Solid-State Ligand-Driven Light-Induced Spin Change at Ambient Temperatures in Bis(dipyrazolylstyrylpyridine)iron(II) Complexes

We previously reported that an Fe^II complex ligated by two (<i>Z</i>)-2,6-di­(1<i>H</i>-pyrazol-1-yl)-4-styrylpyridine ligands (<i><b>Z</b></i><b>-H</b>) presented a solid state ligand-driven light-induced spin change (LD-LISC) upon one-way <i>Z</i>-to-<i>E</i> photoisomerization, although modulation of the magnetism was trivial at ambient temperatures (<i>Chem. Commun.</i> <b>2011</b>, <i>47</i>, 6846). Here, we report the synthesis of new derivatives of <i><b>Z</b></i><b>-H</b>, <i><b>Z</b></i><b>-CN</b> and <i><b>Z</b></i><b>-NO</b>_<b>2</b>, in which electron-withdrawing cyano and nitro substituents are introduced at the 4-position of the styryl group to attain a more profound photomagnetism at ambient temperatures. <i><b>Z</b></i><b>-CN</b> and <i><b>Z</b></i><b>-NO</b>_<b>2</b> undergo quantitative one-way <i>Z</i>-to-<i>E</i> photochromism upon excitation of the charge transfer band both in acetonitrile and in the solid state, similar to the behavior observed for <i><b>Z</b></i><b>-H</b>. In solution, these substituents stabilized the low-spin (LS) states of <i><b>Z</b></i><b>-CN</b> and <i><b>Z</b></i><b>-NO</b>_<b>2</b>, and the behavior was quantitatively analyzed according to the Evans equation. The photomagnetic properties in the solid state, on the other hand, cannot be explained in terms of the substituent effect alone. <i><b>Z</b></i><b>-CN</b> displayed photomagnetic properties almost identical to those of <i><b>Z</b></i><b>-H</b>. <i><b>Z</b></i><b>-CN</b> preferred the high-spin (HS) state at all temperatures tested, whereas photoirradiated <i><b>Z</b></i><b>-CN</b> yielded a lower χ_M<i>T</i> at ambient temperatures. The behavior of <i><b>Z</b></i><b>-NO</b>_<b>2</b> was counterintuitive, and the material displayed surprising photomagnetic properties in the solid state. <i><b>Z</b></i><b>-NO</b>_<b>2</b> occupied the LS state at low temperatures and underwent thermal spin crossover (SCO) with a <i>T</i>_1/2 of about 270 K. The photoirradiated <i><b>Z</b></i><b>-NO</b>_<b>2</b> displayed a higher value of χ_M<i>T</i> and the modulation of χ_M<i>T</i> exceeded that of <i><b>Z</b></i><b>-H</b> or <i><b>Z</b></i><b>-CN</b>. <i><b>Z</b></i><b>-NO</b>_<b>2</b><b>·acetone</b>, in which acetone molecules were incorporated into the crystal lattice, further stabilized the LS state (<i>T</i>_1/2 > 300 K), thereby promoting large modulations of the χ_M<i>T</i> values (87% at 273 K and 64% at 300 K) upon <i>Z</i>-to-<i>E</i> photoisomerization. Single crystal X-ray structure analysis revealed that structural factors played a vital role in the photomagnetic properties in the solid state. <i><b>Z</b></i><b>-H</b> and <i><b>Z</b></i><b>-CN</b> favored intermolecular π–π stacking among the ligand molecules. The coordination sphere around the Fe^II nucleus was distorted, which stabilized the HS state. In contrast, <i><b>Z</b></i><b>-NO</b>_<b>2</b><b>·acetone</b> was liberated from such intermolecular π–π stacking and coordination distortion, resulting in the stabilization of the LS state

Solid-State Ligand-Driven Light-Induced Spin Change at Ambient Temperatures in Bis(dipyrazolylstyrylpyridine)iron(II) Complexes

We previously reported that an Fe^II complex ligated by two (<i>Z</i>)-2,6-di­(1<i>H</i>-pyrazol-1-yl)-4-styrylpyridine ligands (<i><b>Z</b></i><b>-H</b>) presented a solid state ligand-driven light-induced spin change (LD-LISC) upon one-way <i>Z</i>-to-<i>E</i> photoisomerization, although modulation of the magnetism was trivial at ambient temperatures (<i>Chem. Commun.</i> <b>2011</b>, <i>47</i>, 6846). Here, we report the synthesis of new derivatives of <i><b>Z</b></i><b>-H</b>, <i><b>Z</b></i><b>-CN</b> and <i><b>Z</b></i><b>-NO</b>_<b>2</b>, in which electron-withdrawing cyano and nitro substituents are introduced at the 4-position of the styryl group to attain a more profound photomagnetism at ambient temperatures. <i><b>Z</b></i><b>-CN</b> and <i><b>Z</b></i><b>-NO</b>_<b>2</b> undergo quantitative one-way <i>Z</i>-to-<i>E</i> photochromism upon excitation of the charge transfer band both in acetonitrile and in the solid state, similar to the behavior observed for <i><b>Z</b></i><b>-H</b>. In solution, these substituents stabilized the low-spin (LS) states of <i><b>Z</b></i><b>-CN</b> and <i><b>Z</b></i><b>-NO</b>_<b>2</b>, and the behavior was quantitatively analyzed according to the Evans equation. The photomagnetic properties in the solid state, on the other hand, cannot be explained in terms of the substituent effect alone. <i><b>Z</b></i><b>-CN</b> displayed photomagnetic properties almost identical to those of <i><b>Z</b></i><b>-H</b>. <i><b>Z</b></i><b>-CN</b> preferred the high-spin (HS) state at all temperatures tested, whereas photoirradiated <i><b>Z</b></i><b>-CN</b> yielded a lower χ_M<i>T</i> at ambient temperatures. The behavior of <i><b>Z</b></i><b>-NO</b>_<b>2</b> was counterintuitive, and the material displayed surprising photomagnetic properties in the solid state. <i><b>Z</b></i><b>-NO</b>_<b>2</b> occupied the LS state at low temperatures and underwent thermal spin crossover (SCO) with a <i>T</i>_1/2 of about 270 K. The photoirradiated <i><b>Z</b></i><b>-NO</b>_<b>2</b> displayed a higher value of χ_M<i>T</i> and the modulation of χ_M<i>T</i> exceeded that of <i><b>Z</b></i><b>-H</b> or <i><b>Z</b></i><b>-CN</b>. <i><b>Z</b></i><b>-NO</b>_<b>2</b><b>·acetone</b>, in which acetone molecules were incorporated into the crystal lattice, further stabilized the LS state (<i>T</i>_1/2 > 300 K), thereby promoting large modulations of the χ_M<i>T</i> values (87% at 273 K and 64% at 300 K) upon <i>Z</i>-to-<i>E</i> photoisomerization. Single crystal X-ray structure analysis revealed that structural factors played a vital role in the photomagnetic properties in the solid state. <i><b>Z</b></i><b>-H</b> and <i><b>Z</b></i><b>-CN</b> favored intermolecular π–π stacking among the ligand molecules. The coordination sphere around the Fe^II nucleus was distorted, which stabilized the HS state. In contrast, <i><b>Z</b></i><b>-NO</b>_<b>2</b><b>·acetone</b> was liberated from such intermolecular π–π stacking and coordination distortion, resulting in the stabilization of the LS state

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis­(dipyrrinato)­zinc­(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their <i>meso</i>-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state

Structure of Tm@C₈₂(I) Metallofullerene by Single-Crystal X‑ray Diffraction Using the 1:2 Co-Crystal with Octaethylporphyrin Nickel (Ni(OEP))

The molecular structure of Tm@C₈₂ (isomer I) is revealed by single-crystal X-ray diffraction of the 1:2 cocrystal with nickel octaethylporphyrin (Ni­(OEP)). A rotational movement of Tm@C₈₂(I) molecule in the 1:1 cocrystal is dramatically suppressed by the coordination of two Ni­(OEP) ligands in the 1:2 cocrystal. The structure of Tm@C₈₂(I) in the crystal is explained by the orientation disorder with two different orientations. The so-obtained carbon cage structure is <i>C</i>_<i>s</i>(6)–C₈₂. The restricted molecular orientations of Tm@C₈₂(I) in the 1:2 cocrystal are achieved by the molecular dipole moment of Tm@C₈₂(I) that interacts with two Ni­(OEP) ligands. The present study suggests that the intermolecular interactions can reduce the degree of freedom in the orientation of spherical metallofullerene molecules in the crystals and complexes

Optical Properties of Disilane-Bridged Donor–Acceptor Architectures: Strong Effect of Substituents on Fluorescence and Nonlinear Optical Properties

A series of disilane-bridged donor–acceptor architectures <b>1</b>–<b>9</b> containing strong electron-donating and -withdrawing substituents were designed and synthesized in acceptable yields. The substituents substantially affected the fluorescence and nonlinear optical properties of the compounds. In the solid state, the compounds showed purple–blue fluorescence (λ_em = 360–420 nm) with high quantum yields (up to 0.81). Compound <b>3</b>, which had <i>p</i>-<i>N</i>,<i>N</i>-dimethylamino and <i>o</i>-cyano substituents, exhibited optical second harmonic generation (activity 2.9 times that of urea, calculated molecular hyperpolarizability β = 1.6 × 10^–30 esu) in the powder state. Density functional theory calculations for the ground and excited states indicated that both the locally excited state and the intramolecular charge transfer excited state make important contributions to the luminescence behavior

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis­(dipyrrinato)­zinc­(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their <i>meso</i>-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state

Optical Properties of Disilane-Bridged Donor–Acceptor Architectures: Strong Effect of Substituents on Fluorescence and Nonlinear Optical Properties

A series of disilane-bridged donor–acceptor architectures <b>1</b>–<b>9</b> containing strong electron-donating and -withdrawing substituents were designed and synthesized in acceptable yields. The substituents substantially affected the fluorescence and nonlinear optical properties of the compounds. In the solid state, the compounds showed purple–blue fluorescence (λ_em = 360–420 nm) with high quantum yields (up to 0.81). Compound <b>3</b>, which had <i>p</i>-<i>N</i>,<i>N</i>-dimethylamino and <i>o</i>-cyano substituents, exhibited optical second harmonic generation (activity 2.9 times that of urea, calculated molecular hyperpolarizability β = 1.6 × 10^–30 esu) in the powder state. Density functional theory calculations for the ground and excited states indicated that both the locally excited state and the intramolecular charge transfer excited state make important contributions to the luminescence behavior

Bis(dipyrrinato)zinc(II) Complexes: Emission in the Solid State

This Communication reports the first observation of solid-state photoluminescence in bis­(dipyrrinato)­zinc­(II) complexes with various substituents. The report discusses the effect of their substituents on their crystal structures and spectroscopic properties. Their <i>meso</i>-aryl groups are revealed to play important roles in the spectroscopic properties in the solid state

Aggregation-Induced Emission Enhancement from Disilane-Bridged Donor–Acceptor–Donor Luminogens Based on the Triarylamine Functionality

Six novel donor–acceptor–donor organic dyes containing a Si–Si moiety based on triarylamine functionalities as donor units were prepared by Pd-catalyzed arylation of hydrosilanes. Their photophysical, electrochemical, and structural properties were studied in detail. Most of the compounds showed attractive photoluminescence (PL) and electrochemical properties both in solution and in the solid state because of intramolecular charge transfer (ICT), suggesting these compounds could be useful for electroluminescence (EL) applications. The aggregation-induced emission enhancement (AIEE) characteristics of <b>1</b> and <b>3</b> were examined in mixed water/THF solutions. The fluorescence intensity in THF/water was stronger in the solution with the highest ratio of water because of the suppression of molecular vibration and rotation in the aggregated state. Single-crystal X-ray diffraction of <b>4</b> showed that the reduction of intermolecular π–π interaction led to intense emission in the solid state and restricted intramolecular rotation of the donor and acceptor moieties, thereby indicating that the intense emission in the solid state is due to AIEE. An electroluminescence device employing <b>1</b> as an emitter exhibited an external quantum efficiency of up to 0.65% with green light emission. The emission comes solely from <b>1</b> because the EL spectrum is identical to that of the PL of <b>1</b>. The observed luminescence was sufficiently bright for application in practical devices. Theoretical calculations and electrochemical measurements were carried out to aid in understanding the optical and electrochemical properties of these molecules

Solvent-Controlled Doublet Emission of an Organometallic Gold(I) Complex with a Polychlorinated Diphenyl(4-pyridyl)methyl Radical Ligand: Dual Fluorescence and Enhanced Emission Efficiency

A paramagnetic, luminescent organometallic gold­(I) complex Au^I(C₆F₅)­(PyBTM), where PyBTM is a photostable fluorescent polychlorinated diphenyl­(4-pyridyl)­methyl radical, was prepared, and its crystal and electronic structures and magnetic and optical properties were investigated. Magnetic studies using electron spin resonance spectroscopy and a superconducting quantum interference device magnetometer indicated the existence of <i>S</i> = ¹/₂ spin per molecule, with the spin density distributed mainly on the PyBTM ligand. The complex exhibited fluorescence in CHCl₃ with emission peak wavelength (λ_em) of 619 nm and the absolute fluorescence quantum yield (ϕ_em) of 0.04, confirming that Au^I(C₆F₅)­(PyBTM) is the first luminescent organometallic complex with a coordinated luminescent radical. Solvent-dependent unique luminescent characteristics were observed in halogenated solvents (CCl₄, CHCl₃, CH₂Cl₂, and ClCH₂CH₂Cl). ϕ_em decreased, and λ_em shifted to longer wavelengths as the polarity (dielectric constant) of the solvent increased. Notably, the complex in CCl₄ displayed fluorescence with ϕ_em = 0.23, which was quite high in radicals, while showed dual fluorescence in CH₂Cl₂ and ClCH₂CH₂Cl with lifetimes of around 1 and 7 ns for two emissive components. Density functional theory (DFT) and time-dependent (TD)-DFT calculations indicated that the fluorescence occurred from an interligand charge transfer (CT) excited state in CCl₄, in which the C₆F₅ and PyBTM moieties acted as electron donor and acceptor, respectively, while the fluorescence was centered at the PyBTM ligand in the other three solvents. This method, i.e., the formation of an interligand CT state, to enhance ϕ_em is distinctly different from the methods reported previously. The present study revealed that a coordination bond is available for forming emissive CT excited states that lead to high ϕ_em, providing a novel method with greater capability for realizing highly emissive radicals