High-Spin Polymers: Ferromagnetic Coupling of <i>S</i> = 1 Hexaazacyclophane Units up to a Pure <i>S</i> = 2 Polycyclophane

Triarylamines oxidized to radical cations can be used as stable spins sources for the design of high-spin compounds. Here, we present the synthesis of the polyarylamine-containing hexaazacyclophanes linked via <i>meta</i>-terphenyl bridges. Spins, created after oxidation of the polymer, can be coupled magnetically in cyclophane moieties via <i>meta</i>-phenyl and along the polymer chain via <i>meta</i>-terphenyl units. The formation of a quintet spin state was evidenced by pulsed-EPR nutation spectroscopy. Two exchange coupling constants via both couplers were determined experimentally and corresponded to <i>J</i>/<i>k</i> = 89 K in the cyclophane moiety and <i>j</i>/<i>k</i> = 17 K via <i>meta</i>-terphenyl. Most importantly, in this polymer, four spins can be ferromagnetically ordered via both couplers, which leads to the high spin 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

Ferromagnetic Spin Coupling through the 3,4′-Biphenyl Moiety in Arylamine OligomersExperimental and Computational Study

This report describes the study of a dimer <b>d</b>^<b>2+</b> and a linear trimer <b>t</b>^<b>3+</b> of amminium radical cations coupled by 3,4′-biphenyl spin coupling units. The synthesis of the parent diamine and triamine and their optical and electrochemical properties obtained by UV–visible and cyclic voltammetry are presented. The chemical doping of the parent diamine <b>d</b> and triamine <b>t</b> was performed quantitatively to obtain samples containing the corresponding dimer <b>d</b>^<b>2+</b> and trimer <b>t</b>^<b>3+</b> in almost pure high-spin states as evidenced by pulsed EPR nutation spectroscopy. The <i>J</i> coupling constants of the corresponding <i>S</i> = 1 and <i>S</i> = 3/2 spin states were measured (<i>J</i>/<i>k</i> = 135 K) and compared quantitatively to DFT calculations

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

Electrochemical and spectroelectrochemical properties of a series of new penta-ring donor–acceptor compounds, comprising 1,3,4-oxadiazole, 1,3,4-thiadiazole, and 1,2,4-triazole central ring, symmetrically connected to substituted bithiophenes, were investigated. Aromaticity and electrophilic–nucleophilic traits of the aza-heterocyclic units, fostering inductive and resonance effects that translate to conjugation enhancement and electron (de)­localization, were found a major factor determining the key electron properties of ionization potential (IP) and electron affinity (EA) of these molecules. Replacing the alkyl thiophene substituent for an alkoxy one afforded certain control over the two parameters as well. All studied compounds were found to undergo electrochemical polymerization giving p- and n-dopable products, featuring good electrochemical reversibility of their oxidative doping process, as demonstrated by cyclic voltammetry and UV–vis–NIR, EPR spectroelectrochemistry. While electropolymerization of entities differing in the heterodiazole unit was found to conserve the EA value, the IP parameter of polymerization products was found to decrease by 0.6–0.7 eV, affording an asymmetric narrowing of the frontier energy levels gap. Aided by quantum chemical computations, the effects of structure tailoring of the investigated systems are rationalized, pointing to conscious ways of shaping the electronic properties of thiophene class polymers using synthetically convenient heterodiazole π-conjugated units