Machine Learning-Inspired Molecular Design, Divergent Syntheses, and X-Ray Analyses of Dithienobenzothiazole-Based Semiconductors Controlled by S⋠⋠⋠N and S⋠⋠⋠S Interactions.

Inspired by the previous machine-learning study that the number of hydrogen-bonding acceptor (NHBA) is important index for the hole mobility of organic semiconductors, seven dithienobenzothiazole (DBT) derivatives 1 a-g (NHBA=5) were designed and synthesized by one-step functionalization from a common precursor. X-ray single-crystal structural analyses confirmed that the molecular arrangements of 1b (the diethyl and ethylthienyl derivative) and 1c (the di(n-propyl) and n-propylthienyl derivative) in the crystal are classified into brickwork structures with multidirectional intermolecular charge-transfer integrals, as a result of incorporation of multiple hydrogen-bond acceptors. The solution-processed top-gate bottom-contact devices of 1b and 1c had hole mobilities of 0.16 and 0.029 cm2 V-1s-1, respectively.

Chemical Functionalisation and Photoluminescence of Graphene Quantum Dots.

Chemical modification of graphene quantum dots (GQDs) can influence their physical and chemical properties; hence, the investigation of the effect of organic functional groups on GQDs is of importance for developing GQD-organic hybrid materials. Three peripherally functionalised GQDs having a third-generation dendritic wedge (GQD-2), long alkyl chains (GQD-3) and a polyhedral oligomeric silsesquioxane group (GQD-4) were prepared by the Cu(I) -catalysed Huisgen cycloaddition reaction of GQD-1 with organic azides. Cyclic voltammetry indicated that reduction occurred on the surfaces of GQD-1-4 and on the five-membered imide rings at the periphery, and this suggested that the functional groups distort the periphery by steric interactions between neighbouring functional groups. The HOMO-LUMO bandgaps of GQD-1-4 were estimated to be approximately 2 eV, and their low-lying LUMO levels (<-3.9 eV) were lower than that of phenyl-C61 -butyric acid methyl ester, an n-type organic semiconductor. The solubility of GQD-1-4 in organic solvents depends on the functional groups present. The functional groups likely cover the surfaces and periphery of the GQDs, and thus increase their affinity for solvent and avoid precipitation. Similar to GQD-2, both GQD-3 and GQD-4 emitted white light upon excitation at 360 nm. Size-exclusion chromatography demonstrated that white-light emission originates from the coexistence of differently sized GQDs that have different photoluminescence emission wavelengths.

Amorphous Solid Simulation and Trial Fabrication of the Organic Field-Effect Transistor of Tetrathienonaphthalenes Prepared by Using Microflow Photochemical Reactions: A Theoretical Calculation-Inspired Investigation.

The p-type organic semiconductor (OSC) material tetrathieno[2,3-a:3',2'-c:2″,3″-f:3‴,2‴-h]naphthalene (2TTN) and its alkyl-substituted derivatives C(n)-2TTNs (n = 6, 8, and 10) have been developed based on the results of theoretical calculation-inspired investigation. A hole mobility for amorphous C(n)-2TTNs (10(-2)-10(-3) cm(2) V(-1) s(-1)) was accurately predicted by using a novel statistical method in which the geometric mean of the mobilities for many individual small molecular flocks in an amorphous solid was obtained by using molecular mechanical molecular dynamics simulations and quantum chemical calculations. The simulation also suggests that upon increasing the length of alkyl chains in C(n)-2TTNs the mobilities become smaller as a consequence of a decrease in transfer integral values. C(n)-2TTNs are synthesized in a microflow reactor through photoreactions of the corresponding precursors. C(n)-2TTNs are then utilized in the fabrication of organic field-effect transistors (OFETs). Although spin-coated thin films of C(n)-2TTNs are crystalline, the hole mobilities (10(-2)-10(-3) cm(2) V(-1) s(-1)) of trial OFETs decrease upon elongation of the alkyl chains. This finding parallels the results of theoretical simulation. The simulation method for amorphous solids developed in this effort should become a useful tool in studies aimed at designing new OSC materials.

Synthesis of a Conjugated D-A Polymer with Bi(disilanobithiophene) as a New Donor Component.

A new conjugated donor-acceptor (D-A) polymer pDSBT2-BT containing bi(disilano-bisthiophene) and benzothiadiazole as donor and acceptor units, respectively, was prepared. The polymer showed a broad UV-vis absorption band at λmax = 599 nm in chlorobenzene. The absorption band was shifted to λmax = 629 nm when the polymer was measured as a film, indicating enhanced interchain interactions of the polymer. Bulk hetero-junction polymer solar cells (BHJ-PSCs) were fabricated using pDSBT2-BT and PC71BM as host and guest materials, respectively. Optimization of cell fabrication conditions provided a maximal power conversion efficiency of 3.3% and the following cell parameters: Voc = 0.86 V, Jsc = 7.56 mA/cm², and FF = 0.51. Although the efficiency still leaves much to be desired, these data underscore the potential of pDSBT2-BT as a high-voltage polymer solar cell material.

2,6-Dimeth-oxy-9,10-anthraquinone.

The title compound, C(16)H(12)O(4), crystallizes with two half-mol-ecules in the asymmetric unit, each of which is completed by a crystallographic inversion center. The two crystallographically independent mol-ecules have almost the same geometry and are almost planar [maximum deviations = 0.018 (3) and 0.049 (3) Å]. They adopt a conformation in which the C(meth-yl)-O bonds are directed along the mol-ecular short axis [C-C-O-C torsion angles of 179.6 (2) and 178.0 (2)°]. In the crystal, the mol-ecular packing is characterized by a combination of a columnar stacking and a herringbone-like arrangement. The mol-ecules form slipped π-stacks along the b axis, in which there are two kinds of columns differing from each other in their slippage. The inter-planar distances between neighboring mol-ecules are 3.493 (3) for one column and 3.451 (2) Šfor the other.

2,3,6,7-Tetra-meth-oxy-9,10-anthra-quinone.

Mol-ecules of the title compound, C(18)H(16)O(6), are almost planar [maximum deviation = 0.096 (4) Å] and reside on crystallographic centres of inversion. They adopt a conformation in which the C(meth-yl)-O bonds are directed along the mol-ecular short axis [C-C-O-C torsion angles of -175.3 (3) and 178.2 (3)°]. In the crystal, mol-ecules adopt a slipped-parallel arrangement with π-π stacking inter-actions along the a axis with an inter-planar distance of 3.392 (4) Å. Weak C-H⋯O inter-actions link the mol-ecules into sheets parallel to (10-2).

1,7-Diethyl-4,10-diisopropyl-tetra-cene.

The mol-ecule of the title compound, C(28)H(32), is located on a crystallographic inversion center. The ethyl groups are essentially coplanar with the tetra-cene ring, making a torsion angle of -0.4 (4)°. The isopropyl groups adopt an asymmetric conformation with their terminal methyl groups positioned on opposite sides of the tetra-cene plane [the Me-C-C-C torsion angles are -22.5 (4) and 100.9 (3)°]. In the crystal, the mol-ecules adopt an arrangement without significant π-π inter-actions along the stacking direction (y axis).

Thiophene-based twisted bistricyclic aromatic ene with tricoordinate boron: a new n-type semiconductor.

The incorporation of tricoordinate boron into conjugated systems is of current interest in the field of organic electronics. In this study, a tricoordinate boron-embedded thiophene-based bistricyclic aromatic ene (BAE) was synthesized as a new boron-containing conjugated system. The combination of tricoordinate boron and fused thiophene rings imposed the twisted conformation in the BAE structure, resulting in the narrow energy absorption with the low-lying LUMO. Preliminary studies on the application of the highly electron-deficient boron-embedded BAE to organic field-effect transistors (OFETs) were also performed, revealing its moderately high electron mobility.

Synthesis and crystallochromy of 1,4,7,10-tetraalkyltetracenes: tuning of solid-state optical properties of tetracenes by alkyl side-chain length.

We synthesized a series of 1,4,7,10-tetraalkyltetracenes using a new 2,6-naphthodiyne precursor and 2,5-dialkylfurans as starting materials (alkyl=methyl to hexyl). Surprisingly, the solid-state color of the tetracenes ranges through yellow, orange, and red. Both yellow and red solids are obtained for the butyl derivative. Optical properties in solution show no marked differences; however, those in the solid state show characteristics that vary with alkyl side-chain length: methyl, propyl, and pentyl derivatives are orange; ethyl and butyl derivatives are yellow; and another butyl and hexyl derivative are red. X-ray analyses reveal that the molecular structures are planar, semi-chair, or chair forms; the chair form takes a herringbone-like arrangement and the other forms take slipped parallel arrangements. The mechanism of crystallochromy is discussed in terms of molecular structure, crystal packing, and calculations that take account of exciton coupling.

1,4,5,8-Tetra-n-butyl-anthracene.

The mol-ecule of the title compound, C(30)H(42), occupies a special position on an inversion center. The four butyl side chains have all-trans planar conformations, and the alkyl planes are nearly orthogonal to the anthracene plane [C-C-C-C torsion angles of 79.6 (2) and 78.2 (2)°]. The overall mol-ecule has a stair-like shape with the n-butyl groups at the 1 and 8 positions extending towards the same side of the anthracene plane. In the crystal structure, mol-ecules adopt a slipped-parallel arrangement without π-π stacking.

1,4,5,8-Tetra-isopropyl-anthracene.

The mol-ecules of the title compound, C(26)H(34), possess crystallographically imposed inversion symmetry. The anthracene ring system is planar within 0.038 (1) Å. The two methyl groups in each independent isopropyl group are oriented on either side of the anthracene plane. In the crystal structure, the mol-ecules adopt a herringbone-like arrangement without π-π stacking.

Three-dimensional observation of decrease in pulp cavity volume using micro-CT: age-related change.

We investigated three-dimensional decrease in the volume of the pulp chamber caused by age-related secondary dentin formation using micro-CT and evaluated the applicability of the results to evaluation of age taking into account sex, age and tooth type. Decrease was slightly higher in females than in males, and a higher correlation between decrease and aging was observed in females. A comparison between age-groups revealed that decrease progressed between the fifties and sixties in males, and the forties and fifties in females. A stronger correlation between aging and decrease was observed in the mandibular central incisors than in the mandibular second premolars. This correlation was higher than other correlations between sexes and age-groups.

Modulated Photocurrent Spectroscopy Study of the Electronic Transport Properties of Working Organic Photovoltaics: Degradation Analysis.

Electronic transport measurement using modulated photocurrent (MPC) spectroscopy is demonstrated herein in working organic photovoltaics (OPVs) before and after AM1.5G irradiation. OPVs with bulk heterojunction (BHJ) using prototypical donor and acceptor materials, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1-2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] = hieno [3-4-b]thiophenediyl]] (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM), were fabricated. The OPVs had inverted structures (BHJs are formed on transparent conductive oxide substrates). The photovoltaic performance of PTB7:PC71BM OPVs was characterized and the best power conversion efficiency was obtained at PTB7 content of 40 wt%. Electron and hole mobility were determined with MPC spectroscopy in PTB7:PC71BM OPVs and were well balanced at PTB7 content of 40 wt%. Degradation of the photovoltaic performance of PTB7:PC71BM OPVs with PTB7 content of 40 wt% caused by AM1.5G irradiation was studied. MPC spectroscopy showed that the well-balanced mobility was not affected by AM1.5G irradiation. The degradation of OPVs was not due to changes in the electronic transport properties, but mainly to the reduced short circuit current (Jsc) and fill factor (FF). The origin of this reduction is discussed.

Modulated Photocurrent Spectroscopy for Determination of Electron and Hole Mobilities in Working Organic Solar Cells.

Carrier drift mobility is an important physical constant in the charge transport process of organic solar cells (OSCs). Although time-of-flight and space-charge-limited current techniques have been frequently utilized for mobility measurements, the validity of a new method using modulation photocurrent spectroscopy is discussed in this contribution. The advantages of this method are its applicability to working OSCs with optimized device structures and the simultaneous determination of the electron and hole mobilities. These features make it possible to study the relation between the mobility balance and the solar cell characteristics, such as the power conversion efficiency, using only a single working OSC; hence, it is not necessary to fabricate electron-only and hole-only devices for mobility measurements. After carrying out numerical simulations to examine the validity of this method for mobility determination, the dependence of the mobility balance on the mixing ratio of the electron-donor and -acceptor materials is presented.

Beads-on-String-Shaped Poly(azomethine) Applicable for Solution Processing of Bilayer Devices Using a Same Solvent.

Solvent-based deposition techniques for fabrication of organic field-effect transistors (OFETs) generally require orthogonal solvents for deposition of a conjugated polymer layer on a polymer gate insulator layer. Here, we found significantly reduced dissolution rate of the polymeric film in the same solvent after casting a homegeneous polymerization solution of para-bis(3-aminopropyl)hexaisobutyl-substituted T8 cage (1) with terephthalaldehyde. The limited dissolution rate in the solvent provided enough chance for fabrication of a regioregular poly(3-hexylthiophene-2,5-diyl) (P3HT) layer on the present polymer films without using an orthogonal solvent. The rheological properties indicate that physical interaction between the polymer chains provides the significantly reduced dissolution rate after the deposition onto a substrate without any cross-linking treatments.

Photoluminescence Properties of Polymorphic Modifications of Low Molecular Weight Poly(3-hexylthiophene).

The structural and photoluminescence (PL) properties of thin films of poly(3-hexylthophene) (P3HT) with molecular weights (MWs) of 3000 and 13,300 have been investigated. Although high MW P3HT always self-organizes into one packing structure (form I), low MW P3HT forms two different packing structures (forms I and II) depending on the fabrication conditions. In this work, several fabrication techniques have been examined to obtain form II samples with little inclusion of a form I component. It is found that drop-cast thin films of low MW P3HT (form II) exhibit a PL spectrum that is different from that of form I and does not contain the form I component. The PL spectrum can thus be attributed to form II. The differences in PL properties between forms I and II can be understood in terms of weakened interchain interactions due to the longer interchain distance in form II.

Efficient Skin Temperature Sensor and Stable Gel-Less Sticky ECG Sensor for a Wearable Flexible Healthcare Patch.

Wearable, flexible healthcare devices, which can monitor health data to predict and diagnose disease in advance, benefit society. Toward this future, various flexible and stretchable sensors as well as other components are demonstrated by arranging materials, structures, and processes. Although there are many sensor demonstrations, the fundamental characteristics such as the dependence of a temperature sensor on film thickness and the impact of adhesive for an electrocardiogram (ECG) sensor are yet to be explored in detail. In this study, the effect of film thickness for skin temperature measurements, adhesive force, and reliability of gel-less ECG sensors as well as an integrated real-time demonstration is reported. Depending on the ambient conditions, film thickness strongly affects the precision of skin temperature measurements, resulting in a thin flexible film suitable for a temperature sensor in wearable device applications. Furthermore, by arranging the material composition, stable gel-less sticky ECG electrodes are realized. Finally, real-time simultaneous skin temperature and ECG signal recordings are demonstrated by attaching an optimized device onto a volunteer's chest.

Control of the Singlet-Triplet Energy Gap in a Thermally Activated Delayed Fluorescence Emitter by Using a Polar Host Matrix.

The photoluminescence properties of a thermally activated delayed fluorescence emitter, 1,2-bis(carbazol-9-yl)-4,5-dicyanobenzene (2CzPN), doped in a host matrix consisting of 1,3-bis(9-carbazolyl)benzene and a polar inert molecule, camphoric anhydride (CA), in various concentrations have been investigated. It is found that the addition of CA stabilizes only the lowest singlet excited state (S1) of 2CzPN without changing the energy level of the lowest triplet excited state (T1), leading to a reduction in the energy gap between S1 and T1. The maximum reduction of energy gap achieved in this work has been determined to be around 65 meV from the shift of the fluorescence spectrum and the temperature dependence of the photoluminescence decay rate.

Hall Effect in Bulk-Doped Organic Single Crystals.

The standard technique to separately and simultaneously determine the carrier concentration per unit volume (N, cm-3 ) and the mobility (µ) of doped inorganic single crystals is to measure the Hall effect. However, this technique has not been reported for bulk-doped organic single crystals. Here, the Hall effect in bulk-doped single-crystal organic semiconductors is measured. A key feature of this work is the ultraslow co-deposition technique, which reaches as low as 10-9 nm s-1 and enables us to dope homoepitaxial organic single crystals with acceptors at extremely low concentrations of 1 ppm. Both the hole concentration per unit volume (N, cm-3 ) and the Hall mobility (µH ) of bulk-doped rubrene single crystals, which have a band-like nature, are systematically observed. It is found that these rubrene single crystals have (i) a high ionization rate and (ii) scattering effects because of lattice disturbances, which are peculiar to this organic single crystal.

Temperature Dependence of Field-Effect Mobility in Organic Thin-Film Transistors: Similarity to Inorganic Transistors.

Carrier transport in solution-processed organic thin-film transistors (OTFTs) based on dioctylbenzothienobenzothiophene (C8-BTBT) has been investigated in a wide temperature range from 296 to 10 K. The field-effect mobility shows thermally activated behavior whose activation energy becomes smaller with decreasing temperature. The temperature dependence of field-effect mobility found in C8-BTBT is similar to that of others materials: organic semiconducting polymers, amorphous oxide semiconductors and hydrogenated amorphous silicon. These results indicate that hopping transport between isoenergetic localized states becomes dominated in a low temperature regime in these materials.