Π-conjugated Main Chain Research Articles

Synthesis and Magnetic Behavior of Poly(1,3-phenylene)-Based Polyradical Carrying N-tert-Butyl Nitroxide Radicals

Synthesis and magnetic behavior of poly[6-N-oxy-tert-butylamino)biphenyl-3,3′-ylene] (2) are described. Polyradical 2 was prepared the Pd-catalyzed polycondensation of N-tert-butyl-2,4-dibromoaniline with 1,3-phenylenebis(trimethylene boronate), followed by oxidation with 3-chloroperoxybenzoic acid. The degree of polycondensation determined by SEC was ∼18. Polyradical 2 was very stable in both solution and solid state. The spin concentration of 2 determined by ESR was 1.89 × 1021 spins g−1 (0.75 spin per repeating unit). The magnetic susceptibility (χ) measurements of 2 carried out with a SQUID magnetometer showed that the magnetic interaction between the unpaired electron spins was antiferromag-netic (Θ= −0.98 K). No observation of the ferromagnetic interaction was ascribed to twisting of the nitroxide moiety from the π-conjugated main chain. This twisting was confirmed by the X-ray crystallographic analysis of the monomer model radical 1.

Syntheses and solid-state polymerization of diacetylene derivatives bearing dodecylthio groups directly bound tosp-carbons

Diacetylenes were synthesized bearing dodecylthio groups directly bound to the sp-carbons. These compounds afford polydiacetylenes having sulfur atoms directly attached to the π-conjugated main chains. The exciton absorption peaks appear at ca. 750 nm, which is a longer wave length than of conventional polydiacetylenes.

Synthesis and magnetic behaviour of poly(1,3-phenylene)-based polyradical carrying N-tert-butylaminoxyl radicals

The synthesis and magnetic behaviour of poly[6-(N-oxyl-N-tert-butylamino)biphenyl-3,3′-ylene] 2 are described. Polyradical 2 was prepared by the Pd-catalyzed polycondensation of N-tert-butyl-2,4-dibromoaniline and 1,3-phenylenebis(trimethylene boronate), followed by oxidation with 3-chloroperoxybenzoic acid. The degree of polymerisation determined by SEC (size exclusion chromatography) was ∼18. Polyradical 2 was stable in both solution and the solid state. The spin concentrations of 2 determined by EPR and SQUID were 0.75 and 0.82 spin per repeating unit, respectively. Magnetic susceptibility (χ) measurements on 2 were carried out on a SQUID magnetometer and these showed that the magnetic interaction between the unpaired electron spins was antiferromagnetic (θ=–0.98 K). The fact that no ferromagnetic interaction was observed was ascribed to a twisting of the nitroxide moieties from the π-conjugated main chain, and this was confirmed by X-ray crystallographic analysis of the corresponding model monoradical, N-tert-butyl-N-(2,4-diphenylphenyl)aminoxyl.

Preparation and properties of π-conjugated poly(benzimidazole-4,7-diyl)s

Preparation, optical properties, and electrochemical redox behavior of poly(benzimidazole-4,7-diyl)s are reported. Dehalogenation polycondensation of 4,7-dibromobenzimidazole and its derivatives (2-heptyl and 2-phenyl derivatives) with zerovalent nickel complexes gives the corresponding polymers in 72–100% yield. Poly(benzimidazole-4,7-diyl) and its heptyl derivative have molecular weights of 1.3 × 104 and 3.8 × 104, respectively, as determined by light scattering measurements. In non-acidic solvents the polymers give rise to one absorption peak at about 300 nm, which is assigned to a π-π* transition occurring in the benzimidazole monomeric unit, and another absorption peak at a longer wavelength, which is considered to originate from the π-π* transition occurring in the π-conjugated main chain. The π-π* absorption peak, as well as the photoluminescence peak of the polymers, are shifted in acidic media due to protonation. The polymers are electrochemically active regarding reduction (or n-doping) and show electrochromism.

New type of polymer containing 1,1′-ferrocenediyl unit in π-conjugated main chain. Preparation and redox behavior

New ferrocenic polymers formulated as (-FcC≡CArC≡C-)n (Fc=1,1′-ferrocenylene; Ar=p-C6H4, 2,5-pyridinediyl, and 2,5-didodecyl-p-phenylene) have been prepared by a Pd-catalyzed CC coupling polymerization. Electrochemical oxidation of the polymers requires a higher potential than those of ferrocene and poly(ferrocene) owing to bonding to the electron withdrawing -C≡C- group, and their broadened cyclic voltammograms suggest an exchange of electron between the Fc units along the π-conjugated main chain. Mössbauer spectra of iodine adducts of the polymers reveal that the polymer with the p-C6H4 unit (as the Ar unit) is oxidized with iodine whereas the polymer with the 2,5-pyridinediyl is not; the difference is accounted for by the electronic effect and reactivity of the Ar units.

UV Photoelectron Spectroscopy of Substituted Polyacetylenes

Ionization threshold energies of 26 substituted polyacetylenes were determined by ultraviolet photoelectron spectroscopy. Examination of the data obtained, along with data for other polymers, and the energy of the lowest energy electronic excitation revealed that the threshold energies correspond to the photoemission from the highest occupied orbitals in the π-conjugated main chains. For the majority of the polymers, the main origin of the significant variation of threshold energy and electronic excitation energy is ascribed to the change of the degree of π-conjugation due to steric hindrance of substituents. Calculations with Huckel theory gave semiquantitative agreement with the observed results. Polymers with Cl substituents at the main chain also showed a large inductive effect by the electron-withdrawing Cl atom. The HOMO of these polymers was found to be derived from the π-conjugated main chain.

Poly(aryleneethynylene) Type Polymers Containing a Ferrocene Unit in the π-Conjugated Main Chain. Preparation, Optical Properties, Redox Behavior, and Mössbauer Spectroscopic Analysis

Palladium-catalyzed polycondensation between diiodoferrocenes (1,1‘-diiodoferrocene and 1,6-diiodo-1‘,6‘-biferrocene) and diethynyl aromatic compounds HC⋮CArC⋮CH (e.g., 2,5-diethynylpyridine and 2,5-diethynyl-3-hexylthiophene) gives poly(aryleneethynylene) (PAE) type polymers containing the ferrocene unit in the π-conjugated main chain. The prepared polymers include (FcC⋮CPhC⋮C)n, PAE-Fc-1, (FcC⋮CPyC⋮C)n, PAE-Fc-2, and (FcC⋮ChexThC ⋮C)n, PAE-Fc-3 (Fc = 1,1‘-ferrocenylene; Ph = p-phenylene; Py = pyridine-2,5-diyl; hexTh = 3-hexylthiophene-2,5-diyl). 1H-NMR and IR spectra of the polymers are reasonable for their structures. The PAE type polymer containing the pyridine unit (PAE-Fc-2) is soluble in formic acid, and the polymer containing the hexylthiophene unit (PAE-Fc-3) is soluble in common organic solvents such as CHCl3, THF, and benzene. UV−visible spectra of the polymers exhibit a main π−π* absorption peak at about 330 nm and a d−d absorption peak at about 450 nm. The cyclic voltammogram of the polymers in a CH3CN/CH2Cl2 solution shows a reversible Fe(II) ⇄ Fe(III) redox cycle at about 0.25 V vs Ag/Ag+, and the redox peaks are broadened compared with those of low-molecular-weight ferrocenes. Exchange of electrons along the main chain is considered to be the origin of the broadening. The polymers themselves are insulating, however, they are converted into semiconducting materials with conductivity of 10-7 to 10-4 S cm-1 by formation of adducts with iodine. Mössbauer spectra of the polymers reveal oxidation of Fe(II) in the ferrocene unit of PAE-Fc-1 to Fe(III), and the ease of the oxidation reflects the electronic properties of the polymer.

New π-conjugated polymers containing tetrathiafulvalene as the monomeric unit

Four kinds of poly(arylene)- and poly(aryleneethynylene)-type polymers containing TTF units in the π-conjugated main chain, which are susceptible to chemical and electrochemical oxidation, have been prepared by organometallic polycondensation.

Resonant subpicosecond degenerate four-wave mixing for a mainchain polymer with a definite short π conjugation

The subpicosecond time-resolved degenerate four-wave mixing (DFWM) technique is applied to evaluate the third-order optical nonlinearity, χ (3) (ω; ω, −ω, ω), and its decay dynamics for a symmetrical short π-conjugated mainchain polymer, pSBAC for short. The χ (3)/α value of 6 × 10 −14 esu cm for pSBAC is the same as that reported for many other π-conjugated polymers. We propose that the concept of real-space filling accounts for the observed χ (3)/ga value in pSBAC. The picosecond dynamics of the transient grating response for pSBAC is also discussed in comparison with that of the π-conjugated polymers.