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Hybrid Organic‐Inorganic Halide Perovskites (HOIHPs) represent an emerging class of semiconducting materials, widely employed in a variety of optoelectronic applications. Despite their skyrocket growth in the last decade, a detailed understanding on their structure–property relationships is still missing. In this communication, we report two unprecedented perovskite‐like materials based on polyfluorinated imidazolium cations. The two materials show thermotropic liquid crystalline behavior resulting in the emergence of stable mesophases. The manifold intermolecular F ⋅ ⋅ ⋅ F interactions are shown to be meaningful for the stabilization of both the solid‐ and liquid‐crystalline orders of these perovskite‐like materials. Moreover, the structure of the incorporated imidazolium cation was found to tune the properties of the liquid crystalline phase. Collectively, these results may pave the way for the design of a new class of halide perovskite‐based soft materials. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic halide perovskites (HOIHPs) have recently emerged as a flourishing area of research. Their easy and low‐cost production and their unique optoelectronic properties make them promising materials for many applications. In particular, HOIHPs hold great potential for next‐generation solar cells. However, their practical implementation is still hindered by their poor stability in air and moisture, which is responsible for their short lifetime. Optimizing the chemical composition of materials and exploiting non‐covalent interactions for interfacial and defects engineering, as well as defect passivation, are efficient routes towards enhancing the overall efficiency and stability of perovskite solar cells (PSCs). Due to the rich halogen chemistry of HOIHPs, exploiting halogen bonding, in particular, may pave the way towards the development of highly stable PSCs. Improved crystallization and stability, reduction of the surface trap states, and the possibility of forming ordered structures have already been preliminarily demonstrated. [ABSTRACT FROM AUTHOR]

We carried out a systematic evaluation of the packing forces in co-crystals featuring monoiodo- and diiodo-perfluoroalkanes and 1,2,4-oxadiazoles through single crystal X-ray diffraction and theoretical analysis. The molecules assemble via a combination of halogen bonding and specific dispersive interactions involving the perfluorinated units. We quantitatively elucidated the nature and strength of such interactions through solid-state calculations and Hirshfeld surface analysis. One of the co-crystals, formed by two monoiodoperfluorodecane molecules, the longest perfluorinated chain ever solved at the atomic level, allowed us to fully highlight the role of fluorous interactions. [ABSTRACT FROM AUTHOR]

We report halogen‐bonded complexes between 1‐polyfluoroalkyl‐3‐alkylimidazolium iodides and mono‐iodoperfluoroalkanes of different chain lengths or di‐iodoperfluorooctane. 19F NMR analyses revealed that the preferred stoichiometry between the donors and acceptors is 1 : 1 in the cases of the mono‐iodoperfluoroalkanes, and 2 : 1 with di‐iodoperfluorooctane, as a result of the monodentate behavior of the iodide anion (halogen bond acceptor). Single crystal X‐ray diffraction analyses showed the presence of a perfluorinated superanion, which interdigitates with the cation fluorinated chains, favoring the formation of lamellar structures. All of the obtained supramolecular complexes exhibit enantiotropic liquid crystalline phases over a broad range of temperatures. Most of the obtained complexes show melting points lower than 100 °C, two of them being liquid at room temperature, thus representing a new family of fluorinated ionic liquid crystals. [ABSTRACT FROM AUTHOR]

Novel 1,1′-bis(4-alkylphenyl)-[4,4′-bipyridine]-1,1′-diium salts, with alkyl chains of different lengths (8, 10 and 14 carbon atoms) and with different counteranions (Cl−, NTf2−, OTf−, OTs−, PF6−, BPh4−), have been prepared and fully characterized for their thermotropic behavior by polarized optical microscopy (POM), and calorimetric measurements. Almost all the synthesized compounds showed a high thermal stability, a wide temperature range of liquid-crystalline mesophase and, for some of them, the LC transition temperatures were relatively low. These compounds also exhibited electrochromic properties, which have been studied both in solution and in the LC phase, making the new materials very interesting for different opto-electronic applications. [ABSTRACT FROM AUTHOR]

Abstract: Halogen bonding is an increasingly important tool in crystal engineering, and measuring its influence on the local chemical and electronic environment is necessary to fully understand this interaction. Here, we present a systematic crystallographic and solid‐state NMR study of self‐complementary halogen‐bonded frameworks built from the halide salts (HCl, HBr, HI, HI3) of 2‐iodoethynylpyridine and 3‐iodoethynylpyridine. A series of single crystal X‐ray structures reveals the formation of discrete charged dimers in the solid state, directed by simultaneous X−⋅⋅⋅H−N+ hydrogen bonds and C−I⋅⋅⋅X− halogen bonds (X=Cl, Br, I). Each compound was studied using multinuclear solid‐state magnetic resonance spectroscopy, observing 1H to investigate the hydrogen bonds and 13C, 35Cl, and 79/81Br to investigate the halogen bonds. A natural localized molecular orbital analysis was employed to help interpret the experimental results. 1H SSNMR spectroscopy reveals a decrease in the chemical shift of the proton participating in the hydrogen bond as the halogen increases in size, whereas the 13C SSNMR reveals an increased 13C chemical shift of the C−I carbon for C−I⋅⋅⋅X− relative to C−I⋅⋅⋅N halogen bonds. Additionally, 35Cl and 79/81Br SSNMR, along with computational results, have allowed us to compare the C−I⋅⋅⋅X− halogen bond involving each halide in terms of NMR observables. Due to the isostructural nature of these compounds, they are ideal cases for experimentally assessing the impact of different halogen bond acceptors on the solid‐state NMR response. [ABSTRACT FROM AUTHOR]

2-Iodoethynylpyridine and 2-iodoethynyl-1-methyl-imidazole self-assemble under halogen-bonding control into discrete macrocycles, viz. supramolecular triangles. [ABSTRACT FROM AUTHOR]

We demonstrate that halogen bonding (XB) can offer a novel approach for the construction of photoresponsive ionic liquid crystals. In particular, we assembled two new supramolecular complexes based on 1-ethyl-3-methylimidazolium iodides and azobenzene derivatives containing an iodotetrafluoro-benzene ring as XB donor, where the iodide anion acted as an XB acceptor. DSC and X-ray diffraction analyses revealed that the preferred stoichiometry between the XB donors and acceptors is 2 : 1, and that the iodide anions act as bidentate XB-acceptors, binding two azobenzene derivatives. Due to the high directionality of the XB, calamitic superanions are obtained, while the segregation occurring between the charged and uncharged parts of the molecules gives rise to a layered structure in the crystal lattice. Despite the fact that the starting materials are non-mesomorphic, the halogen-bonded supramolecular complexes exhibited monotropic lamellar liquid-crystalline phases over broad temperature ranges, as confirmed with polarized optical microscopy. Due to the presence of the azobenzene moieties, the LCs were photoresponsive, and a LC-to-isotropic phase transition could be obtained by irradiation with UV light. We envisage that the light-induced phase transition, in combination with the ionic nature of the LC, provides a route towards light-induced control over ion transport and conductance in these supramolecular complexes. [ABSTRACT FROM AUTHOR]

Although intensively studied, the high-resolution crystal structure of the peptide DFNKF, the core-segment of human calcitonin, has never been described. Here we report how the use of iodination as a strategy to promote crystallisation and facilitate phase determination, allowed us to solve, for the first time, the single-crystal X-ray structure of a DFNKF derivative. Computational studies suggest that both the iodinated and the wild-type peptides populate very similar conformations. Furthermore, the conformer found in the solid-state structure is one of the most populated in solution, making the crystal structure a reliable model for the peptide in solution. The crystal structure of DFNKF(I) confirms the overall features of the amyloid cross-β spine and highlights how aromatic-aromatic interactions are important structural factors in the self-assembly of this peptide. A detailed analysis of such interactions is reported. [ABSTRACT FROM AUTHOR]

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen-bonded supramolecular anions [C nF2 n+1-I⋅⋅⋅I⋅⋅⋅I-C nF2 n+1]− are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen-bonded liquid crystals, and 2) imidazolium-based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation. [ABSTRACT FROM AUTHOR]

A new and simple method is presented to fluorinate the surfaces of poorly reactive hydrophobic polymers in a more environmentally friendly way using the protein hydrophobin (HFBII) as a nanosized primer layer. In particular, HFBII, via electrostatic interactions, enables the otherwise inefficient binding of a phosphate-terminated perfluoropolyether onto polystyrene, polypropylene, and low-density polyethylene surfaces. The binding between HFBII and the perfluoropolyether depends significantly on the environmental pH, reaching the maximum stability at pH 4. Upon treatment, the polymeric surfaces mostly retain their hydrophobic character but also acquire remarkable oil repellency, which is not observed in the absence of the protein primer. The functionalization proceeds rapidly and spontaneously at room temperature in aqueous solutions without requiring energy-intensive procedures, such as plasma or irradiation treatments. [ABSTRACT FROM AUTHOR]

Halogen bonding, a noncovalent interaction possessing several unique features compared to the more familiar hydrogen bonding, is emerging as a powerful tool in functional materials design. Herein, we unambiguously show that one of these characteristic features, namely high directionality, renders halogen bonding the interaction of choice when developing azobenzene-containing supramolecular polymers for light-induced surface patterning. The study is conducted by using an extensive library of azobenzene molecules that differ only in terms of the bond-donor unit. We introduce a new tetrafluorophenol-containing azobenzene photoswitch capable of forming strong hydrogen bonds, and show that an iodoethynyl-containing azobenzene comes out on top of the supramolecular hierarchy to provide unprecedented photoinduced surface patterning efficiency. Specifically, the iodoethynyl motif seems highly promising in future development of polymeric optical and photoactive materials driven by halogen bonding. [ABSTRACT FROM AUTHOR]

The peptide bond model N-methylacetamide self-assembles with a range of dihalotetrafluorobenzenes forming co-crystals that all show the occurrence of orthogonal hydrogen and halogen bonds. [ABSTRACT FROM AUTHOR]

A new fluorinated push–pull chromophore with good second-order NLO properties even in concentrated solution shows solid state intermolecular aryl–fluoroaryl interactions leading to J-aggregates with intense solid state luminescence. [ABSTRACT FROM AUTHOR]

Haloprogin is a topical antifungal agent. Its structure does not contain any of the functional groups typically exploited in hydrogen bond based co-crystal design. On the other hand, its 1-iodoalkyne moiety is nicely tailored to a crystal engineering strategy based on halogen bonding. Here we describe the formation of three polymorphs of haloprogin and of three co-crystals that this active pharmaceutical ingredient forms with both neutral and ionic co-crystal formers. The halogen bond plays a major role in all of the six structures and the interaction is thus confirmed to be a valuable tool which may complement the hydrogen bond when polymorphs and co-crystals of active pharmaceutical ingredients are pursued. [ABSTRACT FROM AUTHOR]

It is proposed that noncovalent interactions,wherein it is possibleto identify an element or moiety working as the electrophile, arenamed by referring to the Group of the Periodic Table the electrophilicatom belongs to. The resulting terminology generalizes a criterionwhich was used in the recent IUPAC definition of halogen bond andinspired the definition of hydrogen bond. A systematic, unambiguous,and periodic naming is obtained and applies to the majority of theattractive interactions formed by the elements of Groups 1, 2, 13–17and, possibly, to some interactions formed by the elements of otherGroups. [ABSTRACT FROM AUTHOR]

Halogen bonding is an emerging noncovalent interaction for constructing supramolecular assemblies. Though similar to the more familiar hydrogen bonding, four primary differences between these two interactions make halogen bonding a unique tool for molecular recognition and the design of functional materials. First, halogen bonds tend to be much more directional than (single) hydrogen bonds. Second, the interaction strength scales with the polarizability of the bond-donor atom, a feature that researchers can tune through single-atom mutation. In addition, halogen bonds are hydrophobic whereas hydrogen bonds are hydrophilic. Lastly, the size of the bond-donor atom (halogen) is significantly larger than hydrogen. As a result, halogen bonding provides supramolecular chemists with design tools that cannot be easily met with other types of noncovalent interactions and opens up unprecedented possibilities in the design of smart functional materials. [ABSTRACT FROM AUTHOR]

Thein situcryocrystallisation technique has been used to obtain four adducts between hexamethylphosphortriamide and 1,2-dihalotetrafluoroethanes having iodine, bromine and chlorine as halogen-bonding donor atoms. These systems allowed for a precise comparison of different C–X…O synthons. The effectiveness and reliability of the pharmacologically important C–Cl…O synthons are proven. [ABSTRACT FROM AUTHOR]

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (13C, 14/15N, 19F, and 127I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials. Single-crystal X-ray diffraction (XRD) structures of three novel co-crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH3)3N+(CH2)10N+(CH3)3][2 I−]) and different para-dihalogen-substituted benzene moieties (i.e., p-C6X2Y4, X=Br, I; Y=H, F) are presented. 13C and 15N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co-crystal complexes in the solid state. Long-range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using 14N NMR spectroscopy, with a systematic decrease in the 14N quadrupolar coupling constant ( CQ) observed upon halogen bond formation. Attempts at 127I solid-state NMR spectroscopy experiments are presented and variable-temperature 19F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge-including projector augmented-wave (GIPAW) or relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond. [ABSTRACT FROM AUTHOR]

The syntheses and the crystal structures of new multitopicanion-bindingorganic ligands based on a benzenoid scaffold and bearing two or three2-iodo-imidazolium arms are reported. The quite short C–I···Br¯contacts observed in the solid state (0.77 times the normalized contacts)demonstrate the excellent halogen bonding donor ability of iodineatoms in 2-iodoimidazolium cations. The geometric features of obtainedbromide anion adducts afford valuable structural insights for thedesign of effective and selective multitopic anion receptors basedon halogen bonding. [ABSTRACT FROM AUTHOR]

The X-ray diffraction analysis on single crystals obtained from the self-assembly of 1,8-diiodoperfluorooctane 1 with the tetraazahelicene derivative 2 revealed a site-selective pattern of halogen bonds (XBs) in the solid state. Indeed, two non-equivalent XBs drive the formation of an indefinitely repeating pentameric (1)3·(2)2 unit. Interestingly, the N...I-C bonding formation occurred selectively on the pyridazinic/cinnolinic nitrogen atoms of the tetraazahelicene unit, which were preferred over the pyridinic/quinolinic ones. On the basis of molecular electrostatic potential and molecular orbital analyses, DFT calculations predicted and explained well this site-selective XB formation, thus demonstrating to be efficient tools for the prediction of the XB site selectivity in similar polynitrogen systems. [ABSTRACT FROM AUTHOR]

Abstract: The single crystal structures of five co-crystals formed by the reaction of different iodide and bromide salts with di- and triiodoperfluorobenzenes (I-ArF) are reported. All of these perfluorocarbon-hydrocarbon systems are heteromeric three-component systems, wherein the weakly coordinating cations favour the formation of naked halides, which function as electron-donors towards the I-ArF modules. The analysis of the crystal structures shows that I−⋯I–ArF, and Br−⋯I–ArF halogen bonds (XBs) control the self-assembly of the obtained supramolecular architectures. 2D and 3D supramolecular networks have been obtained, wherein naked iodide and bromide anions act as tri-, tetra-, or pentadentate nodes. The selected examples demonstrate that I-ArF modules can be particularly robust and reliable tectons for XB-based coordination of halide ions and afford supramolecular architectures in a rational and predictable way. [ABSTRACT FROM AUTHOR]

This critical reviewdescribes how halocarbons can function as effective binding sites of anions viahalogen bonding, the noncovalent interaction whereby halogen atoms accept electron density. The focus is on the binding and coordination of oxyanions, by far the most numerous class of anions in organic chemistry. It is shown how a large variety of inorganic and organic oxyanions can form discrete adducts and 1D, 2D, or 3D supramolecular networks with chloro-, bromo-, and iodocarbons. Specific examples are discussed in order to identify new supramolecular synthons based on halogen bonding and to outline some general principles for the design of effective and selective receptors based on this interaction. The interaction allows for several other anions to self-assemble with halocarbons and mention is also given to the halogen bonding-based coordination of halides, polycyano- and polyoxometallates (72 references). [ABSTRACT FROM AUTHOR]

The amyloidogenic peptide, DFNKF, forms a steric zipper. Iodination of this widely studied sequence facilitated crystallization and allowed its high‐resolution single crystal structure determination for the first time. The structure unveils the importance of aromatic–aromatic interactions in stabilizing the amyloid self‐assembly. The amino acid side‐chains of facing β‐strands (shown in red and green, respectively) interdigitate like the teeth of a zipper, similar to that of blue jeans. More information can be found in the Full Paper by P. Metrangolo et al. on page 2051 ff. [ABSTRACT FROM AUTHOR]

Review: 76 refs. [ABSTRACT FROM AUTHOR]

Abstract: The supramolecular organization in six solid assemblies involving iodo- and bromoperfluoroarene derivatives is described. Single crystal X-ray analyses show that the formation of the supramolecular architectures is controlled by I−⋯Br–ArF, I−⋯I–ArF, Br−⋯I–ArF, and Cl−⋯I–ArF halogen bondings thus proving the X−⋯X′–ArF supramolecular synthon, where X can be the same as or different from X′, is particularly robust. In five of the described architectures halide anions form two halogen bondings and form infinite chains wherein dihaloperfluoroarenes, which function as bidentate electron acceptors, and halide anions, which function as bidentate electron donors, alternate. This behaviour shows halide anions have a fair tendency to work as bidentate halogen bonding acceptors. [Copyright &y& Elsevier]

Abstract: Herein we present a methodology for improving the power conversion efficiency of organic solar cells made by photoactive layers of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PCBM) of non-optimized microstructure. In our study we achieve a 47% improvement in the power conversion efficiency (PCE) of the device by utilizing a thiophene-based quinoid (QBT) moiety as the third component in the P3HT:PCBM:QBT photoactive layers. Based on a set of independent characterization experiments we address the QBT composition dependent photophysical, electrical, thermal, structural and morphology-related properties of the ternary photovoltaic P3HT:PCBM:QBT system for elucidating the origin of the PCE improvement. In small amounts (0.3–0.6wt%), QBT serves as a nucleation agent, it enlarges the size of the P3HT crystallites by 15% and it increases the fraction of well-ordered P3HT chains in the P3HT:PCBM:QBT layer. The improved microstructure of the photoactive layer in combination with the QBT-assisted photo-induced hole transfer step from PCBM to P3HT, lead to an increase of the charge photogeneration yield in the P3HT:PCBM:QBT triple bulk heterojunction. The relatively small optical gap of QBT facilitates a resonant energy transfer step from the photoexcited PCBM to the QBT followed by a charge transfer process between QBT and the P3HT matrix. Based on these findings we propose general guidelines for the design of next generation functional additives to be used in organic photovoltaics. [Copyright &y& Elsevier]