Dialkoxybithiazole: A New Building Block for Head-to-Head Polymer Semiconductors

Abstract

Polymer semiconductors have received great attention for organic electronics due to the low fabrication cost offered by solution-based printing techniques. To enable the desired solubility/processability and carrier mobility, polymers are functionalized with hydrocarbon chains by strategically manipulating the alkylation patterns. Note that head-to-head (HH) linkages have traditionally been avoided because the induced backbone torsion leads to poor π-π overlap and amorphous film microstructures, and hence to low carrier mobilities. We report here the synthesis of a new building block for HH linkages, 4,4'-dialkoxy-5,5'-bithiazole (BTzOR), and its incorporation into polymers for high performance organic thin-film transistors. The small oxygen van der Waals radius and intramolecular S(thiazolyl)···O(alkoxy) attraction promote HH macromolecular architectures with extensive π-conjugation, low bandgaps (1.40-1.63 eV), and high crystallinity. In comparison to previously reported 3,3'-dialkoxy-2,2'-bithiophene (BTOR), BTzOR is a promising building block in view of thiazole geometric and electronic properties: (a) replacing (thiophene)C-H with (thiazole)N reduces steric encumbrance in -BTzOR-Ar- dyads by eliminating repulsive C-H···H-C interactions with neighboring arene units, thereby enhancing π-π overlap and film crystallinity; and (b) thiazole electron-deficiency compensates alkoxy electron-donating characteristics, thereby lowering the BTzOR polymer HOMO versus that of the BTOR analogues. Thus, the new BTzOR polymers show substantial hole mobilities (0.06-0.25 cm(2)/(V s)) in organic thin-film transistors, as well as enhanced I(on):I(off) ratios and greater ambient stability than the BTOR analogues. These geometric and electronic properties make BTzOR a promising building block for new classes of polymer semiconductors, and the synthetic route to BTzOR reported here should be adaptable to many other bithiazole-based building blocks.

Controlling the mode of operation of organic transistors through side-chain engineering

“…1A). The intramolecular sulfur-oxygen interactions of the head-to-head coupled bithiophene unit is known to induce backbone coplanarity and increase the effective conjugation length of the polymer which should favor efficient charge transport, while decreasing the ionization potential (IP) (28). Using a palladium-catalyzed Stille polycondensation reaction, polymers p(a2T-TT) and p(g2T-TT) were synthesized by reacting 2,5-bis(trimethylstannyl)-thieno [3,2-b] thiophene with equimolar amounts of 5,5′-dibromo-3,3′-bis(tetradecyloxy)-2,2'-bithiophene and 5,5′-dibromo-3,3′-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2′-bithiophene, respectively, as further detailed in the SI Appendix.…”

Synthesis and Characterization of an Alkoxythiazole-thiazolothiazole Semiconducting Polymer for Organic Solar Cells

“…In fact, it was reported that the alkoxythiazole unit can reduce the E g of the polymer similarly as in the case of the alkoxythiophene unit, but can afford a deep E HOMO similarly as in the case of the alkylthiophene unit. 33 We will show the synthesis of the polymer and discuss the properties, ordering structures, and PSC performance.…”

Semi-crystalline A1–D–A2-type copolymers for efficient polymer solar cells

“…Two solubilizing alkoxy side chains at the 5-and 6-positions of BTz induce intra-and/or interchain coulombic interactions via S δ+ -O δ − between the oxygen and sulfur atoms in the neighboring thiophene and BTz moieties. 38,39 The BT moiety is used as the main acceptor, with fluorine atoms at the 5-and 6-positions to modulate the frontier orbital levels and oxidational stability of the resulting polymers. 40,41 This design is expected to yield both a low band gap and a deep HOMO level.…”