Sequence-controlled alternating block polychalcogenophenes: synthesis, structural characterization, molecular properties, and transistors for bromine detection

Sequence-controlled polychalcogenophenes have attracted much interest in terms of synthesis, structure and function in polymer science. For the first time, we developed a new class of alternating block conjugated copolymers denoted as poly(alt-AB)x-b-(alt-AC)y where both blocks are constituted by an alternating copolymer. 3-Hexylthiophene (S), 3-hexylselenophene (Se) and 3-hexyltellurophene (Te) are used as A, B and C units to assemble three sequence-controlled polychalcogenophenes P(SSe)b(STe), P(SSe)b(SeTe) and P(STe)b(SeTe) which are prepared by adding two different Grignard monomers in sequence to carry out Ni(dppp)Cl2-catalyzed Kumada polymerization. The molecular weight, dispersity, and length of each block (x = y) and main-chain sequence can be synthetically controlled via the catalyst transfer polycondensation mechanism. The polymer structures, i.e. alternating block main chain with high side-chain regioregularity, are unambiguously confirmed by 1H-NMR and 13C-NMR. The optical and electrochemical properties of the polymers can be systematically fine-tuned by the composition and ratio of the chalcogenophenes. From GIWAXS measurements, all the polymers exhibited predominantly edge-on orientations, indicating that the packing behaviors of the alternating block polychalcogenophenes with high regioregularity are inherited from the highly crystalline P3HT. P(SSe)b(STe) exhibited a hole OFET mobility of 1.4 × 10-2 cm2 V-1 s-1, which represents one of the highest values among the tellurophene-containing polychalcogenophenes. The tellurophene units in the polymers can undergo Br2 addition to form the oxidized TeBr2 species which results in dramatically red-shifted absorption due to the alternating arrangement to induce strong charge transfer character. The OFET devices using the tellurophene-containing polychalcogenophenes can be applied for Br2 detection, showing high sensitivity, selectivity and reversibility.

Hydroelementation of diynes

This review highlights the hydroelementation reactions of conjugated and separated diynes, which depending on the process conditions, catalytic system, as well as the type of reagents, leads to the formation of various products: enynes, dienes, allenes, polymers, or cyclic compounds. The presence of two triple bonds in the diyne structure makes these compounds important reagents but selective product formation is often difficult owing to problems associated with maintaining appropriate reaction regio- and stereoselectivity. Herein we review this topic to gain knowledge on the reactivity of diynes and to systematise the range of information relating to their use in hydroelementation reactions. The review is divided according to the addition of the E-H (E = Mg, B, Al, Si, Ge, Sn, N, P, O, S, Se, Te) bond to the triple bond(s) in the diyne, as well as to the type of the reagent used, and the product formed. Not only are the hydroelementation reactions comprehensively discussed, but the synthetic potential of the obtained products is also presented. The majority of published research is included within this review, illustrating the potential as well as limitations of these processes, with the intent to showcase the power of these transformations and the obtained products in synthesis and materials chemistry.

Trends in Conjugated Chalcogenophenes: A Theoretical Study

Heavy atom substitution in chalcogenophenes is a versatile strategy for tailoring and ultimately improving conjugated polymer properties. While thiophene monomers are commonly implemented in polymer designs, relatively little is known regarding the molecular properties of the heavier chalcogenophenes. Herein, we use density functional theory (DFT) calculations to examine how group 16 heteroatoms, including the radioactive polonium, affect polychalcogenophene properties including bond length, chain twisting, aromaticity, and optical properties. Heavier chalcogenophenes are more quinoidal in character and consequently have reduced band gaps and larger degrees of planarity. We consider both the neutral and radical cationic species. Upon p-type doping, bond length rearrangement is indicative of a more delocalized electronic structure, which combined with optical calculations is consistent with the polaron-model of charge storage on conjugated polymer chains. A better understanding of the properties of these materials at their molecular levels will inevitably be useful in material design as the polymer community continues to explore more main group containing polymers to tackle issues in electronic devices.

Tellura(benzo)bithiophenes: Synthesis, Oligomerization, and Phosphorescence

A series of planar π-extended Te-containing heteroacenes, termed tellura(benzo)bithiophenes, were synthesized. This new structural class of heterocycle features a tellurophene ring fused to a benzobithiophene unit with aromatic side groups (either -C₆H₄ⁱPr or -C₆H₄OCH₃) positioned at the 2- and 5-positions of the tellurophene moiety. Although attempts to enhance molecular rigidity and extend ring-framework π-delocalization in a cumenyl (-C₆H₄ⁱPr)-capped tellura(benzo)bithiophene led to oxidation (and Te-C bond scission) to form a diene-one, the formation of an oligomeric tellura(benzo)bithiophene was possible via Kumada catalyst-transfer polycondensation (KCTP). Furthermore, one tellura(benzo)bithiophene derivative exhibits orange-red phosphorescence at room temperature in air when incorporated into a poly(methyl methacrylate) host; accompanying TD-DFT computations provided insight into a potential mechanism for the observed phosphorescence.

Synthesis, Structural Characterization, and Optical Properties of Benzene-Fused Tetracyclic and Pentacyclic Stiboles

The expectation that antimony (Sb) compounds should display phosphorescence emissions based on the “heavy element effect” prompted our interest in the introduction of antimony to a biaryl as the bridging atom in a fused heterole system. Herein, the synthesis, molecular structures, and optical properties of novel benzene-fused heteroacenes containing antimony or arsenic atoms are described. The stiboles and arsole were prepared by the condensation of dibromo(phenyl)stibane or dichloro(phenyl)arsine with dilithium intermediates derived from the corresponding dibromo compounds. Nuclear magnetic resonance (NMR) spectroscopy and X-ray crystal analysis revealed that the linear pentacyclic stibole was highly symmetric in both the solution and crystal states. In contrast, the curved pentacyclic stibole adopted a helical structure in solution, and surprisingly, only M helical molecules were crystallized from the racemate. All synthesized compounds produced very weak or no emissions at room temperature or in the solid state. In contrast, the linear penta- and tetracyclic stiboles exhibited clear phosphorescence emissions in the CHCl₃ frozen matrix at 77 K under aerobic conditions.

Bifuran-bridged bisboranes: highly luminescent B-doped oligohetarenes

Boron-doping of oligohetarenes – via classical metathesis or silicon/boron exchange routes – led to strongly luminescent and twofold reversibly reducible oligomers.

Reaction of ketone hydrazones with TeCl4: isolation and reactions of novel divinyl telluride

The reaction of acetophenone hydrazones with TeCl₄ in the presence of DBU gave divinyl tellurides. The reaction of divinyl tellurides with bromine or benzyne afforded the corresponding tellurium dibromides or (E)-2-alkenyl tellurides.

Metallacycle Transfer and its Link to Light-Emitting Materials and Conjugated Polymers

Major advances in optoelectronic technologies (e. g., solar cells, organic light-emitting diodes, etc…) are prefaced by the discovery of new synthetic methodologies. In this review, the key role of the Fagan-Nugent reaction in enabling our team (and others) to gain access to new building blocks for luminescent materials and conjugated polymers bearing p-block elements will be described. The Fagan-Nugent reaction is extremely powerful as a synthetic tool since the efficient zirconium-element atom exchange involved affords a wide range of unsaturated inorganic heterocycles of controllable composition and function.

Photoactivity and optical applications of organic materials containing selenium and tellurium

Sulfur-containing compounds, particularly derivatives of thiophene, are well studied for organic optoelectronic applications. Incorporating selenium or tellurium in place of sulfur imparts different physical properties due to the fundamental differences of these atoms relative to their lighter analogues. This has a profound influence on the properties of molecules and materials that incorporate chalcogens that may ultimately lead to new opportunities and applications. This mini-review will focus on the quantitative and qualitative photophysical characteristics of organic materials containing selenium and tellurium as well as their emerging applications as molecular photoactive species, including light-emitting sensors, triplet sensitizers, and beyond.

The Synthesis and Optoelectronic Applications for Tellurophene-Based Small Molecules and Polymers

Tellurophene-based small molecules and polymers have received great attentions owing to their applications in thin-film transistors, solar cells, and sensors. This article reviews the current progress of the synthesis and applications of tellurophene-based small molecules and polymers. The physicochemical properties and optoelectronic applications of tellurophene-based materials are summarized and discussed. In the end, the challenges and outlook of tellurophene-based materials are presented.

Synthesis of Tellurium-Containing π-Extended Aromatics with Room-Temperature Phosphorescence

A synthesis of tellurium-embedded π-extended aromatics from tellurium powder and readily available cyclic diaryliodonium salts has been developed. The versatility of this method has been demonstrated by the synthesis of various functionalized dibenzotellurophenes (DBTe's), a ladder-type π-system, and a heterosumanene. These compounds demonstrated good air/moisture stability and high thermal stability. Remarkably, many DBTe's exhibited interesting tunable room-temperature phosphorescence (RTP) in the solid state.

Using boryl-substitution and improved Suzuki-Miyaura cross-coupling to access new phosphorescent tellurophenes

A new di(isopropoxy)boryl -B(OⁱPr)₂ tellurophene precursor is described, from which several previously inaccessible phosphorescent borylated tellurophenes are formed via exchange of the -OⁱPr groups. One such tellurophene Mes(ⁱPrO)B-Te-6-B(OⁱPr)Mes, bearing a sterically encumbered mesityl (Mes) substituent at each boron center, exhibits bright yellow-orange phosphorescence in the solid state at room temperature and in the presence of the known quencher O₂. Furthermore, Suzuki-Miyaura cross-coupling between the newly prepared borylated tellurophenes and the test substrate 2-bromothiophene was examined with the pre-catalyst Cl(XPhos)Pd(aminobiphenyl). While more electron deficient boryl groups such as catecholatoboryl (-Bcat) yield significant protodeboronation in place of productive C-C bond formation, efficient formation of the desired thiophene-capped tellurophene thienyl-Te-6-thienyl was noted from tellurophenes bearing the readily accessible pinacolatoboryl (-Bpin) and 1,8-naphthalenediaminatoboryl (-Bdan) functional groups. These findings open the door for the efficient synthesis of aryl tellurophenes and polytellurophenes via the ubiquitous Suzuki-Miyaura coupling of borylated tellurophenes, which was previously hampered by protodeboronation.

Peraryl Arsoles: Practical Synthesis, Electronic Structures, and Solid-State Emission Behaviors

2,3,4,5-Tetraaryl-1-phenylarsoles were synthesized by utilizing safely generated diiodophenylarsine and zirconacyclopentadienes. The obtained peraryl arsoles showed aggregation-induced emission (AIE), where intense emission was observed in the solid states (quantum yields up to 0.61), whereas the corresponding solutions were very weakly emissive. The optical and electronic properties were examined by experimental and computational methods. It was elucidated that the aryl groups at the 2,5-positions affected the frontier orbitals and the aromaticity of the arsole core. On the other hand, those at the 1,3,5-positions were perpendicular to the luminophore and effective for a restriction of aggregation-caused quenching. Because the lone pair of the arsenic atom has a sufficient coordination ability due to the low aromaticity of the arsole moiety, a gold(I) chloride complex of 1,2,3,4,5-pentaphenylarsole was synthesized. The complex formation caused a blue shift of the emission from the bare ligand. Interestingly, the complex showed luminescent mechanochromism; grinding the crystals with a blue emission (λ_em =445 nm) gave amorphous samples with a greenish-blue emission (λ_em =496 nm).

Understanding the Origin of Phosphorescence in Bismoles: A Synthetic and Computational Study

A series of bismuth heterocycles, termed bismoles, were synthesized via the efficient metallacycle transfer (Bi/Zr exchange) involving readily accessible zirconacycles. The luminescence properties of three structurally distinct bismoles were explored in detail via time-integrated and time-resolved photoluminescence spectroscopy using ultrafast laser excitation. Moreover, time-dependent density functional theory computations were used to interpret the nature of fluorescence versus phosphorescence in these bismuth-containing heterocycles and to guide the future preparation of luminescent materials containing heavy inorganic elements. Specifically, orbital character at bismuth within excited states is an important factor for achieving enhanced spin-orbit coupling and to promote phosphorescence. The low aromaticity of the bismole rings was demonstrated by formation of a CuCl π-complex, and the nature of the alkene-CuCl interaction was probed by real-space bonding indicators derived from Atoms-In-Molecules, the Electron Localizability Indicator, and the Non-Covalent Interaction index; such tools are of great value in interpreting nonstandard bonding environments within inorganic compounds.

2,5-Diaryltellurophenes: Effect of Electron-Donating and Electron-Withdrawing Groups on their Optoelectronic Properties

The transformation of 1,2-bis(1-arylvinyl)ditellurides into 2,5-diaryltellurophenes by sequential ditelluride exchange and thermal intramolecular cyclization reactions is presented, and the optoelectronic properties of a series of 2,5-diaryltellurophenes with both electron-donating and electron-withdrawing aryl substituents are disclosed. Furthermore, the multicolored emissive tellurophenes in solution at room temperature have been demonstrated.

Anion recognition by a bidentate chalcogen bond donor

Perfluoroaryl-substituted tellurophenes act as anion receptors through noncovalent chalcogen bonding interactions. Linking two tellurophenes through an ethynylene group results in a significant level of chelate cooperativity, thus demonstrating that chalcogen bonding can be used to achieve multidentate anion recognition.

Synthesis and reactions of 4H-1,4-telluraborine

The 4H-1,4-telluraborine is a shown to be a versatile reagent undergoing both protonolysis and hydroboration, affording a new range of 1,4-telluraborine derivatives.

Lateral Extension of a Benzodithiophene System: Construction of Heteroacenes Containing Various Chalcogens

A series of linear acenes with five fused rings, which contain thiophene, selenophene, and tellurophene as the outmost rings, have been synthesized from well-known benzodithiophene (BDT). It was found that the optical, electrochemical properties and crystal packing motifs could be modulated by changing heteroatoms in the outmost rings.

Versatile telluracycle synthesis via the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds

We report herein a new approach for the synthesis of tellurium-bridged aromatic compounds based on the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds with tellurium(iv) chlorides. A combination of transition metal-catalyzed (migratory) arylmetalation of alkynes and sequential telluration allows for the expedient construction of a library of functionalized benzo[b]tellurophenes. Furthermore, a variety of heteroarene-fused benzotellurophenes and other novel tellurium-embedded polycyclic aromatics can be readily synthesized from the corresponding 2-iodoheterobiaryls.

Facile access to unsymmetrically substituted tellurium–boron based heterocycles

Protonolysis and alkyne exchange reactions are used to give unsymmetrically substituted Te–B based heterocycles.

Probing the nature of peripheral boryl groups within luminescent tellurophenes

In this article our attempts to tune the color of luminescence within a new class of aggregation-induced emission (AIE) active tellurophenes is reported along with computational details that include spin–orbit coupling effects so as to better understand the nature of emission in the phosphorescent tellurophene (B-Te-6-B). Despite not meeting some of the initial synthetic targets, the emission within a borylated tellurophene can be altered with the addition of an N-heterocyclic carbene.

Marriage of heavy main group elements with π-conjugated materials for optoelectronic applications

This review article summarizes recent progress in the synthesis and optoelectronic properties of conjugated materials containing heavy main group elements from Group 13-16 as integral components. As will be discussed, the introduction of these elements can promote novel phosphorescent behavior and support desirable molecular and polymeric properties such as low optical band gaps and high charge mobilities for photovoltaic and thin film transistor applications.

A Mechanistic Study of Halogen Addition and Photoelimination from π-Conjugated Tellurophenes

The ability to drive reactivity using visible light is of importance for many disciplines of chemistry and has significant implications for sustainable chemistry. Identifying photochemically active compounds and understanding photochemical mechanisms is important for the development of useful materials for synthesis and catalysis. Here we report a series of photoactive diphenyltellurophene compounds bearing electron-withdrawing and electron-donating substituents synthesized by alkyne coupling/ring closing or palladium-catalyzed ipso-arylation chemistry. The redox chemistry of these compounds was studied with respect to oxidative addition and photoelimination of bromine, which is of importance for energy storage reactions involving X2. The oxidative addition reaction mechanism was studied using density functional theory, the results of which support a three-step mechanism involving the formation of an initial η(1) association complex, a monobrominated intermediate, and finally the dibrominated product. All of the tellurophene derivatives undergo photoreduction using 430, 447, or 617 nm light depending on the absorption properties of the compound. Compounds bearing electron-withdrawing substituents have the highest photochemical quantum efficiencies in the presence of an alkene trap, with efficiencies of up to 42.4% for a pentafluorophenyl-functionalized tellurophene. The photoelimination reaction was studied in detail through bromine trapping experiments and laser flash photolysis, and a mechanism is proposed. The photoreaction, which occurs by release of bromine radicals, is competitive with intersystem crossing to the triplet state of the brominated species, as evidenced by the formation of singlet oxygen. These findings should be useful for the design of new photochemically active compounds supported by main-group elements.

Influence of the heteroatom on the optoelectronic properties and transistor performance of soluble thiophene-, selenophene- and tellurophene-vinylene copolymers

We report the first soluble poly(3-dodecyl tellurophenylene-vinylene) polymer (P3TeV) by Stille copolymerization and compare its properties to the analogous thiophene and selenophene containing polymers. The optical band gap of the polymers is shown to systematically decrease as the size of the heteroatom is increased, mainly as a result of a stabilization of the LUMO energy, resulting in a small band gap of 1.4 eV for P3TeV. Field effect transistors measurements in variety of architectures demonstrate that the selenophene polymer exhibits the highest mobility, highlighting that increasing the size of the heteroatom is not always beneficial for charge transport.

Palladium-catalysed direct thiolation and selenation of aryl C–H bonds assisted by directing groups

Recent advances on transition-metal-catalyzed direct chalcogenation of C–H bonds with disulfides and diselenides are summarized.