3 research outputs found
Polyfluorinated Naphthalene-bis-hydrazimide for Solution-Grown n-Type Semiconducting Films
Naphthalene tetracarboxylic diimides (NDIs), possessing low-lying and tunable LUMO levels, are of wide interest for their aptitude to provide cost-effective, flexible, and environmentally stable n-type organic semiconductors through simple solution processing. NDI-based aromatic hydrazidimides are herein studied in relation to their chemical and environmental stability and as spin-coated stable thin films. In the case of the pentafluorinated residue, these were found to be crystalline, highly oriented, and molecularly flat (roughness = 0.3 nm), based on optical and atomic force microscopy, X-ray diffraction in specular and grazing incidence geometry, and X-ray reflectivity measurements. A new polymorph, previously undetected during the isolation of bulk powders or in their controlled thermal treatments, is found in the thin film and was metrically and structurally characterized from 2D GIWAXS patterns (monoclinic, P2/c, a = 17.50; b = 4.56; c = 14.24 & Aring;; beta = 84.8 degrees). This new thin-film phase, TF-F5, is formed no matter whether silicon, glass, or polymethylmethacrylate substrates are used, thus opening the way to the preparation of solution-grown flexible semiconducting films. The TF-F5 films exhibit a systematic and rigorous molecular alignment with both orientation and packing favorable to electron mobility (mu = 0.02 cm(2) V-1 s(-1)). Structural and morphological differences are deemed responsible for the absence of measurable conductivity in thin films of polyfluorinated analogues bearing -CF3 residues on the hydrazidimide aromatic rings
Molecular Design and Crystal Chemistry of Polyfluorinated Naphthalene-bis-phenylhydrazimides with Superior Thermal and Polymorphic Stability and High Solution Processability
Naphthalene tetracarboxylic diimides (NDIs) are highly promising air-stable n-type molecular semiconductor candidates for flexible and cost-effective organic solar cells and thermoelectrics. Nonetheless, thermal and polymorphic stabilities of environmentally stable NDIs in the low-to-medium temperature regime (<300 degrees C) remain challenging properties. Structural, thermal, spectroscopic, and computational features of polyfluorinated NDI-based molecular solids (with up to 14 F atoms per NDI molecule) are discussed upon increasing the fluorination level. Slip-stacked arrangement of the NDI cores with suitable pi-pi stacking and systematically short interplanar distances (<3.2 angstrom) are found. All these materials exhibit superior thermal stability (up to 260 degrees C or above) and thermal expansion coefficients indicating a response compatible with flexible polymeric substrates. Optical bandgaps increase from 2.78 to 2.93 eV with fluorination, while LUMO energy levels decrease down to -4.37 eV, as shown per DFT calculations. The compounds exhibit excellent solubility of 30 mg mL(-1) in 1,4-dioxane and DMF
Diacetylene Mixed Langmuir Monolayers for Interfacial Polymerization
Polydiacetylene
(PDA) and its derivatives are promising materials
for applications in a vast number of fields, from organic electronics
to biosensing. PDA is obtained through polymerization of diacetylene
(DA) monomers, typically using UV irradiation. DA polymerization is
a 1â4 addition reaction with both initiation and growth steps
with topochemical control, leading to the âblueâ polymer
form as primary reaction product in bulk and at interfaces. Herein,
the diacetylene monomer 10,12-pentacosadiynoic acid (DA) and the amphiphilic
cationic <i>N</i>,<i>N</i>âČ-dioctadecylthiapentacarbocyanine
(OTCC) have been used to build a mixed Langmuir monolayer. The presence
of OTCC imposes a monolayer supramolecular structure instead of the
typical trilayer of pure DA. Surface pressure, Brewster angle microscopy,
and UVâvis reflection spectroscopy measurements, as well as
computer simulations, have been used to assess in detail the supramolecular
structure of the DA:OTCC Langmuir monolayer. Our experimental results
indicate that the DA and OTCC molecules are sequentially arranged,
with the two OTCC alkyl chains acting as spacing diacetylene units.
Despite this configuration is expected to prevent photopolymerization
of DA, the polymerization takes place without phase segregation, thus
exclusively leading to the red polydiacetylene form. We propose a
simple model for the initial formation of the âblueâ
or âredâ PDA forms as a function of the relative orientation
of the DA units. The structural insights and the proposed model concerning
the supramolecular structure of the âblueâ and âredâ
forms of the PDA are aimed at the understanding of the relation between
the molecular and macroscopical features of PDAs