Concomitant polymorphic forms of 3‐cyclopropyl‐5‐(2‐hydrazinylpyridin‐3‐yl)‐1,2,4‐oxadiazole

The dipharmacophore compound 3‐cyclopropyl‐5‐(2‐hydrazinylpyridin‐3‐yl)‐1,2,4‐oxadiazole, C₁₀H₁₁N₅O, was studied on the assumption of its potential biological activity. Two concomitant polymorphs were obtained on crystallization from isopropanol solution and these were thoroughly studied. Identical conformations of the molecules are found in both structures despite the low difference in energy between the four possible conformers. The two polymorphs differ crucially with respect to their crystal structures. A centrosymmetric dimer formed due to both stacking interactions of the `head‐to‐tail' type and N—H…N(π) hydrogen bonds is the building unit in the triclinic structure. The dimeric building units form an isotropic packing. In the orthorhombic polymorphic structure, the molecules form stacking interactions of the `head‐to‐head' type, which results in their organization in a column as the primary basic structural motif. The formation of N—H…N(lone pair) hydrogen bonds between two neighbouring columns allows the formation of a double column as the main structural motif. The correct packing motifs in the two polymorphs could not be identified without calculations of the pairwise interaction energies. The triclinic structure has a higher density and a lower (by 0.60 kcal mol^?1) lattice energy according to periodic calculations compared to the orthorhombic structure. This allows us to presume that the triclinic form of 3‐cyclopropyl‐5‐(2‐hydrazinylpyridin‐3‐yl)‐1,2,4‐oxadiazole is the more stable.     

Synthesis of Soluble,Alkyne‐Substituted Trideca‐ and Hexadeca‐Starphenes

Two literature‐known TIPS‐ethynyl‐dibromoacenes were prepared and employed to synthesize cyclotrimers by using Yamamoto coupling conditions. Two large, well‐soluble starphenes were isolated in good yields. Crystallographic characterization verifies the triangular shape and shows significant differences in crystal packing.     

Recent Progress in Polycyclic Aromatic Hydrocarbon‐Based Organic Co‐Crystals

Recently, the development of polycyclic aromatic hydrocarbon ( PAH )‐based organic co‐crystals has attracted increasing interest due to their unique packing modes, optic‐electronic properties and various potential applications in electronic, optic‐electronic and magnetic devices. In this account, we mainly discuss the definition, classification, packing patterns, preparation methods, and applications of PAH‐based co‐crystals. Specifically, the main categories of PAH‐based organic co‐crystals, the frequent methods to prepare them, three main packing patterns, their optical and electrical properties, and their potential applications will be presented. Finally, an outlook of this field is provided.     

Tetraalkoxyphenanthrene‐Fused Dehydroannulenes: Synthesis,Self‐Assembly,and Electronic,Optical, and Electrochemical Properties

Novel tetraalkoxyphenanthrene‐fused dehydro[12]‐, [18]‐, and [24]annulenes 1 – 3 were synthesized by using Cu‐mediated or Pd‐catalyzed oxidative macrocyclization reactions as key steps, and their electronic, optical, and electrochemical properties have been investigated in detail. X‐ray crystallographic analysis of a single crystal of 1 a demonstrated that the molecules were arranged longitudinally in a slipped π‐stacked fashion to form a 1D column. ¹H NMR and UV/Vis spectroscopic and cyclic voltammetric analysis in conjugation with nucleus‐independent chemical shift (NICS) calculations for 1 – 3 support that the annulation at the 9,10‐positions of phenanthrene to the dehydroannulene ring enhances the tropicity and decreases the HOMO–LUMO gaps of the molecules relative to the benzannulation and that 1 possesses an antiaromatic character. Self‐association behavior due to π–π stacking in CDCl₃ was observed for 1 and 2 and was quantified by concentration‐dependent ¹H NMR spectroscopic measurements. The self‐assembly of 1 and 2 into well‐defined 1D superstructures with high aspect ratios were obtained, and the morphology and crystallinity of these compounds were investigated by means of SEM and wide‐angle X‐ray diffraction (WAXD) measurements. Furthermore, it was shown that 1 b and 2 b display liquid‐crystalline phases by means of differential scanning calorimetry, polarizing optical microscopy, and variable‐temperature WAXD measurements.     

Mesomorphism,polymerization, and chirality induction in α‐cyanostilbene‐functionalized diacetylene‐assembled films: Photo‐triggered Z/E isomerization

Engineering of molecular stacking arrangement via environmental stimuli is of particular interest in stimuli‐responsive self‐assembling architectures. A novel dual photo‐functionalized diacetylene ((Z)‐CNBE‐DA) molecule was synthesized, in which photo‐responsive cyanostilbene moieties exhibited interesting Z‐E isomerization upon UV light irradiation and could be utilized to modulate mesomorphism, molecular stacking arrangement and resulting polymerization behavior. Rod‐like (Z)‐CNBE‐DA could self‐assemble into well‐defined lamellar structures and the helical polydiacetylene (PDA) chains could be formed upon irradiation with circularly polarized ultraviolet light (CPUL). However, the bent‐shaped (E)‐CNBE‐DA molecules only self‐assembled into irregular loose packing, inhibiting the formation of ordered helical PDA chains upon CPUL irradiation. In this work, we established the links between chemical structures, molecular packing engineering and photophysical properties, which would be of great fundamental value for the rational design of smart soft materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2458–2466     

Crystal‐Packing Trends for a Series of 6,9,12,15,18‐Pentaaryl‐1‐hydro[60]fullerenes

The relationship between the size of the substituents of aryl groups in a series of fifteen 6,9,12,15,18‐pentaaryl‐1‐hydro[60]fullerenes and the solid‐state structures and packing motifs of these compounds has been analyzed. Pentaarylfullerenes have a characteristic “badminton shuttlecock” shape that causes several derivatives to crystallize into columnar stacks. However, many pentaarylfullerenes form non‐stacked structures with, for example, dimeric, layered, diamondoid, or feather‐in‐cavity relationships between molecules. Computational modeling gave a qualitative estimate of the best shape match between the ball and socket surfaces of each pentaarylfullerene. The best match was for pentaarylfullerenes with large, spherically shaped para‐substituents on the aryl groups. The series of pentaarylfullerenes was characterized by single‐crystal X‐ray diffraction. A total of 34 crystal structures were obtained as various solvates and were categorized by their packing motifs.     

Super‐ and Ferroelastic Organic Semiconductors for Ultraflexible Single‐Crystal Electronics

Like silicon, single crystals of organic semiconductors are pursued to attain intrinsic charge transport properties. However, they are intolerant to mechanical deformation, impeding their application in flexible electronic devices. Such contradictory properties, namely exceptional molecular ordering and mechanical flexibility, are unified in this work. We found that bis(triisopropylsilylethynyl)pentacene (TIPS‐P) crystals can undergo mechanically induced structural transitions to exhibit superelasticity and ferroelasticity. These properties arise from cooperative and correlated molecular displacements and rotations in response to mechanical stress. By utilizing a bending‐induced ferroelastic transition of TIPS‐P, flexible single‐crystal electronic devices were obtained that can tolerate strains (?) of more than 13 % while maintaining the charge carrier mobility of unstrained crystals (μ>0.7 μ₀). Our work will pave the way for high‐performance ultraflexible single‐crystal organic electronics for sensors, memories, and robotic applications.     

Novel Ladder π‐Conjugated Materials—Sila‐Pentathienoacenes: Synthesis,Structure, and Electronic Properties

A novel series of ladder π‐conjugated materials—sila‐pentathienoacenes ( Si‐PTA ) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on molecular packing. A densely packed structure with an interfacial distance of about 3.66 Å between the adjacent molecules is observed for the compound with shorter alkyl chains. However, a large interfacial distance (7.99 Å) is obtained for another compound because of the insertion of long alkyl chains between two planes. The investigation of the optical and electrochemical properties shows that the silylene bridge incorporated into the pentathienoacene framework exerts a clear effect on the electronic properties by the σ*–π* conjugation. Although only a slight enhancement is observed for the HOMO levels, with respect to that of pentathienoacene, the LUMO levels are significantly lowered. The observed electronic properties are consistent with the theoretical calculations.     

5‐Amino‐1‐naphthol: two‐dimensional sheets built up from R44(18) rings formed by O—H...N,N—H...O and π–π interactions

The crystal structure of the title compound, C₁₀H₉NO, (I), contains intermolecular O—H...N and N—H...O hydrogen bonds which together form sheets parallel to the (001) plane containing rings with an unusual R₄⁴(18) motif. These rings are additionally stabilized by an intermolecular π–π stacking interaction. The significance of this study lies in the comparison drawn between the molecular structure of (I) and those of related compounds (1,5‐diaminonaphthalene, 8‐amino‐2‐naphthol, 3‐amino‐2‐naphthol and aniline), which shows a close similarity in the noncoplanar orientation of the amine group and the aromatic moiety. Comparison of the crystal structures of (I) and several of its simple analogues (1‐naphthol, naphthalene‐1,4‐diol, naphthalene‐1,5‐diol and 4‐chloro‐1‐naphthol) shows a close similarity in the packing of the molecules, which form π‐stacks along the shortest crystallographic axes with a substantial spatial overlap between adjacent molecules.     

Functional Corannulene: Diverse Structures,Enhanced Charge Transport,and Tunable Optoelectronic Properties

Chemical functionalization of various hydrocarbons, such as coronene, corannulene, and so forth, shows good promise in electronics applications because of their tunable optoelectronic properties. By using quantum chemical calculations, we have investigated the changes in the corannulene buckybowl structure, which greatly affect its electronic and optical properties when functionalized with different electron‐withdrawing imide groups. We find that the chemical nature and position of functional groups strongly regulate the stacking geometry, π‐stacking interactions, and electronic structure. Herein, a range of optoelectronic properties and structure–property relationships of various imide‐functionalized corannulenes are explored and rationalized in detail. In terms of carrier mobility, we find that the functionalization strongly affects the reorganization energy of corannulene, while the enhanced stacking improves hopping integrals, favoring the carrier mobility of crystals of pentafluorophenylcorannulene‐5‐monoimide. The study shows a host of emerging optoelectronic properties and enhancements in the charge‐transport characteristics of functionalized corannulene, which may find possible semiconductor and electronics applications.     

Thienoacene‐Fused Pentalenes: Syntheses,Structures, Physical Properties and Applications for Organic Field‐Effect Transistors

Three soluble and stable thienoacene‐fused pentalene derivatives ( 1 – 3 ) with different π‐conjugation lengths were synthesized. X‐ray crystallographic analysis and density functional theory (DFT) calculations revealed their unique geometric and electronic structures due to the interaction between the aromatic thienoacene units and antiaromatic pentalene moiety. As a result, they all possess a small energy gap and show amphoteric redox behaviour. Time dependent (TD) DFT calculations were used to explain their unique electronic absorption spectra. These new compounds exhibited good thermal stability and ordered packing in solid state and thus their applications in organic field‐effect transistors (OFETs) were also investigated. The highest field‐effect hole mobility of 0.016, 0.036 and 0.001 cm² V^?1 s^?1 was achieved for solution‐processed thin films of 1 – 3 , respectively.     

Synthesis of Three‐Dimensional Butterfly Slit‐Cyclobisazaanthracenes and Hydrazinobisanthenes through One‐Step Cyclodimerization and Their Properties

New three‐dimensional (3D) π‐conjugated molecules, butterfly‐shaped slit‐cyclobisazaanthracenes, were synthesized in high yields by Ni‐mediated one‐step cyclodimerization of dibromoazaanthracenes with a dimethylacridine, phenothiazine, or acridone skeleton. The 3D slit butterfly shape was formed by folded azaanthracene skeletons. Closure of the slit via N?N bond formation afforded hydrazinobisanthenes with an embedded hydrazine structure in a bisanthene skeleton, which exhibited a 3D butterfly or a 2D plane structure depending on the type of heterocycle used. Extensive study of the stereoselective chemical reactivity of the butterfly shape, X‐ray analysis, DFT calculations, electrochemical/chemical oxidations, and photophysical measurements revealed that the properties of these materials included stereoselective oxidation, a rigid or flexible butterfly shape, dynamic conformational behavior, unique crystal‐packing structures, excellent electron donation with low oxidation potential, a radical cation, a long absorption wavelength, and fluorescence property.     

Neutral and Oxidized Triisopropylsilyl End‐Capped Oligothienoacenes: A Combined Electrochemical,Spectroscopic, and Theoretical Study

This work presents an analysis of the structural, electrochemical, and optical properties of a family of triisopropylsilyl end‐capped oligothienoacenes (TIPS‐ Tn ‐TIPS, n=4–8) by combining cyclic voltammetry, spectroscopic techniques, and quantum‐chemical calculations. TIPS‐ Tn ‐TIPS compounds form stable radical cations, and dications are only obtained for the longest oligomers (n=7 and 8). Oxidation leads to the quinoidization of the conjugated backbone, from which electrons are mainly extracted. The absorption and fluorescence spectra show partially resolved vibronic structures even at room temperature, due to the rigid molecular geometry. Two well‐resolved vibronic progressions are observed at low temperatures due to the vibronic coupling, with normal modes showing wavenumbers of ≈1525 and ≈480 cm^?1. Optical absorption bands display remarkable bathochromic dispersion with the oligomer length, indicative of the extent of π conjugation. The optical properties of the oxidized compounds are characterized by in situ UV/Vis/NIR spectroelectrochemistry. The radical cation species show two intense absorption bands emerging at energies lower than in the neutral compounds. The formation of the dication is only detected for the heptamer and the octamer, and shows a new band at intermediate energies. Optical data are interpreted with the help of density functional theory calculations performed at the B3LYP/6‐31G** level, both for the neutral and the oxidized compounds.     

Attractive Dispersion Interactions Versus Steric Repulsion of tert‐Butyl groups in the Crystal Packing of a D3h‐Symmetric Tris(quinoxalinophenanthrophenazine)

The crystalline packing of a π‐extended D_3h‐symmetric triptycene reveals a particular π stacking motif with an almost‐eclipsed arrangement of adjacent π planes despite the steric repulsion of tert‐butyl substituents. Four model compounds were analyzed by using single‐crystal X‐ray diffraction and theoretical calculations to study the influence of dispersion interactions of molecular parts and understand the relationship between the molecular structure and this unique packing motif.     

Synthesis and Solid‐State Structures of a Tetrathiafulvalene‐Conjugated Bistetracene

A tetrathiafulvalene (TTF)‐conjugated bistetracene was synthesized and characterized in the molecular electronic structures based on the spectroscopic measurements and the single‐crystal X‐ray diffraction analysis. UV/Vis absorption and electrochemical measurements of 5 revealed the considerable electronic communication between two tetracenedithiole units by through‐bond and/or through‐space interactions. The difference in the crystal‐packing structures of 5 , showing polymorphism, results in a variety of intermolecular electronic‐coupling pattern. Of these, the π‐stacking structure of 5 A gave a large transfer integral of HOMOs (97 meV), which value is beyond hexacene and rubrene, thus, quite beneficial to achieve the high hole mobility.     

Steric and Electronic Influence on the Coordination Aptitude of 4‐Formylpiperazine‐1‐Carbodithioate Towards Triorganotin(IV) Moieties

A fascinating ligand, 4‐formylpiperazinium 4‐formylpiperazine‐1‐carbodithioate (L‐salt) has been reacted with two electronically and sterically different trimethyltin(IV) chloride and triphenyltin(IV) chloride. The complexes 1 and 2 were characterized by elemental analysis, spectroscopic techniques, and X‐ray single crystal analysis. The latter technique confirmed the polymeric and monomeric nature of 1 and 2 , respectively. Both 1 and 2 showed intriguing molecular packing properties in the solid state. However, the packing of 1 is more interesting and unique where one‐dimensional polymer chains self assemble in two‐over‐two saltire‐shaped fashion to provide an overall multilayered structure. The different behavior of L toward two different tin(IV) compounds can be attributed to different electronic and steric environments around metal center.     

Unilaterally Fluorinated Acenes: Synthesis and Solid‐State Properties

The rapid development of organic electronics is closely related to the availability of molecular materials with specific electronic properties. Here, we introduce a novel synthetic route enabling a unilateral functionalization of acenes along their long side, which is demonstrated by the synthesis of 1,2,10,11,12,14‐hexafluoropentacene ( 1 ) and the related 1,2,9,10,11‐pentafluorotetracene ( 2 ). Quantum chemical DFT calculations in combination with optical and X‐ray absorption spectroscopy data indicate that the single‐molecule properties of 1 are a connecting link between the organic semiconductor model systems pentacene (PEN) and perfluoropentacene (PFP). In contrast, the crystal structure analysis reveals a different packing motif than for the parent molecules. This can be related to distinct F???H interactions identified in the corresponding Hirshfeld surface analysis and also affects solid‐state properties such as the exciton binding energy and the sublimation enthalpy.     

N‐tert‐Butyl‐N′‐[5‐cyano‐2‐(4‐methylphenoxy)phenylsulfonyl]urea,a new TXA2 receptor antagonist

The title compound, C₁₉H₂₁N₃O₄S, crystallizes in the space group P2/c with two molecules in the asymmetric unit. The conformation of both molecules is very similar and is mainly determined by an intramolecular N—H...O hydrogen bond between a urea N atom and a sulfonyl O atom. The O and second N atom of the urea groups are involved in dimer formation via N—H...O hydrogen bonds. The intramolecular hydrogen‐bonding motif and conformation of the C—SO₂—NH(C=O)—NH—C fragment are explored and compared using the Cambridge Structural Database and theoretical calculations. The crystal packing is characterized by π–π stacking between the 5‐cyanobenzene rings.     

Conformational disorder in 4‐(5,5′‐dibromo‐2′‐chloro‐4,4′‐bipyridyl‐2‐yl)benzaldehyde: role of π–π and halogen interactions

The crystal packing of the title compound, C₁₇H₉Br₂ClN₂O, is governed by strong π–π stacking, where molecules are tightly bound within infinite (100) planes; these planes interact mainly through non‐optimal π–π stacking where arene rings are noticeably displaced from perfect overlap, and also through halogen–halogen interactions. The aldehyde group shows conformational disorder, with a significant population difference between the two conformers; this difference is rationalized by the energetic analysis of the crystal packing using the PIXEL method, which also allows a decomposition of intermolecular interaction energy into Coulombic, polarization, dispersion and repulsion contributions. Using such an analysis, it is found that the main reason for this unequal population of the two conformers in the crystal is two hydrogen bonds that are present only for the major conformer.     

4,10‐Dibromoanthanthrone as a New Building Block for p‐Type,n‐Type,and Ambipolar π‐Conjugated Materials

New p‐type, n‐type, and ambipolar molecules were synthesized from commercially available 4,10‐dibromoanthanthrone dye. Substitution at the 4,10‐ and 6,12‐positions with different electron‐rich and electron‐poor units allowed the modulation of the optoelectronic properties of the molecules. A bis(dicyanovinylene)‐functionalized compound was also prepared with a reduction potential as low as ?50 mV versus Ag⁺ with a crystalline two‐dimensional lamellar packing arrangement. These characteristics are important prerequisites for air‐stable n‐type organic field‐effect transistor applications.