A Self-Threading Polythiophene: Defect-Free Insulated Molecular Wires Endowed with Long Effective Conjugation Length

Abstract

Herein, we report on a self-threading polythiophene whose conjugated molecular wire is sheathed within its own cyclic side chains. The defect-free insulating layer prevents electronic cross-communication between the adjacent polythiophene backbone even in the solid film. Notably, the covalently linked cyclic side chains extend the effective conjugation length of the interior polythiophene backbone, which results in an excellent intrawire hole mobility of 0.9 cm(2) V(-1) s(-1).

Synthesis of Unsheathed Insulated Molecular Wires

“…As reported previously, the bithiophene backbone in 3 is planarized owing to the strapped structure, 5 while that in 4 is known to be twisted. 9 Because of the difference in planarity, 3 and 4 should have distinct electronic structures.…”

“…8 If the monomer 4 was randomly incorporated into the poly-3 backbone, then the effective conjugation of the poly-3 backbone should be significantly reduced; for example, in the case of poly-3 8 4 2 , the poly-3 backbone could be stochastically segmented into conjugation as small as a tetramer or pentamer. 5 Nonetheless, the ππ* transition of the poly-3 backbone at 500600 nm was scarcely affected by 4, thus corroborating the block copolymer structure. Importantly, the spectra could be deconvolved into those of poly-3 and poly-4, which is consistent with the compositions of each block determined by 1 H NMR spectroscopy.…”

“…6 In fact, we have recently succeeded in the synthesis of diblock copolymers (poly-2) consisting of unsheathed P3HT and sheathed polythiophene. Although the CTP method is expected to yield such unprecedented polymer structures, the monomer scope still remains limited in terms of both electronic and steric effects, 7 and we have not yet succeeded in the synthesis of other IMWs such as poly-3 through the CTP method.Poly-3 was synthesized through Yamamoto polymerization, 5 and in this regard, one report from the Scherf group 8 has attracted our interest. They synthesized block copolymers of poly[2,7-(9,9-dialkyl)fluorene] and poly(2,6-(4,4-dialkyl)-4H-cyclopenta[2,1-b:3,4-b¤]dithiophene) using Yamamoto polymerization conditions despite the fact that the propagation proceeds through the step-growth mechanism (Scheme 2).…”

“…Poly-3 was synthesized through Yamamoto polymerization, 5 and in this regard, one report from the Scherf group 8 has attracted our interest. They synthesized block copolymers of poly[2,7-(9,9-dialkyl)fluorene] and poly(2,6-(4,4-dialkyl)-4H-cyclopenta[2,1-b:3,4-b¤]dithiophene) using Yamamoto polymerization conditions despite the fact that the propagation proceeds through the step-growth mechanism (Scheme 2).…”

Twisting poly(3-substituted thiophene)s: cyclopolymerization of gemini thiophene monomers through catalyst-transfer polycondensation

“…33 A previous study by our group, conceptually related to the present study, has demonstrated that the dihedral angle of bithiophene is affected by cyclic side chains. [34][35][36][37] In STBm/n (Scheme 2), the movable range of the dihedral angle of the bithiophene backbone was defined by the length of the strap. The longer the strap, the larger the fluctuation of the dihedral angle (Scheme 2c).…”