Synthesis of π-Conjugated Polymer Possessing Mercapto-Substituted 1,3-Butadiene-1,4-diyl Units by Reaction of Regioregular Organometallic Polymer Having Titanacyclopentadiene Moieties in the Main Chain

Editing of polymer backbones

Polymers are at the epicentre of modern technological progress and the associated environmental pollution. Considerations of both polymer functionality and lifecycle are crucial in these contexts, and the polymer backbone - the core of a polymer - is at the root of these considerations. Just as the meaning of a sentence can be altered by editing its words, the function and sustainability of a polymer can also be transformed via the chemical modification of its backbone. Yet, polymer modification has primarily been focused on the polymer periphery. In this Review, we focus on the transformations of the polymer backbone by defining some concepts fundamental to this topic (for example, 'polymer backbone' and 'backbone editing') and by collecting and categorizing examples of backbone editing scattered throughout a century's worth of chemical literature, and outline critical directions for further research. In so doing, we lay the foundation for the field of polymer backbone editing and hope to accelerate its development.

Parallel synthesis of donor-acceptor π-conjugated polymers by post-element transformation of organotitanium polymer

The donor-acceptor type π-conjugated polymers having heterole units were prepared by the reaction of a regioregular organometallic polymer having both reactive titanacyclopentadiene and electron-donor thiophene-2,5-diyl units in the main chain with electrophiles such as diphenyltin dichloride, dichlorophenylphosphine, and diiodophenylarsine. For example, a polymer having electron-accepting phosphole unit was obtained in 54% yield whose number-average molecular weight (Mn) and molecular weight distribution (Mw/Mn) were estimated as 3,000 and 1.9, respectively. The obtained polymer exhibits a high highest occupied molecular orbital (HOMO) and low lowest unoccupied molecular orbital (LUMO) energy levels (-5.13 eV and -3.25 eV, respectively) due to the electron-donating thiophene and electron-accepting phosphole units. Reflecting upon the alternating structure of thiophene and phosphole, the polymer exhibits a band gap energy level (Eg) of 1.78 eV which is narrower than that of a derivative of poly(thiophene) (Eg = 2.25 eV).

Synthesis and optoelectronic properties of air-stable π-conjugated polymers containing both thiophene-2,5-diyl and fused titanacycle units

π-Conjugated poly(arylene ethynylene)s containing both thiophene-2,5-diyl and fused metallacycles units in their alternating sequence were synthesized and their optoelectronic features were studied by the UV-vis spectra.

An air-stable organometallic polymer containing titanafluorene moieties obtained by the Sonogashira-Hagihara cross-coupling polycondensation

The synthesis of a polymer containing alternating titanafluorene and arylene ethynylene moieties is described. The polymerization of a 2,7-dibromo-9-titanafluorene derivative with 1,4-dioctyloxy-2,5-diethynylbenzene is carried out at 70 °C for 48 h in tetrahydrofuran (THF) in the presence of palladium dichloride/4,5-bis(diphenylphosphino)-9,9-dimethylxanthene as a catalyst and diisopropylamine as a base to produce a dark red polymer. The polymer thus obtained is soluble in organic solvents and stable towards both air and moisture. In the UV-vis absorption spectrum of the polymer, the absorption maxima (λ_max) are observed at 321 nm and 395 nm, which are bathochromically shifted compared to those of a model compound of the repeating unit, a 2,7-bis(phenylethynyl)titanafluorene derivative (λ_max = 309 nm and 364 nm). The optical band gap (E_g) of the polymer is estimated to be 2.8 eV on the basis of the absorption onset, which is narrower than that of the model compound (3.1 eV).

Tellurophene-containing π-conjugated polymers with unique heteroatom–heteroatom interactions by post-element-transformation of an organotitanium polymer

A unique π-conjugated tellurophene-containing polymer that possesses fully coplanar ring units through a tellurium–oxygen interaction, was prepared by the post-element-transformation of a titanacyclopentadiene-containing reactive precursor.

Te-Li Exchange Reaction of Tellurophene-Containing π-Conjugated Polymer as Potential Synthetic Tool for Functional π-Conjugated Polymers

On the basis of the facts that tellurophene-containing π-conjugated polymers are obtainable from organotitanium polymers and that the tellurium atoms in the tellurophene derivatives can be transformed into lithium atoms, the synthesis of reactive lithiated polymer precursor and its transformations into some functionalized π-conjugated polymers are described. A regioregular organometallic polymer having 1,4-dilithio-1,3-butadiene and 9,9-dioctylfluorene-2,7-diyl units is generated by the reaction of a tellurophene-containing polymer having the number-average molecular weight (M_n ) and molecular weight distribution (M_w /M_n ) of 5890 and 1.9, respectively, with n-butyllithium (2.4 equiv.) at -78 °C to -60 °C for 3 h. The lithiated polymer thus prepared is subjected to reactions with electrophiles to produce functionalized π-conjugated polymers. For example, a π-conjugated polymer possessing 1,4-bis(tri-n-butylstannyl)-1,3-butadiene-1,4-diyl unit is obtained in 67% yield by the reaction with tri-n-butyltin chloride (2.4 equiv.) at -60 °C to ambient temperature for 12 h in tetrahydrofuran, whose M_n and M_w /M_n are estimated as 7320 and 2.5, respectively, by size exclusion chromatography. The absorption maximum and onset of the obtained polymer are observed at 380 and 465 nm, respectively, in the UV-vis spectrum, from which the optical band gap of the polymer is estimated as 2.67 eV.

Synthesis of Stannole-Containing π-Conjugated Polymers by Post-Element Transformation of Organotitanium Polymer

The synthesis of stannole-2,5-diyl-containing π-conjugated polymers by the post-element transformation of a regioregular organotitanium polymer is described. For example, a 1,1-diphenylstannole-containing polymer is obtained in 83% yield by the reaction of a regioregular organotitanium polymer, which is prepared from 1,4-bis(2-ethylhexyloxy)-2,5-diethynylbenzene and a low-valent titanium complex with diphenyltin dichloride at -50 °C to ambient temperature. The number-average molecular weight and molecular weight distribution (M_n and M_w /M_n ) of the stannole-containing polymer are estimated as 4800 and 1.8, respectively. The obtained polymer is found to have the extended π-conjugated backbone and relatively low-lying lowest unoccupied molecular orbital (LUMO) energy level (-3.12 eV), which is supported by its UV-vis absorption spectrum and cyclic voltammetric (CV) analysis. In addition, the stannole-containing polymer is found to be applicable to a chemosensor for fluoride anion where the color and photoluminescence intensity of the polymer solution exhibits a distinct change in the presence of a fluoride anion.

The Dawn of Functional Organoarsenic Chemistry

Organoarsenic chemistry was actively studied until the middle of 20th century. Although various properties of organoarsenic compounds have been computationally predicted, for example, frontier orbital levels, aromaticity, and inversion energies, serious concern to the danger of their synthetic processes has restricted experimental studies. Conventional synthetic routes require volatile and toxic arsenic precursors. Recently, nonvolatile intermediate transformation (NIT) methods have been developed to safely access functional organoarsenic compounds. Important intermediates in the NIT methods are cyclooligoarsines, which are prepared from nonvolatile inorganic precursors. In particular, the new approach has realized experimental studies on conjugated arsenic compounds: arsole derivatives. The elucidation of their intrinsic properties has triggered studies on functional organoarsenic chemistry. As a result, various kinds of arsenic-containing π-conjugated molecules and polymers have been reported for the last few years. In this minireview, progress of this recently invigorated field is overviewed.

Metal-Free, Multicomponent Synthesis of Pyrrole-Based π-Conjugated Polymers from Imines, Acid Chlorides, and Alkynes

Multicomponent coupling reactions (MCRs) are becoming increasingly used in the synthesis of macromolecules, as they can allow the rapid generation of libraries of materials as a method to tune properties. MCRs could prove particularly useful in the synthesis of π-conjugated polymers in which structural changes are necessary for fine-tuning of electronic properties. We describe here the first metal-free multicomponent approach to conjugated polymers. This reaction exploits the coupling of imines, acid chlorides, and (catechyl)PPh to generate phospha-münchnone-containing polymers, which can be converted to poly(pyrroles) via cycloaddition. The platform allows for the efficient synthesis of families of high molecular weight polymers in one step from readily available monomers.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Synthesis of π-Conjugated Polymers Containing Phosphole Units in the Main Chain by Reaction of an Organometallic Polymer Having a Titanacyclopentadiene Unit

A regioregular organometallic polymer possessing titanacyclopentadiene units in the main chain, which was obtained by the reaction of terminal diyne and a low-valent titanium complex, was subjected to the reaction with dichlorophosphines to give π-conjugated polymers with phosphole or phosphole oxide units in the main chain. For example, a phenylphosphole-containing polymer was obtained in 76% yield by the reaction with dichlorophenylphosphine, whose number-average molecular weight (M_n) and molecular weight distribution (M_w/M_n) were estimated to be 6100 and 1.9, respectively, by GPC. The polymer was found to have an extended π-conjugated system, and its lowest unoccupied molecular orbital (LUMO) energy level was remarkably low (-3.28 eV) as supported by its UV-vis absorption spectrum and cyclic voltammetric (CV) analysis. Also, the polymer exhibits orange photoluminescence with an emission maximum (E_max) of 595 nm and a quantum yield (Φ) of 0.10.