Tetraaza[1.1.1.1]<i>m</i>,<i>p</i>,<i>m</i>,<i>p</i>‑cyclophane Diradical Dications Revisited: Tuning Spin States by Confronted Arenes

Diradical dications of two kinds of alternate-<i>meta</i>-<i>para</i>-linked tetraazacyclophanes in which <i>p</i>-phenylene (<b>1</b>) and 9,10-anthracenylene (<b>2a</b>) moieties are embedded in their macrocyclic backbones were successfully isolated as air-stable salts. The structures of <b>1</b>²⁺ and <b>2a</b>²⁺ were elucidated by X-ray analysis, and significantly different types of structural deformation led to different spin density distributions due to the steric demand of the confronted arene moieties. The singlet–triplet energy gaps were determined to be +0.3 kcal mol^–1 (+151 K) and −1.0 kcal mol^–1 (−503 K) by SQUID measurements, indicating the triplet ground state for <b>1</b>²⁺ and the singlet ground state for <b>2a</b>²⁺

Tetraaza[1₄]- and Octaaza[1₈]paracyclophane: Synthesis and Characterization of Their Neutral and Cationic States

Two kinds of aza­[1_<i>n</i>]­paracyclophanes, tetraaza­[1₄]­paracyclophane (<b>P4</b>) and octaaza­[1₈]­paracyclophane (<b>P8</b>), were synthesized as the smallest and the largest monodisperse macrocyclic oligomers of polyaniline ever made. Herein we report the electronic nature of the cationic species of these two macrocycles with different ring size. By combining ESR spectroscopy and DFT calculations it was suggested that <b>P4</b>^·+ was classified as delocalized class III or poised on the class II/III borderline while <b>P8</b>^·+ was regarded as a localized class II mixed-valence system. We successfully isolated the dication of <b>P4</b> as a stable dicationic salt <b>P4</b>²⁺·2­[SbF₆]⁻, and the structure of <b>P4</b>²⁺ was determined by X-ray crystal analysis. Variable-temperature NMR measurements for <b>P4</b>²⁺·2­[SbF₆]⁻ unequivocally showed that <b>P4</b>²⁺ was a 22π electron system with a singlet ground state. The supercharged hexacation of <b>P8</b> was also isolated as <b>P8</b>⁶⁺·6­[SbCl₆]⁻, and X-ray crystal analysis revealed that <b>P8</b>⁶⁺ includes one SbCl₆^– anion in its macrocyclic cavity

<i>Meta</i>–<i>Para</i>-Linked Octaaza[1₈]cyclophanes and Their Polycationic States

Octaazacyclophanes, octaaza­[1₈]<i>m</i>,<i>p</i>,<i>m</i>,<i>p</i>,<i>m</i>,<i>p</i>,<i>m</i>,<i>p</i>-cyclophane (<b>2</b>) and octaaza­[1₈]<i>m</i>,<i>p</i>,<i>p</i>,<i>p</i>,<i>m</i>,<i>p</i>,<i>p</i>,<i>p</i>-cyclophane (<b>3</b>), as ring-size extended congeners of tetraaza­[1₄]<i>m</i>,<i>p</i>,<i>m</i>,<i>p</i>-cyclophane were synthesized, and the electronic states of their polycationic species were investigated by quantum chemical calculations, electrochemical measurements (cyclic voltammetry (CV) and differential pulse voltammetry (DPV)), UV–vis–NIR spectroelectrochemical measurements, and pulsed electron spin resonance (ESR) spectroscopy. These octaazacyclophanes exhibited multiredox activities depending on different linkage patterns along the macrocyclic molecular skeletons, and both molecules were oxidizable up to their respective octacations. Spectroelectrochemical measurements demonstrated that <i>p</i>-phenylenediamine (PD) moieties in <b>2</b> could be converted from the semiquinoidal structure to the quinoidal sturcture with increasing oxidation number, whereas higher oxidation states of <b>3</b> did not show definite quinoidal deformation of PD moieties. A pulsed ESR spectrum gave evidence about formation of the almost pure spin-triplet state for <b>3</b>²⁺, whereas the high-spin states of <b>2</b>²⁺ and <b>2</b>⁴⁺ are virtually degenerate with the competing low-spin states even at low temperatures, probably due to the fragility of spin-coupling pathway caused by facile conformational changes

Landscape of Charge Carrier Transport in Doped Poly(3-hexylthiophene): Noncontact Approach Using Ternary Combined Dielectric, Paramagnetic, and Optical Spectroscopies

We report on a comprehensive measurement system for mobility and energy states of charge carriers in matter under dynamic chemical doping. The temporal evolution of the iodine doping process of poly­(3-hexylthiophene) (P3HT) was monitored directly through electron paramagnetic resonance (EPR) and optical absorption spectroscopy, as well as differential electrical conductivity by the microwave conductivity measurement. The increase in conductivity was observed after the EPR intensity reached a maximum and declined thereafter, and the conductivity finally reached ∼80 S cm^–1. The carrier species changed from a paramagnetic polaron with an estimated mobility of μ_P+ ≈ 2 × 10^–3 cm² V^–1 s^–1 to an antiferromagnetic polaron pair with μ_PP+ ≈ 0.6 cm² V^–1 s^–1. The technique presented here can be a ubiquitous method for rapid and direct observation of charge carrier mobility and energy states in p-type semiconducting materials as a completely noncontact, experimental, and quantitative technique

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiaza­pentacene (DHDAP) units (<b>1</b>) was investigated as the first example of this kind of molecule. The tetramer <b>1</b> showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure <b>1</b> exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10^–3. The absolute configuration of the enantiomers of <b>1</b> was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of <b>1</b> with SbCl₆^– counterions. The solutions of enantiopure <b>1</b>²⁺·2­[SbCl₆^–] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiaza­pentacene (DHDAP) units (<b>1</b>) was investigated as the first example of this kind of molecule. The tetramer <b>1</b> showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure <b>1</b> exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10^–3. The absolute configuration of the enantiomers of <b>1</b> was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of <b>1</b> with SbCl₆^– counterions. The solutions of enantiopure <b>1</b>²⁺·2­[SbCl₆^–] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiaza­pentacene (DHDAP) units (<b>1</b>) was investigated as the first example of this kind of molecule. The tetramer <b>1</b> showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure <b>1</b> exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10^–3. The absolute configuration of the enantiomers of <b>1</b> was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of <b>1</b> with SbCl₆^– counterions. The solutions of enantiopure <b>1</b>²⁺·2­[SbCl₆^–] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiaza­pentacene (DHDAP) units (<b>1</b>) was investigated as the first example of this kind of molecule. The tetramer <b>1</b> showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure <b>1</b> exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10^–3. The absolute configuration of the enantiomers of <b>1</b> was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of <b>1</b> with SbCl₆^– counterions. The solutions of enantiopure <b>1</b>²⁺·2­[SbCl₆^–] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli

Hash-Mark-Shaped Azaacene Tetramers with Axial Chirality

The tetramers of azapentacene derivatives with unique hash mark (#)-shaped structures were prepared in a quite facile manner. The #-shaped tetramers are optically active due to possessing extended biaryl skeletons, and the structure of the tetramer composed of four dihydrodiaza­pentacene (DHDAP) units (<b>1</b>) was investigated as the first example of this kind of molecule. The tetramer <b>1</b> showed characteristic chiroptical properties reflecting its orthogonally arranged quadruple DHDAP moieties, as well as redox activity. The solution of enantiopure <b>1</b> exhibited intense circularly polarized luminescence (CPL) with a dissymmetry factor of 2.5 × 10^–3. The absolute configuration of the enantiomers of <b>1</b> was experimentally determined by X-ray crystal analysis for the dication salt of the enantiomer of <b>1</b> with SbCl₆^– counterions. The solutions of enantiopure <b>1</b>²⁺·2­[SbCl₆^–] also showed NIR circular dichroism (CD) spectra over the entire range from visible to 1100 nm, enabling the modulation of the chiroptical properties by redox stimuli

Isolable Triradical Trication of Hexaaza[1₆]paracyclophane with Embedded 9,10-Anthrylenes: A Frustrated Three-Spin System

A new derivative of hexaaza­[1₆]­paracyclophane in which <i>p</i>-phenylenes are alternately replaced by 9,10-anthrylenes was prepared to investigate the impact on overall π-conjugation as well as conformational change of the macrocycle. The charge and spin distribution for one-electron and three-electron oxidation of the macrocycle was elucidated by means of electrochemical, spectroelectrochemical, EPR spectroscopic, and SQUID magnetometric methods. In particular, the triradical trication was successfully isolated as an air-stable salt, and moreover, its structure was disclosed by X-ray analysis. The triradical trication was characterized as a spin-frustrated three-spin system with the antiferromagnetic exchange interaction (<i>J</i>/<i>k</i>_B ≃ – 74 K)