Stable [48]‐, [50]‐, and [52]Dodecaphyrins(1.1.0.1.1.0.1.1.0.1.1.0): The Largest Hückel Aromatic Molecules

[52]Dodecaphyrin(1.1.0.1.1.0.1.1.0.1.1.0) was quantitatively oxidized with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) to the corresponding [50]dodecaphyrin. Further oxidation of [50]dodecaphyrin with MnO₂ quantitatively afforded [48]dodecaphyrin. Of the three, [50]dodecaphyrin showed Hückel aromatic character as the largest aromatic molecule reported to date. Protonation of [50]dodecaphyrin with methanesulfonic acid (MSA) led to the formation of a planar tetraprotonated species that displayed a sharp and intense Soret‐like band at 906 nm with ε=6.5×10⁵ M ^?1 cm^?1 and Q‐band‐like bands at 1346 and 1600 nm.     

Photomagnetic and nonlinear optical properties in cis‐trans green fluoroprotein chromophore coupled Bis‐imino nitroxide diradicals

The current study extends an earlier investigation (Bhattacharya, et al., Phys. Chem. Chem. Phys. 2012, 14, 6905) to further explore various photomagnetic and optical properties of bis‐imino nitroxide, that is, (IN)₂‐based green fluorescent protein (GFP) chromophore coupled diradicals revealing new significant features. The conversion mechanisms of selected trans‐isomers into their corresponding cis‐conformers are discussed in detailed using a number of recently‐developed density functional theory (DFT) functionals based on the Minnesota suite of DFT‐models as well as using some other DFT functionals developed earlier. To provide a more in‐depth analysis of variations in magnetic properties as trans‐conformers (singlet ground‐state) convert into their cis‐analogues (triplet ground‐state), the changes in exchange magnetic coupling constants J are compared with the variation of the selected aromaticity indices. The aromaticity indices include the nuclear independent chemical shift [NICS(0)] values calculated at the center of ring structures and the harmonic oscillator model of aromaticity. Furthermore, the investigation of static nonlinear optical response properties in the (IN)₂‐based GFP chromophore coupled diradicals reveal unusually large static first hyperpolarizabilities for these systems which is highly significant for practical applications in optics and optoelectronics. © 2015 Wiley Periodicals, Inc.     

Theoretical investigation on icosahedral C60(FeCp)12: A hybrid of C60 and ferrocene

A perfect hybrid complex C₆₀(FeCp)₁₂ is predicted using density functional theory method_. This fullerene derivative could be view as a C₆₀ cage of which each C₅ ring coordinates a (FeCp) ligand. Theoretical calculation reveals that it has a large lowest unoccupied molecular orbital–highest unoccupied molecular orbital gap (2.53 eV) and keeps the I_h symmetry of C₆₀. But the C? C bond length of its inner C₆₀ cage trends to be uniform, which is quite different from the bonding character of C₆₀ fullerene. Further investigation reveals that the chemical bonding, TDOS and the aromaticity of the (C₅FeCp) unit in C₆₀(FeCp)₁₂ are similar as those of ferrocene molecule, which indicates the similarity of their electronic properties. So, this compound could be viewed as the combination of ferrocene molecules. Thus, its unconventional formation process from 12 Fe(Cp)₂ is proposed and the reaction energy is calculated. As the C₆₀(FeCp)₁₂ compound has the geometry framework as C₆₀ and the electronic characters as ferrocene, it would inherit the outstanding properties from both two molecules and have wild potential applications in nanochemistry. We hope our study could give some references for the further investigation and experimental synthesis research of the C₆₀(FeCp)₁₂ compound. © 2015 Wiley Periodicals, Inc.     

Tuning aromaticity in trigonal alkaline earth metal clusters and their alkali metal salts

In this work, we analyze the geometry and electronic structure of the [X_nM₃]^n?2 species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo‐[M₃]^2? unit. The cyclo‐[M₃]^2? ring is held together through a three‐center two‐electron bond of σ‐character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo‐[M₃]^2? ring and leads to a change from σ‐aromaticity in the bound state of the cyclo‐[M₃]^2? to π‐aromaticity in the XM₃^? and X₂M₃ metallic clusters. Our results also show that the aromaticity of the cyclo‐[M₃]^2? unit in the X₂M₃ metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M₃ ring. The Na₂Mg₃, Li₂Mg₃, and X₂Ca₃ clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M₃ ring, whereas X₂Be₃ and K₂Mg₃ keep its aromaticity relatively constant along this process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Is Free Cyclooctatetraene Dianion an Aromatic System? A Quantum Chemistry Study

To investigate whether free cyclooctatetraene dianion (COT^2?) is aromatic, quantum chemistry methods were used to optimize its structure. Based on the optimized structures, the natural population analysis (NPA) charge, bond order, delocalization energy, nucleus‐independent chemical shift (NICS), and harmonic oscillator model of aromaticity (HOMA) values were computed by DFT‐B3LYP method with basis set 6‐311++G**, which shows that COT^2? is not aromatic as it is not planar and has different bond lengths and bond orders, smallest delocalization energy and positive NICS values. To further confirm the finding, the changes of NICS and energy against ring distortion angle were scanned. The COT^2? has positive NICS values all along the angle from 180° to 120° while other aromatic systems always have negative values. The energy scanning suggests that COT^2? should have the weakest capability to maintain its planar structure. All the calculations strongly indicate that COT^2? is not aromatic. This study also suggests that NICS scan might be a good approach to judge aromaticity.     

Synthesis and Properties of a New Class of Fully Conjugated Azahexacene Analogues

Acenes are a traditional class of polycyclic aromatic hydrocarbons (PAHs) which attracted considerable interest during the last decade because of their outstanding p‐channel semiconductor properties. More recently, N‐heteroacenes have been prepared. These molecules have been shown to be more stable and can exhibit n‐channel semiconductor properties. Inspired by these archetype PAHs, we synthesized a novel class of highly persistent azahexacene analogues 3 a – d . These molecules are composed of a core of four fused five‐membered rings derived from their respective diketopyrrolopyrroles. These new π‐conjugated scaffolds show broad and intense absorption in the visible region and possess low‐lying HOMO and LUMO levels, leading to much better stability compared to that of acenes and most heteroacenes.     

Reversible Redox Reaction Between Antiaromatic and Aromatic States of 32π‐Expanded Isophlorins

32π‐antiaromatic expanded isophlorins with a varying number of thiophene and furan rings adopt either planar, ring‐inverted, or twisted conformations depending on the number of furan rings in the macrocycle. However, they exhibit identical reactivity with respect to their oxidation to aromatic 30π‐dicationic species under acidic conditions. These 32π‐antiaromatic macrocycles can also be oxidized with [Et₃O⁺SbCl₆^?]and NOBF₄ to generate dications, thus confirming ring oxidation of macrocycles. Furthermore, they can be reduced back to their parent 32π‐antiaromatic state by triethylamine, Zn, or FeCl₂. Single‐crystal X‐ray diffraction analysis confirmed a figure‐eight conformation for a hexafuran system, which opens to a planar structure upon oxidation.     

芳香性研究的最新进展: Möbius芳烃和富勒烯基芳香性全反式[18]轮烯

芳香性反式轮烯结构富勒烯具有高共轭性, 是潜在的优良的光能捕获分子. 综述了Möbius芳烃和芳香性反式轮烯结构富勒烯的合成和性质研究的最新进展, 并展望了其今后的发展方向.     

Heat-Resistant Properties in the Phosphorescence of trans-Bis[β-(iminomethyl)aryloxy]platinum(II) Complexes: Effect of Aromaticity on d–π Conjugation Platforms

The heat-resistant properties towards thermal emission quenching of trans-bis[(β-iminomethyl)aryloxy]platinum(II) complexes bearing 3-iminomethyl-2-naphtholato- ( 1 ), 1-iminomethyl-2-naphtholato- ( 2 ), 2-iminomethyl-1-naphtholato- ( 3 ), and 2-iminomethyl-1-phenolato ( 4 ) moieties, and a mechanistic rationale of these properties, are described in this report. Complex 1 a , with N,N′-dipentyl groups, exhibits intense red emission in 2-methyl-2,3,4,5-tetrahydrofuran (2-MeTHF) at 298 K, whereas the analogues 2 a – 4 a are less or non-emissive under the same measurement conditions. All four complexes are highly emissive at 77 K. The heat-resistant properties toward thermal emission quenching (Φ_{298 K}/Φ_{77 K}) increase in the order 1 a (0.52)> 2 a (0.09)> 3 a (0.02)>> 4 a (0.00). We investigated the emission decay and thermal-deactivation processes using density functional theory (DFT), time-dependent (TD) DFT, and double-hybrid density functional theory (DHDF) calculations of N,N′-diethyl forms 1 b – 4 b , and discuss the results with a focus on the energy levels, molecular structures, and electronic configurations in the triplet excited states. The energy differences between the triplet metal–ligand charge transfer (³MLCT) state and minimum-energy crossing point between the lowest triplet state and singlet ground state (MECP) increase in the order 1 a > 2 a , 3 a > 4 a , consistent with the experimental results for the heat-resistant properties of these complexes. The origin of the present structure dependence of the ³MLCT–MECP energy gap is ascribed to the ease or difficulty of the high-lying d_σ* orbital participating in the MECP upon thermal structural distortion. The structure dependence in energy gaps between the π* and d_σ* orbitals, which is key for facilitating the thermal deactivation process, is rationally correlated with the extent of aromaticity on the coordination platforms ( 1 b >( 2 b , 3 b )> 4 b ).     

Synthesis and properties of hybrid porphyrin tapes

Hybrid porphyrin tapes 3 and 4 , consisting of a mixture of 3,5‐di‐tert‐butylphenyl‐substituted donor‐type Zn^II–porphyrins and pentafluorophenyl‐substituted acceptor‐type Zn^II–porphyrins, were prepared by a synthetic route involving cross‐condensation reaction of a Ni^II–porphyrinyldipyrromethane and pentafluorophenyldipyrromethane with pentafluorobenzaldehyde followed by appropriate demetalation, remetalation, and oxidative ring‐closure reaction. The Ni^II‐substituted porphyrin tapes 5 (Ni‐Zn‐Ni) and 6 (Ni‐H₂‐Ni) were also prepared through similar routes. The hybrid porphyrin tapes 3 and 4 are more soluble and more stable than normal porphyrin tapes 1 and 2 consisting of only donor‐type Zn^II–porphyrins. The solid‐state and crystal packing structures of 3 , 4 , and 5 were elucidated by single‐crystal X‐ray diffraction analysis. Singly meso–meso‐linked hybrid porphyrin arrays 12 and 14 exhibit redox potentials that roughly correspond to each constituent porphyrin segments, while the redox potentials of the hybrid porphyrin tapes 3 and 4 are positively shifted as a whole. The two‐photon absorption (TPA) values of 1–6 were measured by using a wavelength‐scanning open aperture Z‐scan method and found to be 1900, 21 000, 2200, 27 000, 24 000, and 26 000 GM, respectively. These results illustrate an important effect of elongation of π‐electron conjugation for the enhancement of TPA values. The hybrid porphyrin tapes show slightly larger TPA values than the parent ones.