Near‐Infrared Quadrupolar Chromophores Combining Three‐Coordinate Boron‐Based Superdonor and Superacceptor Units

Herein, two new quadrupolar acceptor‐π‐donor‐π‐acceptor (A‐π‐D‐π‐A) chromophores have been prepared featuring a strongly electron‐donating diborene core and strongly electron‐accepting dimesitylboryl (BMes₂) and bis(2,4,6‐tris(trifluoromethyl)phenyl)boryl (B^FMes₂) end groups. Analysis of the compounds by NMR spectroscopy, X‐ray crystallography, cyclic voltammetry, and UV/Vis‐NIR absorption and emission spectroscopy indicated that the compounds have extended conjugated π‐systems spanning their B₄C₈ cores. The combination of exceptionally potent π‐donor (diborene) and π‐acceptor (diarylboryl) groups, both based on trigonal boron, leads to very small HOMO–LUMO gaps, resulting in strong absorption in the near‐IR region with maxima in THF at 840 and 1092 nm and very high extinction coefficients of ca. 120 000 m ^?1 cm^?1. Both molecules also display weak near‐IR fluorescence with small Stokes shifts.     

Toward Electrochemically Controllable Tristable Three‐Station [2]Catenanes

Encouraged by the prospect of producing an electrochemical, color‐switchable red–green–blue (RGB) dye compound, we have designed, synthesized, and characterized two three‐station [2]catenanes. Both are composed of macrocyclic polyethers containing three π‐electron‐rich stations, which act as recognition sites for a π‐electron‐deficient tetracationic cyclophane. The molecular structures of the two three‐station [2]catenanes were characterized fully by mass spectrometry and ¹H NMR spectroscopy. To anticipate the relative occupancies of the three stations in each [2]catenane by the cyclophane, model compounds with the same constitutions in the vicinity of the stations were synthesized. The relative ground‐state populations of the three stations occupied in both [2]catenanes were estimated from the thermodynamic parameters for 1:1 complexes between all these model compounds and the cyclophane, obtained from isothermal titration calorimetry (ITC). The electrochemical and electromechanical properties of the three‐station [2]catenanes were analyzed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry (SEC). The first three‐station [2]catenane was found to behave like a bistable system, whereas the second can be described as a quasi‐tristable system.     

Synthesis of Planar Chiral Iridacycles by Cationic Metal π‐Coordination: Facial Selectivity,and Conformational and Stereochemical Consequences

Facial selectivity during the π‐coordination of pseudo‐tetrahedral iridacycles by neutral (Cr(CO)₃), monocationic (Cp*Ru⁺), and biscationic (Cp*Ir²⁺) metal centers was directly influenced by the coulombic imbalance in the coordination sphere of the chelated Ir center. We also showed by using theoretical calculations that the feasibility of the related metallacycles that displayed metallocenic planar chirality was dependent to the presence of an electron‐donating group, such as NMe₂, which contributed to the overall stability of the complexes. When the π‐bonded moiety was the strongly electron‐withdrawing Cp*Ir²⁺ group, the electron donation from NMe₂ resulted in major conformational changes, with a barrier to rotation of about 17 kcal mol^?1 for this group that became spectroscopically diastereotopic (high‐field ¹H NMR spectroscopy). This peculiar property is proposed as a means to introduce a new type of constitutional chirality at the nitrogen center: planar chirality at tertiary aromatic amines.     

Molecular design of a “molecular syringe” mimic for metal cations using a 1,3‐alternate calix[4]arene cavity

The chemically switchable actions well imitate the function of a “molecular syringe,” has been studied in theory using the 1,3‐alternate calix [4]arene bearing a nitrogen‐containing crown cap at one side and a bis(ethoxyethoxy) group at another side by the π‐basic calixtube as a pipette and the crown ring as a rubber cap. The model is characterized by geometry optimization using density functional theory (DFT) at B3LYP/6‐31G level. The obtained optimized structures are used to perform natural bond orbital (NBO) and frequency analysis. The electron‐donating heteroatoms: O and N offer lone pair electrons to the contacting RY* (1‐center Rydberg) or LP* (1‐center valence antibond lone pair) orbitals of K⁺, Ag⁺. The results indicate that when the nitrogen atom in the crown ring is protonated, K⁺ and Ag⁺ will be pushed out to the bis(ethoxyethoxy) side through a π‐basic calixtube. When the nitrogen·H⁺ in the crown ring is deprotonated, K⁺ and Ag⁺ are sucked back to the crown‐capped side again. In the course of the coordination, both the intermolecular electrostatic interactions and the cation‐π interactions between the metal ion and π‐orbitals of the two pairs facing inverted benzene rings play a significant role. It is believed that this prototype of a “molecular syringe” is a novel molecular architecture for the action of metal cations. © 2010 Wiley Periodicals, Inc. J Comput Chem 2010     

One‐, Two‐, and Three‐Electron Reduction of a Cyclic Alkyl(amino)carbene–SbCl3 Adduct

A cyclic alkyl(amino)carbene readily reacts with SbCl₃ to form the corresponding Sb^III adduct. One‐electron reduction gives rise to the first example of a neutral antimony‐centered radical characterized in solution. Two‐electron reduction affords a Lewis base stabilized chloro‐stibinidene, whereas three‐electron reduction gives an antimony diatomic species capped by two carbenes. The radical has been characterized by EPR spectroscopy, while the structure of the other three species has been ascertained by single‐crystal X‐ray diffraction. In these four species, the formal oxidation state of the metalloid diminishes from III, to II, to I, and finally 0.     

A Zwitterionic Phosphonio‐1, 2, 4‐Diazaphospholide and Neutral 1, 2, 4‐Diazaphosphole — A Comparative Study of Molecular Structures and Co‐ordination Properties

The bis‐phosphonio‐1, 2, 4‐diazaphospholide salt ( 1 [Cl]) reacts with complex boron hydrides under selective extrusion of one PPh₃ moiety to give borane adducts of a novel zwitterionic phosphonio‐1, 2, 4‐diazaphospholide. Both the Et₃B adduct 2b and the free zwitterionic heterocycle 3 , which was liberated by further reaction of 2b with NEt₃, were characterized by spectroscopic data and 2b , as well, by a single crystal X‐ray diffraction study. The comparison of the structural data with those of a neutral 1, 2, 4‐diazaphosphole and a lithium‐1, 2, 4‐diazaphospholide which was formed by deprotonation of the parent 1, 2, 4‐diazaphosphole 4a discloses trends in endocyclic bonding distances which can be rationalized in terms of a charge dependent shift in the π‐electron distribution. First studies of the co‐ordination properties reveal for both 2b and 4a a marked preference to bind two M(CO)₅‐fragments (M = Cr, W) via the lone‐pairs of the phosphorus and one nitrogen atom; mononuclear complexes with P‐co‐ordinated heterocycles are formed as intermediates. A single crystal X‐ray diffraction study of the dinuclear complex [Cr₂(CO)₁₀(μ₂‐C₂H₃N₂P‐κP, κN)] ( 10a ) together with spectroscopic studies (including ¹⁸³W NMR studies of tungsten complexes) suggests that M→L back donation is more efficient for P‐ than for N‐bound metal fragments. No evidence for π‐co‐ordination of the 1, 2, 4‐diazaphosphole ring to a Cr(CO)₃ fragment was obtained.     

Synthesis and characterization of six‐arm star polystyrene‐block‐poly (3‐hexylthiophene) copolymer by combination of atom transfer radical polymerization and click reaction

A novel six‐arm star block copolymer comprising polystyrene (PS) linked to the center and π‐conjugated poly (3‐hexylthiophene) (P3HT) was successfully synthesized using a combination of atom transfer radical polymerization (ATRP) and click reaction. First, star‐shaped PS with six arms was prepared via ATRP of styrene with the discotic six‐functional initiator, 2,3,6,7,10,11‐hexakis(2‐bromoisobutyryloxy)triphenylene. Next, the terminal bromides of the star‐shaped PS were substituted with azide groups. Afterward, the six‐arm star block copolymer PS‐b‐P3HT was prepared using the click coupling reaction of azide‐terminated star‐shaped PS with alkynyl‐terminated P3HT. Various techniques including ¹H NMR, Fourier‐transform infrared and size‐exclusion chromatography were applied to characterize the chemical structures of the intermediates and the target block copolymers. Their thermal behaviors and optical properties were investigated using differential scanning calorimetry and UV–vis spectroscopy. Moreover, atomic force microscopy (AFM) was utilized to observe the morphology of the star block copolymer films. In comparison with two linear diblock copolymer counterparts, AFM results reveal the effect of the star block copolymer architecture on the microphase separation‐induced morphology in thin films. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ladder‐Type π‐Conjugated 4‐Hetero‐1,4‐dihydrophosphinines: A Structure–Property Study

π‐Conjugated six‐membered 1,4‐dihydrophosphinines containing a heteroatom (Si, P, S) at the 4 position were synthesized and systematically studied. X‐ray crystallographic analyses showed that the central six‐membered heterocyclic rings are almost planar. The sum of the angles around the phosphorus atom increases by 23° from the trivalent phosphorus to the phosphonium atom in the thiaphosphinine system, which is consistent with the NMR spectroscopic studies. UV/Vis spectroscopy and theoretical calculations revealed that the communication between the phosphorus center and the benzothiophene moiety is enhanced by the incorporation of a sulfur atom into the molecular scaffold. The increased conjugation endows the thiaphosphinines with interesting emission properties. Theoretical calculations supported the postulation that the orbital coupling between the π system and a σ* orbital could be enhanced in the thiaphosphinine system, especially through a phosphonium center. Cyclic voltammetry studies revealed that the thiaphosphinine oxide, thiaphosphonium, and cis‐diphosphinine oxide exhibit quasi‐reversible reduction processes, which demonstrate that simple changes in the bridge heteroatoms help to efficiently tune the redox properties of the ladder‐type 4‐hetero‐1,4‐dihydrophosphinines.     

Poly[aqua(μ2‐benzene‐1,4‐dicarboxylato)(μ2‐4,4′‐bipyridine N,N′‐dioxide)cadmium(II)], a threefold interpenetrating diamond net

In the title compound, [Cd(C₈H₄O₄)(C₁₀H₈N₂O₂)(H₂O)]_n, (I), each Cd^II atom is seven‐coordinated in a distorted monocapped trigonal prismatic coordination geometry, surrounded by four carboxylate O atoms from two different benzene‐1,4‐dicarboxylate (1,4‐bdc) anions, two O atoms from two distinct 4,4′‐bipyridine N,N′‐dioxide (bpdo) ligands and one water O atom. The Cd^II atom and the water O atom are on a twofold rotation axis. The bpdo and 1,4‐bdc ligands are on centers of inversion. Each crystallographically unique Cd^II center is bridged by the 1,4‐bdc dianions and bpdo ligands to give a three‐dimensional diamond framework containing large adamantanoid cages. Three identical such nets are interlocked with each other, thus directly leading to the formation of a threefold interpenetrated three‐dimensional diamond architecture. To the best of our knowledge, (I) is the first example of a threefold interpenetrating diamond net based on both bpdo and carboxylate ligands. There are strong linear O—H...O hydrogen bonds between the water molecules and carboxylate O atoms within different diamond nets. Each diamond net is hydrogen bonded to its two neighbors through these hydrogen bonds, which further consolidates the threefold interpenetrating diamond framework.     

Multistep π Dimerization of Tetrakis(n‐decyl)heptathienoacene Radical Cations: A Combined Experimental and Theoretical Study

Radical cations of a heptathienoacene α,β‐substituted with four n‐decyl side groups (D4T7 ^{. +}) form exceptionally stable π‐dimer dications already at ambient temperature (Chem. Comm. 2011 , 47, 12622). This extraordinary π‐dimerization process is investigated here with a focus on the ultimate [D4T7 ^{. +}]₂ π‐dimer dication and yet‐unreported transitory species formed during and after the oxidation. To this end, we use a joint experimental and theoretical approach that combines cyclic voltammetry, in situ spectrochemistry and spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The impact of temperature, thienoacene concentration, and the nature and concentration of counteranions on the π‐dimerization process is also investigated in detail. Two different transitory species were detected in the course of the one‐electron oxidation: 1) a different transient conformation of the ultimate [D4T7 ^{. +}]₂ π‐dimer dications, the stability of which is strongly affected by the applied experimental conditions, and 2) intermediate [D4T7]₂ ^{. +} π‐dimer radical cations formed prior to the fully oxidized [D4T7]₂ ^{. +} π‐dimer dications. Thus, this comprehensive work demonstrates the formation of peculiar supramolecular species of heptathienoacene radical cations, the stability, nature, and structure of which have been successfully analyzed. We therefore believe that this study leads to a deeper fundamental understanding of the mechanism of dimer formation between conjugated aromatic systems.     

The ability of Ex2Box4+ to interact with guests containing π‐electron‐rich and π‐electron‐poor moieties

The ability of Ex 2 Box⁴⁺ as a host, able to trap guests containing both π‐electron rich (polycyclic aromatic hydrocarbons‐PAHs) and π‐electron poor (quinoid‐ and nitro‐PAHs) moieties was investigated to shed light on the main factors that control the host–guest (HG) interaction. The nature of the HG interactions was elucidated by energy decomposition (EDA‐NOCV), noncovalent interaction (NCI), and magnetic response analyses. EDA‐NOCV reveals that dispersion contributions are the most significant to sustain the HG interaction, while electrostatic and orbital contributions are very tiny. In fact, no significant covalent character in the HG interactions was observed. The obtained results point strictly to NCIs, modulated by dispersion contributions. Regardless of whether the guests contain π‐electron‐rich or π‐electron‐poor moieties, and no significant charge‐transfer was observed. All in all, HG interactions between guests 3‐14 and host 2 are predominantly modulated by π‐π stacking.     

A Dicyanomethylene‐Substituted Triangulene: Effects of Molecular‐Symmetry Reduction and Electron‐Accepting Substituents on a Fused Polycyclic Neutral π‐Radical System

A triangulene‐based C₂‐symmetric 33 π‐conjugated stable neutral π‐radical, 2^. , which possesses two dicyanomethylene groups and one oxo group, has been designed, synthesized, and isolated as an analogue of tris(dicyanomethylene) derivative 1^. and trioxo derivative TOT^. with C₃ symmetry. Effects of molecular‐symmetry reduction and electron‐accepting substituents on this fused polycyclic neutral π‐radical system were studied in terms of their molecular structure, electronic‐spin structure, and electrochemical and optical properties with the help of theoretical calculations. Interestingly, this system ( 2^. ) has a four‐stage redox ability, like TOT^. , as well as low frontier energy levels and a small SOMO–LUMO gap, similar to 1^. , in spite of the loss of the degenerate LUMOs in symmetry‐lowered 2^. , which is associated with the attachment of the weaker electron‐accepting oxo group instead of the dicyanomethylene group in 1^. . These prominent results are attributable to the structural and electronic properties in the triangulene‐based highly delocalized fused polycyclic neutral π‐radical system.     

All‐Metal Antiaromaticity in Sb4‐Type Lanthanocene Anions

Antiaromaticity, as introduced in 1965, usually refers to monocyclic systems with 4n π electrons. This concept was extended to all‐metal molecules after the observation of Li₃Al₄^? in the gas phase. However, the solid‐phase counterparts have not been documented to date. Herein, we describe a series of all‐metal antiaromatic anions, [Ln(η⁴‐Sb₄)₃]^3?(Ln=La, Y, Ho, Er, Lu), which were isolated as the K([2.2.2]crypt) salts and identified by single‐crystal X‐ray diffraction. Based on the results obtained from the chemical bonding analysis, multicenter indices, and the electron‐counting rule, we conclude that the core [Ln(η⁴‐Sb₄)₃]^3? fragment of the crystal has three locally π‐antiaromatic Sb₄ fragments. This complex represents the first locally π‐antiaromatic all‐metal system in the solid state, which is stabilized by interactions of the three π‐antiaromatic units with the central metal atom.     

Calculated geometries of dications of bis odd‐membered π‐ring systems containing a NCN fragment and related π‐systems. An opposite out‐of‐plane rotation of the 4n π‐ring subsystems

Quantum chemical calculations have been carried out on dications of bis odd‐membered π‐ring systems containing a NCN fragment and related π‐systems. An opposite out‐of‐plane rotation of both subsystems was found if these systems contain 4n π‐electrons (antiaromatic). A planar situation was found for 4n+2 π‐electrons (aromatic). The geometric representations could be compared with X‐ray crystallographic three‐dimensional structures of related compounds. Calculations at different levels clearly show that separation of the σ‐ and π‐electron contribution is an effective way to elucidate the origin of the geometrical changes. We also give attention to some fundamental aspects of the subsystems related to the 1,3‐azolium cations because of their biochemical relevance such as fast C₂? H proton exchange. We postulate that at least two molecules of water are involved in this process. The significance of a trigonal pyramidal (TP) geometry has been emphasized. © 2001 Wiley Periodicals, Inc. Int J Quantum Chem, 2001     

Multi‐input–Multi‐output Molecular Response System Based on Dynamic Redox Behavior of Hexaphenylethane‐type Electron Donors with the Tetrahydrophenanthrazepine Skeleton: Strong Chiroptical Signals through the Transmission of Point Chirality to Helicity

The title heterocyclic donors undergo reversible C? C bond formation/cleavage upon electron transfer (dynamic redox behavior). The helical sense in both neutral and cationic states is interconvertible by facile ring flipping. The π‐type asymmetric center on the azepine nitrogen atom induces a significant degree of diasteromeric preference, thus endowing strong CD activity based on exciton coupling. Chiroptical properties could be modified not only by redox reactions but also by heat and protonation. The present redox pairs can serve as unprecedented three‐way‐input (e, H⁺, Δ) and two‐way‐output (UV/Vis, CD) response systems.     

Phosphonio‐benzophospholide Zwitterions as Bridging 8e‐Donor Ligands: Synthetic and Mechanistic Studies

Reactions of the phosphonio‐benzophospholide π‐complexes 3a, b[Cr] with [M(CO)₅(olefin)] or of the σ‐complexes 2a, b[M] (M = Cr, Mo, W) with [M(CO)₃(aren)] lead to the first binuclear complexes 4a, b[CrM] featuring phosphonoio‐benzophospholides as μ‐bridging 8e‐donor ligands to two group 6 metal atoms. The constitution of the products was determined by spectroscopic and X‐ray diffraction studies. Mixed complexes with both group 6 and 7 metals were not accessible. Mechanistic studies showed that the reactions follow a complicated mechanism whose single steps may involve transfer of either M(CO)_n fragments or single CO ligands between complexes; the latter are associated with a σ/π‐coordination isomerization of the benzophospholide unit. Competition between both reaction channels can lead to the formation of product mixtures whose composition is controlled by the relative thermodynamic stabilities of the products. Computational studies suggest that in the more stable isomer of heterobimetallic complexes 4a, b[MM′] end‐on coordination to the heavier and side‐on coordination to the lighter metal atom is preferred.     

Nanofiltration membranes based on poly(vinylidene fluoride‐co‐chlorotrifluoroethylene)‐graft‐poly(styrene sulfonic acid)

Graft copolymers comprising poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) backbone and poly(styrene sulfonic acid) side chains, i.e. P(VDF‐co‐CTFE)‐g‐PSSA were synthesized using atom transfer radical polymerization (ATRP) for composite nanofiltration (NF) membranes. Direct initiation of the secondary chlorinated site of CTFE units facilitates grafting of PSSA, as revealed by FT‐IR spectroscopy. The successful “grafting from” method and the microphase‐separated structure of the graft copolymer were confirmed by transmission electron microscopy (TEM). Wide angle X‐ray scattering (WAXS) also showed the decrease in the crystallinity of P(VDF‐co‐CTFE) upon graft copolymerization. Composite NF membranes were prepared from P(VDF‐co‐CTFE)‐g‐PSSA as a top layer coated onto P(VDF‐co‐CTFE) ultrafiltration support membrane. Both the rejections and the flux of composite membranes increased with increasing PSSA concentration due to the increase in SO₃H groups and membrane hydrophilicity, as supported by contact angle measurement. The rejections of NF membranes containing 47 wt% of PSSA were 83% for Na₂SO₄ and 28% for NaCl, and the solution flux were 18 and 32 L/m² hr, respectively, at 0.3 MPa pressure. Copyright © 2008 John Wiley & Sons, Ltd.     

Independent Generation and Time‐Resolved Detection of 2′‐Deoxyguanosin‐N2‐yl Radicals

Guanine radicals are important reactive intermediates in DNA damage. Hydroxyl radical (HO^.) has long been believed to react with 2′‐deoxyguanosine (dG) generating 2′‐deoxyguanosin‐N1‐yl radical (dG(N1‐H)^.) via addition to the nucleobase π‐system and subsequent dehydration. This basic tenet was challenged by an alternative mechanism, in which the major reaction of HO^. with dG was proposed to involve hydrogen atom abstraction from the N2‐amine. The 2′‐deoxyguanosin‐N2‐yl radical (dG(N2‐H)^.) formed was proposed to rapidly tautomerize to dG(N1‐H)^.. We report the first independent generation of dG(N2‐H)^. in high yield via photolysis of 1 . dG(N2‐H)^. is directly observed upon nanosecond laser flash photolysis (LFP) of 1 . The absorption spectrum of dG(N2‐H)^. is corroborated by DFT studies, and anti‐ and syn‐dG(N2‐H)^. are resolved for the first time. The LFP experiments showed no evidence for tautomerization of dG(N2‐H)^. to dG(N1‐H)^. within hundreds of microseconds. This observation suggests that the generation of dG(N1‐H)^. via dG(N2‐H)^. following hydrogen atom abstraction from dG is unlikely to be a major pathway when HO^. reacts with dG.     

Thiophene‐Based,Radial π‐Conjugation: Synthesis,Structure, and Photophysical Properties of Cyclo‐1,4‐phenylene‐2′,5′‐thienylenes

The synthesis of cyclo‐1,4‐phenylene‐2′,5′‐thienylenes (CPTs) as the first example of a thiophene‐based, radially π‐conjugated system is described. X‐ray crystal structures, UV‐vis absorption and emission spectra, and theoretical studies revealed the unique structural and photophysical properties of CPTs. With all of these unique structural and photophysical properties, the radially π‐conjugated CPTs are expected to open a door for the discovery and development of new functional organic materials.