Tricationic States Research Articles

Reversible Multielectron Release from Redox-Active Three-Dimensional Molecular Barrels with Ruthenium-Alkenyl Moieties.

Three-dimensional molecular barrels Ru6-4 and Ru6-5 were synthesized in high yields from dinuclear ruthenium-vinyl clamps and tritopic triphenylamine-derived carboxylate linkers and characterized by multinuclear NMR spectroscopy including 1H-1H COSY and 1H DOSY measurements, high-resolution electrospray ionization mass spectrometry, and X-ray crystallography. The metal frameworks of the cages adopt the shape of twisted trigonal prisms, and they crystallize as racemic mixtures of interdigitating Δ- and Λ-enantiomers with a tight columnar packing in Ru6-4. Electrochemical studies and redox titrations revealed that the cages are able to release up to 11 electrons on the voltammetric timescale and that their cage structures persist up to the hexacation level. IR and UV-vis-near-infrared spectroelectrochemical studies confirm substituent-dependent intramolecular electronic communication within the π-conjugated 1,3-divinylphenylene backbone in the tricationic states, where all three divinylphenylene-bridged diruthenium clamps are present in mixed-valent radical cation states. The formation of 1:3 charge-transfer salts with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as the electron acceptor is also demonstrated.

Shuttling Rates, Electronic States, and Hysteresis in a Ring-in-Ring Rotaxane.

The trisradical recognition motif between a 4,4′-bipyridinium radical cation and a cyclo-bis-4,4′-bipyridinium diradical dication has been employed previously in rotaxanes to control their nanomechanical and electronic properties. Herein, we describe the synthesis and characterization of a redox-active ring-in-ring [2]rotaxane BBR·8PF6 that employs a tetraradical variant of this recognition motif. A square-shaped bis-4,4′-bipyridinium cyclophane is mechanically interlocked around the dumbbell component of this rotaxane, and the dumbbell itself incorporates a smaller bis-4,4′-bipyridinium cyclophane into its covalently bonded structure. This small cyclophane serves as a significant impediment to the shuttling of the larger ring across the dumbbell component of BBR8+, whereas reduction to the tetraradical tetracationic state BBR4(+•) results in strong association of the two cyclophanes driven by two radical-pairing interactions. In these respects, BBR·8PF6 exhibits qualitatively similar behavior to its predecessors that interconvert between hexacationic and trisradical tricationic states. The rigid preorganization of two bipyridinium groups within the dumbbell of BBR·8PF6 confers, however, two distinct properties upon this rotaxane: (1) the rate of shuttling is reduced significantly relative to those of its predecessors, resulting in marked electrochemical hysteresis observed by cyclic voltammetry for switching between the BBR8+/BBR4(+•) states, and (2) the formally tetraradical form of the rotaxane, BBR4(+•), exhibits a diamagnetic ground state, which, as a result of the slow shuttling motions within BBR4(+•), has a long enough lifetime to be characterized by 1H NMR spectroscopy.

Synthesis, Structures, and Electrochemical Properties of New Extensively Conjugated TTF

Abstract Extensively conjugated tetrathiafulvalene (TTF) derivatives substituted with a TTF-fused 1,4-dithiafulven-6-yl group 4 have been synthesized. Theoretical calculation and X-ray crystal structure analysis of 4a demonstrated that the conformation A, in which the two TTF units are linearly oriented, is slightly more stable than the conformation B, which adopted orthogonal arrangement of two TTF units in the neutral state. Cyclic voltammetry revealed the presence of the intramolecular 1,5-S···S interaction that brings about the stabilization of the conformation B in the tricationic state.

Vibrational dynamics in dendridic oligoarylamines by Raman spectroscopy and incoherent inelastic neutron scattering.

Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent inelastic neutron scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C-H motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selection rules and the local geometry of the dendrimers yielding mainly C-C and C-N deformation modes with those of C-H nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some inhomogeneity of the oxidation.

ChemInform Abstract: ESR of the Cationic Triradical of 1,3,5-Tris(diphenylamino)benzene.

The ESR spectrum of the cationic triradical of 1,3,5-tris(diphenylamino)benzene (TDAB) is discussed. The tricationic state of TDAB was observed by means of cyclic voltammetry. The orange cationic triradical was prepared by oxidation of TDAB with trifluoroacetic anhydride in the presence of tetra-n-butylammonium tetrafluoroborate in CH 2 Cl 2 . The ESR spectrum of the randomly oriented radicals in the CH 2 Cl 2 glass agrees well with the theoretical prediction of a quartet (S=3/2) spin state with a zero-field splitting parameter D' of 13.1 G (0.0012 cm -1 )

Interatomic Coulombic decay and its dynamics in NeAr following K-LL Auger transition in the Ne atom

We analyze in detail the accessible relaxation pathways via electron emission of the Ne2+Ar states populated via the K-LL Auger decay of Ne+(1s−1)Ar. In particular, we concentrate on the “direct” interatomic Coulombic decay (ICD) of the Ne2+(2s−12p−1)Ar weakly bound doubly ionized states into the manifold of the Ne2+(2p−2)–Ar+(3p−1) repulsive triply ionized ones. To carry out the present study the potential energy curves of the NeAr ground state, the core ionized state Ne+(1s−1)Ar, the relevant dicationic and tricationic states, and the corresponding ICD transition rates have been computed using accurate ab initio methods and basis sets. The total and partial ICD electron spectra are computed within the framework of the time-dependent theory of wave packet propagation. Thereby, the impact of nuclear dynamics accompanying the electronic decay on the computed ICD-electron spectra is investigated in detail.

Amine-based organic high-spin systems; a room-temperature-stable one-dimensional oligoaryl triamine-based trication

A triamine, 2,2′,4,4′-tetrabromo-3″,4″-dimethyl-5,5′-bis(di(4-methylphenyl)amino)triphenylamine, was designed and synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurements revealed that the triamine gives stable mono-, di-, and tricationic states at ambient temperature. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triamine-based trication was generated by chemical oxidation at room temperature, and the triamine was quantitatively recovered upon reduction. The electronic ground state of the trication is discussed.

On the interatomic electronic processes following Auger decay in neon dimer

The accessible relaxation channels of the electronic states of Ne(++)-Ne and Ne(3+)-Ne populated by KLL Auger decay are studied. In particular, we address the "direct" and "exchange" interatomic Coulombic decays (ICDs) and the electron-transfer-mediated decay following the population of one-site states Ne(++)(2s(-2))-Ne and Ne(++)(2s(-1)2p(-1) (1)P)-Ne. Radiative charge transfer of the low lying Ne(++)(2p(-2))-Ne states, three-electron ICD process from the Ne(++)(2s(-2))-Ne states, as well as charge transfer at the points of curve crossing of the lowest in energy Ne(3+)(2p(-3))-Ne states are also discussed. To carry out the present study, we have calculated the potential energy curves (from 1.75 to 5.00 A) of the ground state Ne(2), the core ionized state Ne(+)(1s(-1))-Ne, and the dicationic and tricationic states with energies in the range of 45-140 eV using accurate ab initio methods and basis sets. Apart from being of interest by themselves, the results obtained may be helpful in interpreting the recent measurements of interatomic electronic processes following Auger decay in neon dimer [K. Kreidi et al., J. Phys. B 41, 101002 (2008)].

Direct Observation of Mixed‐Valence and Radical Cation Dimer States of Tetrathiafulvalene in Solution at Room Temperature: Association and Dissociation of Molecular Clip Dimers Under Oxidative Control

We have observed the mixed-valence and radical cation dimer states of a glycoluril-based molecular clip with tetrathiafulvalene (TTF) sidewalls at low concentration (1 mM) at room temperature. This molecular clip has four consecutive anodic steps in its cyclic voltammogram, which suggests a sequential oxidation of these TTF sidewalls to generate species existing in several distinct charge states: neutral monomers, mixed-valence dimers, radical cation dimers, and fully oxidized tetracationic monomers. The observation of characteristic NIR spectroscopic absorption bands at approximately 1650 and 830 nm in spectroelectrochemistry experiments supports the presence of intermediary mixed-valence and radical cation dimers, respectively, during the oxidation process. The stacking of four TTF radical cations in the dimer led to the appearance of a charge-transfer band at approximately 946 nm. Nanoelectrospray ionization mass spectrometry was used to verify the tricationic state and confirm the existence of other different charged dimers during the oxidation of the molecular clip.

On the doubly ionized states of Ar2 and their intra- and interatomic decay to Ar23+

Potential energy curves of the Auger state Ar+(2p(-1))-Ar, the different one- and two-site dicationic states Ar2 ++ (with energies in the range of 32-77 eV), and the lowest two-site tricationic states Ar++ - Ar+ (with energies in the range of 64-76 eV) computed using elaborated ab initio methods are reported. The accessible relaxation channels of the electronic states of Ar++ - Ar populated by Auger decay are studied. In particular, we study in detail the interatomic Coulombic decay following the population of one-site satellite states of Ar++(3s(-1)3p(-1))-Ar recently observed experimentally. Other relaxation pathways of Ar++ - Ar, including radiative charge transfer, nuclear dynamics through curve crossing, and intra-atomic decay processes are also investigated.

Amine-based organic high-spin systems: Synthesis, electrochemical and spectroscopic studies of polyalkylated one-dimensional oligoaryl triamines

A polyalkylated triamine, 2,2′,4,4′-tetrabromo-4″-methyl-5,5′-bis(di(3,4-di-methylphenyl)amino)triphenylamine, was designed and successfully synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurement revealed that the triamine gives stable mono- and dicationic states and fairly unstable tricationic state. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triplet state of the dication was confirmed by ESR spectroscopy.

Organic high-spin systems of oligoarylamines: Properties of tetraaryl-m-phenylendiamine oligocations as examined by electron transfer stopped-flow method

Abstract Three types of N,N,N′,N′-tetraaryl-1,3-phenylenediamines with bromo atoms as protecting groups were designed and synthesized. Electrochemical and novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding short-lived mono- and dicationic states. Useful molecular design rules for stabilizing the dicationic states of N,N,N′,N′-tetraaryl-1,3-phenylenediamines as precursors for positively charged high-spin systems were elucidated. An extended system, 3,3′-bis(diphenylamino)triphenylamine in the tricationic state with four bromo groups was also examined, being confirmed to give a ground-state triplet dication by ESR spectroscopy.

Ab Initio MO Study of the Cationic States of 1,3,5-Triazine and Hexahydro-1,3,5-triazine

Electronic structures of cationic states (2+ and 3+) of 1,3,5-triazine (TA) and its derivative hexahydro-1,3,5-triazine (HTA) are discussed with the ab initio molecular-orbital method including the electron correlation by the Moller−Plesset (MP) perturbation treatment. It has been found that σ-radical spins give rise to low- and high-spin states in both TA and HTA. The present calculation at the MP3 level predicts that the spin multiplicity of the ground state of dicationic TA is a high-spin state triplet while that of tricationic TA is a doublet. On the other hand, low- and high-spin states are almost degenerate in both the dicationic and the tricationic states of HTA. This result will hopefully lead to the discovery of a high-spin state occurring from σ-radical spins in molecules containing heteroatoms as the spin accommodators.

Polycationic High-Spin States of One- And Two-Dimensional (Diarylamino)Benzenes as Studied By Pulsed Esr/Electron Spin Transient Nutation (Estn) Spectroscopy

Polycationic high-spin states of star-burst molecules based on (diarylamino)benzenes have been studied by cw and pulsed ESR spectroscopy. An electron spin transient nutation (ESTN) method based on pulsed ESR spectroscopy was applied to the dicationic and tricationic high-spin states of N,N,n',n'-tetra(4-anisyl)-2,4-dimethyl-1,5-phenylenediamine and N,N,n′,n′,N″,N″-hexa(4-anisyl)-1,3,5-triaminobenzene, respectively, in order to identify the spin multiplicity of the polycationic states. The observed 2D nutation spectra of the dicationic and tricationic states unequivocally showed that the dicationic and tricationic states are ground-state triplet and quartet, respectively.

Pulsed ESR/ENDOR and ESTN(Electron Spin Transient Nutation) study of polycationic high-spin states of one-and two-dimensional (diarylamino)benzenes

Polycationic high-spin states of 1,3-bis(diarylamino)benzenes, 1,3,5-tris(diarylamino)benzenes, and their homologues have been studied by cw and pulsed ESR/ENDOR spectroscopy. An electron spin transient nutation (ESTN) method based on pulsed ESR spectroscopy was applied to the dicationic and tricationic high-spin states of N,N,N′,N″-tetra(4-anisyl)-2,4-dimethyl-1,5phenylenediamine and N,N,N′,N′,N″,N″-hexa(4-anisyl)-1,3,5-triaminobenzene, respectively, in order to identify the spin multiplicity of the polycationic states. The observed 2D nutation spectra of the dicationic and tricationic states unequivocally showed that the dicationic and tricationic states are ground-state triplet and quartet, respectively. We have also carried out cw-and pulsed ENDOR measurements to the tricationic state of 1,3,5-tris(diarylamino)benzene, clarifying the electronic structure of the cationic quartet spin state. On the central phenyl ring there are carbon sites with large π-spin densities which are additively brought from each diarylamino moiety by spin polarization mechanism. In the triplet and quartet ground states, the topological spin polarization mechanism is dominant for forming the high-spin states.

ESR of the cationic triradical of 1,3,5-tris(diphenylamino)benzene

The ESR spectrum of the cationic triradical of 1,3,5-tris(diphenylamino)benzene (TDAB) is discussed. The tricationic state of TDAB was observed by means of cyclic voltammetry. The orange cationic triradical was prepared by oxidation of TDAB with trifluoroacetic anhydride in the presence of tetra-n-butylammonium tetrafluoroborate in CH 2 Cl 2 . The ESR spectrum of the randomly oriented radicals in the CH 2 Cl 2 glass agrees well with the theoretical prediction of a quartet (S=3/2) spin state with a zero-field splitting parameter D' of 13.1 G (0.0012 cm -1 )