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This work presents a general strategy for integrating photoresponsive molecules into liquid crystal elastomers (LCEs) using Diels–Alder chemistry. The method introduces various photochromes, offering a scalable route for multifunctional LCEs. 

The crystal structures of two intermediates, 4-amino-3,5-difluorobenzonitrile, C₇H₄F₂N₂(I), and ethyl 4-amino-3,5-difluorobenzoate, C₉H₉F₂NO₂(II), along with a visible-light-responsive azobenzene derivative, diethyl 4,4′-(diazene-1,2-diyl)bis(3,5-difluorobenzoate), C₁₈H₁₄F₄N₂O₄(III), obtained by four-step synthetic procedure, were studied using single-crystal X-ray diffraction. The molecules ofIandIIdemonstrate the quinoid character of phenyl rings accompanied by the distortion of bond angles related to the presence of fluorine substituents in the 3 and 5 (ortho) positions. In the crystals ofIandII, the molecules are connected by N—H...N, N—H...F and N—H...O hydrogen bonds, C—H...F short contacts, and π-stacking interactions. In crystal ofIII, only stacking interactions between the molecules are found. 

The title compound, systematic name tris(μ₂-perfluoro-o-phenylene)(μ₂-3-phenyl-4H-chromen-4-one)-triangulo-trimercury, [Hg₃(C₆F₄)₃(C₁₅H₁₀O₂)], crystallizes in the monoclinicP2₁/nspace group with one flavone (FLA) and one cyclic trimeric perfluoro-o-phenylenemercury (TPPM) molecule per asymmetric unit. The FLA molecule is located on one face of the TPPM acceptor and is linked in an asymmetric coordination of its carbonyl oxygen atom with two Hg centers of the TPPM macrocycle. The angular-shaped complexes pack in zigzag chains where they stackviatwo alternating TPPM–TPPM and FLA–FLA stacking patterns. The distance between the mean planes of the neighboring TPPM macrocycles in the stack is 3.445 (2) Å, and that between the benzo-γ-pyrone moieties of FLA is 3.328 (2) Å. The neighboring stacks are interdigitated through the shortened F...F, CH...F and CH...π contacts, forming a dense crystal structure. 

Three amidine-based ligands were used in the crystal design of a series of mononuclear Zn(II) complexes. Interaction of zinc chloride, ZnCl2, with N-2-pyridylimidoyl-2-pyridylamidine (Py2ImAm) resulted in complexes [Zn(Py2ImAm)2] (1) and [ZnCl2(Py2ImAm)] (2). In [Zn(Py2ImAm)2] (1, monoclinic, P21/c), the metal ion was coordinated with the bidentate pocket of the anionic form of Py2ImAm, while in [ZnCl2(Py2ImAm)] (2, monoclinic, P21/n), the tridentate coordination to a neutral Py2ImAm was completed by two chloride anions. This structural variation was achieved by a pH-controlling strategy using the weak base triethylamine (TEA). Otherwise, three ionic complexes were obtained with 2-amidinopyridine (PyAm) and Zinc(II), [ZnCl(PyAm)2]Cl (3, triclinic, P-1), [ZnCl(PyAm)2]2[ZnCl4]·C2H5OH (4, monoclinic, P21/n), and [ZnCl(PyAm)2]2Cl·CH3OH (5, triclinic, P-1). They comprised the same [ZnCl(PyAm)2]+ monocation with a butterfly-like shape provided by the bidentate chelate coordination of two PyAm neutral entities and a chloride ligand. In a similar butterfly shape, ionic complex [ZnCl(PmAm)2]2[ZnCl4] (6, monoclinic, C2/c) comprised the mononuclear [ZnCl(PmAm)2]+ cations with two bidentate chelate-coordinated 2-amidinopyrimidine (PmAm) as neutral ligands. The Zn(II) pentacoordinated arrangement in 3–6 was variable, from square pyramidal to trigonal bipyramidal. The reported compounds’ synthetic protocols, crystal structures and photoluminescence properties are discussed. 

A Cu^IIcoordination polymer,catena-poly[[[aquacopper(II)]-bis(μ-4-aminobenzoato)-κ²N:O;κ²O:N] monohydrate], {[Cu(pABA)₂(H₂O)]·H₂O}_n(pABA =p-aminobenzoate, C₇H₄NO₂⁻), was synthesized and characterized. It exhibits a one-dimensional chain structure extended into a three-dimensional supramolecular assembly through hydrogen bonds and π–π interactions. While the twinned crystal shows a metrically orthorhombic lattice and an apparent space groupPbcm, the true symmetry is monoclinic (space groupP2/c), with disordered Cu atoms and mixed roles of water molecules (aqua ligand/crystallization water). The luminescence spectrum of the complex shows an emission at 345 nm,cf.349 nm forpABAH. 

For a series of substituted dithieno[3,2-a:2′,3′-c]phenazine derivatives X-ray diffraction studies have been carried out. 

Structures of three cocrystals of nootropic racetams were studied. They included two cocrystals of phenylpiracetam (PPA) with 4-hydroxybenzoic acid (HBA) with different stoichiometries, PPA·HBA and PPA·2HBA, and cocrystal of 2-(4-phenyl-2-oxopyrrolidin-1-yl)-N’-isopropylideneacetohydrazide (PPAH) with 4-hydroxybenzamide (HBD), PPAH·HBD·(acetone solvate). X-ray study of the pure forms of PPA and PPAH was also carried out to identify variations of molecular synthons under the influence of conformers. The cocrystal structures revealed the diversity of supramolecular synthons namely, amide-amide, amide-acid, acid-acid, and hydroxyl-hydroxyl; however, very similar molecular chains were found in PPA and PPA·2HBA, and similar molecular dimers in PPAH and PPAH·HBD. In addition, conformational molecular diversity was observed as disorder in PPA·2HBA as it was observed earlier for rac-PPA that allows for the consideration that cocrystal as an example of partial solid solution. Quantum chemical calculations of PPA and PPAH conformers demonstrated that for most conformers, energy differences do not exceed 2 kcal/mol that suggests the influence of packing conditions (in this case R- and S-enantiomers intend to occupy the same molecular position in crystal) on molecular conformation. 

A new pseudopolymorph of berberine, 9,10-dimethoxy-5,6-dihydro-2 H -7λ 5 -[1,3]dioxolo[4,5- g ]isoquinolino[3,2- a ]isoquinolin-7-ylium chloride methanol monosolvate, C 20 H 18 NO 4 + ·Cl − ·CH 3 OH, was obtained during co-crystallization of berberine chloride with malonic acid from methanol. The berberine cations form dimers, which are further packed in stacks. The title structure was compared with other reported solvates of berberine chloride: its dihydrate, tetrahydrate, and ethanol solvate hemihydrate. Hirshfeld analysis was performed to show the intermolecular interactions in the crystal structure of the title compound, and its fingerprint plots were compared with those of the already studied solvates. 

1,3-Dimethyl-2,3-dihydrobenzo[d]imidazoles,1H, and 1,1',3,3'-tetramethyl-2,2',3,3'-tetrahydro-2,2'-bibenzo[d]imidazoles,1₂, are of interest as n-dopants for organic electron-transport materials. Salts of 2-(4-(dimethylamino)phenyl)-4,7-dimethoxy-, 2-cyclohexyl-4,7-dimethoxy-, and 2-(5-(dimethylamino)thiophen-2-yl)benzo[d]imidazolium (1g–i⁺, respectively) have been synthesized and reduced with NaBH₄to1gH,1hH, and1iH, and with Na:Hg to1g₂and1h₂. Their electrochemistry and reactivity were compared to those derived from 2-(4-(dimethylamino)phenyl)- (1b⁺) and 2-cyclohexylbenzo[d]imidazolium (1e⁺) salts.E(1⁺/1^•) values for 2-aryl species are less reducing than for 2-alkyl analogues, i.e., the radicals are stabilized more by aryl groups than the cations, while 4,7-dimethoxy substitution leads to more reducingE(1⁺/1^•) values, as well as cathodic shifts inE(1₂^•+/1₂) andE(1H^•+/1H) values. Both the use of 3,4-dimethoxy and 2-aryl substituents accelerates the reaction of the1Hspecies with PC₆₁BM. Because 2-aryl groups stabilize radicals,1b₂and1g₂exhibit weaker bonds than1e₂and1h₂and thus react with 6,13-bis(triisopropylsilylethynyl)pentacene (VII) via a “cleavage-first” pathway, while1e₂and1h₂react only via “electron-transfer-first”.1h₂exhibits the most cathodicE(1₂^•+/1₂) value of the dimers considered here and, therefore, reacts more rapidly than any of the other dimers withVIIvia “electron-transfer-first”. Crystal structures show rather long central C–C bonds for1b₂(1.5899(11) and 1.6194(8) Å) and1h₂(1.6299(13) Å).