Aromatic Micelles as a New Class of Aqueous Molecular Flasks.

Micelles are a versatile class of molecular assemblies typically composed of aliphatic molecules with hydrophilic groups. Polyaromatic molecules with hydrophilic groups, on the other hand, usually do not assemble into micellar structures in water but rather form columnar, π-stacked architectures. This Minireview article focuses on the recent development of aqueous micellar nanostructures with multiple oligoarylene rods or polyaromatic panels. The new micelles with spherical polyaromatic shells, which we name "aromatic micelles", serve as functional molecular flasks with superior binding abilities for medium to very large molecules in water.

Ethyl 4-(9H-carbazol-9-yl)benzoate: fivefold superstructure with ten crystallographically independent molecules refined from a twinned crystal.

The photophysical properties of organic fluorophores are sensitive to the local sterics of the surrounding environment. Restriction of torsional motion in aggregates and crystals can give rise to enhanced emissive behavior. N-Aryl-substituted carbazoles serve an essential role as ubiquitous host matrices for organic light-emitting diodes, due to their large band gaps and high triplet energies, and so studies connecting photophysical behaviors with detailed crystallographic structural information are important. To elucidate the structural changes involved in the excited-state charge-transfer processes of N-aryl-substituted carbazoles with ester withdrawing groups, ethyl 4-(9H-carbazol-9-yl) benzoate, C21H17NO2, was synthesized. The compound crystallizes with ten independent molecules in the asymmetric unit that pack together through moderate C-H...π interactions between carbazole units (2.5-2.9 Å) and π-stacks of benzoate groups (3.8-3.9 Å) between neighboring molecules. Four of the ten independent molecules show disorder by rotation of the ethyl carboxylate groups, with major occupancy rates between 0.931 (3) and 0.840 (3). The attached benzoate groups are also disordered, with identical occupancies, to compensate for the altered steric profile of the misaligned ethyl ester groups. For two molecules, the disorder extends to the entire carbazole units as well. Torsion angles between the nonplanar carbazole and benzoate groups range from θ = 44.8 to 57.2°, while those between the benzoate planes and the carboxylate COO atoms vary from α = 6.4 to 15.7°. The crystal is twinned by pseudomerohedry. The superstructure can be reduced to a hypothetical averaged parent structure in the space group Pbcn with Z' = 1, displaying fourfold disorder. Variable-temperature data collection shows that there is no phase transition between the disordered supercell and the hypothetical parent structure; supercell reflections persist up to 350 K. We propose that the disorder and variation in torsion angles result from frustrated close-packing and necessitate a unit cell with a high Z' number.

Solution-state photophysics of N-carbazolyl benzoate esters: dual emission and order of states in twisted push-pull chromophores.

The stepwise photoinduced charge transfer in a series of N-carbazolyl benzoate ester push-pull chromophores has been studied in solution. Dual emission from the locally excited (LE, the lowest-energy singlet excited state of 1Lb nature localized on the carbazole donor) and the highly polarized, intramolecular charge-transfer states of (pre)-twisted type (TICT states) is observed in non-polar and polar solvents. Ultrafast transient spectroscopy reveals that the excitation into the 1Lb LE state is followed by rapid (∼ps) charge separation into an emissive TICT state. Excitation into the second singlet excited state localized on the carbazole (S2) with 1La nature results in sub-100 fs population of both 1Lb and TICT states.

Crystal structure of poly[[[µ4-5-(9H-carbazol-9-yl)isophthalato][µ3-5-(9H-carbazol-9-yl)isophthalato]bis-(di-methyl-formamide)(methanol)dizinc] di-methyl-formamide monosolvate].

The structure of the polymeric title compound, {[Zn2(C20H11NO4)2(C3H7NO)2(CH3OH)]·C3H7NO} n , comprises carbazolylisophthalate moieties connecting dimetallic tetra-carboxyl-ate zinc secondary building units (SBUs) parallel to [100] and [010], leading to a layer-like arrangement parallel to (001). Each SBU consists of two Zn atoms in slightly distorted tetra-hedral and octa-hedral coordination environments [Zn⋯Zn = 3.5953 (6) Å]. Three carboxyl-ate groups bridge the two Zn atoms in a µ2-O:O' mode, whereas the fourth coordinates through a single carboxyl-ate O atom (µ1-O). The O atoms of two di-methyl-formamide (DMF) and one methanol mol-ecule complete the Zn coordination spheres. The methanol ligand inter-acts with the noncoordinating DMF mol-ecule via an O-H⋯O hydrogen bond of medium strength. Carbazoles between the layers inter-digitate through weak C-H⋯.π inter-actions to form a laminar solid stacked along [010]. Two kinds of C-H⋯π inter-actions are present, both with a distance of 2.64 Å, between the H atoms and the centroids, and a third C-H⋯π inter-action, where the aromatic H atom is located above the carbazole N-atom lone pair (H⋯N = 2.89 Å). Several C-H⋯O inter-actions occur between the coordinating DMF mol-ecule, the DMF solvent mol-ecule, and ligating carboxyl-ate O atoms.

A supramolecular approach for designing emissive solid-state carbazole arrays.

Reactions of 5-(9H-carbazol-9-yl)-isophthalate and metal salts provide laminar metal organic frameworks (MOFs) wherein interlayer interactions of the pendant carbazoles engender extended aromatic stacks or non-stacked structures with enhanced solid-state emission. These studies emphasize that MOFs serve as versatile supramolecular platforms to direct the aggregation and electroptical behaviours of organic chromophores.

Multi-responsive metal-organic lantern cages in solution.

Soluble copper-based M4L4 lantern-type metal-organic cages bearing internal amines were synthesized. The solution state integrity of the paramagnetic metal-organic cages was demonstrated using NMR, DLS, MS, and AFM spectroscopy. 1D supramolecular pillars of pre-formed cages or covalent host-guest complexes selectively formed upon treatment with 4,4'-bipyridine and acetic anhydride, respectively.

Molecular architectures of multi-anthracene assemblies.

Anthracene, with its molecular panel-like shape and robust photophysical behaviour, is a versatile building block that is widely used to construct attractive and functional molecules and molecular assemblies through covalent and non-covalent linkages. The intrinsic photophysical, photochemical and chemical properties of the embedded anthracenes often interact to engender desirable chemical behaviours and properties in multi-anthracene assemblies. This review article focuses on molecular architectures with linear, cyclic, cage, and capsule shapes, each containing three or more anthracene subunits.

Manisyl-substituted polypyridine coordination compounds: Metallo-supramolecular networks of interdigitated double helices assembled via CH...pi and pi-pi interactions.

A series of ML(2) coordination compounds of manisyl-substituted 2-pyridin-2-yl-1,10-phenanthrolines (pherpys) and 2,2':6',2''-terpyridines (terpys) with Fe(ii), Co(ii), Ni(ii), Cu(ii), Zn(ii), Ru(ii), and Os(ii), were synthesized. The pyridyl-phenanthroline-metal complexes form isomorphous crystals (space group Pcca), except for the zinc complex, which is isostructural but not isomorphous (space group P2(1)/c). Traces of the Ru complex induce the Zn complex to crystallize in the Pcca modification. Terpyridine complexes are isostructural but divided into two subgroups (Pnna and C2/c). Within the crystal lattice, the dications arrange into two-dimensional sheets of interdigitated left- and right-handed double helices via CHpi and pi-pi interactions of the pendant manisyl functionalities. All of the complexes exhibit weak ligand charge transfer (LCT) emission in solution at room temperature and the osmium complexes possess an emissive metal to ligand charge transfer (MLCT) state.

ON/OFF red emission from azaporphine in a coordination cage in water.

Red-emissive molecules have important applications as chemosensors, biological tags, and new light source materials but are severely limited by solubility and the tendency to form nonemissive aggregrates. Here we present an unusual example where a coordination cage sequesters and maintains the red-emissive properties of tetraazaporphine (TAP) in aqueous solution. Additionally, encapsulation within the highly cationic host lowers the pK(a) of the TAP interior protons, leading to the formation of an acid/base ON/OFF fluorescent switch.

Engineering discrete stacks of aromatic molecules.

Intrigued by transannular interactions occurring in stacked aromatic molecules, chemists have long endeavored to engineer discrete stacks of specific lengths and orientation. The maturation of self-assembly methodologies has shifted the focus away from utilizing covalent scaffolds to harnessing non-covalent interactions such as ionic interactions, hydrogen bonds, metal-ligand interactions, and aromatic interactions. Aromatic molecules often assemble into ill-defined, infinite aggregates and thus multiple self-assembly techniques must be combined to achieve the desired stack size and conformations. This critical review briefly highlights covalent scaffolds of stack aromatics before focusing on modern self-assembly based strategies for engineering discrete stacks of aromatic molecules (149 references).

Energy transfer in a mechanically trapped exciplex.

Host-guest complexes involving M(6)L(4) coordination cages can display unusual photoreactivity, and enclathration of the very large fluorophore bisanthracene resulted in an emissive, mechanically trapped intramolecular exciplex. Mechanically linked intramolecular exciplexes are important for understanding the dependence of energy transfer on donor-acceptor distance, orientation, and electronic coupling but are relatively unexplored. Steady-state and picosecond time-resolved fluorescence measurements have revealed that selective excitation of the encapsulated guest fluorophore results in efficient energy transfer from the excited guest to an emissive host-guest exciplex state.

Photophysics of manisyl-substituted 2-pyridin-2-yl-1,10-phenanthrolines. Dual emission dependent on structure and solvent.

Systematic variation of the substitution pattern of 2-pyridin-2-yl-1,10-phenanthrolines with 4-methoxy-2,6-dimethylphenyl (manisyl) groups alpha, beta, and gamma to the nitrogen atoms results in a 3 x 3 array of pyridyl-phenanthrolines displaying low to high quantum yields (Phi(f) = 0.03-0.60). Photophysical studies elucidated a duality of emissive states: a weakly emissive, locally excited state, similar to the (1)pi,pi state of phenanthroline; and a strongly emissive, charge-transfer state, dependent on manisyl regiochemistry and solvent polarity. Ab initio calculations underscore the similarities in the electronic structures of phenanthroline and pyridyl-phenanthrolines rather than between terpyridine and pyridyl-phenanthroline.

Functional molecular flasks: new properties and reactions within discrete, self-assembled hosts.

The application of self-assembled hosts as "molecular flasks" has precipitated a surge of interest in the reactivity and properties of molecules within well-defined confined spaces. The facile and modular synthesis of self-assembled hosts has enabled a variety of hosts of differing sizes, shapes, and properties to be prepared. This Review briefly highlights the various molecular flasks synthesized before focusing on their use as functional molecular containers--specifically for the encapsulation of guest molecules to either engender unusual reactions or unique chemical phenomena. Such self-assembled cavities now constitute a new phase of chemistry, which cannot be achieved in the conventional solid, liquid, and gas phases.

Synthesis of aryl-substituted 2-pyridyl-1,10-phenanthrolines; a series of oriented terpyridine analogues.

A 3 x 3 matrix of manisyl (4-methoxy-2,6-dimethylphenyl) substituted pyridyl-1,10-phenanthrolines has been synthesized by utilizing a general palladium catalyzed cross-coupling procedure. The directionality of these terdentate ligands will generate chiral octahedral ML(2) complexes, potentially useful for the metal templated synthesis of topologically chiral structures.