Synthetic Routes to Polyheteroacenes:  Characterization of a Heterocyclic Ladder Polymer Containing Phenoxathiinium-type Building Blocks

Abstract

The synthetic routes to ladder polymers that consist of benzenetetrayl subunits with oxo and methylsulfonio linkages are described. As the key intermediate, poly(phenylene oxide)s having pendant methylsulfenyl groups are prepared by copper-catalyzed oxidative polymerization of the corresponding phenols with O2. The oxidation of the polymer with an equimolar amount of H2O2 in the presence of acetic acid effects the high-yielding conversion of methylsulfenyl to methylsulfinyl groups without the formation of the undesired methylsulfonyl groups. The superacidified condensation of the resulting polymer (Swern reaction of aryl sulfoxides) under dilution conditions induces the polymer-analogous intramolecular electrophilic ring-closing reaction of the hydroxymethylphenylsulfonium cation onto the adjacent benzene ring to yield the required ladder polymer, which has proved to be a semiconductor with an intrinsic electric conductivity of 2 × 10-5 S/cm. A comparison of the spectroscopic properties of the ladder polymer with those of the model compounds such as 5-methylphenoxathiinium triflate and phenoxathiin discloses π-electron delocalization over the methylsulfonio linkages, demonstrating the efficacy of the ladderization for p−π/d−π interactions in arylsulfonium moieties. This synthetic approach permits the thio and alkylsulfonio ladder linkages for a variety of phenyl ethers to form in high yields.

Heteropolyacene with Thianthrenium Ring Systems ProvingπElectron Delocalization over S Atoms

“…Interestingly, the dihedral angle of the benzene rings in 2b is intermediate between those of thianthrene (50.658) and its cation radical (68). [20] The small dihedral angle in 2b reflects the delocalization of p electrons from the benzene rings into the methylsulfonio moiety through a p-d/d-d interaction [20,21] (vide infra). Additional support for this interpretation is provided by three features that warrant attention.…”

“…[16,22] A heteropolyacene 6 having phenoxathiinium-type repeating units was also prepared. [21] Taking into account the lack of such donor -acceptor interaction between oxo and methylsulfonio linkages, one could ascribe the smaller band gap in 6 only to the p-electron delocalization through the polymer backbone. [21] The polymer 5 in the present study can serve as an additional example to prove the proposed p-p/d-p interaction in heteropolyacene containing methylsulfonio moieties.…”

“…[21] Taking into account the lack of such donor -acceptor interaction between oxo and methylsulfonio linkages, one could ascribe the smaller band gap in 6 only to the p-electron delocalization through the polymer backbone. [21] The polymer 5 in the present study can serve as an additional example to prove the proposed p-p/d-p interaction in heteropolyacene containing methylsulfonio moieties. In 1 H NMR, the methylsulfonio resonance of 5 appeared at a lower magnetic field than the methylsulfinyl resonance of 4, consistent with the spectral change upon the conversion of 1 to 2.…”

Polymerization of 4,6-diaminoisophthalic acid-type monomers bearing anthranilic acid ester and isatoic anhydride moieties

“…For example, the phenoxathiinium-type ladder polymers show higher stability against thermolysis than corresponding non-ladder polymers. 1 In addition, the study of electron mobility in field-effect transistors demonstrates a large enhancement in carrier mobility in ladder-type poly(benzobisimidazobenzophenanthroline) compared with its non-ladder analog. 2 Many types of ladder polymers have been synthesized via bond formation between repetitive units of a linear polymer.…”

Emerging Organosulfonium Electrophiles as Unique Reagents for Carbon–Sulfur Bond Formation: Prospects in Synthetic Chemistry of Organosulfur Compounds

“…Polymer-analogous reaction of poly(arylene oxide)s containing the sulfinyl functionality yielded the corresponding heterocyclic ladder polymer containing the phenoxathiinium-type building blocks via ring closure and demethylation. 53 A heteropolyacene with phenothiazinium repeating units was similarly obtained from the corresponding prepolymer. 54 The synthetic utility of sulfonium ions RS + and their equivalents as reagents is thus widely spread, especially for those in electrophilic additions and substitutions.…”