Copper‐Modified Covalent Triazine Frameworks as Non‐Noble‐Metal Electrocatalysts for Oxygen Reduction

The electrochemical oxygen reduction reaction (ORR) is an important cathode reaction of various types of fuel cells. The development of electrocatalysts composed only of abundant elements is a key goal because currently only platinum is a suitable catalyst for ORR. Herein, we synthesized copper‐modified covalent triazine frameworks (CTF) hybridized with carbon nanoparticles (Cu‐CTF/CPs) as efficient electrocatalysts for the ORR in neutral solutions. The ORR onset potential of the synthesized Cu‐CTF/CP was 810 mV versus the reversible hydrogen electrode (RHE; pH 7), the highest reported value at neutral pH for synthetic Cu‐based electrocatalysts. Cu‐CTF/CP also displayed higher stability than a Cu‐based molecular complex at neutral pH during the ORR, a property that was likely as a result of the covalently cross‐linked structure of CTF. This work may provide a new platform for the synthesis of durable non‐noble‐metal electrocatalysts for various target reactions.     

The relationship between the chemical structures of dihydropyrazine derivatives and DNA strand-breakage activity

Dihydropyrazine, a compound derived from sugars, possesses DNA strand-breakage activity. The relationship between the activity as assayed using pBR 322 ccc-DNA and the chemical structures of derivatives of dihydropyrazine (DHPs) has been investigated. The addition of Cu(2+) enhanced the activity remarkably. The introduction of a methyl or phenyl group onto the DHP ring or a cyclohexyl group fused onto the DHP ring also increased the activity. These properties indicated that the activity was due to the facility of electron release from the DHP ring, followed by radical generation. The determination of ionization potential and electrostatic potential values, and bond dissociation energy via semi-empirical MO calculations suggested strongly that the activity is induced by a DHP ring structure that contains a configuration suitable for hyperconjugation.     

Synthesis of polyethers containing cyclodipeptide moiety in the main chain

The dichlorodihydropyrazines derived from 2,5‐diketopiperazine were treated with diols in a basic condition to afford polyethers containing cyclodipeptide moiety in the main chain, which were found to be degraded into amino acid components in an acidic condition. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 927–933, 2001     

Long cycles passing through a specified path in a graph

For a graph G and an integer k ≥ 1, let ς_k(G) = d_G(v_i): {v₁, …, v_k} is an independent set of vertices in G}. Enomoto proved the following theorem. Let s ≥ 1 and let G be a (s + 2)-connected graph. Then G has a cycle of length ≥ min{|V(G)|, ς₂(G) − s} passing through any path of length s. We generalize this result as follows. Let k ≥ 3 and s ≥ 1 and let G be a (k + s − 1)-connected graph. Then G has a cycle of length ≥ min{|V(G)|, − s} passing through any path of length s. © 1998 John Wiley & Sons, Inc. J. Graph Theory 29: 177–184, 1998     

Full variational molecular orbital method: Application to the positron-molecule complexes

Optimal Gaussian-type orbital (GTO) basis sets of positron and electron in positron-molecule complexes are proposed by using the full variational treatment of molecular orbital (FVMO) method. The analytical expression for the energy gradient with respect to parameters of positronic and electronic GTO such as the orbital exponents, the orbital centers, and the linear combination of atomic orbital (LCAO) coefficients, is derived. Wave functions obtained by the FVMO method include the effect of electronic or positronic orbital relaxation explicitly and satisfy the virial and Hellmann–Feynman theorems completely. We have demonstrated the optimization of each orbital exponent in various positron-atomic and anion systems, and estimated the positron affinity (PA) as the difference between their energies. Our PA obtained with small basis set is in good agreement with the numerical Hartree–Fock result. We have calculated the OH⁻ and [OH⁻; e⁺] species as the positron-molecular system by the FVMO method. This result shows that the positronic basis set not only becomes more diffuse but also moves toward the oxygen atom. Moreover, we have applied this method to determine both the nuclear and electronic wave functions of LiH and LiD molecules simultaneously, and obtained the isotopic effect directly. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 491–501, 1998     

On the Existence of a Long Path Between Specified Vertices in a 2-Connected Graph

 Let G be a 2-connected graph with maximum degree Δ (G)≥d, and let x and y be distinct vertices of G. Let W be a subset of V(G)−{x, y} with cardinality at most d−1. Suppose that max{d _G(u), d _G(v)}≥d for every pair of vertices u and v in V(G)−({x, y}∪W) with d _G(u,v)=2. Then x and y are connected by a path of length at least d−|W|. Received: February 5, 1998 Revised: April 13, 1998     

Note on a theorem of Farkas and Kra

The Ramanujan Journal - The aim of this paper is to prove a nonvanishing result for derivatives of $$L$$-functions inside the critical strip analogous to Kohnen (J Number Theory 67:182–189,...     

Synthesis of π‐conjugated copolymers composed of benzo[2,1,3]thiadiazole and thiophene units bearing various alkyl groups and their application to photovoltaic cells

π‐Conjugated polymers, PTOTBT , PTEHTBT , and PTt‐BTBT , composed of benzothiadiazole as an electron accepting unit and terthiophene as an electron donating unit in the backbone were prepared. PTOTBT , PTEHTBT , and PTt‐BTBT contained side chain groups of n‐octyl, 2‐ethylhexyl, and t‐butyl groups, respectively. Solubility, optical and thermal properties of the polymers showed strong dependences on their side chain groups. PTEHTBT having 2‐ethylhexyl groups in the side chain exhibited absorption maximum (λ_max) at longer wavelength (565 nm) than PTOTBT (534 nm) and PTt‐BTBT (495 nm). PTOTBT showed higher thermal stability than the others. The prepared polymers were employed to polymer solar cells (PSCs) with a configuration of ITO/PEDOT‐PSS/polymer: PC₆₁BH/LiF/Al. Power conversion efficiency of the PSC‐based on PTEHTBT was 1.32%. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Polythiophenes bearing electron‐withdrawing groups in the side chain and their application to bulk heterojunction solar cells

Soluble polythiophenes bearing strong electron withdrawing groups, dicyanoethenyl [? CH?C(CN)₂] (PTDCN) and cyano‐methoxycarbonylethenyl [? CH?C(CO₂Me)CN] (PTCNME), in the side chains have been prepared. Optical band gaps calculated from onset absorption were 1.70 eV and 1.73 eV for PTDCN and PTCNME, respectively. Highest occupied molecular orbital energy levels measured with a surface analyzer (AC‐2) were ?5.53 eV and ?5.29 eV for PTDCN and PTCNME, respectively, which were much lower than that of poly(3‐hexylthiophene) (?4.81 eV). To investigate photovoltaic properties, bulk heterojunction polymer solar cells based on PTDCN and PTCNME were fabricated with a structure of ITO/PEDOT:PSS/active layer/LiF/Al, where the active layer was a blend film of polymer and [6,6]‐phenyl C₆₁ butyric acid hexyl ester (PC₆₁BH). Solar cell parameters were estimated from current density–voltage (J–V) characteristics under the illumination of AM1.5 at 100 mW/cm². The solar cell based on the blend film of PTCNME:PC₆₁BH (1:1) showed power conversion efficiency (PCE) of 0.72% together with the open current voltage (V_oc) of 0.61 V, the short current density (J_sc) of 3.90 mA/cm², and the fill factor of 30.3%. The PCE of a solar cell fabricated from PTDCN in a similar way was 0.56%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Photochemistry of fac‐[Re(bpy)(CO)3Cl]

The photochemistry of fac‐[Re(bpy)(CO)₃Cl] ( 1 a ; bpy=2,2′‐bipyridine) initiated by irradiation using <330 nm light has been investigated. Isomerization proceeded in THF to give the corresponding mer‐isomer 1 b . However, in the presence of a small amount of MeCN, the main product was the CO‐ligand‐substituted complex (OC‐6‐24)‐[Re(bpy)(CO)₂Cl(MeCN)] ( 2 c ; bpy=2,2′‐bipyridine). In MeCN, two isomers, 2 c and its (OC‐6‐34) form ( 2 a ), were produced. Only 2 c thermally isomerized to produce the (OC‐6‐44) form 2 b . A detailed investigation led to the conclusion that both 1 b and 2 c are produced by a dissociative mechanism, whereas 2 a forms by an associative mechanism. A comparison of the ultrafast transient UV‐visible absorption, emission, and IR spectra of 1 a acquired by excitation using higher‐energy light (e.g., 270 nm) and lower‐energy light (e.g., 400 nm) gave detailed information about the excited states, intermediates, and kinetics of the photochemical reactions and photophysical processes of 1 a . Irradiation of 1 a using the higher‐energy light resulted in the generation of the higher singlet excited state with τ≤25 fs, from which intersystem crossing proceeded to give the higher triplet state (³HES( 1 )). In THF, ³HES( 1 ) was competitively converted to both the triplet ligand field (³LF) and metal‐to‐ligand charge transfer (³M LCT) with lifetimes of 200 fs, in which the former is a reactive state that converts to [Re(bpy)(CO)₂Cl(thf)]⁺ ( 1 c ) within 10 ps by means of a dissociative mechanism. Re‐coordination of CO to 1 c gives both 1 a and 1 b . In MeCN, irradiation of 1 a by using high‐energy light gives the coordinatively unsaturated complex, which rapidly converted to 2 c . A seven‐coordinate complex is also produced within several hundred femtoseconds, which is converted to 2 a within several hundred picoseconds.