Tracking Structural Evolution during Symmetry‐Breaking Charge Separation in Quadrupolar Perylene Bisimide with Time‐Resolved Impulsive Stimulated Raman Spectroscopy

Elucidating structural roles in photoinduced charge transfer is indispensable, as nuclear rearrangements are simultaneously usually involved in the dynamics. However, it is hard to evaluate whether the structural changes occur or not by using conventional time‐resolved electronic spectroscopy. Here, time‐resolved impulsive stimulated Raman spectroscopy is applied to record the evolution of vibrational snapshots during charge‐separation dynamics of donor–acceptor–donor‐type quadrupolar perylene bisimide in real time. Drastic frequency shifts were observed for several Raman bands with their population kinetics, thus symmetry‐breaking charge separation accompanies significant structural changes, as supported by (TD)‐DFT calculations. A comparison between time‐resolved Raman spectra of the neutral S₁ state and the radical anion species shows that the spectral signatures, especially in high‐frequency regions, provide important clues to bond length alternation patterns in the PBI core.     

Gaussian和Multiwfn软件在判断蒽和菲芳香性上的应用

利用Gaussian软件对蒽和菲分子进行几何优化,在Multiwfn软件中运用等化学屏蔽表面(ICSS)和电子定域化函数(ELF)方法对蒽和菲进行了芳香性分析,并使分析结果可视化。结果表明,Gaussian和Multiwfn软件结合可以直观地解释蒽和菲不同环的芳香性差异,将分析结果应用于课堂教学,可以使课堂教学更加直观可视化。     

Tracking Structural Evolution during Symmetry-Breaking Charge Separation in Quadrupolar Perylene Bisimide with Time-Resolved Impulsive Stimulated Raman Spectroscopy

Elucidating structural roles in photoinduced charge transfer is indispensable, as nuclear rearrangements are simultaneously usually involved in the dynamics. However, it is hard to evaluate whether the structural changes occur or not by using conventional time-resolved electronic spectroscopy. Here, time-resolved impulsive stimulated Raman spectroscopy is applied to record the evolution of vibrational snapshots during charge-separation dynamics of donor–acceptor–donor-type quadrupolar perylene bisimide in real time. Drastic frequency shifts were observed for several Raman bands with their population kinetics, thus symmetry-breaking charge separation accompanies significant structural changes, as supported by (TD)-DFT calculations. A comparison between time-resolved Raman spectra of the neutral S₁ state and the radical anion species shows that the spectral signatures, especially in high-frequency regions, provide important clues to bond length alternation patterns in the PBI core.     

Synthesis and Predetermined Supramolecular Chirality of Carbohydrate‐Functionalized Perylene Bisimide Derivatives

Eight carbohydrate‐modified perylene bisimides ( PBI‐4 lac‐2 lac , PBI‐4 lac‐2 Man , PBI‐4 lac‐2 Gal , PBI‐4 lac‐2 Mal , PBI‐4 Man‐2 Man , PBI‐4 Man‐2 lac , PBI‐4 Man‐2 Gal and PBI‐4 Man‐2 Mal ) were synthesized, and the following predetermined supramolecular chirality rule was found: perylene bisimides modified with disaccharides (D ‐lactose and D ‐maltose) at the imide position generated right‐handed chirality, and those modified with monosaccharides (D ‐mannose and D ‐galactose) generated left‐handed chirality, when D ‐lactose or D ‐mannose was substituted in the bay positions of perylene bisimides with amide bonds as the linking spacers. These results may be because of the difference in the stacking angle of the perylene bisimide backbones induced by the steric effect and the additional hydrogen bonds between the disaccharide residues. This study provides an important design rule for predetermined chiral self‐assembly of perylene bisimides.     

A Serendipitous Rendezvous with a Four‐Center Two‐Electron Bonded Intermediate in the Aerial Oxidation of Hydrazine

Oxidation by dioxygen has a rich repertoire of mechanistic intricacies. Herein, we report a hitherto unknown paradigm of dioxygen activation reaction which propagates through a four center two electron (4c–2e) bound species. Using static DFT and ab initio quantum chemical techniques we have unraveled the oxidation pathway for hydrazine and its methylated analogues by dioxygen which involves formation of this unconventional 4c–2e bonded species en route to the oxidation products. Inconvertible evidence in favor of such an unprecedented dioxygen activation route is provided by capturing the events of formation of the 4c–2e species in aqueous phase for hydrazine and its congeners and the experimentally observed products from the respective 4c–2e species, like H₂O₂ and N₂H₂, diazene in the case of hydrazine using Car–Parrinello molecular dynamics simulations.     

Synthesis,Aromaticity and Photophysical Behaviour of Ferrocene‐ and Ruthenocene‐Appended Semisynthetic Chlorin Derivatives

Two novel synthetic strategies to covalently link a metallocene electron‐donor unit to a chlorin ring are presented. In one approach, pyropheophorbide a is readily converted into its 13¹‐ferrocenyl dehydro derivative by nucleophilic addition of the ferrocenyl anion to the 13¹‐carbonyl group. In another approach, the corresponding 13¹‐pentamethylruthenocenyl derivative is synthesised from 13¹‐fulvenylchlorin by a facile ligand exchange/deprotonation reaction with the [RuCp*(cod)Cl] (Cp*=pentamethylcyclopentadienyl; cod=1,5‐cyclooctadiene) complex. The resulting metallocene–chlorins exhibit reduced aromaticity, which was unequivocally supported by ring‐current calculations based on the gauge‐including magnetically induced current (GIMIC) method and by calculated nucleus‐independent chemical shift (NICS) values. The negative ring current in the isocyclic E ring suggests the antiaromatic character of this moiety and also clarifies the spontaneous reactivity of the complexes with oxygen. The oxidation products were isolated and their electrochemical and photophysical properties were studied. The ruthenocene derivatives turned out to be stable under light irradiation and showed photoinduced charge transfer with charge‐separation lifetimes of 152–1029 ps.     

Tetrabenzoperipentacene: Stable Five‐Electron Donating Ability and a Discrete Triple‐Layered β‐Graphite Form in the Solid State

An oxidative ring‐closure reaction of a tetranaphthylpyrene derivative led to the synthesis of a 56 all‐carbon conjugated tetrabenzoperipentacene. In the single‐crystal X‐ray structure, three molecules make a triple‐layered cluster by π‐stacking, wherein each layer rotates by 120°, and is thus considered a petit β‐graphite. As for the optical properties, the Stokes shift is extremely small (10 cm^?1), thus indicating its remarkably rigid framework. The tetrabenzoperipentacene exhibits reversible five‐electron oxidation waves in cyclic voltammetry, and is regarded as a counterpart to the fullerene C₆₀ in terms of stable multicharge‐storage nanocarbon materials.     

σ‐Aromaticity in an Unsaturated Ring: Osmapentalene Derivatives Containing a Metallacyclopropene Unit

In general, aromaticity can be clarified as π‐ and σ‐aromaticity according to the type of electrons with major contributions. The traditional π‐aromaticity generally describes the π‐conjugation in fully unsaturated rings whereas σ‐aromaticity may stabilize fully saturated rings with delocalization caused by σ‐electron conjugation. Reported herein is an example of σ‐aromaticity in an unsaturated three‐membered ring (3 MR), which is supported by experimental observations and theoretical calculations. Specifically, when the 3 MR in cyclopropaosmapentalene is cleaved by ethane through two isodesmic reactions, both of them are highly endothermic (+29.7 and +35.0 kcal mol^?1). These positive values are in sharp contrast to the expected exothermicity, thus indicating aromaticity in the 3 MR. Further nucleus‐independent chemical shift and anisotropy of the current‐induced density calculations reveal the nature of σ‐aromaticity in the unsaturated 3 MR.     

Fused Corrole Dimers Interconvert between Nonaromatic and Aromatic States through Two‐Electron Redox Reactions

A singly linked corrole dimer was synthesized by condensation of a dipyrromethane‐1‐carbinol with 1,1,2,2‐tetrapyrroethane. Oxidation of the dimer gave doubly linked corrole dimers 9 and 10 as the first examples of fused corrole dimers involving a meso–meso linkage. Dimers 9 and 10 exhibit characteristic ¹H NMR spectra, absorption spectra, excited‐state dynamics, and two‐photon absorption (TPA) values, which indicate the nonaromatic nature of 9 and the aromatic nature of 10 . Interestingly, 9 is fairly stable despite its unusual 2H‐corrole structure, which has been ascribed to the presence of two direct connections between the individual corrole units.     

A Stable All‐Thiophene‐Based Core‐Modified [38]Octaphyrin Diradicaloid: Conformation and Aromaticity Switch at Different Oxidation States

A soluble and stable core‐modified [38]octaphyrin, MC‐T8 , containing eight thiophene rings was synthesized by Yamamoto coupling followed by oxidative dehydrogenation. X‐ray crystallographic analysis revealed a nearly planar backbone, and the molecule is globally aromatic with a dominant 38π conjugation pathway. The dication MC‐T8²⁺ is antiaromatic, and the backbone is distorted, with a different orientation of the thiophene rings. The tetracation MC‐T8⁴⁺ becomes aromatic again, with a shallow‐bowl‐shaped geometry. Both the neutral compound and the dication demonstrated open‐shell diradical character with a small singlet–triplet energy gap (?2.70 kcal mol^?1 for MC‐T8 and ?3.78 kcal mol^?1 for MC‐T8²⁺ ), and they are stable owing to effective spin delocalization.     

Global Aromaticity in Macrocyclic Cyclopenta‐Fused Tetraphenanthrenylene Tetraradicaloid and Its Charged Species

A stable cyclopenta‐fused tetraphenanthrenylene macrocycle, CPTP‐M , was synthesized, and the structure was confirmed by X‐ray crystallographic analysis. It exhibits a large radical character (number of unpaired electron, N_U=3.52) and a small singlet–triplet energy gap (ΔE_S‐T=?2.8 kcal mol^?1 by SQUID). Its backbone contains 60 ([4n]) conjugated π electrons and is globally antiaromatic. NMR measurements and theoretical calculations revealed that its dication/dianion is globally aromatic owing to the existence of [4n?2]/[4n+2] π‐conjugated electrons. Remarkably, the ring‐current map of the tetraanion shows a unique ring‐in‐ring structure, with a diamagnetic outer ring and a paramagnetic inner ring. Accordingly, both the inner‐rim and outer‐rim protons are deshielded in its ¹H NMR spectrum. The tetraanion can be regarded as an isoelectronic structure of the known octulene, which shows similar electronic properties.     

Electronic Interactions of n‐Doped Perylene Diimide Groups Appended to Polynorbornene Chains: Implications for Electron Transport in Organic Electronics

A polymer consisting of a polynorbornene backbone with perylene diimide (PDI) pendant groups on each monomeric unit is synthesized via ring opening metathesis polymerization. The PDI pendant groups along the polymer backbone, studied by UV–vis absorption, fluorescence emission, and electron paramagnetic resonance spectroscopy in addition to electrochemical methods, show evidence of molecular aggregation and corresponding electronic coupling with neighboring groups, which forms pathways for efficient electron transport from one group to another in a specific reduced form. When n‐doped, the title polymer shows redox conductivity of 5.4 × 10⁻³ S cm⁻¹, comparable with crystalline PDI materials, and is therefore a promising material for use in organic electronics.     

Triplet‐State Aromaticity of 4nπ‐Electron Monocycles: Analysis of Bifurcation in the π Contribution to the Electron Localization Function

The π contribution to the electron localization function (ELF) is used to compare 4nπ‐ and (4n+2)π‐electron annulenes, with particular focus on the aromaticity of 4nπ‐electron annulenes in their lowest triplet state. The analysis is performed on the electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all‐carbon annulenes are set up: the span in the bifurcation values ΔBV(ELF_π) should be small, ideally zero, and the bifurcation value for ring closure of the π basin RCBV(ELF_π) should be high (≥ 0.7). On the basis of these criteria, nearly all 4nπ‐electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)π‐electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D_4h and D_8h symmetry, respectively, the RCBV(ELF_π) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of α‐ and β‐electrons.