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.     

Guanine-containing copper(II) complexes: synthesis, X-ray structures and magnetic properties

Three new compounds of formula {[Cu(gua)(H(2)O)(3)](BF(4))(SiF(6))(1/2)}(n) (1), {[Cu(gua)(H(2)O)(3)](CF(3)SO(3))(2).H(2)O}(n) (2) and [Cu(gua)(2)(H(2)O)(HCOO)]ClO(4).H(2)O.1/2HCOOH] (3) [gua = 2-amino-1H-purin-6(9H)-one] showing the unprecedented coordination of neutral guanine, have been synthesised and structurally characterized. The structures of the compounds 1 and 2 contain uniform copper(II) chains of formula [Cu(gua)(H(2)O)(3)](n)(2n+), where the copper atoms are bridged by guanine ligands coordinated via N(3) and N(7). The electroneutrality is achieved by uncoordinated tetrafluoroborate and hexafluorosilicate (1) and triflate (2). Each copper atom in 1 and 2 is five-coordinated in a distorted square pyramidal environment: two water molecules in trans positions and the N(3) and N(7a) nitrogen atoms of two guanine ligands build the basal plane whereas a water molecule fills the axial position. The values of the copper-copper separation across the bridging guanine ligand are 7.183(1) (1) and 7.123(1) A (2). is an ionic salt whose structure is made up of mononuclear [Cu(gua)(2)(H(2)O)(HCOO)](+) cations and perchlorate anions plus water and formic acid as crystallization molecules. The two guanine ligands in the cation are coordinated to the copper centre through the N(9) atom. The copper atom in 3 is four-coordinated with two monodentate guanine molecules in the trans position, a water molecule and a monodenate formate ligand building a quasi square planar surrounding. Magnetic susceptibility measurements for 1 and 2 in the temperature range 1.9-300 K show the occurrence of significant intrachain antiferromagnetic interactions between the copper(ii) ions across the guanine bridge [J = -9.6(1) (1) and -10.3(1) cm(-1) (2) with H = -J summation operator(i)S(i).S(i+1)].     

Facile synthesis, crystal structures, and high-spin cationic states of all-para-brominated oligo(N-phenyl-m-aniline)s.

Syntheses of both the dimer (3) and the trimer (4) of all-para-brominated poly(N-phenyl-m-aniline)s (2c) were achieved in a one-pot procedure from the parent nonbrominated oligomers and benzyltrimethylammonium tribromide [(BTMA)Br(3)]. An X-ray crystallographic analysis revealed that 4 has a U-shaped structure, suggesting that 2c easily adopts helical structures. Furthermore, the redox properties were investigated by the UV-vis and EPR measurements. It was confirmed that the both 3 and 4 can be oxidized into the dications 3(2+) and 4(2+) with triplet spin-multiplicity.     

Two transition metal supramolecular compounds based on 2-(4-isopropylbenzoyl)benzoic acid: syntheses,crystal structures,and luminescent properties

Two new supramolecular compounds, [Zn₂(L)₃(4,4′-bpy)(OH)]_n (1) and [Cd(L)₂(2,2′-bpy)(H₂O)]·2H₂O (2) (HL?=?2-(4-isopropylbenzoyl)benzoic acid, 4,4′-bpy?=?4,4′-bipyridine, 2,2′-bpy?=?2,2′-bipyridine), have been hydrothermally synthesized and characterized by elemental analysis, infra-red spectroscopy, thermal gravimetric analyzes, and single-crystal X-ray diffraction. 1 exhibits 1-D chain and 2 is 0-D mononuclear. They are both linked into 2-D supramolecular layers by non-covalent interactions. Luminescence properties were also investigated.     

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.     

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.     

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     

Photophysical properties of oligo(2,3-thienyleneethynylene)s

Photophysical properties of oligo(2,3-thienyleneethynylene)s (nTE, n denotes the number of thiophene rings, n = 2, 3) in benzene were investigated using steady-state, time-resolved fluorescence, and transient absorption spectroscopies. For 2TE, generation of the radiative S2 and nonradiative S1 states was confirmed. Upon excitation, the S2 state was initially generated and deactivated to the S1 state within 10 ps. The S1 state exhibited the transient absorption band at 470 nm, of which the lifetime was estimated to be 5.3 ns. In the case of 3TE, on the other hand, it was revealed that the radiative S1 state with a transient absorption peak at 650 nm was generated upon excitation. The T1 states of nTE were generated from the S1 states. The quantum yields were estimated to be 0.52 and 0.54 for 2TE and 3TE, respectively. Extremely fast reactions in the higher triplet excited state were indicated for both 2TE and 3TE.     

Molecular brushes based on poly(amino acid)s: synthesis,structures, and applications

Polymer science is witnessing rapid advancements in the precision construction of synthetic macromolecules. Beyond the impressive advances in molecular brush, the integration of poly(amino acid)s into bottlebrush architectures leads to a novel class of materials known as molecular brushes based on poly(amino acid)s (MBPAs). These materials not only possess biorelated functions but also enable the incorporation of the diverse secondary structures found in poly(amino acid)s into the bulk polymers. Here we present a comprehensive and critical summary of three synthetic strategies and three different constructions for MBPAs. Furthermore, we highlight their potential in the development of advanced materials for a broad range of applications, encompassing antimicrobial activity, pharmaceutical delivery, and bioimaging.     

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.     

Synthesis and physical properties of triptycene-based oligo(p-phenyleneethynylene)s

A series of symmetrical and unsymmetrical triptycene-based oligo(op-phenyleneethynylene)s were synthesized by deprotection of the acetone protected terminal alkynes, followed by Sonogashira coupling reactions. The photophysical properties of triptycene-based OPEs both in solution and solid state have been investigated by UV–Vis and fluorescence spectroscopy. Interestingly, the obtained compounds show strong fluorescence with partly high quantum yields in solid state, which suggested that triptycene moieties have not only prevented the intermolecular aggregation but also enforced the coplanarity of OPEs backbone in the solid state.     

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.     

Calix[4]arene-thiacrown-5 di(carboxylic acid) regioisomers as metal ion extractants

A regioisomer of a previously reported p-tert-butylcalix[4]arene-1,3-thiacrown-5 di(carboxylic acid) is prepared in which the thiacrown ring attachment sites are moved from distal phenolic oxygens of a cone p-tert-butylcalix[4]arene scaffold to proximal phenolic oxygens. The influence of this structural variation in the di-ionizable calixcrown ligand on competitive solvent extractions of alkali metal cations and of alkaline earth metal cations and single species solvent extractions of Hg²⁺ and Pb²⁺ from aqueous solutions into chloroform is evaluated.     

First synthesis and electronic properties of cyano(oligo)phenothiazines

(Oligo)phenothiazinyl nitriles were synthesized in good to very good yields from bromo (oligo)phenothiazines via the Beller cyanation protocol either under conductive or under dielectric heating using NMP as a solvent. Their electronic properties were determined by absorption and emission spectroscopy and cyclic voltammetry. Cyano(oligo)phenothiazines display large Stokes-shifts (5800-8300 cm⁻¹) and substantial quantum yields (11-27%). Their reversible oxidation potentials are considerably shifted anodically due to the electron-withdrawing character of the cyano group.     

A controlled, iterative synthesis and the electronic properties of oligo[(p-phenyleneethynylene)-alt-(2,5-siloleneethynylene)]s

An introductory series of conjugated siloleneethynylene co-oligomers has been prepared from a key 2-chloro-5-iodosilole intermediate via site-specific cross-coupling reactions. The tetramer (9) and pentamer (10) both exhibit absorption maxima matching those of the corresponding silole copolymers. Extinction coefficients for the oligomers in this series are large, and in the case of the pentamer (10) the value exceeds 180 000 M(-1) cm(-1). The compounds all emit in the visible region with the greatest quantum efficiencies being 8.97 x 10(-2) (monomer) and 2.99 x 10(-2) (pentamer).     

Preparation and X-ray structures of 3-[Bis(trifluoroacetoxy)iodo]benzoic acid and 3-[hydroxy(tosyloxy)iodo]benzoic acid: new recyclable hypervalent iodine reagents

Preparation, structural characterization, and reactivity of 3-[bis(trifluoroacetoxy)iodo]benzoic acid and 3-[hydroxy(tosyloxy)iodo]benzoic acid, new recyclable iodine(III) reagents derived from 3-iodosylbenzoic acid, are described. The reduced form of these reagents, 3-iodobenzoic acid, can be easily recovered from the reaction mixtures using ion-exchange resin or basic aqueous workup followed by acidification with HCl.