Herringbone Packing Research Articles

Strain induced polymorphism and band structure modulation in low-temperature 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene single crystal

Organic semiconductors are inherently soft, making it possible to increase their mobilities by strains. Such a unique feature can be exploited directly in flexible electronics for improved device performance. The 2,7-dioctyl[1]benzothieno[3,2-b][1]-benzothiophene derivative, C8-BTBT is one of the best small-molecule hole transport materials. Here, we demonstrated its band structure modulation under strains by combining the non-equilibrium molecular dynamics simulations and first-principles calculations. We found that the C8-BTBT lattice undergoes a transition from monoclinic to triclinic crystal system at the temperature below 160 K. Both shear and uniaxial strains were applied to the low-temperature triclinic phase of C8-BTBT, and polymorphism was identified in the shear process. The band width enhancement is up to 8% under 2% of compressive strain along the x direction, and 14% under 4% of tensile strain along the y direction. The band structure modulation of C8-BTBT can be well related to its herringbone packing motifs, where the edge to face and edge to edge pairs constitute two-dimensional charge transport pathways and their electronic overlaps determine the band widths along the two directions respectively. These findings pave the way for utilizing strains towards improved performance of organic semiconductors on flexible substrates, for example, by bending the substrates.

4-Phenyl-1-[(1R,4R)-1,7,7-trimethyl-2-oxobicyclo[2.2.1]heptan-3-ylidene]hydrazinecarbothioamide

In the title compound, C17H21N3OS [common nomenclature: (R)-camphor 4-phenylthiosemicarbazone], the N—N—C—(S)—N fragment deviates slightly from planarity, with a maximum deviation of 0.0259 (12) Å for the hydrazinic N atom, and makes an angle of 29.55 (0)° with the aromatic ring. The molecular structure is stabilized by an intramolecular N—H...O hydrogen bond and a short N—H...N interaction with graph-set motifsS(6) andS(5), respectively. In the crystal, the centrosymmetric arrangement of the molecules resembles a herringbone packing motif along [001]. As a result of the steric effects of the camphor entity, an apolar organic periphery and the intramolecular nature of the hydrogen bonds, neither strong nor relevant intermolecular interactions are observed.

Crystal structures of 6-chloro-indan-1-one and 6-bromo-indan-1-one exhibit different inter-molecular packing inter-actions.

The two title compounds are analogs of 1-indanone that are substituted at the 6-position with chlorine and bromine. Although very similar in mol-ecular structure, the crystal structures are not isomorphous and reveal that 6-chloro-indan-1-one, C9H7ClO (I), and 6-bromo-indan-1-one, C9H7BrO (II), exhibit unique inter-molecular packing motifs. The mol-ecules of the chloro analog (I) pack with a herringbone packing motif of C-H⋯O inter-actions, whereas the bromo derivative (II) packs with offset face-to-face π-stacking, C-H⋯O, C-H⋯Br and Br⋯O inter-actions. Compound (II) was refined as a two-component non-merohedral twin, BASF 0.0762 (5).

1,3‐Diaryl‐β‐diketone Organic Crystals with Red Amplified Spontaneous Emission

In this study, 1-[4-(dimethylamino)phenyl]-3-(1-hydroxynaphthalen-2-yl)propane-1,3-dione (DPHND) was designed and synthesized to construct red-emissive organic solids. Although DPHND was weakly yellow fluorescent in organic solvents, its emission intensity showed a significant enhancement when a relatively large amount of poor solvent was added, and displayed typical aggregation-induced enhanced emission (AIEE). Notably, the crystals formed by a solution-diffusion approach showed bright red fluorescence (λem =621 nm), which was greatly redshifted by about 60 nm compared with that in solution. Molecules in crystals took a planar conformation and formed a herringbone packing structure, which effectively avoided π⋅⋅⋅π interactions, and hence contributed to the enhancement of the fluorescent quantum yield. The fluorescence spectrum of the long striplike crystals of DPHND gradually narrowed accompanied by a dramatic enhancement of the intensity when the pump energy of the laser beam was increased (355 nm), which indicated that these red-emissive crystals displayed typical amplified spontaneous emission (ASE). In addition, DPHND with an extended π-conjugated structure clearly improved its thermostability compared with the previously reported analogues, which may pave the way for its application in future electrically driven organic solid-state lasers.

Synthesis, characterization, and transistor applications of new linear small molecules: Naphthyl-ethynyl-anthracene-based small molecules containing different alkyl end group

A novel small molecule consisting of triple bond-bridged naphthalene-anthracene core was synthesized with either a pentyl or decyl end group. The linear and planar shape of naphthalene-anthracene core allowed herringbone packing pattern with enhanced conjugation length and close molecular packing structure. The film morphology of naphthalene-anthracene based small molecules was also affected by the pentyl and decyl groups. The pentyl substituted molecule exhibited more unified and ordered packing patterns than did the decyl substituted example, which showed at least two polymorphs. The p-type semiconducting properties of the two new molecules were characterized by organic field-effect transistor measurements. In annealed devices at 80 °C, the field-effect mobility of pentyl analogue was 0.045 cm2/(V∙s), which was about 3 times higher than the decyl substituted compound.

Smectic-A and Hexatic-B Liquid Crystal Phases of Sanidic Alkyl-Substituted Dibenzo[fg,op]naphthacenes

Despite longstanding interest in liquid crystalline compounds with simple rod- or disc-like shapes (calamitics or discotics), very few examples of the analogous board-shaped, or "sanidic", liquid crystals exist. A new series of alkyl-substituted dibenzo[fg,op]naphthacenes have been prepared by planarization of o-phenylene precursors through dehydrohalogenation. Their photophysical properties have been studied in dichloromethane. Liquid crystal phase behavior was characterized by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. All of the compounds exhibit monotropic liquid crystal phases on cooling from the isotropic phase. The compounds with shorter alkyl (pentyl and heptyl) chains exhibit the uniaxial smectic-A phase analogous to that of simple calamitic mesogens. The compounds with longer alkyl (nonyl, undecyl, and tridecyl) chains exhibit a new smectic liquid crystal phase featuring short-range positional order with an apparent rectangular lattice in the smectic layers, that is, an orthogonal biaxial hexatic-B. The molecular arrangement in this phase likely corresponds to a distorted herringbone packing of the board-shaped structures. Further, the compound with nonyl chains exhibits an underlying smectic-B phase. DFT calculations show that the cores of the mesogens are twisted into C2-symmetric saddle-shaped geometries because of steric interactions along their rims. The liquid crystal phases and their structures are discussed in the context of the compounds' board-like shapes and intercore interactions.

Investigations of new potential photo-acid generators: crystal structures of 2-[(E)-2-phenyl-ethen-yl]phenol (ortho-rhom-bic polymorph) and (2E)-3-(2-bromo-phen-yl)-2-phenyl-prop-2-enoic acid.

The title compounds, C14H12O, (I), and C15H11BrO2, (II), were prepared and characterized as part of our studies of potential new photo-acid generators. In (I), which crystallizes in the ortho-rhom-bic space group Pca21, compared to P21/n for the previously known monoclinic polymorph [Cornella & Martin (2013 ▸). Org. Lett. 15, 6298-6301], the dihedral angle between the aromatic rings is 4.35 (6)° and the OH group is disordered over two sites in a 0.795 (3):0.205 (3) ratio. In the crystal of (I), mol-ecules are linked by O-H⋯π inter-actions involving both the major and minor -OH disorder components, generating [001] chains as part of the herringbone packing motif. The asymmetric unit of (II) contains two mol-ecules with similar conformations (weighted r.m.s. overlay fit = 0.183 Å). In the crystal of (II), both mol-ecules form carboxyl-ate inversion dimers linked by pairs of O-H⋯O hydrogen bonds, generating R 2 (2)(8) loops in each case. The dimers are linked by pairs of C-H⋯O hydrogen bonds to form [010] chains.

Soluble Dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene Derivatives for Solution-Processed Organic Field-Effect Transistors

We demonstrate a new approach to solution-processable dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) derivatives that can afford good thin-film transistors having mobilities higher than 0.1 cm(2) V(-1) s(-1). The key molecular design strategy is the introduction of one branched alkyl group at the edge of the DNTT core, which improves solubility while retaining semiconducting characteristics in the thin-film state. Dialkylation, i.e., the introduction of two branched alkyl groups on the DNTT core, had a detrimental effect on the semiconducting properties. Although the physicochemical properties of the mono- and dialkylated derivatives at the molecular level were almost the same, the thin-film absorption spectra and the ionization potentials (IPs) were markedly different, indicating that the intermolecular interaction in the thin-film state was affected by the number of alkyl groups. Indeed, the packing structures of the monoalkylated DNTTs in the thin-film state, which were estimated from the XRD patterns, were similar to that of parent DNTT, indicating the existence of the lamella structure with the herringbone packing motif. In sharp contrast, the XRD patterns of the dialkylated DNTT thin films showed poor crystallinity, and the packing structures were significantly different from that of parent DNTT. All the results of structural characterization in the thin-film state and evaluation of device characteristics of the DNTT derivatives with branched alkyl groups indicate that the introduction of a branched alkyl group in the molecular long-axis direction is an effective way to solubilize the rigid, largely π-extended organic semiconducting core without interfering with the semiconducting characteristics in the thin-film state.

Crystal structure of solifenacin hydrogen succinate, C23H27N2O2(HC4H4O4)

The crystal structure of solifenacin hydrogen succinate [C23H27N2O2(HC4H4O4)] has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Solifenacin hydrogen succinate crystallizes in space groupP21(#4) witha= 6.477 03(2),b= 7.830 95(2),c= 23.848 72(7) Å,β= 90.2373(3)°,V= 1209.63(1) Å3, andZ= 2. The hydrogen succinate anions form a chain linked by strong hydrogen bonds parallel to thea-axis. Discrete N–H···O hydrogen bonds lie on the sides of this chain, resulting in a layer parallel to theab-plane rich in hydrogen bonds. Halfway between these layers the molecules meet in a herringbone packing of aromatic rings. The powder pattern has been submitted to ICDD for inclusion in future releases of the Powder Diffraction File™.

Anisole at 100 K: the first crystal structure determination.

The simplest alkyl aryl ether, anisole (methoxybenzene), C7H8O, is a feedstock chemical and is widely used in the pharmaceutical industry. The structure of anisole at 100 K, as determined by single-crystal X-ray analysis, is reported. A crystal (m.p. 236 K) suitable for X-ray diffraction was obtained from the melt. The title compound crystallizes in the centrosymmetric space group P2(1)/c with two molecules in the asymmetric unit (Z' = 2). Both crystallographically distinct molecules adopt a virtually flat (Cs-symmetric) conformation. The arrangement of the molecules in the solid state appears to be governed by close packing. No face-to-face π-π stacking of the molecules is observed, but rather edge-to-face interactions result in a herringbone packing motif.

Molecular Packing of Metal-Organic Langmuir-Blodgett Films on Differently Passivated Si(001) Surfaces

Langmuir-Blodgett films of standard amphiphilic molecules like cadmium arachidate (CdA) and nickel arachidate (NiA) are deposited on differently passivated (OH-, H- and Br-passivated) Si(001) surfaces and molecular packing information from the top layer of all the films are obtained using atomic force microscopy (AFM). Molecular-resolution images, containing the information of molecular packing, are clearly obtained from the CdA films as the top surfaces are atomically flat, however, for the NiA films the information of the surface modulations are actually obtained due to the lack of top surface flatness. Triclinic packing of CdA molecules are obtained from the OH- and Br-terminated Si (OH-Si and Br-Si respectively), whereas herringbone packing are obtained from the H-terminated Si (H-Si). However, relatively loosely packing of NiA molecules causes molecular tilting which creates surface modulations and depending upon the substrate type the modulation covers nearly four (H-Si), six (Br-Si) and twelve (OH-Si) molecular area.

Fused thiophene-pyrrole-containing ring systems up to a heterodecacene.

A new class of π-conjugated polycyclic hydrocarbons that promises interesting electronic properties is presented. The synthesis and extension of the S,N-heteroacene series consisting of only five-membered heterocyclic rings up to a very long, stable, and still soluble decacene SN10 is realized by multiple Pd-catalyzed aminations of halogenated thiophene precursors as key reactions. These novel heteroacenes were characterized by optical spectroscopy and electrochemistry providing interesting structure-property relationships. Nearly complete bond-length equalization in the inner part of the conjugated backbone and an unusual herringbone packing in the solid state underline the structural features of these novel systems.

Two isostructural halogen derivatives of 9-ethylcarbazole: crystal structure, Hirshfeld surface analysis, and structural comparison with other simple analogs

This article describes a detailed study of the molecular packing and intermolecular interactions in crystals of two derivatives of 9-ethylcarbazole, i.e., 3-chloro- and 3-bromo-9-ethylcarbazole (1 and 2, respectively). A significance of this study lies both in the comparison drawn between the crystal structures of these compounds and those of several of their simple analogs [i.e., 3,6-dibromo-9-ethylcarbazole (3), 3,6-dibromo-9-methylcarbazole (4), 3,6-dibromocarbazole (5), 3-bromocarbazole (6), 3,6-diiodocarbazole (7), 9-ethylcarbazole (8), 9-methylcarbazole (9) and carbazole (10)], and in the preliminary assessment of their suitability as active materials for organic electronics. This comparison shows a close similarity in the packing of molecules of three of them (i.e., 3, 4, 6) that form the π-stacks along the shortest crystallographic axes, with a substantial spatial overlap between adjacent molecules in the stacks, depending mainly on the length of substituent at position 9 of carbazole skeleton and on the ratio of (%C···H)/(%C···C) interactions. Similar to them, in the crystal structures of 1 and 2 there is slipped face-to-face π···π interaction, but in contrast this interaction connects two molecules of these compounds into the dimers that are further connected by C–H···π interaction. The molecular packing in crystals of these compounds is intermediate between the arrangement of molecules of 3, 4, and 6, where the slipped π-stacking is predominant, and the typical herringbone packing in compounds 5 and 7–10. Thus, it can be supposed that out of ten compounds analyzed here, only 3, 4, and 6 will turn to be the most promising materials for device applications (particularly for field-effect transistors).

Single-crystal field-effect transistors of new Cl₂-NDI polymorph processed by sublimation in air.

Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (β-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (α-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm(2) V(-1) s(-1) (α-phase) and up to 3.5 cm(2) V(-1) s(-1) (β-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on β-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm(2) V(-1) s(-1). The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.

Role of crystallinity of non-fullerene acceptors in bulk heterojunctions

The role of crystallinity of pentancene-based acceptors in BHJ solar cells is elucidated. The sandwich herringbone packing motif leads to higher performance than cofacial packing.

Electrochemical and structural analysis of a novel symmetrical bis-Schiff base with herringbone packing motif

A novel symmetrical bis-Schiff base was synthesized and characterized by means of single crystal X-ray diffraction, FT-IR and NMR spectroscopy, elemental, TG/DSC and electrochemical analysis. The synthesized molecule represents a rare example of symmetrical bis-Schiff base with uncondensed primary amino group as the final reaction product. The molecule is planar, with largest deviation of aminophenyl benzene ring from the plane calculated through the aliphatic chain in the amount of 4.93(1)°. In the crystal, the molecules are primarily linked by hydrogen bonds involving primary amino groups and weak CH⋯π interactions. Consequently, these interactions are arranging molecules into herringbone packing motif. The FT-IR and NMR spectra indicated presence of both imino and amino groups in dissolved and solid state, therefore confirming consistency of the studied material and also molecular structure determined by X-ray diffraction. Electrochemical study has shown that the oxidation of the investigated Schiff base is irreversible, diffusion controlled process and that the oxidation products are adsorbed on the glassy carbon electrode surface.

Impact of Edge-Core Structures and Substituent Effects on the Electronic and Charge-Transport Properties of Heteroaromatic Ring-Fused Oligomers

Herein, we systematically studied the electronic and conducting properties of the thiophene-fused polycyclic aromatic compounds and their analogues and discussed in detail the influences of edge-core structure, heteroatom substitution, and functionalization on their field-effect transistor properties and solid-state packing motifs. It was found that the influence of edge-core structure and heteroatom substitution on the electronic properties and reorganization energies of semiconducting materials mainly originates from the variations of the frontier molecular orbital charge distributions and the steric hindrance as well as the conjugate degree of compounds. Moreover, our results also showed that the fusion of benzene rings at the longitudinal end could effectively decrease energy barrier of charge injection and reorganization energies and change the molecular arrangement from herringbone packing to π stacking, which provides a promising way to functionalize organic semiconducting molecules.

Crystal structures of 5,6-dimethyl-1,2,3,4-tetrahydro-1,10-phenanthroline and its benzene sulfonate

Single crystals of 5,6-dimethyl-1,2,3,4-tetrahydro-1,10-phenanthroline (1), as well as its benzene sulfonate, i.e. (bsa) · (1H) (2) (bsaH = benzenesulfonic acid), were synthesized and characterized by elemental analysis (EA), infrared spectrometry (IR) and single crystal X-ray diffraction (SCD). The neutral molecules of 1 adopt a slipped herringbone packing mode in solid state. Whereas, the 1H+ cations in compound 2 form ion pairs with neighboring (bsa)-anions, and show a one-dimensional cross-stacking mode. Crystal data of 1: Monoclinic, space group P21/n, a = 8.2650(18), b = 10.744(2), c = 13.149(3) A, β = 107.194(3)°, Z = 4, V = 1115.4(4) A3, Crystal data of 2: Monoclinic, space group P21/c, a = 7.572(3), b = 10.106(4), c = 23.137(9) A, β = 93.802(5)°, Z = 4, V = 1766.6(12) A3.

Crystal structure of 4-meth-oxy-quinazoline.

The title compound, C9H8N2O, is almost planar, with the C atom of the meth­oxy group deviating from the mean plane of the quinazoline ring system (r.m.s. deviation = 0.011 Å) by 0.068 (4) Å. In the crystal, mol­ecules form π–π stacks parallel to the b-axis direction [centroid–centroid separation = 3.5140 (18) Å], leading to a herringbone packing arrangement.

Crystal structure of asymmetric organic semiconductor 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene

A full X-ray crystal structure analysis of 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10), reported to be a promising semiconducting component for high-performance organic thin-film transistors, has been carried out. The analysis revealed the formation of a bilayer-type crystal structure composed of alternating antiparallel polar monomolecular layers that are formed by the herringbone packing of asymmetric molecules. The large and highly isotropic calculated intermolecular interactions within the two-dimensional semiconducting layers indicate the potentially excellent semiconducting performance of Ph-BTBT-C10.