Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C60 and Triphenylamine–Corrole‐C60 Donor–Acceptor Conjugates

Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C₆₀ , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C₆₀) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C₆₀ . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from ¹ TPA* to the corrole and subsequent electron transfer from ¹corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor^?+ in Cor‐C₆₀ and TPA‐Cor^?+ in TPACor‐C₆₀ ) and fullerene radical anion (C₆₀^??), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k_CS, was found to be about 10¹¹ s^?1, suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k_CS, the rate of charge recombination, k_CR, was also found to be rapid (k_CR≈10¹⁰ s^?1), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of ³corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of ³corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.     

Photoelectron—photoion-coincidence measurements on 2,4-hexadiyne

2,4-Hexadiyne cations in their first excited electronic state òE_ureveal a decay by an effective competition between fluorescence and fragmentation. The present photoelectron—photoion-coincidence study of 2,4-hexadiyne cation provides individual breakdown diagrams for the parent ion and the seven dominant fragment ions, C₆H₅⁺, C₆H₄⁺, C₅H₃⁺, C₄H₄⁺, C₄ H₃⁺, C₄H₂⁺, C₃H₃⁺ in the ionisation energy regions populated by He(Iα) excitation. Additional information concerning the rate constants and the kinetic energy released on the formation of C₆H₅⁺ and C₄H₃⁺ are deduced from the time-of-flight (TOF) distributions of these ions. The appearance potentials for the two fragments C₄H₃⁺ and C₄H₂⁺ could also be measured, as these lie well within the third band of the He(Iα)-PE spectrum.     

A photo-ionization study of organosulfur ring compounds: Thiirane,thietane and tetrahydrothiophene

The gas phase heats of formation of several organosulfur cations were determined from thiirane, thietane and tetrahydrothiophene precursor molecules by photoionization mass spectrometry. Heats of formation at 0 K and 298 K are reported for the following ions: [H₂CS]^+˙, [H₃CS]⁺, [C₂H₃S]⁺, [C₂H₄S]^+˙, [C₃H₅S]⁺, [C₃H₆S]^+˙, [C₄H₇S]⁺ and [C₄H₈S]^+˙. The [C₄H₇S]⁺ (m/z 87), [C₂H₄S]^+˙ (m/z 60), [C₂H₃S]⁺ (m/z 59), [C₄H₇]⁺ (m/z 55), [C₄H₆]^+˙ (m/z 54) and [CH₂S]^+˙ (m/z 46) ions are produced from metastable tetrahydrothiophene ions at photon energies between 10.2 and 10.7 eV. Decay rates of internal energy selected parent ions to the m/z 60, 59, 55 and 54 fragments were measured by threshold photoelectron-photoion coincidence, the results of which are compared to statistical theory (RRKM/QET) calculations. The [C₂H₄S]^+˙ ion from tetrahydrothiophene is found to have the thioacetaldehyde structure. From the measured [C₂H₄S]^+˙ onset a ΔH = 50±8 kJ mol^?1 was calculated for the thioacetaldehyde molecule.     

Strongly Phosphorescent Neutral Rhenium(I) Isocyanoborato Complexes: Synthesis,Characterization, and Photophysical,Electrochemical, and Computational Studies

A new series of neutral isocyanoborato rhenium(I) diimine complexes [Re(CO)₃(N^N)(CNBR₃)], where N^N=bpy, 4,4′‐Me₂bpy, phen, 4,7‐Me₂phen, 2,9‐Me₂phen, 3,4,7,8‐Me₄phen; R=C₆F₅, C₆H₅, Cl, 4‐ClC₆H₄, 3,5‐(CF₃)₂C₆H₃, with various isocyanoborate and diimine ligands of diverse electronic and steric nature have been synthesized and characterized. The X‐ray crystal structures of six complexes have also been determined. These complexes displayed intense bluish green to yellow phosphorescence at room temperature in dichloromethane solution. The photophysical and electrochemical properties of these complexes had been investigated. To elucidate the electronic structures and transitions of these complexes, DFT and TD‐DFT calculations have been performed, which revealed that the lowest‐energy electronic transition associated with these complexes originates from a mixture of MLCT [dπ(Re)→π*(N^N)] and LLCT [π(CNBR₃)→π*(N^N)] transitions.     

Study of Electronic,Optical Absorption and Emission in Pure and Metal‐Decorated Graphene Nanoribbons (C29H14‐X; X=Ni,Fe, Ti,Co+, Al+, Cu+): First Principles Calculations

Density functional theory (DFT) and time‐dependent density functional theory (TDDFT) calculations were performed with the basis sets 6‐31G for DFT and 6‐31G(d), 6‐31+G(d,p) for TDDFT on pure graphene nanoribbon (GNR) C₃₀H₁₄ and metal‐decorated C₂₉H₁₄‐X (MGNRs; X=Ni, Fe, Ti, Co⁺, Al⁺, and Cu⁺). The metal/carbon ratio (X:C 3.45 %) and the doping site were fixed. Electronic properties, that is, the dipole moment, binding energy, and HOMO–LUMO gaps, were calculated. The absorption and emission properties in the visible range (λ=400–720 nm) were determined. Optical gaps, absorption and emission wavelengths, oscillator strengths, and dominant transitions were calculated. Pure graphene was found to be the most stable form. However, of the MGNRs, C₂₉H₁₄?Co⁺ and C₂₉H₁₄?Al⁺ were found to be the most and least stable, respectively. All GNRs were found to have semiconducting nature. The optical absorption of pure graphene undergoes a shift on metal doping. Emission from the pure graphene followed Kasha′s rule, unlike the metal‐doped GNRs.     

Mixed‐Valence Ruthenium Complexes Rotating through a Conformational Robin–Day Continuum

The conformational energy landscape and the associated electronic structure and spectroscopic properties (UV/Vis/near‐infrared (NIR) and IR) of three formally d⁵/d⁶ mixed‐valence diruthenium complex cations, [{Ru(dppe)Cp*}₂(μ‐C≡CC₆H₄C≡C)]⁺, [ 1 ]⁺, [trans‐{RuCl(dppe)₂}₂(μ‐C≡CC₆H₄C≡C)]⁺, [ 2 ]⁺, and the Creutz–Taube ion, [{Ru(NH₃)₅}₂(μ‐pz)]⁵⁺, [ 3 ]⁵⁺ (Cp=cyclopentadienyl; dppe=1,2‐bis(diphenylphosphino)ethane; pz=pyrazine), have been studied using a nonstandard hybrid density functional BLYP35 with 35 % exact exchange and continuum solvent models. For the closely related monocations [ 1 ]⁺ and [ 2 ]⁺, the calculations indicated that the lowest‐energy conformers exhibited delocalized electronic structures (or class III mixed‐valence character). However, these minima alone explained neither the presence of shoulder(s) in the NIR absorption envelope nor the presence of features in the observed vibrational spectra characteristic of both delocalized and valence‐trapped electronic structures. A series of computational models have been used to demonstrate that the mutual conformation of the metal fragments—and even more importantly the orientation of the bridging ligand relative to those metal centers—influences the electronic coupling sufficiently to afford valence‐trapped conformations, which are of sufficiently low energy to be thermally populated. Areas in the conformational phase space with variable degrees of symmetry breaking of structures and spin‐density distributions are shown to be responsible for the characteristic spectroscopic features of these two complexes. The Creutz–Taube ion [ 3 ]⁵⁺ also exhibits low‐lying valence‐trapped conformational areas, but the electronic transitions that characterize these conformations with valence‐localized electronic structures have low intensities and do not influence the observed spectroscopic characteristics to any notable extent.     

Collisional activation study of cyclic polysulfides

Cyclic polysulfides isolated from higher plants, model compounds and their electron impact induced fragment ions have been investigated by various mass spectrometric methods. These species represent three sets of sulfur compounds: C₃H₆S_x (x=1?6), C₂H₄S_x (x=1?5) and CH₂S_x (x=1?4). Three general fragmentation mechanisms are discussed using metastable transitions: (1) the unimolecular loss of structural parts (CH₂S, CH₂ and S_x); (2) fragmentations which involve ring opening reactions, hydrogen migrations and recyclizations of the product ions ([M? CH₃]⁺, [M? CH₃S]⁺, [M? SH]⁺ and [M? CS₂]^+˙); and (3) complete rearrangements preceding the fragmentations ([M? S₂H]⁺ and [M? C₂H₄]^+˙). The cyclic structures of [M]^+˙ and of specific fragment ions have been investigated by comparing the collisional activation spectra of model ions. On the basis of these results the cyclic ions decompose via linear intermediates and then recyclizations of the product ions occur. The stabilities of the fragment ions have been determined by electron efficiency vs electron energy curves.     

Zur Koordinationschemie des Rhenium(VII). V. Trioxo-trichlororhenate(VII) mit stickstoffhaltigen Kationen

Coordination Chemistry of Rhenium(VII). V. Trioxotrichlororhenates(VII) with Nitrogen-containing Cations Complex compounds of the composition A₂ReO₃C₃ were obtained by reaction of ReO₃Cl with the chlorides ACl (A = (CH₃)₄N⁺, (C₂H₅)₄N⁺, PyH⁺, ChinH⁺ (CH₃)₃NH⁺ and CH₃Py⁺) in inert solvents. It has been decuced from the Re? O stretching vibrations of the IR spectra, that the anion ReO₃Cl in connection with the cations (CH₃)₄N⁺ resp. (C₂H₅)₄N⁺ has the symmetry C_3v (cis-configuration). It is probable, that in cations including a NH-group a decrease of the symmetry towards C_s arises by means of the hydrogen bondings.     

Positive chemical ionization triple‐quadrupole mass spectrometry and ab initio computational studies of the multi‐pathway fragmentation of phthalates

We report the first positive chemical ionization (PCI) fragmentation mechanisms of phthalates using triple‐quadrupole mass spectrometry and ab initio computational studies using density functional theories (DFT). Methane PCI spectra showed abundant [M + H]⁺, together with [M + C₂H₅]⁺ and [M + C₃H₅]⁺. Fragmentation of [M + H]⁺, [M + C₂H₅]⁺ and [M + C₃H₅]⁺ involved characteristic ions at m/z 149, 177 and 189, assigned as protonated phthalic anhydride and an adduct of phthalic anhydride with C₂H₅⁺ and C₃H₅⁺, respectively. Fragmentation of these ions provided more structural information from the PCI spectra. A multi‐pathway fragmentation was proposed for these ions leading to the protonated phthalic anhydride. DFT methods were used to calculate relative free energies and to determine structures of intermediate ions for these pathways. The first step of the fragmentation of [M + C₂H₅]⁺ and [M + C₃H₅]⁺ is the elimination of [R? H] from an ester group. The second ester group undergoes either a McLafferty rearrangement route or a neutral loss elimination of ROH. DFT calculations (B3LYP, B3PW91 and BPW91) using 6‐311G(d,p) basis sets showed that McLafferty rearrangement of dibutyl, di(‐n‐octyl) and di(2‐ethyl‐n‐hexyl) phthalates is an energetically more favorable pathway than loss of an alcohol moiety. Prominent ions in these pathways were confirmed with deuterium labeled phthalates. Copyright © 2010 John Wiley & Sons, Ltd.     

Conformer-Specific Dissociation Dynamics in Dimethyl Methylphosphonate Radical Cation

The dynamics of the dimethyl methylphosphonate (DMMP) radical cation after production by strong field adiabatic ionization have been investigated. Pump-probe experiments using strong field 1300 nm pulses to adiabatically ionize DMMP and a 800 nm non-ionizing probe induce coherent oscillations of the parent ion yield with a period of about 45 fs. The yields of two fragments, PO₂C₂H₇⁺ and PO₂CH₄⁺, oscillate approximately out of phase with the parent ion, but with a slight phase shift relative to each other. We use electronic structure theory and nonadiabatic surface hopping dynamics to understand the underlying dynamics. The results show that while the cation oscillates on the ground state along the P=O bond stretch coordinate, the probe excites population to higher electronic states that can lead to fragments PO₂C₂H₇⁺ and PO₂CH₄⁺. The computational results combined with the experimental observations indicate that the two conformers of DMMP that are populated under experimental conditions exhibit different dynamics after being excited to the higher electronic states of the cation leading to different dissociation products. These results highlight the potential usefulness of these pump-probe measurements as a tool to study conformer-specific dynamics in molecules of biological interest.     

Mass spectrometry of π-complexes of transition metals : XVII. Ionm̄olecule reaction products in mass spectra of mixtures of π-cyclopentadienyl- and π-arenemetal carbonyls with aromatic and heterocyclic compounds

Ion—molecule reactions occur in the ionization chamber of a mass spectrometer during the combined vaporization of arenechromium tricarbonyls (ArCr(CO)₃, Ar = C₆H₆, C₆H₅Cl, C₆H₅N(CH₃)₂, C₄H₄S, C₄H₄Se) and cyclopentadienylmetal carbonyls (C₅H₄RM(CO)_n, M and R = Mn, H;Mn, Cl; Mn, Br; Mn, COCH₃; Re, H; V, H) with various aromatic and heterocyclic compounds (L). In all cases secondary ions of sandwich type [ArCrL]⁺ or [C₅H₄RML]⁺ containing a new metalligand bond are formed.     

Two anilinium salts: anilinium hydrogenphosphite and anilinium hydrogenoxalate hemihydrate

In the title compounds, C₆H₅NH₃⁺·H₂PO₃^? and C₆H₅NH₃⁺·C₂HO₄^?·0.5H₂O, the NH₃⁺ groups of the anilinium ion are ordered at room temperature. The rotation of these groups along the N—C_aryl bond, which is often observed at room temperature in other anilinium compounds, is prevented by hydrogen bonds between the NH₃⁺ group and the anions. In both compounds, the geometry of the cation is significantly distorted from D_6h to a symmetry close to C_2v. The angle ipso to the substituent is significantly larger than 120°, as expected from the σ‐electron‐withdrawing character of the NH₃⁺ group.     

Bis(tetra‐n‐butylammonium) (a redetermination at 150 K) and bis(tetraphenylarsonium) bis(1,3‐dithiole‐2‐thione‐4,5‐dithiolato)zinc(II) (at 300 K)

The title compounds are salts of the general form (Q⁺)₂[Zn(dmit)₂]^2?, where dmit corresponds to the ligand (C₃S₅)^? present in both and Q⁺ to the counter‐cations (ⁿBu₄N)⁺ [or C₁₆H₃₆N⁺] and (Ph₄As)⁺ [or C₂₄H₂₀As⁺], respectively. In the first case, Zn is in the 4e special positions of space group C2/c and hence the [Zn(dmit)₂]^2? dianion possesses twofold axial crystallographic symmetry. Including these, there are now 11 known examples of [Zn(dmit)₂]^2? or its analogues, with O replacing the exocyclic thione S, and [Zn(dmio)₂]^2? dianions in nine structures with various Q. Comparison of these reveals a remarkable variation in details of the conformation which the dianion may adopt in terms of Zn coordination, equivalence of the Zn—S bond lengths, displacement of Zn from the plane of the ligand and overall dianion shape.     

Mass spectrometry of homoadamantane derivatives

Homoadamantane derivatives can be divided into two groups according to their mass spectra. To the first group belong compounds with electron attracting substituents (COOH, CI, COOCH₃, Br); compounds with electron releasing substituents (OCH₃, OH, NH₃, NHCOCH₃) constitute the second group. The most characteristic feature of the first group compounds is the splitting off of the substituent. The hydrocarbon fragment [C₁₁H₁₇]⁺ thus formed then loses olefin molecules with the formation of corresponding ionic species C_11?nH_17?2n. The 3-substituted compounds of this group undergo thermal Wagner-Meerwein type rearrangements into adamantane derivatives, resulting in the [C₁₀H₁₅]⁺ (m/e 135) ion formation; this is the main difference between 1- and 3-substituted homoadamantanes. The series of [C_nH_2n?6X]⁺ ions (where X = OCH₃, OH, NH₂, NHCOCH₃, n = 6 to 10) are characteristic of the mass spectra of the second group compounds, the ion [C₆H₆X]⁺, [M ? C₅H₁₁]⁺ being the most abundant. The intensity ratio of [M ? C₅H₁₁]⁺ to [M ? C₄H₉]⁺ ions is 10:1 for 1-substituted and 3:1 for 3-substituted compounds of this group, allowing the location of the substituent. Some individual features of the spectra are also reported.     

Synthesis, Raman, X-ray diffraction, and density functional studies of antimony(III) heterotetracycles displaying intramolecular transannular interactions O → Sb

A set of compounds of general formula [{S(C₆H₃S)₂O}SbHal] [Hal = Cl (1), Br (2), I (3)] has been synthesized and studied by Raman and NMR spectroscopy as well as quantum chemical DFT calculations. X-ray diffraction studies of compound 2 revealed that the oxygen atom participates as donor and the antimony atom plays the role of acceptor, adopting a Ψ-distorted trigonal bi-pyramidal geometry, where the eight-membered central ring displays a boat–boat conformation. Furthermore, a series of DFT calculations was performed on compounds 1–3 as well as calculations on the non-synthesized heterotetracyclic systems [{S(C₆H₃S)₂O}SbF] (4a) and the cation [{S(C₆H₃S)₂O}Sb]⁺ (5a). The theoretic study at DFT level indicates as the electronegativity increases at exocyclic substituent along the set of compounds, the interaction is stronger. Moreover, the topological analysis of electronic density showed the existence of critical points along the O → Sb direction which prompted us to suggest the existence of a dative bond.     

Cationic Niobium-Sandwich and Piano-Stool Complexes

The syntheses of the homoleptic bis(arene) niobium cations [Nb(arene)₂]⁺ (arene = C₆H₃Me₃, C₆H₅Me) with 16 valence electrons and heteroleptic arene-carbonyl cations [(CO)Nb(arene)₂]⁺ (arene = C₆H₃Me₃, C₆H₅Me) and [(arene)M(CO)₄]⁺ (arene = C₆H₃Me₃, C₆H₆) obeying 18 valence electrons are described. Stabilization of these complexes was achieved by using the weakly coordinating anions [Al(OR^F)₄]⁻ or [F{Al(OR^F)₃}₂]⁻ (R^F = C(CF₃)₃). The limits of two synthesis routes starting from neutral Nb(arene)₂ (arene = C₆H₃Me₃, C₆H₅Me) or [NEt₄][M(CO)₆] (M = Nb, Ta) were investigated. All compounds were analyzed by single crystal X-ray determination, vibrational and NMR spectroscopy. DFT calculations were executed to support the experimental data.     

Calorimetric studies on phase transitions arising from orientational order-disorder of the molecular axes of ferrocene and its derivatives

Heat capacities of the channel inclusion compound, Fe(C₅D₅)₂ · 3(NH₂)₂CS, and two ferrocenium salts, [Fe(C₅H₅)(C₆H₆)]⁺ (PF₆)⁻ and [Fe(C₅H₅)₂]⁺ (PF₆)⁻, have been measured with adiabatic calorimeters between 13 and 393 K. Five phase transitions were found for Fe(C₅D₅)₂ · 3(NH₂)₂CS corresponding to those for Fe(C₅H₅)₂ · 3(NH₂)₂CS. The dominant phase transitions at 145.8 and 160.6 K are responsible for the onset of reorientational order-disorder of the molecular axis of Fe(C₅D₅)₂ in the clathrate cavity. The mass-effect of the guest ferrocene molecule on the phase transitions was not remarkable. The ferrocenium salt, [Fe(C₅H₅)(C₆H₆]⁺(PF₆)⁻, exhibited four phase transitions and two glass transition phenomena at low temperatures while its analog, [Fe(C₅H₅)₂]⁺(PF₆)⁻, brought about only three phase transitions without showing the glass transition. The higher-temperature phase transitions in these two salts have been assigned to the reorientational order-disorder mechanism of the molecular axes of the cations in the pseudo-cavities formed by eight PF⁻₆ anions. For the origin of the lower-temperature phase transitions in these two salts, three possibilities have been discussed. Among them, plausible origin is likely to be an order-disorder change of PF⁻₆ anion in the lattice. An important unsettled problem common to these three compounds is a question whether or not the Fe(C₅D₅)₂ and the cations, [Fe(C₅H₅)(C₆H₆)]⁺ and [Fe(C₅H₅)₂]⁺, are still reorienting around their molecular axes even at the lowest-temperature phase.     

Nascent Rotational Distributions of MgH in Reaction of Mg(4s 1S0) with H2 and HD

The nascent rotational distributions of MgH(X²σ⁺, v″ = 0, 1) resulting from the reaction of Mg(4s¹S₀) with H₂ and HD have been determined by using the laser pump-probe technique. Like the case of Mg(¹P₁), the distributions appear to be bimodal which peak mainly at high N(26) with minor peaks at low N(6). There are no apparent differences when the escaping mass is doubled. The similarity between product rotational distributions from the 4S state and those from the 3P state, and no evidence of a kinematic isotope effect, reveal that a harpoon-type mechanism may be operative. Our ab initio calculations reveal that in the entrance channel on the 3¹A₁ surface in C_2v symmetry or ¹σ⁺ surface in C_∞v symmetry for 4S state, the reaction may lake place via a series of non-adiabatic curve crossings with the ionic Mg⁺H₂^? potential surface.     

Isolation of a Three‐Coordinate Boron Cation with a Boron–Sulfur Double Bond

The reaction of the bulky bis(imidazolin‐2‐iminato) ligand precursor (1,2‐(L^MesNH)₂‐C₂H₄)[OTs]₂ ( 1 ²⁺ 2[OTs]^?; L^Mes=1,3‐dimesityl imidazolin‐2‐ylidene, OTs=p‐toluenesulfonate) with lithium borohydride yields the boronium dihydride cation (1,2‐(L^MesN)₂‐C₂H₄)BH₂[OTs] ( 2 ⁺ [OTs]^?)_. The boronium cation 2 ⁺ [OTs]^? reacts with elemental sulfur to give the thioxoborane salt (1,2‐(L^MesN)₂‐C₂H₄)BS[OTs] ( 3 ⁺ [OTs]^?). The hitherto unknown compounds 1 ²⁺ 2[OTs]^?, 2 ⁺ [OTs]^?, and 3 ⁺ [OTs]^? were fully characterized by spectroscopic methods and single‐crystal X‐ray diffraction. Moreover, DFT calculations were carried out to elucidate the bonding situation in 2 ⁺ and 3 ⁺. The theoretical, as well as crystallographic studies reveal that 3 ⁺ is the first example for a stable cationic complex of three‐coordinate boron that bears a B?S double bond.     

Electron impact studies. CXII—The properties of positive ions produced by charge stripping from negative ions. [C6H5O]+, [C6H5S]+ and [C7H7S]+

The dissociative spectrum of the [C₆H₅S]⁺ ion derived by charge inversion from [C₆H₅S]^?, shows a variety of fragmentations including the competitive losses of H?, C₃H₄ and the formation of [CHS]⁺. The spectrum of a deuteriated derivative shows that these three processes are preceded or accompanied by H/D scrambling. The corresponding [C₆H₅O]⁺ species also undergoes hydrogen scrambling prior to fragmentation. In marked contrast, the ion [p-MeC₆H₄S]⁺ does not undergo hydrogen randomization between the methyl and aryl groups, and positional integrity is retained during fragmentation. These results are compared with the properties of the same ions produced by conventional ionization.