3 research outputs found
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<sup>–3</sup> cm<sup>2</sup>/(V
s), on–off ratio of 10<sup>5</sup>, 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
Molecularly Smooth Single-Crystalline Films of Thiophene–Phenylene Co-Oligomers Grown at the Gas–Liquid Interface
Single
crystals of thiophene–phenelyne co-oligomers (TPCOs)
have previously shown their potential for organic optoelectronics.
Here we report on solution growth of large-area thin single-crystalline
films of TPCOs at the gas–liquid interface by using solvent–antisolvent
crystallization, isothermal slow solvent evaporation, and isochoric
cooling. The studied co-oligomers contain identical conjugated core
(5,5′-diphyenyl-2,2′-bithiophene) and different terminal
substituents, fluorine, trimethylsilyl, or trifluoromethyl. The fabricated
films are molecularly smooth over areas larger than 10 × 10 μm<sup>2</sup>, which is of high importance for organic field-effect devices.
The low-defect structure of the TPCO crystals is suggested from the
monoexponential kinetics of the PL decay measured in a wide dynamic
range (up to four decades) and from low crystal mosaicity assessed
by microfocus X-ray diffraction. The TPCO crystal structure is solved
using a combination of X-ray and electron diffraction. The terminal
substituents affect the crystal structure of TPCOs, bringing about
the formation of a noncentrosymmetric crystal lattice with a crystal
symmetry <i>Cc</i> for the bulkiest trimethylsilyl terminal
groups, which is unusual for linear conjugated oligomers. Comparing
the different crystal growth techniques, it is concluded that the
solvent–antisolvent crystallization is the most robust for
fabrication of single-crystalline TPCOs films. The possible nucleation
and crystallization mechanisms operating at the gas–solution
interface are discussed
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