Ethynyl Linker Research Articles

Doubly Coarctate-Stabilized Carbenes: Synthetic and Computational Studies

Isoindazoles joined by an ethynyl linker to either a phenyltriazene or a phenyldiazene moiety were synthesized, and their subsequent reactivity was examined. Computations suggest that these molecules could rearrange at moderate temperatures via carbene intermediates that are doubly stabilized by coarctate conjugation. The experimental results corroborate the calculations, as the transient carbene can either be trapped with oxygen or undergo ring-opening to afford a rearranged product. Additional calculations illustrate some design principles that might lead to stable carbenes that are the global minimum on the coarctate hypersurface.

Enhancing the performance of a thieno[3-4-b]pyrazine based polymer solar cell by introducing ethynylene linkages

Alternating low bandgap π-conjugated polymers consisting of 5,7-dithien-2-yl-thieno[3-4-b]pyrazine and phenylene linked directly (PP-DTTP) and by ethynylene linkages (PPE-DTTP) have been prepared in high yields by Suzuki coupling polymerization and Sonogashira condensation, respectively. Thin films of PPE-DTTP and PP-DTTP exhibit an optical bandgap of 1.55 and 1.36eV, respectively, and the devices provide estimated power conversion efficiencies (PCE) of 0.82% and 0.30%, respectively, in bulk heterojunction solar cells with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as the acceptor. Preliminary optimizations of the devices based on PPE-DTTP gave 1.20% PCE, which ranks in one of the best PCEs of thieno[3-4-b]pyrazines based solar cells. After the introduction of ethynylene linkages in PPE-DTTP, a higher open circuit voltage and a higher short circuit current were obtained with no loss of the fill factor though PPE-DTTP has a higher bandgap, therefore PPE-DTTP shows better performance, which was contributed by the more efficient intramolecular electron transport in PPE-DTTP demonstrated by the hole mobility results and quantum chemistry calculations.

1,3‐Diethynylbicyclo[1.1.1]pentane, a Useful Molecular Building Block

Abstract1,3‐Diethynylbicyclo[1.1.1]pentane (DEBCP) has been found to be a valuable molecular building block mostly for the synthesis of extended, rigid, rod‐like molecules. With its straightforward linear geometry, DEBCP can be used as a nonconjugated alternative to more frequently used π‐conjugated, rod‐like building blocks. Examples of reactions that introduce DEBCP into larger structures are (1) the reaction of DEBCP lithium acetylides with electrophiles such as TMSCl, CO2, and Ph2PCl, (2) Sonogashira–Hagihara cross‐coupling reactions with aryl or heteroaryl iodides or bromides, and (3) umpolung reactions that afford the corresponding dibromo and diiodo derivatives of DEBCP, which then successfully react with tert‐C‐cuprates derived from p‐ and m‐dicarbadodecaboranes or bicyclopentanes. These umpolung reactions afforded a new class of molecular rods that combine carborane or bicyclo[1.1.1]pentane cages with ethynylene linkers. Many of the DEBCP derivatives were studied by single‐crystal X‐ray diffraction. They form well‐organized arrays of molecular rotors, the DEBCP units, and so can be considered as examples of artificial molecular‐size machines.

A highly fluorescent DNA toolkit: synthesis and properties of oligonucleotides containing new Cy3, Cy5 and Cy3B monomers

Cy3B is an extremely bright and stable fluorescent dye, which is only available for coupling to nucleic acids post-synthetically. This severely limits its use in the fields of genomics, biology and nanotechnology. We have optimized the synthesis of Cy3B, and for the first time produced a diverse range of Cy3B monomers for use in solid-phase oligonucleotide synthesis. This molecular toolkit includes phosphoramidite monomers with Cy3B linked to deoxyribose, to the 5-position of thymine, and to a hexynyl linker, in addition to an oligonucleotide synthesis resin in which Cy3B is linked to deoxyribose. These monomers have been used to incorporate single and multiple Cy3B units into oligonucleotides internally and at both termini. Cy3B Taqman probes, Scorpions and HyBeacons have been synthesized and used successfully in mutation detection, and a dual Cy3B Molecular Beacon was synthesized and found to be superior to the corresponding Cy3B/DABCYL Beacon. Attachment of Cy3, Cy3B and Cy5 to the 5-position of thymidine by an ethynyl linker enabled the synthesis of an oligonucleotide FRET system. The rigid linker between the dye and nucleobase minimizes dye–dye and dye–DNA interactions and reduces fluorescence quenching. These reagents open up new future applications of Cy3B, including more sensitive single-molecule and cell-imaging studies.

Chemistry of Anthracene–Acetylene Oligomers XX: Synthesis, Structures, and Self‐Association of Anthracene–Anthraquinone Cyclic Compounds with Ethynylene Linkers

We have synthesized anthracene-acetylene oligomers, which contained one 10-substituted anthracene unit and one anthraquinone unit, by cyclization with Sonogashira coupling. X-ray analysis revealed an almost-planar framework and significant out-of-plane deformation around the inner carbonyl moiety because of steric hindrance. These compounds underwent self-association in solution and their association constants for monomer-dimer exchange were determined by variable-concentration (1)H NMR measurements in CDCl(3): 8 mol(-1) L (10-substituent: isopropyl), <5 mol(-1) L (methoxy), and 19 mol(-1) L (octyloxy). These results were discussed on the basis of spectroscopic and molecular-orbital analysis. A linear molecular assembly of the octyloxy compound at a liquid/graphite interface was observed by STM measurements.

Synthesis and optical properties of perylene diimide derivatives with triphenylene-based dendrons linked at the bay positions through a conjugated ethynyl linkage

A number of groups including trimethylsilyl, phenyl, triphenylene, and triphenylene-based dendron have been linked to the bay positions of a perylene diimide (PDI) core through an ethynyl bridge. The photophysical properties of the resulting bay-substituted PDI derivatives have been carefully studied in different solvents and as thin films. Without any capping group, the two ethynyl bay-substituted PDI derivates PAT and PRT both aggregate strongly even in dilute solutions but in different perylene-perylene π–π stacking modes; PRT aggregates through slipped (or longitudinal) stacking while PAT self-assembles by rotational (or cross) stacking. With capping groups, the perylene core stacking is completely blocked for PATS in both solution and solid film. For PRTS, the slipped stacking is observed only for its film sample, while for PTB, association only occurs after excitation (excimer formation). When triphenylene or triphenylene-based G1 dendron is attached to the acetylene bridge, the resulting donor–acceptor systems (PTG0 and PTG1) exhibit strong electronic coupling between the dendritic donors and the PDI acceptor, leading to significantly red-shifted absorption bands. The conjugated linkage also facilitates photoinduced electron transfer from the triphenylene or triphenylene dendron to the PDI core, effectively quenching fluorescence emissions of both the donor and the acceptor. The significantly red-shifted absorption bands and the efficient photoinduced electron transfer observed on PTG0 and PTG1 indicate that these new PDI derivatives may find applications in solar cells.

Using C60-bodipy dyads that show strong absorption of visible light and long-lived triplet excited states as organic triplet photosensitizers for triplet–triplet annihilation upconversion

The synthesis of visible light-harvesting C60-bodipy dyads (bodipy = boron-dipyrromethene), and the study of the photophysical properties and the application of dyads as heavy-atom free organic triplet photosensitizers for triplet–triplet annihilation (TTA) based upconversion, are reported. By attaching carbazole units to the π-core of the bodipy chromophore via an ethynyl linker, the absorption wavelength of the antenna in the dyads is readily tuned from 504 nm for the unsubstituted bodipy, to 538 nm (one carbazole unit, ε = 61 800 M−1 cm−1) and 597 nm (two carbazole units, ε = 58 200 M−1 cm−1). Upon photoexcitation at 538 nm (dyad C-1) or 597 nm (dyad C-2), intramolecular energy transfer from the antenna to the C60 unit occurs, and as a result, the singlet excited state of the C60 unit is populated. Subsequently, with the intrinsic intersystem crossing (ISC) of C60, the triplet excited state of the C60 unit is produced (τT up to 24.5 μs). Thus, without the need for any heavy atoms, the triplet excited state of the dyads was populated upon visible light excitation. The population of the C60-localized triplet excited state of the dyads was confirmed by nanosecond time-resolved transient difference absorption spectra and spin density analysis. The dyads were used as triplet photosensitizers for TTA upconversion and upconversion quantum yields of up to 2.9% were observed.

Photoinduced energy transfer processes in hybrid organic–inorganic multichromophoric arrays arranged on a truxene-based platform

The synthesis, photophysical characterization and energy-transfer features of a series of hybrid truxene derivatives peripherally decorated with inorganic Os-containing polypyridine units and organic Bodipy dyes are reported. The photoactive terminal units are coupled to the central truxene scaffold by rigid ethynyl linkers in a star-shaped arrangement. The absorption range widely covers the UV-Vis spectrum and the Os (3)MLCT or the Bodipy triplet act as final collectors of the absorbed energy.

Synthesis and characterization of perylene–bithiophene–triphenylamine triads: studies on the effect of alkyl-substitution in p-type NiO based photocathodes

We report the synthesis of new donor–π–acceptor (D–π–A) dyes and their application in dye-sensitized solar cells (DSCs) with nickel(II) oxide (NiO)-based photocathodes. These D–π–A sensitizers incorporate a triphenylamine donor, a bithiophene π-bridge, and a perylenemonoimide (PMI) acceptor group. Two carboxylate groups attached to the triphenylamine afford strong anchoring to the NiO surface. The dyes in this series were varied firstly by the inclusion of an ethynyl linker between bithiophene and the triphenylamine moieties (1vs. 2), thereby increasing the length of the conjugated bridge. Despite very similar optoelectronic properties, the ethynyl-containing dye 2 showed a ∼25% improvement in power conversion efficiency in p-DSCs compared to 1, mostly attributed to the increased current density. Contrary to initial expectations, there was no major influence of the distance between the PMI unit of the dye and the NiO surface on the photoinduced dye anion lifetime, as measured by nanosecond transient absorption spectroscopy (TAS). Furthermore, altering the position of the alkyl chains on the bridging bithiophene in 3 and 4 resulted in a modest red shift in the dye absorption on account of increased charge delocalisation between the PMI and the π-bridge, owing to a reduced torsion angle between the PMI and the adjacent thiophene unit. Quantum-chemical DFT calculations were performed in order to evaluate these torsion angles and to study their influence on the electron density distribution in the relevant molecular orbitals. These changes of the molecular structure of the isomeric dyes 3 and 4 did not translate into improved photovoltaic performance, which is primarily attributed to lower charge photogeneration rates probed by transient absorption spectroscopy. While for p-type DSCs impressive overall solar-to-electric conversion efficiency of 0.04–0.10% under full sun illumination (simulated AM1.5G sunlight, 100 mW cm−2) and a broad incident photon to current efficiency (IPCE) response (350–700 nm) is demonstrated for these new dyes, the study clearly shows the need for judicious design rules for p-type sensitizers for application in photocathodic DSCs.

A Highly C70 Selective Shape-Persistent Rectangular Prism Constructed through One-Step Alkyne Metathesis

Dynamic covalent chemistry (DCC) provides an intriguing and highly efficient approach for building molecules that are usually thermodynamically favored. However, the DCC methods that are efficient enough to construct large, complex molecules, particularly those with three-dimensional (3-D) architectures, are still very limited. Here, for the first time, we have successfully utilized alkyne metathesis, a highly efficient DCC approach, to construct the novel 3-D rectangular prismatic molecular cage COP-5 in one step from a readily accessible porphyrin-based precursor. COP-5 consists of rigid, aromatic porphyrin and carbazole moieties as well as linear ethynylene linkers, rendering its shape-persistent nature. Interestingly, COP-5 serves as an excellent receptor for fullerenes. It forms 1:1 complexes with C(60) and C(70) with association constants of 1.4 × 10(5) M(-1) (C(60)) and 1.5 × 10(8) M(-1) (C(70)) in toluene. This represents one of the highest binding affinities reported so far for purely organic fullerene receptors. COP-5 shows an unprecedented high selectivity in binding C(70) over C(60) (K(C70)/K(C60) > 1000). Moreover, the binding between the cage and fullerene is fully reversible under the acid-base stimuli, thus allowing successful separation of C(70) from a C(60)-enriched fullerene mixture (C(60)/C(70), 10/1 mol/mol) through the "selective complexation-decomplexation" strategy.

Synthesis and Characterization of Poly(5,8-quinoxaline ethynylene)s

A majority of conjugated organic polymers are electron-rich materials, with far fewer electron-poor (i.e., electron accepting) analogues. Here we report the synthesis and preliminary characterization of new class of electron-poor poly(arylene ethynylene)s (PAEs) that contain 5,8-quinoxaline ethynylene repeat units. While various PAE copolymers consisting of alternating electron-rich and electron-poor units display lower bandgaps than poly(phenylene ethynylene)s, the poly(5,8-quinoxaline ethynylene) (PQE) reported in this study has a higher electron affinity and lower bandgap (2.25 eV) than many of these donor–acceptor materials. In comparison to poly(5,8-quinoxaline)s (PQs), which do not have an ethynylene linkage between the quinoxalines, the PQE has a red-shifted absorption spectrum that is consistent with a more highly conjugated and planar backbone. In addition, the PQE has a lower electrochemical reduction potential than both a corresponding PQ and a donor–acceptor alternating PAE copolymer that contains the quinoxaline unit as the electron-poor component.

A New Metal Carboxylate Framework Based on Porphyrin with Extended π‐Conjugation

AbstractWe have designed a new tetracarboxylporphyrin building block, ZnTCPEP‐H4, and used it in the construction of a novel porphyrin‐based metal carboxylate framework, [Zn4(μ3‐OH)2(H2O)2(ZnTCPEP‐H)2(DABCO)]·2DMF·10.5H2O(Zn4·ZnTCPEP·DABCO). The framework forms a 3D network linked by tetranuclear Zn cluster nodes {Zn4(μ3‐OH)2(H2O)2}, ZnTCPEP‐H4, and DABCO. The ZnTCPEP‐H4 building block exhibits extended π‐conjugation from the porphyrin core to the terminal carboxyl groups via ethynyl linkers attached to the porphyrin core. The Zn4·ZnTCPEP·DABCO framework gives rise to a 3D porous structure containing open channels with cross sections of approximately 10 × 10 and 7 × 7 Å. It has a BET surface area of 461 m2/g and a Langmuir surface area of 581 m2/g. A hydrogen adsorption capacity of 0.86 wt.‐% was determined for Zn4·ZnTCPEP·DABCO at 77 K and 0.1 MPa.

Chemistry at Boron: Synthesis and Properties of Red to Near-IR Fluorescent Dyes Based on Boron-Substituted Diisoindolomethene Frameworks

A general method for the synthesis of difluorobora-diisoindolomethene dyes with phenyl, p-anisole, or ethyl-thiophene substituents has been developed. The nature of the substituents allows modulation of the fluorescence from 650 to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl or ethyl residues is facile using Grignard reagents. Several X-ray molecular structures have been determined, allowing establishment of structure-fluorescence relationships. When the steric crowding around the boron center is severe, the aromatic substituents α to the diisoindolomethene nitrogens are twisted out of coplanarity, and hypsochromic shifts are observed in the absorption and emission spectra. This shift reached 91 nm with ethyl substituents compared to fluoro groups. When ethynyl linkers are used, the core remains flat, and a bathochromic shift is observed. All the fluorophores exhibit relatively high quantum yields for emitters in the 650-800 nm region. When perylene or pyrene residues are connected to the dyes, almost quantitative energy transfer from them to the dye core occurs, providing large virtual Stokes shifts spanning from 8000 to 13,000 cm(-1) depending on the nature of the dye. All the dyes are redox active, providing the Bodipy radical cation and anion in a reversible manner. Stepwise reduction or oxidation to the dication and dianion is feasible at higher potentials. We contend that the present work paves the way for the development of a new generation of stable, functionalized luminophores for bioanalytical applications.

Discovery of 5-(arenethynyl) hetero-monocyclic derivatives as potent inhibitors of BCR–ABL including the T315I gatekeeper mutant

Ponatinib (AP24534) was previously identified as a pan-BCR-ABL inhibitor that potently inhibits the T315I gatekeeper mutant, and has advanced into clinical development for the treatment of refractory or resistant CML. In this study, we explored a novel series of five and six membered monocycles as alternate hinge-binding templates to replace the 6,5-fused imidazopyridazine core of ponatinib. Like ponatinib, these monocycles are tethered to pendant toluanilides via an ethynyl linker. Several compounds in this series displayed excellent in vitro potency against both native BCR-ABL and the T315I mutant. Notably, a subset of inhibitors exhibited desirable PK and were orally active in a mouse model of T315I-driven CML.

One-Photon Photophysics and Two-Photon Absorption of 4-[9,9-Di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2′:6′,2′′-terpyridine and Their Platinum Chloride Complexes

The synthesis, one-photon photophysics and two-photon absorption (2PA) of three dipolar D-π-A 4-[9,9-di(2-ethylhexyl)-7-diphenylaminofluoren-2-yl]-2,2':6',2''-terpyridine and their platinum chloride complexes with different linkers between the donor and acceptor are reported. All ligands exhibit (1)π,π* transition in the UV and (1)π,π*/(1)ICT (intramolecular charge transfer) transition in the visible regions, while the complexes display a lower-energy (1)π,π*/(1)CT (charge transfer) transition in the visible region in addition to the high-energy (1)π,π* transitions. All ligands and the complexes are emissive at room temperature and 77 K, with the emitting excited state assigned as the mixed (1)π,π* and (1)CT states at RT. Transient absorption from the ligands and the complexes were observed. 2PA was investigated for all ligands and complexes. The two-photon absorption cross-sections (σ(2)) of the complexes (600-2000 GM) measured by Z-scan experiment are much larger than those of their corresponding ligands measured by the two-photon induced fluorescence method. The ligand and the complex with the ethynylene linker show much stronger 2PA than those with the vinylene linker.

Linker effects on optoelectronic properties of alternate donor–acceptor conjugated polymers

In this study, three conjugated polymers (DA1, DA2 and DA3) with different linkers between an electron-rich unit (3,4-didodecylthiophene as electron donor, D) and an electron-deficient unit (benzothiadiazole as electron acceptor, A) were synthesized via Suzuki, Heck and Sonogashira polycondensation, respectively. The D and Agroups are connected in three different ways: without any linker (DA1), by a vinylene linker (DA2), and by an ethynylene linker (DA3). Among these three polymers, DA2 exhibited the lowest bandgap (Eg) at 1.65 eV and the highest planarity evidenced by the smallest dihedral angle (1°) between the donor and acceptor units. The femtosecond up-conversion fluorescence measurement showed that DA1 and DA3 exhibited a rise process for the energetically downhill excitonic energy transfer (EET) in a timescale of sub-ps to several ps, while DA2 exhibited a decay process in such downhill EET. In addition, DA2 showed the shortest time constant of ∼4.6 ps for torsional relaxation with the highest amplitude at ∼43.1% among all the three polymers. This suggested that the vinylene linker has the fastest torsional relaxation from a flexible ground-state structure to a more rigid planar geometry, which may reduce conformational defects and improve exciton migration. This work studied the linker effects between the D and A units on the alternate D–Apolymers and may shed light on the design of new D–Apolymers with improved properties.

Structural Mechanism of the Pan‐BCR‐ABL Inhibitor Ponatinib (AP24534): Lessons for Overcoming Kinase Inhibitor Resistance

The BCR-ABL inhibitor imatinib has revolutionized the treatment of chronic myeloid leukemia. However, drug resistance caused by kinase domain mutations has necessitated the development of new mutation-resistant inhibitors, most recently against the T315I gatekeeper residue mutation. Ponatinib (AP24534) inhibits both native and mutant BCR-ABL, including T315I, acting as a pan-BCR-ABL inhibitor. Here, we undertook a combined crystallographic and structure-activity relationship analysis on ponatinib to understand this unique profile. While the ethynyl linker is a key inhibitor functionality that interacts with the gatekeeper, virtually all other components of ponatinib play an essential role in its T315I inhibitory activity. The extensive network of optimized molecular contacts found in the DFG-out binding mode leads to high potency and renders binding less susceptible to disruption by single point mutations. The inhibitory mechanism exemplified by ponatinib may have broad relevance to designing inhibitors against other kinases with mutated gatekeeper residues.

ChemInform Abstract: Rod‐Like Conjugated Molecules with Ethynylene Linkage and Pyridazine Moieties: Synthesis and Light Emitting Properties.

AbstractA series of title compounds are prepared using Sonogashira cross‐coupling and condensation reactions.

The synthesis and spectroscopic characterization of poly( p-phenylene ethynylene) with 3-connected BODIPY end groups

A novel 3-connected BODIPY end-capped poly( p-phenylene ethynylene) and a matching model compound were synthesized by palladium-catalyzed cross-coupling reaction. The structures were confirmed using 1H NMR, UV–vis spectrophotometry and fluorescence spectroscopy. Both the polymer and the model compound showed absorption and emission bands characteristic for the BODIPY chromophore and the p-phenylene ethynylene linker. However, while upon excitation of the p-phenylene ethynylene linker energy transfer occurs for nearly 100% in the model compound, it is only a minor decay channel of the singlet excited state of the p-phenylene ethynylene linker in the polymer.

Synthesis of Functionalized Triazatriangulenes for Application in Photo‐Switchable Self‐Assembled Monolayers

AbstractVarious triazatriangulenes are synthesized by nucleophilic attack at the central C atom of triazatriangulenium ions. The molecular functions, especially azobenzenes, are fixed via an ethynyl linker by in situ deprotection of trimethylsilylalkynes. The structure of two of these molecules is further investigated by X‐ray crystallography. The photo‐induced trans/cis‐isomerization of the azobenzene substituted derivatives is analyzed in solution and shows great promise for the preparation of switchable functionalized monolayers, as the triazatriangulenes are known for their self‐assembly on gold surfaces.1