Easily Processable Highly Ordered Langmuir-Blodgett Films of Quaterthiophene Disiloxane Dimer for Monolayer Organic Field-Effect Transistors

Self-assembly of highly soluble water-stable tetramethyldisiloxane-based dimer of α,α′-dialkylquaterthiophene on the water–air interface was investigated by Langmuir, grazing incidence X-ray diffraction, and X-ray reflectivity techniques. The conditions for formation of very homogeneous crystalline monolayer Langmuir-Blodgett (LB) films of the oligomer were found. Monolayer organic field-effect transistors (OFETs) based on these LB films as a semiconducting layer showed hole mobilities up to 3 × 10^–3 cm²/(V s), on–off ratio of 10⁵, small hysteresis, and high long-term stability. The electrical performance of the LB films studied is close to that for the same material in the bulk or in the monolayer OFETs prepared from water vapor sensitive chlorosilyl derivatives of quaterthiophene by self-assembling from solution. These findings show high potential of disiloxane-based LB films in monolayer OFETs for large-area organic electronics

Effect of Molecular Structure of α,α′-Dialkylquaterthiophenes and Their Organosilicon Multipods on Ordering, Phase Behavior, and Charge Carrier Mobility

We report on bulk structures of a family of quaterthiophene (<b>4T</b>) derivatives with linear and branched end groups such as α,α′-dihexylquaterthiophene (<b>Hex-4T-Hex</b>), α,α′-didecyl-quaterthiophene (<b>Dec-4T-Dec</b>) and α,α′-bis­(2-ethylhexyl)­quaterthiophene (<b>EH-4T-EH</b>), tetramethyldisiloxane-based dimers <b>D2-Und-4T-EH</b> and <b>D2-Und-4T-Hex</b>, and carbosilane-siloxane-based tetramers <b>D4-Und-4T-EH</b> and <b>D4-Und-4T-Hex</b>. The dimers and tetramers contain undecylenic (<b>Und</b>) spacers between the disiloxane and <b>4T</b>- units of the molecule. The impact of the molecular architecture on the bulk structure at different temperatures is addressed with X-ray diffraction and differential scanning calorimetry. For all of the studied quaterthiophene-containing organosilicon multipods the formation of <b>4T</b>-crystal sublattice is observed. The alkyl periphery plays an important role in the molecular packing and thermal stability of the ordered phase. They can stabilize or destabilize the crystal phase, depending on their length and architecture. The quaterthiophenes with 2-ethylhexyl end groups adopt a zig-zag conformation in the crystalline state at room temperature. This change of conformation leads to a significant decrease of the polymorphic transition and isotropization temperatures. The efficiency of <b>4T</b> packing in the sublattice is estimated from the molecular cross-section (S) in the plane normal to the molecular axis. Correlations between S and field-effect charge carrier mobility are established

Luminescent Organic Semiconducting Langmuir Monolayers

In recent years, monolayer organic field-effect devices such as transistors and sensors have demonstrated their high potential. In contrast, monolayer electroluminescent organic field-effect devices are still in their infancy. One of the key challenges here is to create an organic material that self-organizes in a monolayer and combines efficient charge transport with luminescence. Herein, we report a novel organosilicon derivative of oligothiophene–phenylene dimer <b>D2-Und-PTTP-TMS</b> (D2, tetramethyldisiloxane; Und, undecylenic spacer; P, 1,4-phenylene; T, 2,5-thiophene; TMS, trimethylsilyl) that meets these requirements. The self-assembled Langmuir monolayers of the dimer were investigated by steady-state and time-resolved photoluminescence spectroscopy, atomic force microscopy, X-ray reflectometry, and grazing-incidence X-ray diffraction, and their semiconducting properties were evaluated in organic field-effect transistors. We found that the best uniform, fully covered, highly ordered monolayers were semiconducting. Thus, the ordered two-dimensional (2D) packing of conjugated organic molecules in the semiconducting Langmuir monolayer is compatible with its high-yield luminescence, so that 2D molecular aggregation per se does not preclude highly luminescent properties. Our findings pave the way to the rational design of functional materials for monolayer organic light-emitting transistors and other optoelectronic devices