Room-Temperature Multiple Phosphorescence from Functionalized Corannulenes: Temperature Sensing and Afterglow Organic Light-Emitting Diode.

Corannulene-derived materials have been extensively explored in energy storage and solar cells, however, are rarely documented as emitters in light-emitting sensors and organic light-emitting diodes (OLEDs), due to low exciton utilization. Here, we report a family of multi-donor and acceptor (multi-D-A) motifs, TCzPhCor, TDMACPhCor, and TPXZPhCor, using corannulene as the acceptor and carbazole (Cz), 9,10-dihydro-9,10-dimethylacridine (DMAC), and phenoxazine (PXZ) as the donor, respectively. By decorating corannulene with different donors, multiple phosphorescence is realized. Theoretical and photophysical investigations reveal that TCzPhCor shows room-temperature phosphorescence (RTP) from the lowest-lying T1 ; however, for TDMACPhCor, dual RTP originating from a higher-lying T1 (T1 H ) and a lower-lying T1 (T1 L ) can be observed, while for TPXZPhCor, T1 H -dominated RTP occurs resulting from a stabilized high-energy T1 geometry. Benefiting from the high-temperature sensitivity of TPXZPhCor, high color-resolution temperature sensing is achieved. Besides, due to degenerate S1 and T1 H states of TPXZPhCor, the first corannulene-based solution-processed afterglow OLEDs is investigated. The afterglow OLED with TPXZPhCor shows a maximum external quantum efficiency (EQEmax ) and a luminance (Lmax ) of 3.3 % and 5167 cd m-2 , respectively, which is one of the most efficient afterglow RTP OLEDs reported to date.

Propeller, Linear, Cruciform and Stellate Spiro-bicarbazolium Salts.

A general synthetic approach to halogenated tetraaryl-ammonium salts has been developed and illustrated crystallographically. Bromide ammonium salts used as common synthetic intermediates together with Suzuki coupling of these bromides to a family of boronic acids provided a simplified strategy for arylation. Resolution of the C2 subset of spiro-bicarbazolium derivatives led to the first examples of enantiopure spiro-bicarbazoliums and the assignment of their absolute configuration by comparison of computational and experimental electronic circular dichroism (ECD) spectra. An ECD comparison with Prelog's spirobifluorenes is provided. The absolute configuration of the meta-bromide spiro-bicarbazolium salt was confirmed by anomalous scattering. Cruciform and stellate tetra-substituted salts provide a test of the limits of the methodology, and their structures suggest them to be candidates for MOF building blocks.

Cooperative Weak Dispersive Interactions Actuate Catalysis in a Shape-Selective Abiological Racemase.

A simple abiological host-guest system demonstrates racemase activity with catalytic rate enhancements of 104 without employing traditional functional groups. Cooperative weak interactions enhanced through shape-complementarity between the catalyst active site and the reaction transition state drive this activity, as proposed by Pauling for enzymes. In analogy to the Jencks' concept of catalytic antibodies, it is shown that a hapten resembling the planar transition state of the bowl inversion acts as a potent inhibitor of this catalytic process. In contrast, no substrate/product inhibition is detected, and a relatively weak binding of the substrate is observed (Ka ≈ 102 M-1 at 293 K). This simple box-and-bowl system demonstrates that shape selectivity arising from cooperative dispersive forces suffices for the emergence of a catalytic system with an enzyme-like thermodynamic profile.

The chemistry of branched condensed phosphates.

Condensed phosphates may exist as linear, cyclic or branched structures. Due to their important role in nature, linear polyphosphates have been well studied. In contrast, branched phosphates (ultraphosphates) remain largely uncharacterised, because they were already described in 1950 as exceedingly unstable in the presence of water, epitomized in the antibranching-rule. This rule lacks experimental backup, since, to the best of our knowledge, no rational synthesis of defined ultraphosphates is known. Consequently, detailed studies of their chemical properties, reactivity and potential biological relevance remain elusive. Here, we introduce a general synthesis of monodisperse ultraphosphates. Hydrolysis half-lives up to days call the antibranching-rule into question. We provide evidence for the interaction of an enzyme with ultraphosphates and discover a rearrangement linearizing the branched structure. Moreover, ultraphosphate can phosphorylate nucleophiles such as amino acids and nucleosides with implications for prebiotic chemistry. Our results provide an entry point into the uncharted territory of branched condensed phosphates.

Synthesis and Acidity of 5-(m-Terphenyl-2'-yl)-1H-tetrazoles: Evidence for an Enhanced Polar-π Effect Compared to Carboxylic Acids.

The polar-π effect on tetrazoles, medicinal chemistry isosteres of carboxylate, is tested by a Hammett pKa (microtitration) analysis over a series of 5-(m-terphenyl-2'-yl)-1H-tetrazoles. A comparison with m-terphenyl-2'-yl-carboxylic acids supports the isostere analogy also in response to environmental changes. Computational (B97D/def2TZVPPD) extension of the series plus a scan of solvents (vacuum to water) demonstrates the trend with the dielectric constant. The effect is energetically small but may make statistically significant contributions to the tetrazole pharmacological profile.

Generalized Analytic Approach for Determination of Multidimensional Franck-Condon Factors: Simulated Photoelectron Spectra of Polynuclear Aromatic Hydrocarbons.

An enhanced generalized analytic approach for determination of multidimensional Franck-Condon Factors (FCFs) enables efficient computational prediction of photoelectron spectra for large-dimensional systems. Incorporation of the automated assignment of Cartesian coordinate handedness and coordinate superposition between the ground and excited electronic states satisfies the Eckart conditions and allows evaluation of the Duschinsky effect. The model shows excellent agreement with experiments for the determination of FCFs and photoelectron spectra of a series of increasing dimensions polynuclear hydrocarbons (PAHs), including naphthalene, anthracene, phenanthrene, and pyrene. In addition, a high-resolution prediction of the PES for the 84-dimensional PAH corannulene provides motivation for an additional experimental study. For FCFs, coordinate transformation between the initial and final states rather than the dimension of the systems more greatly influences the complexity of the spectral band shapes.

One-Pot Domino Carbonylation Protocol for Aromatic Diimides toward n-Type Organic Semiconductors.

Aromatic diimides are one of the most important chromophores in the construction of n-type organic semiconductors, which lag far behind their p-type counterpart but are necessary for ambipolar transistors, p-n junctions and organic complementary circuits. Herein, we establish a facile one-pot domino synthetic protocol for aromatic diimides via palladium-catalyzed carbonylation of tetrabromo aromatic precursors. Taking tetrabromocorannulene (TBrCor) and tetrabromo-2,7-di-tert-butylpyrene (TBrPy) as the typical examples, we obtained diimide derivatives in yields of about 50 %, one order of magnitude higher than that of the traditional multi-step diimidization. As demonstrated in the case of corannulene diimide, the efficient diimidization not only allows the LUMO levels to be lowered significantly but also provides an ordered and closer packing structures, opening up possibilities to the development of n-type semiconducting materials based on a variety of aromatic systems.

An S10-Symmetric 5-Fold Interlocked [2]Catenane.

The reaction of sym-pentakis(4-aminothiophenyl)corannulene with 2-formyl-6-methylpyridine and CuI or 2-formyl-1,10-phenanthroline and MII (M = Co, Zn) yields an S10-symmetric 5-fold interlocked [2]catenane of two interpenetrating [CuI5L2]5+ cages or D5-symmetric [MII5L2]10+ cages, respectively. The new structures were characterized by X-ray crystallography, NMR spectroscopy, and mass spectrometry. Density functional theory computations point to dispersive energies on par with traditional covalent bond energies. Subcomponent exchange reactions favored formation of the [CoII5L2]10+ cage over the [CuI10L4]10+ catenane. The single cage and catenane each cocrystallized with a corannulene guest to form a bowl-in-bowl substructure.

X-ray Crystallography and Unexpected Chiroptical Properties Reassign the Configuration of Haliclonadiamine.

Haliclonadiamine and papuamine are bis-indane marine natural products isolated from the marine sponge Haliclona sp. Their relative structures were previously reported to differ by inversion at only one of their eight shared stereocenters. Here X-ray crystallography shows the opposite to be true: papuamine has a 1R,3S,8R,9S,14S,15R,20S,22R configuration, while haliclonadiamine has a 1S,3R,8S,9R,14R,15S,20R,22R configuration. Paradoxically the ECD of each structure displays a negative Cotton effect. X-ray crystallography reveals the two structures adopt similar conformations of their 13-membered macrocyclic core that comprises a configurationally relevant diene. B97x-D/Def2-TZVPP-(MeOH)-calculated ECD supports the diene configuration with the macrocycle dominating the ECD Cotton effect for haliclonadiamine and papuamine. Additional crystallographic and chiroptical analyses of three sponge samples from geographically distant locations indicate this pair of natural products always exists as a configurationally related couple. The co-discovery of a biosynthetic precursor, halichondriamine C, present in these same Haliclona samples must be considered when discussing any biosynthetic pathway. Taken together, this work justifies a reassignment of haliclonadiamine's structure and opens the question of how this complex stereochemical relationship between haliclonadiamine and palauamine arises biosynthetically.

Involvement of aryl hydrocarbon receptor in the cytotoxicity of corannulene and its derivatives.

Despite numerous studies on the toxicities of planar polycyclic aromatic hydrocarbons (PAHs), very little is known about the toxicological profiles of non-planar PAHs. In the present study, the cytotoxicity of corannulene (COR), a typical bowl-shaped PAH with a myriad of applications in the area of material chemistry, and benzo[a]pyrene (BaP), a typical planar PAH with similar molecular weight, were systematically compared in various cell lines. Compared with BaP, exposure to COR resulted in less cytotoxic responses in both human (HepG2) and murine (Hepa1-6) hepatoma cells, which was characterized with a slower cellular accumulation as well as a weaker induction of cytochrome P450 1 (CYP1/Cyp1) isozymes. Knockdown of aryl hydrocarbon receptor (AhR) by siRNA attenuated the inductive effect of COR on CYP1A/Cyp1a mRNA levels in these two cell lines. Further analysis revealed that derivatization greatly influenced the cytotoxicity of COR, which was positively correlated with their binding affinities to the AhR, as demonstrated by in silico molecular docking. Overall, these results suggest that AhR appears to be involved in the cytotoxic responses of COR and its derivatives, providing a fundamental understanding of the biological effects of bowl-like PAHs.

Fluorous Corannulenes: Ab initio Predictions and the Synthesis of sym-Pentafluorocorannulene.

Ten sym-penta and deca-X substituted corannulenes (1-10; X=H, F, CH3 , or CF3 ) define a library of fluorous compounds comprising high symmetry non-planar aromatic compunds. They provide a group of structurally similar, yet physically distinct structures manifesting special chemical behavior related to their degree of fluorination. Owing to their bowl forms, corannulene derivatives are distinct from planar polynuclear aromatic compounds; they have relatively high dipole moments, accept 1-4 electrons, and display room temperature fluorescence as well as low temp phosphorescence. Electronic structure theory predicts the bowl inversion barrier and physical properties. The syntheses of sym-pentafluorocorannulene by an efficient late stage fluorination affords a key derivative to calibrate predictions.

Synthesis of Modified Nucleoside Oligophosphates Simplified: Fast, Pure, and Protecting Group Free.

Phosphoramidite analogues of modified cyclotriphosphates provide a general and step-economical synthesis of nucleoside triphosphates and analogues on scale without the need for protecting groups. These reagents enable rapid access to pure nucleoside oligophosphates and a range of other analogues that were previously difficult to obtain (e.g., NH, CH2, CCl2, and CF2 replacements for O, phosphono- and phosphoimidazolides, -morpholidates, -azidates, and -fluoridates). DFT calculations demonstrate that the selectivity of the cyclotriphosphate opening reactions proceeds via an in-line substitution mechanism that displaces the least charged leaving group.

Fivefold Symmetry and 2D Crystallization: Self-Assembly of the Buckybowl Pentaindenocorannulene on a Cu(100) Surface.

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion-enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two-dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C-H⋅⋅⋅π bonding.

Graphene Grown from Flat and Bowl Shaped Polycyclic Aromatic Hydrocarbons on Cu(111).

The growth of carbon layers, defective graphene, and graphene by deposition of polycyclic aromatic hydrocarbons (PAHs) on Cu(111) is studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Two different PAHs are used as starting materials: the buckybowl pentaindenocorannulene (PIC) which contains pentagonal rings and planar coronene (CR). For both precursors, with increasing sample temperature during deposition, porous carbon aggregates (350 °C), dense carbon layers (400-450 °C), disordered defective graphene (500 °C-550 °C), and extended graphene (≥600 °C) are obtained. No significant differences for defective graphene grown from PIC and CR are observed. C 1s X-ray photoelectron spectra of PIC and CR derived samples grown at 350-550 °C exhibit a characteristic C-Cu low binding energy component. Preparation at ≥600 °C eliminates this C-Cu species and only C-C bonded carbon remains.

Azaindenocorannulenes: Synthesis, Properties, and Chirality.

Palladium-catalyzed intramolecular arylation provides bowl-shaped azaindenocorannulenes 7-9. Crystals of 8 show bowl-in-bowl columnar stacking. A substituent model rationalizes the first reduction potential of 18 related molecular bowls. The absolute configurations of bowls 7 and 9 are correlated with VCD and ECD spectra. The bowl inversion barrier of 9 (>190 kJ/mol) shows it to be more inert configurationally than chiral biaryl, phosphenes, or [ n]helicenes.

Corannurylene Pentapetalae.

Despite the great advances in the synthesis of diverse nonplanar graphenoids, investigations into the relationship between structural features and intermolecular interactions still present significant challenges. Herein, the novel nonplanar graphenoid structure, corannurylene pentapetalae (CRP), obtained via bottom-up syntheses of hybridization between perylene diimide (PDI) planar fragments and a corannulene curved core, is presented. Single crystal studies reveal a D5-symmetric as well as a C2-symmetric graphenoid corannurylene pentapetalae. The D5-symmetric structure has a unique honeycomb lattice with two chiral honeycomb layers alternately stacked, whereas the C2-symmetric CRP forms dimer units via π-π stacking. Transistor devices demonstrate that, without any π-π stacking, the honeycomb lattice of the D5-symmetric CRP has the potential to also facilitate electron transport.

Chiral Atropisomeric Indenocorannulene Bowls: Critique of the Cahn-Ingold-Prelog Conception of Molecular Chirality.

Chiral corannulenes abound, but suffer generally from configurational lability associated with bowl-to-bowl inversion, thus obviating questions of stereogenicity and stereoelement construction. In contrast, peri-annulated corannulenes show greatly increased barriers for bowl-to-bowl inversion; specifically indenocorannulenes invert on a time scale too slow to observe by normal NMR methods and raise the possibility of creating chiral atropisomeric bowl-shaped aromatics. Two methods for preparing indenocorannulene from simple 2-haloarylcorannulenes-silyl cation C-F activation, and Pd-mediated C-Cl activation[5] -enable the synthesis of an array of such chiral atropisomeric indenocorannulenes. Resolution of the enantiomers by high-performance liquid chromatography over chiral support phases motivates the study of chiroptical properties, the assignment of absolute "Cartesian" configuration, and the assessment of configurational stability. These studies bring into question any systematic assignment of nontrivial stereoelements (i.e. not the molecule in its entirety) and refute any assertion of congruence between "Cahn-Ingold-Prelog elements" and the physical or "Cartesian" basis of chirality.

Kurt†M. Mislow (1923-2017).

Kurt M. Mislow, Hugh Stott Taylor Professor of Chemistry Emeritus at Princeton University, died peacefully on October 5th, 2017 at the age of 94. Through the use of non-numerical mathematical models to conceptualize molecular form and function, Mislow pioneered the development of a modern stereochemistry, with contributions including the chiroptical properties of biaryls, resolution of phosphine oxides, and the use of NMR spectroscopy for the study of stereodynamic processes.