Dual phosphorescent emissions from conformers of iridium complex rotors.

The chiral iridium rotors Ir(ppy)(pyX)Cl (X = CC-SiR, R = alkyl) remarkably contain two distinct rotational conformers in the ground (S) and excited (T) states that can be detected by NMR and emission measurements respectively at variable temperatures. The observed phosphorescent emissions, vibronic (involving L = ppy) and broad (L = pyX), arise from different triplet ligand to metal charge transfers from the two rotational conformers at distinct MLCT excited states. Both conformers exist in these Ir(ppy)(pyX)Cl rotors due to the electron-withdrawing, conjugated substituent X.

Light Activated Release of Nitrile Ligands from -Ru(L)(PPh)(nitrile) Complexes.

A series of -RuL(PPh)(nitrile) and {RuL(PPh)}.-μ-(nitrile)-based complexes [where L = 2,2'-(3,4-diphenyl-pyrrole-2,5-diyl)dipyridine (dpp), di(pyridin-2-yl)isoindoline-1,3-diimine (bpi), or 4-(4-methoxyphenyl)-6-phenyl-2,2'-bipyridine (Pbpy); and nitrile = 1,4-dibenzontirile, 4-ethynylbenzonitrile, or dicyanamide] were synthesized and characterized, and their electrochemical and photochemical behaviors were investigated. Those complexes that contained a significant nitrile contribution to their MLLCT show a release of their nitrile ligand (when L = dpp or Pbpy and the nitrile ligand = 4-dibenzontirile, or 4-ethynylbenzonitrile) with dissociation constants up to 8.

Scrolling in Supramolecular Gels: A Designer's Guide.

Gelation by small molecules is a topic of enormous importance in catalysis, nanomaterials, drug delivery, and pharmaceutical crystallization. The mechanism by which gelators self-organize into a fibrous gel network is poorly understood. Herein, we describe the crystal structures and gelation properties of a library of bis(urea) compounds and show, via molecular dynamics simulations, how gelator aggregation progresses from a continuous pattern of supramolecular motifs to a homogeneous fiber network.

Connectivity-Dependent Conductance of 2,2'-Bipyridine-Based Metal Complexes.

The present work provides an insight into the effect of connectivity isomerization of metal-2,2'-bipyridine complexes. For that purpose, two new 2,2'-bipyridine (bpy) ligand systems, 4,4'-bis(4-(methylthio)phenyl)-2,2'-bipyridine (L) and 5,5'-bis(3,3-dimethyl-2,3-dihydrobenzothiophen-5-yl)-2,2'-bipyridine (L) were synthesized and coordinated to rhenium and manganese to obtain the corresponding complexes MnL(CO)Br, ReL(CO)Br, MnL(CO)Br, MoL(CO) and ReL(CO)Br. The experimental and theoretical results revealed that coordination to the para system, i.

Single-Molecule Conductance Behavior of Molecular Bundles.

Controlling the orientation of complex molecules in molecular junctions is crucial to their development into functional devices. To date, this has been achieved through the use of multipodal compounds (i.e.

Pathway complexity in fibre assembly: from liquid crystals to hyper-helical gelmorphs.

Pathway complexity results in unique materials from the same components according to the assembly conditions. Here a chiral acyl-semicarbazide gelator forms three different gels of contrasting fibre morphology (termed 'gelmorphs') as well as lyotropic liquid crystalline droplets depending on the assembly pathway. The gels have morphologies that are either hyperhelical (HH-Gel), tape-fibre (TF-Gel) or thin fibril derived from the liquid crystalline phase (LC-Gels) and exhibit very different rheological properties.

Platinum(II) Complexes of Nonsymmetrical -Coordinating Ligands: Unimolecular and Excimeric Luminescence Properties and Comparison with Symmetrical Analogues.

A series of seven new platinum(II) complexes PtLCl have been prepared, where L is an -coordinating ligand comprising a benzene ring 1,3-disubstituted with two different azaheterocycles. In PtLCl, one heterocycle is a simple pyridine ring, while the other is an isoquinoline, a quinoline, a pyrimidine (L, L, L), or a -CF- or -OMe-substituted pyridine (L and L). PtLCl incorporates both a -CF and a -OMe-substituted pyridine.

Vapor Sorption and Halogen-Bond-Induced Solid-Form Rearrangement of a Porous Pharmaceutical.

A porous, nonsolvated polymorph of the voltage-gated sodium channel blocker mexiletine hydrochloride absorbs iodine vapor to give a pharmaceutical cocrystal incorporating an ICl anion that forms a halogen-π interaction with the mexiletine cations. The most thermodynamically stable form of the compound does not absorb iodine. This example shows that vapor sorption is a potentially useful and underused tool for bringing about changes in pharmaceutical solid form as part of a solid form screening protocol.

Extensive Polymorphism in the Molecular Ferroelectric 18-Crown-6 Oxonium Tetrachloro-Gallium(III).

The materials property of ferroelectricity is intimately linked with symmetry-changing phase transitions. Characterizing such transitions is therefore essential for understanding molecular ferroelectrics. In this paper, we explore the temperature and thermal history dependence of polymorphic phase transitions in the multiaxial molecular ferroelectric 18-crown-6 oxonium tetrachloro-gallium(III).

Rupturing aromaticity by periphery overcrowding.

The balance between strain relief and aromatic stabilization dictates the form and function of non-planar π-aromatics. Overcrowded systems are known to undergo geometric deformations, but the energetically favourable π-electron delocalization of their aromatic ring(s) is typically preserved. In this study we incremented the strain energy of an aromatic system beyond its aromatic stabilization energy, causing it to rearrange and its aromaticity to be ruptured.

Tuning Emission Lifetimes of Ir(C^N)(acac) Complexes with Oligo(phenyleneethynylene) Groups.

Emissive compounds with long emission lifetimes (μs to ms) in the visible region are of interest for a range of applications, from oxygen sensing to cellular imaging. The emission behavior of Ir(ppy)(acac) complexes (where ppy is the 2-phenylpyridyl chelate and acac is the acetylacetonate chelate) with an oligo(-phenyleneethynylene) (OPE3) motif containing three para-rings and two ethynyl bridges attached to acac or ppy is examined here due to the accessibility of the long-lived OPE3 triplet states. Nine Ir(ppy)(acac) complexes with OPE3 units are synthesized where the OPE3 motif is at the acac moiety (aOPE3), incorporated in the ppy chelate (pOPE3) or attached to ppy via a durylene link (dOPE3).

Highly Thermally Resistant Bisamide Gelators as Pharmaceutical Crystallization Media.

Three simple bisamide derivatives (, and ) with different structural modifications were synthesized with easy synthetic procedures in order to test their gel behaviour. The outcomes showed that hydrogen bonding was essential in gel formation; for this reason, only provided satisfactory gels. The presence of methoxy groups in and the alkyl chains in hindered the hydrogen bonding between N-H and C=O that occurred .

Platinum(IV) Complexes with Tridentate, -Coordinating Ligands: Synthesis, Structures, and Luminescence.

Platinum(II) complexes of -cyclometalating ligands based on 6-phenyl-2,2'-bipyridine (HL) have been widely investigated for their luminescence properties. We describe how PtLCl and five analogues with differently substituted aryl rings, PtLCl, can be oxidized with chlorine and/or iodobenzene dichloride to generate Pt(IV) compounds of the form Pt(-L)Cl ( = 1-6). The molecular structures of several of them have been determined by X-ray diffraction.

Near-infrared electroluminescence beyond 940 nm in Pt(N^C^N)X complexes: influencing aggregation with the ancillary ligand X.

We present a study of aggregate excited states formed by complexes of the type Pt(N^C^N)X, where N^C^N represents a tridentate cyclometallating ligand, and X = SCN or I. These materials display near-infrared (NIR) photoluminescence in film and electroluminescence in NIR OLEDs with = 720-944 nm. We demonstrate that the use of X = SCN or I modulates aggregate formation compared to the parent complexes where X = Cl.

Designer Gelators for the Crystallization of a Salt Active Pharmaceutical Ingredient-Mexiletine Hydrochloride.

We report an approach to obtain drug-mimetic supramolecular gelators, which are capable of stabilizing metastable polymorphs of the pharmaceutical salt mexiletine hydrochloride, a highly polymorphic antiarrhythmic drug. Solution-phase screening led to the discovery of two new solvated solid forms of mexiletine, a type C 1,2,4-trichlorobenzene tetarto-solvate and a type D nitrobenzene solvate. Various metastable forms were crystallized within the gels under conditions which would not have been possible in solution.

Understanding the Interaction of Gluconamides and Gluconates with Amino Acids in Hair Care.

A hair care mixture formed from a gluconamide derivative and 3-hydroxypropyl ammonium gluconate is known to strengthen hair fibers; however, the mechanism by which the mixture affects hair is unknown. To give insight into the aggregation of the target gluconamide and potential interactions between the gluconate-derived mixture and hair fibers, a range of systems were characterized by X-ray crystallography namely two polymorphic forms of the target gluconamide and three salts of 3-hydroxypropylammonium with sulfuric acid, methane sulfonic acid, and oxalic acid. The gluconamide proves to aggregate and becomes a supramolecular gelator in aniline and benzyl alcohol solution.

Integral Role of Water in the Solid-State Behavior of the Antileishmanial Drug Miltefosine.

Miltefosine is a repurposed anticancer drug and currently the only orally administered drug approved to treat the neglected tropical disease leishmaniasis. Miltefosine is hygroscopic and must be stored at subzero temperatures. In this work, we report the X-ray structures of miltefosine monohydrate and methanol solvate, along with 12- and 14-carbon chain analogue hydrates and a solvate.

Divergent Approach for -Heteroleptic Cyclometalated Iridium Complexes Using Triisopropylsilylethynyl-Substituted Synthons.

-heteroleptic cyclometalated iridium complexes of the form Ir(L)(acac), where L is a substituted 2-phenylpyridine derivative and acac is an acetylacetonato ligand, are a useful class of luminescent organometallic complexes for a range of applications. Related -heteroleptic complexes of the form Ir(L)(L)(acac) offer the potential advantage of greater functionality through the use of two different cyclometalated ligands but are, in general, more difficult to obtain. We report the synthesis of divergent - and -heteroleptic triisopropylsilylethynyl-substituted intermediate complexes that can be diversified using a "chemistry-on-the-complex" approach.

The "Magic Linker": Highly Effective Gelation from Sterically Awkward Packing.

Bis(urea)s based on the 4,4'-methylenebis(2,6-diethylphenylene) (4,4'-MDEP) spacer are highly effective low molecular weight gelators, and the first single crystal structure of a bis(urea) based on this spacer is reported. The structure is a conformational isomorph with eight crystallographically independent molecules (' = 8) arranged in four tennis-ball type dimers with the 2,6-diethylphenylene units adopting five different conformations in the ratio 4:5:3:2:2. The awkward shape and conformational promiscuity arising from the orientations of the ethyl groups in this system is linked to its gelation behavior.

Extended Conjugation Attenuates the Quenching of Aggregation-Induced Emitters by Photocyclization Pathways.

Herein, we expose how the antagonistic relationship between solid-state luminescence and photocyclization of oligoaryl alkene chromophores is modulated by the conjugation length of their alkenyl backbones. Heptaaryl cycloheptatriene molecular rotors exhibit aggregation-induced emission characteristics. We show that their emission is turned off upon breaking the conjugation of the cycloheptatriene by epoxide formation.

The Role of the Fused Ring in Bicyclic Triazolium Organocatalysts: Kinetic, X-ray, and DFT Insights.

Bicyclic triazolium scaffolds are widely employed in -heterocyclic carbene (NHC) organocatalysis. While the incorporation of a fused ring was initially for synthetic utility in accessing chiral, modular triazolyl scaffolds, recent results highlight the potential for impact upon reaction outcome with the underpinning origins unclear. The common first step to all triazolium-catalyzed transformations is C(3)-H deprotonation to form the triazolylidene NHC.

Novel ruthenium complexes bearing bipyridine-based and N-heterocyclic carbene-supported pyridine (NCN) ligands: the influence of ligands on catalytic transfer hydrogenation of ketones.

Transfer hydrogenation (TH) is a powerful synthetic tool in the production of secondary alcohols from ketones by using a non-H hydrogen source along with metal catalysts. Among homogeneous catalysts, Ru(II) complexes are the most efficient catalysts. In our research, six novel ruthenium(II) complexes bearing bipyridine-based ligands [Ru(L1)Cl] (1), [Ru(L1)(PPh)Cl]Cl (2) and [Ru(L2)Cl] (3) and N-heterocyclic carbene-supported pyridine (NCN) ligands [RuCp(L3)]PF (4), [RuCp*(L3)]PF (5), and [Ru(-cymene)(L3)Cl]PF (6) (where L1 = 6,6'-bis(aminomethyl)-2,2'-bipyridine, L2 = 6,6'-bis(dimethylaminomethyl)-2,2'-bipyridine and L3 = 1,3-bis(2-methylpyridyl)imidazolium bromide) were synthesised and characterised by NMR spectroscopy, HRMS, and X-ray crystallography.

Structure and hydration of polyvinylpyrrolidone-hydrogen peroxide.

The structure of the commercially important polyvinylpyrrolidone-hydrogen peroxide complex can be understood by reference to the co-crystal structure of a hydrogen peroxide complex and its mixed hydrates of a two-monomer unit model compound, bisVP·2HO. The mixed hydrates involve selective water substitution into one of the two independent hydrogen peroxide binding sites.

Carborane photochromism: a fatigue resistant carborane switch.

A dithienylethene molecule involving carborane clusters shows remarkable fatigue resistance and high contrast visual colour changes when irradiated with alternating ultraviolet and visible light. The fluorescence of this assembly can be switched on and off when irradiated in the solid state but not in the solution state.