Synthesis and Self‐Assembly of Cyclic 2,7‐Anthrylene Ethynylene 1,3‐Phenylene Ethynylene Trimer with a Planar Conformation

Cyclic arylene ethynylene hexamer 1 , composed of alternating 2,7‐anthrylene ethynylene units and meta‐phenylene ethynylene units, was synthesized. It shows C₃ symmetry and possesses a flat and rigid conformation with a large equilateral triangle‐like cavity. Macrocycle 1 self‐associates through π–π stacking interactions between the anthracene‐containing macrocyclic aromatic cores with indefinite‐association constant K_E=6980 m ^?1 in CDCl₃ at 303 K. Macrocycle 1 also self‐assembles into π‐stacked nanofibers in the drop‐cast film.     

Polymers with alternating anthracene and phenylene building blocks linked by ethynylene and/or vinylene units: Studying structure‐properties‐relationships

Four conjugated polymers ( P1 – P4 ) consisting of alternating anthracene‐9,10‐diyl and 1,4‐phenylene building blocks connected via ethynylene as well as vinylene ( P1 and P2 ), ethynylene‐only ( P3 ), and vinylene‐only ( P4 ) moieties, respectively, were synthesized and studied. The phenylene units in all four polymers bear 2‐ethylhexyloxy side‐chains to promote good solubility. The three polymers with vinylene units ( P1 , P2 , and P4 ) were prepared using the Horner–Wadsworth–Emmons reaction. For the synthesis of the arylene‐ethynylene polymer P3, the palladium‐catalyzed Sonogashira cross‐coupling reaction was used. The polymers were characterized by NMR, Fourier transform infrared spectroscopy, and Raman spectroscopy. Photophysical, absorption and photoluminescence, and electrochemical properties were studied. Spectroscopic ellipsometry measurements were performed to gain more insight on the optical properties. In addition, the transport properties were investigated using admittance spectroscopy. The bulk hole mobility and its dependence on the electric field were evaluated for P1 and P2 . © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 129–143     

Synthesis,characterization, and structure–property investigation of conformationally rigid regioisomers of poly(p‐phenylene ethynylene)s

A series of rigid poly(p‐phenylene ethynylene)s ( PPE1 – PPE4 ) with biphenyl‐ ( M1–M3 ) and phenyl‐ ( M4 ) side groups is prepared from appropriately functionalized monomers. Herein, the solution and solid state absorption studies show the polymers have adopted twisted and rigid conformations, as supported by deep HOMO energy levels (?5.76 to ?5.81 eV). The absorption maxima of PPE1–PPE3 are shifted to shorter wavelength (λ_max = 375–381 nm) as compared to linear poly(p‐phenylene ethynylene)s (446 nm), implying a nonplanar conformation. The self‐assembly of polymers into fibers is examined using scanning electron microscopy. The fibers are not observed in PPE4 with short phenyl side group, suggesting the important role of the interplay between rigidity, position, and size of the side chains toward the formation of fibers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3652–3662     

Multiple‐Stimulus‐Responsive Supramolecular Gels and Regulation of Chiral Twists: The Effect of Spacer Length

A new class of homologous gelators, LG₁₂‐(CH₂)_n‐BSA, composed of bipyridinyl groups, L ‐glutamic moieties having double dodecyl chains, and linked alkyl spacers with different lengths were synthesized. It was found that these gelators could immobilize medium‐polarity solvents readily and the behaviors of these gels showed a dependence on the spacer length. Of all the gels, the LG₁₂‐(CH₂)₁₁‐BSA gels exhibited self‐healing property and multiple‐stimulus responsibility, such as heating, shaking, and sonication. The investigation of CD spectra indicated that the supramolecular chirality, which was attributed to the chiral transfer from the chiral center to the assemblies, was also closely related to the length of methylene spacers. The longer the alkyl spacers, the weaker the transmitted supramolecular chirality. Only LG₁₂‐(CH₂)₁‐BSA gelators, which had the shortest spacers, formed right‐handed nanoscale chiral twists owing to crowded hydrogen bonding interactions. Moreover, the high‐polarity solvent DMF was found to be able to regulate the chiral twist as well as its pitch length readily.     

Charge carrier mobility,photovoltaic, and electroluminescent properties of anthracene‐based conjugated polymers bearing randomly distributed side chains

This article reports on the synthesis, characterization, and properties of various anthracene‐containing poly (p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene) (PPE‐PPV) polymers (AnE‐PVs) bearing statistical distributions of various side chains. Primarily, the ratio of linear octyloxy and branched 2‐ethylhexyloxy side chains at the poly(p‐phenylene vinylene) (PPV) parts was varied, leading to the polymers stat, stat1, and stat2. Furthermore, polymers also containing asymmetric substituted PPV and poly(p‐phenylene ethynylene) units (bearing methoxy and 2‐ethylhexyloxy side chains) were prepared yielding stat3, stat4, and stat5. These materials exhibit a broad variation in their photovoltaic properties. It is once more shown that side chains and their distribution can crucially affect the photovoltaic device performance. The introduction of units with asymmetric substitution into these systems seems to be harmful for their utilization in photovoltaic applications. Organic field‐effect transistors were fabricated to investigate hole mobilities in these new materials. Large variance was observed, falling in the range of almost two orders of magnitude, indicating rather different π–π stacking behavior of the polymer backbones owing to side‐chain modifications. Moreover, a selection of the new polymeric systems was investigated regarding their potential for light‐emitting diode (LED) applications. Polymer LEDs using the polymers AnE‐PVstat, ‐stat3, ‐stat4, and ‐stat5, as the active layer showed turn‐on voltage of ～2 V and exhibited red light emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Enantiopure Double‐Helical Phenylene Ethynylene Cyclophynes with the 2,2′‐Binaphthyl Template

New types of enantiopure compounds were synthesized to gain better insight into the structural features of phenylene ethynylene cyclophynes. Besides the previously obtained meta‐substituted arylene ethynylenes, 1 , ortho‐connected phenylene ethynylene units were incorporated to give cyclophynes with ortho/meta and ortho/ortho connection modes, 2 and 3 . Furthermore, a diphenylethyne component was also accommodated in 4 . Both ab initio calculations and NMR spectra suggest a large amount of strain for 2 but less strain for 3 and 1 a , the latter having the smallest ring size among cyclophynes with the meta/meta connection mode. The CD spectra of 2 and 3 showed a characteristic shoulder at around 340 nm, similar to the case of 1 a . This implies that the aromatic acetylene bonds cross over each other in the double‐helical structure. These results indicate that chirality information is useful for probing the persistency of molecular shape.     

Ethynylene‐containing donor–acceptor alternating conjugated polymers: Synthesis and photovoltaic properties

Four ethynylene‐containing donor‐acceptor alternating conjugated polymers P1 – P4 with 2,5‐bis(dodecyloxy) substituted phenylene or carbazole as the donor unit and benzothiadiazole (BTZ) as the acceptor unit were synthesized and used as donor polymers in bulk heterojunction polymer solar cells. The optical, electrochemical, and photovoltaic properties of these four polymers with the ethylene unit located at different positions of the polymer chains were systematically investigated. Our results demonstrated that absorption spectra and the HOMO and LUMO energy levels of polymers could be tuned by varying the position of the ethynylene unit in the polymer chains. Photovoltaic devices based on polymer/PC₇₁BM blend films spin coated from chloroform and dichlorobenzene solutions were investigated. For all four polymers, open circuit voltages (V_oc) higher than 0.8 V were obtained. P4 , with ethynylene unit between BTZ and thiophene, shows the best performance among these four polymers, with a V_oc of 0.94 V, a J_sc of 4.2 mA/cm², an FF of 0.40, and a PCE of 1.6%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

One‐Step Synthesis of [16]Helicene

A single‐strand arylene–vinylene precursor containing four phenylene and three naphthylene units linked together with six vinylene spacers undergoes helical folding via sextuple photocyclization to give a [16]helicene core in a single step. The phenylene and naphthylene units are arranged in the precursor such that unfavorable side reactions (anthracene or benzoperylene formation) are avoided, and this is the key to the success of the one‐step synthesis of [16]helicene, which is the longest [n]helicene that has been synthesized to date.     

Synthesis of [?CH2C(CO2Et)2CH2Ar?]n polymers and their unique optical properties by through‐space interactions between Ar and CO groups

Polymers of type [? CH₂C(CO₂Et)₂CH₂Ar? ]_n (Ar = 1,4‐phenylene, 2,6‐naphthylene, 9,10‐anthrylene, or 1,4‐phenylene‐ethynylene‐1,4‐phenylene) were synthesized by alkylation of diethyl malonate with XCH₂ArCH₂X (X = Cl or Br). These polymers exhibited unexpectedly enhanced UV absorption and strong, broad, bathochromically shifted fluorescence spectra compared with the parent Ar compounds. The origin of these photophysical characteristics was postulated to be a configuration interaction between the π→π* excitation of the aromatic moiety and the n→π* excitation of the carbonyl moiety on the trimethylene tether via intramolecular charge transfer. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Light‐Powered Self‐Healable Metallosupramolecular Soft Actuators

Supramolecular functional materials able to respond to external stimuli have several advantages over their classical covalent counterparts. The preparation of soft actuators with the ability to respond to external stimuli in a spatiotemporal fashion, to self‐repair, and to show directional motion, is currently one of the most challenging research goals. Herein, we report a series of metallopolymers based on zinc(II)–terpyridine coordination nodes and bearing photoisomerizable diazobenzene units and/or solubilizing luminescent phenylene–ethynylene moieties. These supramolecular polymers act as powerful gelating agents at low critical gelation concentrations. The resulting multiresponsive organogels display light‐triggered mechanical actuation and luminescent properties. Furthermore, owing to the presence of dynamic coordinating bonds, they show self‐healing abilities.     

Advantage of the N‐Alkylation Strategy for Retaining the Molecular Planarity for Oligothiophene/Imidazole/1,10‐Phenanthroline‐Based Heterocyclic Semiconducting and Fluorescent Compounds

A family of planar oligothiophene/imidazole/1,10‐phenanthroline (OTIP)‐based heterocyclic, aromatic, semiconducting, and fluorescent compounds with N‐substituted alkyl chains (allyl, n‐butyl, n‐octyl, n‐dodecyl, and n‐cetyl) have been designed and synthesized. They all have specific N‐coordination sites, various donor–acceptor spacers, good molecular planarity, suitable solubility, and high thermal stability. In comparison with conventional double β‐alkylation of the thiophene ring, our results reveal that the single imidazole N‐alkylation strategy for OTIPs has the advantage of maintaining the planarity of the whole molecule, in addition to improving the solubility, which can be clearly verified by the small dihedral angles between adjacent thiophene/imidazole/1,10‐phenanthroline (TIP) rings in eight X‐ray single‐crystal structures. In particular, n‐dodecyl‐ and n‐cetyl‐substituted OTIPs ( 7 and 8 ) with the same molecular length of 2.37 nm (M_W=939 and 1052), show good molecular planarity with the aforementioned dihedral angles of 8.9(5) and 10.4(5)°. Furthermore, special attention has been paid to the physicochemical properties of seven symmetrical OTIPs ( 6 – 8 , 13 – 15 , and 19 ), including two to six thiophene rings in the middle of their molecular structures. To the best of our knowledge, this is the first synthetic, structural, and spectral investigation into the N‐alkylation of OTIP‐based compounds.     

Synthesis,Electrochemical, and Optical Properties of a Novel PPV/PPE Block‐Copolymer

Summary: A novel poly(p‐phenylene vinylene) (PPV)/poly(p‐phenylene ethynylene) (PPE) block‐copolymer was synthesized by a cross‐coupling polycondensation with Pd(PPh₃)₂Cl₂ and a phase‐transfer catalyst, and was confirmed by ¹H NMR and IR spectroscopy and elemental analysis. The thermal, electrochemical, and photoluminescent properties of the new copolymer have been investigated. The incorporation of triple bonds into the cyano‐substituted PPV (CN‐PPV) backbone leads to higher oxidation and reduction potentials than poly(2‐methoxy‐5‐(2‐ethylhexyloxy)‐p‐phenylene vinylene) (MEH‐PPV) and CN‐PPV, potentially making the copolymer a good electron‐transporting material for use in a light‐emitting‐diode device.

The cyclic voltammogram of the novel poly(p‐phenylene vinylene) (PPV)/poly(p‐phenylene ethynylene) (PPE) block‐copolymer synthesized here.     

Phenylene‐Bridged Core‐Modified Planar Aromatic Octaphyrin: Aromaticity,Photophysical and Anion Receptor Properties

The synthesis of a planar expanded meso porphyrin with an intramolecular para‐phenylene‐bridged core is reported. The planarity of the octaphyrin macrocycle was confirmed by single‐crystal X‐ray structural analysis, in which the bridged para‐phenylene unit deviated by 27° from the mean macrocyclic plane. Spectroscopic analyses and theoretical calculations suggested that the macrocycle was Hückel aromatic and followed a major [34 π] single‐conjugation pathway, which indicated that the bridging para‐phenylene unit was not involved in the macrocyclic conjugation. Analysis of the photophysical properties of this system by steady‐state absorption/fluorescence spectroscopy and transient absorption spectroscopy revealed moderate enhancement in the parameters of the octaphyrin as compared to its non‐bridged octaphyrin congeners, which was attributed to the planarity and rigidity of the macrocycle as imposed by the bridging para‐phenylene unit. Preliminary anion‐binding studies revealed that the protonated macrocycle bound selectively with chloride ions through N?H???Cl hydrogen‐bonding interactions.     

Ordered nanostructures from self‐assembly of H‐shaped coil–rod–coil molecules

A new class of π‐conjugated, skewed H‐shaped oligomers, consisting of biphenyl, phenylene vinylene, and phenylene ethynylene units as the rigid segment, were synthesized via Sonogashira coupling and Wittig reactions. The coil segments of these molecules were composed of poly(ethylene oxide) (PEO) or PEO with lateral methyl groups between the rod and coil segment, respectively. The experimental results revealed that the lateral methyl groups attached to the surface of the rod and coil segments dramatically influenced the self‐assembling behavior of the molecules in the crystalline phase. H‐shaped rod–coil molecules containing a lateral methyl group at the surface of the rod and PEO coil segments self‐assemble into a two‐dimensional columnar or a three‐dimensional body‐centered tetragonal nanostructures in the crystalline phase, whereas molecules lacking a lateral methyl group based on the PEO coil chain self‐organize into lamellar or hexagonal perforated lamellar nanostructures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 85–92     

Novel fluorescent (p‐phenylene ethynylene)‐calix[4]arene‐based polymer: Design,synthesis, and properties

A novel fluorescent (p‐phenylene ethynylene)‐calix[4]arene‐based polymer ( CALIX‐PPE ) has been successfully synthesized by cross‐coupling polymerization of bis‐calix[4]arene 1 with 1,4‐diethynylbenzene. The polycondensation was carried out in toluene/NEt₃ at 35 °C for 24 h, using PdCl₂(PPh₃)₂/CuI as the catalytic system, furnishing CALIX‐PPE in excellent isolated yields (higher than 95%, several runs). The yellow polymer is freely soluble in several nonprotic organic solvents. The GPC trace of the isolated polymer showed a monomodal distribution and a number‐average molecular weight of 23,300 g mol^?1 (M_w/M_n = 2.05). No evidence was found in the structural analysis (FTIR and ¹H/¹³C NMR) regarding the formation of alkyne homocoupled segments along the polymer chain. For comparative purposes, the synthesis of an analogous poly(p‐phenylene ethynylene) containing p‐t‐butyl‐phenoxymethyl side chains ( TBP‐PPE ) was also undertaken. A great similarity was found between the photophysical properties of CALIX‐PPE and TBP‐PPE in solution (UV–vis and laser induced luminescence), clearly demonstrating their unique dependence on the structure and conformation of the conjugated PPE backbone. The fluorescence spectra of polymers are of nearly identical shape, displaying their maximum emission around 420 nm. The calculated solution photoluminescence quantum yields of CALIX‐PPE and TBP‐PPE are of similar magnitude (?_{F( CALIX‐PPE )} = 0.43; ?_{F( TBP‐PPE )} = 0.51). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6477–6488, 2008     

Oligo(p-phenylene ethynylene)-BODIPY derivatives: synthesis, energy transfer, and quantum-chemical calculations

The synthesis and energy‐transfer properties of a series of oligo(p‐phenylene ethynylene)–BODIPY ( OPEB ) cassettes are reported. A series of oligo(p‐phenylene ethynylene)s ( OPE s) with different conjugated chain lengths as energy donor subunit in the energy‐transfer system were capped at both ends with BODIPY chromophores as energy‐acceptor subunits. The effect of the conjugated chain of OPE s on energy transfer in the OPEB cassettes was investigated by UV/Vis and fluorescence spectroscopy and modeling. With increasing number n of phenyl acetylene units (n=1–7), the absorption and emission maxima of OPEn are bathochromically shifted. In the OPEBn analogues, the absorption maximum assigned to the BODIPY moieties is independent of the length of the OPE spacer. However, the relative absorption intensity of the BODIPY band decreases when the number of phenyl acetylene units is increased. The emission spectra of OPEBn are dominated by a band peaking at 613 nm, corresponding to emission of the BODIPY moieties, regardless of whether excitation is at 420 or 550 nm. Furthermore, a very small band is observed with a maximum between 450 and 500 nm, and its intensity relative to that of the BODIPY emission increases with increasing n, that is, the excited state of OPE subunits is efficiently quenched in OPEBn by energy transfer to the BODIPY moieties. Energy transfer (ET) from OPEn to BODIPY in OPEBn is very efficient (all Φ_ET values are greater than 98 %) and only slightly decreases with increasing length of the OPE units. These results are supported by theoretical studies that show very high energy transfer efficiency (Φ_ET>75 %) from the OPE spacer to the BODIPY end‐groups for chains with up to 15–20 units.     

Helical Folding Competing with Unfolded Aggregation in Phenylene Ethynylene Foldamers

The folding and aggregation behavior of a pair of oligo(phenylene ethynylene) (OPE) foldamers are investigated by means of UV/Vis absorption and circular dichroism spectroscopy. With identical OPE backbones, two foldamers, 1 with alkyl side groups and 2 with triethylene glycol side chains, manifest similar helical conformations in solutions in n‐hexane and methanol, respectively. However, disparate and competing folding and aggregation processes are observed in alternative solvents. In cyclohexane, oligomer 1 initially adopts the helical conformation, but the self‐aggregation of unfolded chains, as a minor component, gradually drives the folding–unfolding transition eventually to the unfolded aggregate state completely. In contrast, in aqueous solution (CH₃OH/H₂O) both folded and unfolded oligomer 2 appear to undergo self‐association; aggregates of the folded chains are thermodynamically more stable. In solutions with a high H₂O content, self‐aggregation among unfolded oligomers is kinetically favored; these oligomers very slowly transform into aggregates of helical structures with greater thermodynamic stability. The folded–unfolded conformational switch thus takes place with the free (nonaggregated) molecules, and the very slow folding transition is due to the low concentration of molecularly dispersed oligomers.     

Poly(p‐phenylene ethynylene) Incorporating Sterically Enshrouding m‐Terphenyl Oxacyclophane Canopies

A sterically encumbered m‐terphenyl oxacyclophane substituted with two aryl iodide substituents has been prepared as a versatile monomer for the preparation of π‐conjugated polymers. The monomer has been used to prepare a poly(p‐phenylene ethynylene) derivative (P1) incorporating oxacyclophane units as canopies that shield one side of the π‐system from inter‐chain interactions. The photophysical properties of P1 in dilute solution compare well to those of a poly(p‐phenylene ethynylene) derivative (P2) that lacks the canopy. The presence of the steric canopy leads to a diminished inter‐chain interaction in the solid state and enhances the kinetic response of P1 to vapors of nitro‐organics such as TNT, presumably by increasing the permeability of P1 to these analytes over that of P2.

     

Solution‐Processable n‐Type Organic Field‐Effect Transistor (OFET) Materials Based on Carbonyl‐Bridged Bithiazole and Dioxocyclopentene‐Annelated Thiophenes

A series of electronegative π‐conjugated compounds composed of carbonyl‐bridged bithiazole and alkyl‐substituted dioxocyclopenta[b]thiophene were synthesized as a candidate for solution‐processable n‐type organic semiconductor materials and characterized on the basis of photophysical and electrochemical properties. Cyclic voltammetry measurements showed that the first half‐wave reduction potentials of these compounds are between −0.97 and −1.14 V versus ferrocene/ferrocenium, which corresponds to lowest unoccupied molecular orbital energy levels between −3.83 and −3.66 eV. Thanks to hexyl or dodecyl groups in the molecules, the compounds are sufficiently soluble to realize the fabrication of their thin films through a spin‐coating method. As a result, the prepared organic field‐effect transistors based on these newly developed compounds exhibited n‐channel characteristics not only under vacuum but also in air, and the best field‐effect electron mobility observed under vacuum was 0.011 cm² V⁻¹ s⁻¹ with an on/off ratio of 10⁸ and a threshold voltage of 16 V.     

Synthesis,Properties, and Remarkable 2 D Self‐Assembly at the Liquid/Solid Interface of a Series of Triskele‐Shaped 5,11,17‐Triazatrinaphthylenes (TrisK)

A series of 5,11,17‐triazatrinaphthylene (TrisK) derivatives, large disk‐like π‐conjugated molecules with C_3h symmetry, has been synthesised by following an optimised synthetic pathway. The synthesis was performed by a four‐step protocol based on the N‐arylation of 1,3,5‐tribromobenzene with appropriate anthranilate derivatives. This strategy permits the generation of either chlorinated ( TrisK‐Cl‐OCn ) or non‐chlorinated ( TrisK‐H‐OCn ) alkoxy‐substituted derivatives (OC_nH_2n+1 with n=3, 10, 12 and 16), thus providing additional versatility in the control of the structure–property relationships. The electronic properties of the various TrisK compounds have been characterised in solution by absorption and emission spectroscopies as well as cyclic voltammetry. The crystal structure of 2,8,14‐propyloxy‐5,11,17‐triazatrinaphthylene TrisK‐H‐OC3 has been determined by X‐ray diffraction analysis, which revealed the presence of stabilising weak intermolecular H bonds. Scanning tunnelling microscopy (STM) at the liquid/solid interface has revealed the remarkable 2D self‐assembling properties of the TrisK compounds. In particular, it has shown that TrisK‐H‐OC12 forms three concomitant self‐organised 2D phases with different row‐packing arrangements. This 2D polymorphism arises from slow ordering due to the presence of three long dodecyloxy chains on the molecular backbone. Individual molecules can be imaged with spectacular intramolecular resolution, thus providing the possibility of correlating the STM features with the calculated charge density distribution.