic acid ester (3) via Pd-catalyzed cross-coupling reactions. TEM and spectroscopic studies demonstrate that the reaction of 4-(phenylethynyl)dithiobenzoate with alkylamine-protected gold nanoparticles (AuNPs) produces the corresponding organocarbodithioate-functionalized AuNPs.     

Synthesis of dendritic oligo(aryl sulfone)s as supports for synthesis

A short, divergent route to G₁ oligo(aryl sulfone)s and a G₂ oligo(aryl sulfone) dendrimer using nucleophilic aromatic substitution reactions is described. A range of tetrasubstituted pentasulfones are proposed for applications as homogeneous supports for synthesis. Key to achieving selectivity in the syntheses is the activation of leaving groups by sulfide to sulfone oxidation. Preparation of the G₂ oligo(aryl sulfone) is low-yielding due to competition from SET processes that are interesting from a mechanistic point of view. The utility of the supports is exemplified with a four step synthesis of a dipeptide and by ‘react and release’ synthesis of amides.     

The synthesis and condensation of oligo(phenylenevinylene)s with alkoxysilyl end groups

Monodisperse alkoxylated oligo(phenylenevinylene)s with 3, 4, or 5 benzene rings were connected to reactive di- and triethoxysilanes, either directly or via flexible spacers. Aminopropylsilanes were condensed with stilbenoid aldehydes and subsequently reduced to amines, for the direct, rigid connection, the Heck reaction and also cross-metathesis with vinyl silanes proved to be successful routes. Hydrolysis of the ethoxysilanes leads to polymerisable cyclosiloxanes or curable three-dimensional networks with pendent chromophores.     

Facile synthesis of 9,10-diarylphenanthrenes and poly(9,10-diarylphenanthrene)s

One-pot reduction of 9,10-diaryl-9,10-dihydrophenanthrene-9,10-diols to 9,10-diarylphenanthrenes was achieved with Zn/H+ in acetic acid. Accordingly, various novel phenanthrenes and polyphenanthrenes with efficient blue emission were easily synthesized.     

Efficient synthesis and properties of soluble aliphatic oligo(spiroorthocarbonate)s from pentaerythritol derivatives

A series of soluble oligo(spiroorthocarbonate)s (OSOCs) were synthesized by polycondensation of tetraethylorthocarbonate with pentaerythritol derivatives. The pentaerythritol derivatives used herein were synthesized from pentaerythritol by attaching substituents on it to improve the solubility of themselves and the resulting OSOCs. The structures of the OSOCs were confirmed by NMR spectroscopy and MALDI‐TOF mass analysis. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 792–798     

Oxalate-bridged dirhenium(I) hexacarbonyl complexes: synthesis, reactions, and crystal structures

The complex [{Re(CO)₅}₂(μ,η¹:η¹-C₂O₄)] 1 undergoes thermal decarbonylation to give [Re₂(CO)₆(C₂O₄)]_n, which reacts with triphenylphosphine and trans-1,2-bis(diphenylphosphino)ethylene (dppene) to give anti-[Re₂(PPh₃)₂(CO)₆(μ,η²:η²-C₂O₄)] 2 and [Re₂(μ-dppene)(CO)₆(μ,η²:η²-C₂O₄)] 4, respectively. Complex 2 is oxidized on prolonged exposure to air (1 week) to form anti-[Re₂(OPPh₃)₂(CO)₆(μ,η²:η²-C₂O₄)] 3. In the presence of excess dppene, the complex [Re₂(μ-dppene)₂(CO)₆(μ,η¹:η¹-C₂O₄)] 5 is also formed alongside 4. With the chelating diphosphine 1,3-bis(diphenylphosphino)propane (dppp), the complex [(η²-dppp)Re(CO)₃(μ,η¹:η¹-C₂O₄)Re(CO)₃(η²-dppp)] 6 is formed. The structures of 3 and 4 have been determined by X-ray crystallography. The dppene ligand in complex 4 adopts an unusual “syn” conformation wherein the two phosphorus lone pairs of electrons are eclipsed, thus forming an “A-frame” type of bridge.