Thermoelectric Properties of Benzothieno-Benzothiophene Self-Assembled Monolayers in Molecular Junctions.

We report a combined experimental (C-AFM and SThM) and theoretical (DFT) study of the thermoelectric properties of molecular junctions made of self-assembled monolayers on Au of thiolated benzothieno-benzothiophene (BTBT) and alkylated BTBT derivatives (C8-BTBT-C8). We measure the thermal conductance per molecule at 15 and 8.8 pW/K, respectively, among the lowest values for molecular junctions so far reported (10-50 pW/K).

Toward On-Demand Polymorphic Transitions of Organic Crystals via Side Chain and Lattice Dynamics Engineering.

Controlling polymorphism, namely, the occurrence of multiple crystal forms for a given compound, is still an open technological challenge that needs to be addressed for the reliable manufacturing of crystalline functional materials. Here, we devised a series of 13 organic crystals engineered to embody molecular fragments undergoing specific nanoscale motion anticipated to drive cooperative order-disorder phase transitions. By combining polarized optical microscopy coupled with a heating/cooling stage, differential scanning calorimetry, X-ray diffraction, low-frequency Raman spectroscopy, and calculations (density functional theory and molecular dynamics), we proved the occurrence of cooperative transitions in all the crystalline systems, and we demonstrated how both the molecular structure and lattice dynamics play crucial roles in these peculiar solid-to-solid transformations.

Impact of hydrophilic side chains on the thin film transistor performance of a benzothieno-benzothiophene derivative.

Side-chain engineering in molecular semiconductors provides a versatile toolbox for precisely manipulating the material's processability, crystallographic properties, as well as electronic and optoelectronic characteristics. This study explores the impact of integrating hydrophilic side chains, specifically oligoethylene glycol (OEG) units, into the molecular structure of the small molecule semiconductor, 2,7-bis(2(2-methoxy ethoxy)ethoxy) benzo[]benzo[4,5] thieno[2,3-] thiophene (OEG-BTBT). The investigation includes a comprehensive analysis of thin film morphology and crystallographic properties, along with the optimization of deposition parameters for improving the device performance.

Coherence in Polycrystalline Thin Films of Twisted Molecular Crystals.

Helicoidal crystallites in rhythmically banded spherulites manifest spectacular optical patterns in small molecules and polymers. It is shown that concentric optical bands indicating crystallographic orientations typically lose coherence (in-phase twisting) with growth from the center of nucleation. Here, coherence is shown to increase as the twist period decreases for seven molecular crystals grown from the melt.

Memory Effect by Melt Crystallization Observed in Polymorphs of a Benzothieno-Benzothiophene Derivative.

This work provides a comprehensive illustration of a crystalline melt memory effect recorded for three solvates of the 2,7-bis(2-(2-methoxyethoxy)ethoxy)benzo[]benzo[4,5] thieno[2,3-]thiophene (OEG-BTBT) molecule with dichloromethane (DCM) molecules. Combined optical microscopy and X-ray diffraction measurements at different temperatures are used to get an overview of the structural and morphological properties like melting points, isotropic transition temperatures, induction times, and crystallization kinetics of the three forms. An outstanding observation is made upon annealing the three polymorphs at temperatures well above their respective melting points as well as above the optical clearance temperature.

Transiently delocalized states enhance hole mobility in organic molecular semiconductors.

Evidence shows that charge carriers in organic semiconductors self-localize because of dynamic disorder. Nevertheless, some organic semiconductors feature reduced mobility at increasing temperature, a hallmark for delocalized band transport. Here we present the temperature-dependent mobility in two record-mobility organic semiconductors: dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]-thiophene (DNTT) and its alkylated derivative, C8-DNTT-C8.

Enantiopure Dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophenes: Reaching High Magnetoresistance Effect in OFETs.

Chiral molecules are known to behave as spin filters due to the chiral induced spin selectivity (CISS) effect. Chirality can be implemented in molecular semiconductors in order to study the role of the CISS effect in charge transport and to find new materials for spintronic applications. In this study, the design and synthesis of a new class of enantiopure chiral organic semiconductors based on the well-known dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) core functionalized with chiral alkyl side chains is presented.

Exploring the effects of graphene and temperature in reducing electron beam damage: A TEM and electron diffraction-based quantitative study on Lead Phthalocyanine (PbPc) crystals.

High-resolution transmission electron microscopy (TEM) of organic crystals, such as Lead Phthalocyanine (PbPc), is very challenging since these materials are prone to electron beam damage leading to the breakdown of the crystal structure during investigation. Quantification of the damage is imperative to enable high-resolution imaging of PbPc crystals with minimum structural changes. In this work, we performed a detailed electron diffraction study to quantitatively measure degradation of PbPc crystals upon electron beam irradiation.

High throughput processing of dinaphtho[2,3-:2',3'-]thieno[3,2-]thiophene (DNTT) organic semiconductors.

The deposition of organic semiconductors (OSCs) using solution shearing deposition techniques is highly appealing for device implementation. However, when using high deposition speeds, it is necessary to use very concentrated OSC solutions. The OSCs based on the family of dinaphtho[2,3-:2',3'-]thieno[3,2-]thiophene (DNTT) have been shown to be excellent OSCs due to their high mobility and stability.

Temperature-induced polymorphism of a benzothiophene derivative: reversibility and impact on the thin film morphology.

The identification of polymorphs in organic semiconductors allows for establishing structure-property relationships and gaining understanding of microscopic charge transport physics. Thin films of 2,7-bis(octyloxy)[1]benzothieno[3,2-]-benzothiophene (CO-BTBT-OC) exhibit a substrate-induced phase (SIP) that differs from the bulk structure, with important implications for the electrical performance in organic field effect transistors (OFETs). Here we combine grazing incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) to study how temperature affects the morphology and structure of CO-BTBT-OC films grown by physical vapor deposition on SiO.

Charge Transport in Twisted Organic Semiconductor Crystals of Modulated Pitch.

Many molecular crystals (approximately one third) grow as twisted, helicoidal ribbons from the melt, and this preponderance is even higher in restricted classes of materials, for instance, charge-transfer complexes. Previously, twisted crystallites of such complexes present an increase in carrier mobilities. Here, the effect of twisting on charge mobility is better analyzed for a monocomponent organic semiconductor, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole (BDT), that forms twisted crystals with varied helicoidal pitches and makes possible a correlation of twist strength with carrier mobility.

1D-Confinement Inhibits the Anomaly in Secondary Relaxation of a Fluorinated Polymer.

We present an experimental study of the dynamics of a well-pronounced secondary relaxation observed in bulk and ultrathin films of the fluorinated copolymer poly(vinylidene fluoride--hexafluoropropylene) (PVdF-HFP). In proximity to the glass transition, an anomalous phenomenon is observed: the β-relaxation slows down upon heating. Measurements as a function of the film thickness show that this exceptional behavior gradually vanishes upon confinement at the nanoscale level.

Dinaphthotetrathienoacenes: Synthesis, Characterization, and Applications in Organic Field-Effect Transistors.

The charge transport of crystalline organic semiconductors is limited by dynamic disorder that tends to localize charges. It is the main hurdle to overcome in order to significantly increase charge carrier mobility. An innovative design that combines a chemical structure based on sulfur-rich thienoacene with a solid-state herringbone (HB) packing is proposed and the synthesis, physicochemical characterization, and charge transport properties of two new thienoacenes bearing a central tetrathienyl core fused with two external naphthyl rings: naphtho[2,3-b]thieno-[2''',3''':4'',5'']thieno[2″,3″:4',5']thieno[3',2'-b]naphtho[2,3-b]thiophene (DN4T) and naphtho[1,2-b]thieno-[2''',3''':4'',5'']thieno[2'',3'':4',5']thieno[3',2'-b]naphtho[1,2-b]thiophene are presented.

High-Performance Humidity Sensing in π-Conjugated Molecular Assemblies through the Engineering of Electron/Proton Transport and Device Interfaces.

The development of systems capable of responding to environmental changes, such as humidity, requires the design and assembly of highly sensitive and efficiently transducing elements. Such a challenge can be mastered only by disentangling the role played by each component of the responsive system, thus ultimately achieving high performance by optimizing the synergistic contribution of all functional elements. Here, we designed and synthesized a novel [1]benzothieno[3,2-][1]benzothiophene derivative equipped with hydrophilic oligoethylene glycol lateral chains (OEG-BTBT) that can electrically transduce subtle changes in ambient humidity with high current ratios (>10) at low voltages (2 V), reaching state-of-the-art performance.

Molecular Disorder in Crystalline Thin Films of an Asymmetric BTBT Derivative.

The molecule 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) is an organic semiconductor with outstanding performance in thin-film transistors. The asymmetric shape of the molecule causes an unusual phase behavior, which is a result of a distinct difference in the molecular arrangement between the head-to-head stacking of the molecules versus head-to-tail stacking. Thin films are prepared at elevated temperatures by crystallization from melt under controlled cooling rates, thermal-gradient crystallization, and bar coating at elevated temperatures.

Effect of the Organic Semiconductor Side Groups on the Structural and Electronic Properties of Their Interface with Dopants.

Two derivatives of [1]benzothieno[3,2-b][1]benzothiophene (BTBT), namely, 2,7-dioctyl-BTBT (C8-BTBT) and 2,7-diphenyl-BTBT (DPh-BTBT), belonging to one of the best performing organic semiconductor (OSC) families, have been employed to investigate the influence of the substitutional side groups on the properties of the interface created when they are in contact with dopant molecules. As a molecular p-dopant, the fluorinated fullerene CF is used because of its adequate electronic levels and its bulky molecular structure. Despite the dissimilarity introduced by the OSC film termination, dopant thin films grown on top adopt the same (111)-oriented FCC crystalline structure in the two cases.

Tuning Spin Current Injection at Ferromagnet-Nonmagnet Interfaces by Molecular Design.

There is a growing interest in utilizing the distinctive material properties of organic semiconductors for spintronic applications. Here, we explore the injection of pure spin current from Permalloy into a small molecule system based on dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) at ferromagnetic resonance. The unique tunability of organic materials by molecular design allows us to study the impact of interfacial properties on the spin injection efficiency systematically.

Molecular Semiconductors for Logic Operations: Dead-End or Bright Future?

The field of organic electronics has been prolific in the last couple of years, leading to the design and synthesis of several molecular semiconductors presenting a mobility in excess of 10 cm V s . However, it is also started to recently falter, as a result of doubtful mobility extractions and reduced industrial interest. This critical review addresses the community of chemists and materials scientists to share with it a critical analysis of the best performing molecular semiconductors and of the inherent charge transport physics that takes place in them.

Chasing the "Killer" Phonon Mode for the Rational Design of Low-Disorder, High-Mobility Molecular Semiconductors.

Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron-phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high-mobility molecular semiconductors, state-of-the-art quantum mechanical simulations of the vibrational modes and the ensuing electron-phonon coupling constants are combined with experimental measurements of the low-frequency vibrations using inelastic neutron scattering and terahertz time-domain spectroscopy. In this way, the long-axis sliding motion is identified as a "killer" phonon mode, which in some molecules contributes more than 80% to the total thermal disorder.

N-Doped TiO Photocatalyst Coatings Synthesized by a Cold Atmospheric Plasma.

This work presents a simple, fast (20 min treatment), inexpensive, and highly efficient method for synthesizing nitrogen-doped titanium dioxide (N-TiO) as an enhanced visible light photocatalyst. In this study, N-TiO coatings were fabricated by atmospheric pressure dielectric barrier discharge (DBD) at room temperature. The composition and the chemical bonds of the TiO and N-TiO coatings were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS).

Insight from electron density and energy framework analysis on the structural features of F-TCNQ (x = 0, 2, 4) family of molecules.

In this study, the nature and characteristics of the intramolecular and intermolecular interactions in crystal structures of the fluoro-substituted 7,7,8,8-tetracyanoquinodimethane (TCNQ) family of molecules, i.e. F-TCNQ (x = 0, 2, 4), are explored.

Polymorphism of terthio-phene with surface confinement.

The origin of unknown polymorphic phases within thin films is still not well understood. This work reports on crystals of the molecule terthio-phene which were grown by thermal gradient crystallization using glass-plate substrates. The crystalline domains displayed a plate-like morphology with an extended lateral size of about 100 µm, but a thickness of only a few µm.

Terthiophene Functionalized Conjugated Triarm Polymers Containing Poly(fluorene-2,7-vinylene) Arms Having Different Cores-Synthesis and Their Unique Optical Properties.

Optical properties of three types of terthiophene (3T) functionalized conjugated triarm (star-shaped) polymers consisting of poly(9,9-di--octyl-fluorene-2,7-vinylene) (PFV) arms and different [2,4,6-tri(biphenyl)benzene (TBP), 1,3,5-tri(benzyl)benzene (TBB), and triphenylamine (TPA)] cores, prepared by combined olefin metathesis with Wittig coupling, have been studied. Relative intensities [increases in the higher vibronic bands, (0, 1) fluorescence (FL)] of the fully conjugated TPA-core polymers, TPA(PFV-3T), in the fluorescence (FL) spectra in tetrahydrofuran (toluene) solution were higher than those in the other triarm polymers, TBP(PFV-3T), TBB(PFV-3T), whereas no significant differences were observed in their UV-vis spectra; notable temperature dependences were not observed in the UV-vis and FL spectra (at -5, 25, and 55 °C). Remarkable differences were not observed in the spectra in these polymer thin films, whereas λ values red-shifted due to the formation of -type aggregates.