NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion

New pincer–Pt complexes coordinated by (nitronyl nitroxide)-2-ide radical anion were prepared as stable compounds in high yields. The structures of these Pt complexes and the oxidized complexes were unequivocally determined by spectral and crystal structure analyses. The oxidation potential of the nitronyl nitroxide moiety in these complexes was shifted in the negative direction by ∼0.6 V as a result of coordination to the Pt­(II) atom

NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion

New pincer–Pt complexes coordinated by (nitronyl nitroxide)-2-ide radical anion were prepared as stable compounds in high yields. The structures of these Pt complexes and the oxidized complexes were unequivocally determined by spectral and crystal structure analyses. The oxidation potential of the nitronyl nitroxide moiety in these complexes was shifted in the negative direction by ∼0.6 V as a result of coordination to the Pt­(II) atom

Trimeric Assembly of Dendritic Light-Harvesting Antenna with Two Kinds of Porphyrin Cores

A trimeric assembly of light-harvesting antennas was prepared using a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction between a dendrimer having a zinc diethynyldiphenylporphyrin core (ZnDEDPP) with two azide terminals and two equivalents of dendrimers having a zinc tetraphenylporphyrin core (ZnTPP) with one ethynyl terminal. The absorptions of the trimer appear in a longer-wavelength region compared to monomeric references in toluene; however, there is almost no shift in wavelength in 1,1,2,2-tetrachloroethane (TCE). Fluorescence spectra of the trimer show that the singlet energy transfer from ZnTPP to ZnDEDPP takes place more effectively in toluene than in TCE. These absorption and fluorescence studies are compatible with solvent-dependent conformation; the extended forms of the trimers are favored by solvation in polar TCE, and the folded conformation is stabilized by the attractive van der Waals and dipole–dipole interactions between the dendritic chains in nonpolar toluene

2,11-Dibromo-13,14-dimesityl-5,8-dioxapentaphene: A Stable and Twisted Polycyclic System Containing the <i>o</i>‑Quinodimethane Skeleton

A stable <i>o</i>-quinodimethane (<i>o</i>QDM) derivative, 2,11-dibromo-13,14-dimesityl-5,8-dioxapentaphene (<b>3</b>) was synthesized, and its structure and properties were investigated. The X-ray structural analysis showed a significantly twisted π-framework and a clear bond-length alternation in the central <i>o</i>QDM skeleton. Owing to the quinoidal conjugation, <b>3</b> exhibited a broad absorption band in the visible region (up to 700 nm) and amphoteric redox behavior. Furthermore, radical cation <b>3</b>^•+ was isolated, and its electronic structure was elucidated by spectroscopic measurements

Jonas Dryander to James Edward Smith

Believes Smith is right to include an index of the genera for "Flora Britannica" but that the English index should be at the end and approves of the title. [John] Sibthorp's plants have now been laid out in the herbarium

NCN Pincer–Pt Complexes Coordinated by (Nitronyl Nitroxide)-2-ide Radical Anion

New pincer–Pt complexes coordinated by (nitronyl nitroxide)-2-ide radical anion were prepared as stable compounds in high yields. The structures of these Pt complexes and the oxidized complexes were unequivocally determined by spectral and crystal structure analyses. The oxidation potential of the nitronyl nitroxide moiety in these complexes was shifted in the negative direction by ∼0.6 V as a result of coordination to the Pt­(II) atom

Construction of Snowflake-Shaped Dendritic Covalent Assemblies with Rigid Conjugated Networks

A convergent method for the construction of shape-persistent nanoscale assemblies with conjugated backbones was developed. The copper-free Sonogashira coupling reaction was successfully applied to the formation of multiple covalent connections between conjugated terminals (iodide substituted aryl groups) of AB₂-type outer components and four conjugated terminals (acetylenic bonds) of an inner A₄-type core dendrimer. The conjugated networks in the starting components are expanded during the assembly process to afford nanoscale dendritic conjugated networks of the type A₄(AB₂)₄, which have a porphyrin core, and longer (3.9 or 4.5 nm) and shorter (1.6 nm) conjugated chains. Fluorescence measurements revealed that singlet energy is effectively transferred in the assemblies from peripheral benzyl ether units and conjugated chains to the free base porphyrin core

Synthesis and Higher-Order Structure of Linear Dendrimeric Assemblies

A series of linear covalent assemblies of dendrimers with conjugated backbones were synthesized by means of an iterative divergent and convergent method in which copper-catalyzed acetylene–azide cycloaddition reactions were used to form flexible linkages. UV–vis and fluorescence spectra indicate that dendrimeric assemblies have a strong propensity to adopt folded conformations in which conjugated backbones adopt planar conformations. The folded conformation is stabilized by strong attractive van der Waals and dipole–dipole interactions between the dendrimers

Magnetic Control of the Charge-Separated State Lifetime Realized by Covalent Attachment of a Platinum Complex

Dynamics of the photogenerated charge-separated (CS) state is studied for a newly synthesized molecular triad, in which the donor (D) dimethoxytriphenylamine, 1,3-bis­(2-pyridylimino)­isoindolate platinum (BPIPt), and the acceptor (A) naphthaldiimide are linked with a triethynylbenzene unit (BPIPt–DA). Photoexcitation of BPIPt gives rise to generation of a long-lived (∼4 μs) CS state BPIPt–D⁺A^–, of which the lifetime is considerably increased by an applied magnetic field of 270 mT. The positive magnetic field effect (MFE) is in contrast to the negative MFE for the reference DA molecule, which indicates successful switching of the initial spin state of the CS state from singlet to triplet. Simulations of the MFE and time-resolved electron paramagnetic resonance show that spin-selective charge recombination and spin relaxation are unaffected by attachment of BPIPt. The minimum impact of heavy atom substitution on the electronic and magnetic properties has been realized by the small electronic coupling mediated by the rigid <i>meta</i>-triethynylbenzene

Very Long-Lived Photoinduced Charge-Separated States of Triphenylamine–Naphthalenediimide Dyads in Polymer Matrices

Photoinduced electron transfer was studied in dyads (<b>dyad1</b> and <b>dyad2</b>) containing triphenylamine (MTA) and naphthalenediimide (MNDI) linked with oligo­(phenylene­ethynylene) dispersed in rigid polymer matrices of polystyrene (PS), poly­(vinyl chloride), and poly­(methyl methacrylate). Photoexcitation of these dyads yielded long-lived charge-separated (CS) states involving MTA⁺ and MNDI^<b>–</b>. The quantum yields of charge separation in <b>dyad1</b> and <b>dyad2</b> were approximately 0.4 and 0.3, respectively, in the polymer matrices. The CS lifetime for <b>dyad2</b> in PS was longer (400 ms) than those in poly­(vinyl chloride) (120 ms) and poly­(methyl methacrylate) (65 ms) at 298 K. In addition, CS state had a very long lifetime of 5.4 s in glassy toluene at 100 K. Below glass transition temperatures, polymer side chain motions with various relaxation rates should affect the charge recombination processes. The energy gap (Δ<i>G</i>) and outer-sphere reorganization energy (λ) in the charge recombination process were estimated using a slow-frequency component for dielectric constants. By use of Δ<i>G</i> and λ values, the matrix dependence of the CS lifetimes was successfully rationalized based on Marcus theory, and the charge recombination process in PS with low polarity and high polarizability should be in a deeper inverted region than the other polymer matrices. It also suggested that the rigidity of the polymer effectively suppressed intramolecular motions promoting the charge recombination process