Polycondensation of 1‐(2‐pyrimidinyl)pyrrole with 2,7‐dibromo‐9,9‐dioctylfluorene via Ru‐catalyzed direct arylation gives the corresponding conjugated polymer with a molecular weight of 19 800 in 86% yield. The introduction of directing group, 2‐pyrimidinyl substituent, into the pyrrole monomer induces ortho‐metalation and provides the site‐selective direct arylation polycondensation at the α‐position of pyrrole unit without the protection of β‐position. The removal of 2‐pyrimidinyl substituent on the pyrrole unit proceeds efficiently and results in the enhancement of coplanarity along the main chain of the polymer.
The phase relations and equations of state of ZrO 2 and HfO 2 high-pressure polymorphs have been investigated by means of in situ observation using multi-anvil type high-pressure devices and synchrotron radiation. Baddeleyite (monoclinic ZrO 2 ) transforms to two distorted fluorite (CaF 2 )-type phases at 3-4 GPa depending on temperature: an orthorhombic phase, orthoI, below 600 °C and a tetragonal phase, which is one of the high-temperature forms of ZrO 2 , above 600 °C. Both orthoI and tetragonal phases then transform into another orthorhombic phase, orthoII, with a cotunnite (PbCl 2 )-type structure above 12.5 GPa and the phase boundary is almost independent of temperature. OrthoII is stable up to 1800 °C and 24 GPa. In case of HfO 2 , orthoI is stable from 4 to 14.5 GPa below 1250-1400 °C and transforms to the tetragonal phase above these temperatures. OrthoII of HfO 2 appears above 14.5 GPa and is stable up to 1800 °C at 21 GPa. The unit cell parameters and the volumes of these high-pressure phases have been determined as functions of pressure and temperature. The orthoI/tetragonal-to-orthoII transition of both ZrO 2 and HfO 2 is accompanied by about 9% volume decrease. The bulk moduli of orthoII calculated using Birch-Murnaghan's equations of state are 296 GPa and 312 GPa for ZrO 2 and HfO 2 , respectively. Since orthoII of both ZrO 2 and HfO 2 are quenchable to ambient conditions, these are candidates for super-hard materials. 相似文献
We prepared perylene dications 1 2+ and 2 2+ by using “capped” perylene derivatives, and for the first time, successfully obtained single crystals of a perylene dication 1 2+ that enabled us to perform its structural analysis. We realized that the substituted aryl groups on perylene control the positions of positive charges, thus the remaining electronic system satisfies Clar's sextet rule toward the highest number of localized sextets. Experimental and theoretical evidence proved that Clar's aromatic π‐sextet rule could be applied even for the dicationic perylenes in a very simple way. 相似文献
The potential use of circularly polarized luminescence for object identification in a sensor application is demonstrated. New luminescence probes using pyrene derivatives as sensor luminophores were developed. (R,R)‐Im2Py and (S,S)‐Im2Py contain two chiral imidazole moieties at 1,6‐positions through ethynyl spacers (angle between spacers ca. 180°). The probe molecules spontaneously self‐assemble into chiral stacks (P or M helicity) upon coordination to metal ions with tetrahedral coordination (Zn2+). The chiral probes display neither circular dichroism (CD) nor circularly polarized luminescence (CPL) without metal ions. However, (R,R)‐Im2Py and (S,S)‐Im2Py exhibit intense chiroptical activity (CD and CPL) upon self‐assembly with Zn2+ ions. (R,R)‐Im2Py and (S,S)‐Im2Py with chemical stimuli‐responsibility allow sensing using the CPL signal as detection output, enabling us to discriminate between a signal from the target analyte and that from non‐target species. 相似文献
The accelerating effect of Sc(3+) on the electron-transfer (ET) reduction of the p-benzoquinone derivative 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ) by 10,10'-dimethyl-9,9'-biacridine ((AcrH)(2)) at 233 K changes to a decelerating effect with increasing reaction temperature; the observed second-order rate constant k(et) decreases with increasing Sc(3+) concentration at high concentrations of Sc(3+) at 298 K. At 263 K the k(et) value remains constant with increasing Sc(3+) concentration. Such a remarkable difference with regard to dependence of k(et) on [Sc(3+)] between low and high temperatures results from the difference in relative activity of two ET pathways that depend on temperature, one of which affords 1:1 complex TolSQ*(-)-Sc(3+), and the other 1:2 complex TolSQ*(-)-(Sc(3+))(2) with additional binding of Sc(3+) to TolSQ*(-)-Sc(3+). The formation of TolSQ*(-)-Sc(3+) and TolSQ*(-)-(Sc(3+))(2) complexes was confirmed by EPR spectroscopy in the ET reduction of TolSQ in the presence of low and high concentrations of Sc(3+), respectively. The effects of metal ions on other ET reactions of quinones to afford 1:1 and 1:2 complexes between semiquinone radical anions and metal ions are also reported. The ET pathway affording the 1:2 complexes has smaller activation enthalpies DeltaH( not equal) and more negative activation entropies DeltaS( not equal) because of stronger binding of metal ions and more restricted geometries of the ET transition states as compared with the ET pathway to afford the 1:1 complexes. 相似文献
Semiquinone radical anion of 1-(p-tolylsulfinyl)-2,5-benzoquinone (TolSQ(*-)) forms a strong hydrogen bond with protonated histidine (TolSQ(*-)/His x 2 H(+)), which was successfully detected by electron spin resonance. Strong hydrogen bonding between TolSQ(*-) and His x 2 H(+) results in acceleration of electron transfer (ET) from ferrocenes [R2Fc, R = C5H5, C5H4(n-Bu), C5H4Me] to TolSQ, when the one-electron reduction potential of TolSQ is largely shifted to the positive direction in the presence of His x 2 H(+). The rates of His x 2 H(+)-promoted ET from R2Fc to TolSQ exhibit deuterium kinetic isotope effects due to partial dissociation of the N-H bond in His x 2 H(+) at the transition state, when His x 2 H(+) is replaced by the deuterated compound (His x 2 D(+)-d6). The observed deuterium kinetic isotope effect (kH/kD) decreases continuously with increasing the driving force of ET to approach kH/kD = 1.0. On the other hand, His x 2 H(+) also promotes a hydride reduction of TolSQ by an NADH analogue, 9,10-dihydro-10-methylacridine (AcrH2). The hydride reduction proceeds via the one-step hydride-transfer pathway. In such a case, a large deuterium kinetic isotope effect is observed in the rate of the hydride transfer, when AcrH2 is replaced by the dideuterated compound (AcrD2). In sharp contrast to this, no deuterium kinetic isotope effect is observed, when His x 2 H(+) is replaced by His x 2 D(+)-d6. On the other hand, direct protonation of TolSQ and 9,10-phenanthrenequinone (PQ) also results in efficient reductions of TolSQH(+) and PQH(+) by AcrH2, respectively. In this case, however, the hydride-transfer reactions occur via the ET pathway, that is, ET from AcrH2 to TolSQH(+) and PQH(+) occurs in preference to direct hydride transfer from AcrH2 to TolSQH(+) and PQH(+), respectively. The AcrH2(*+) produced by the ET oxidation of AcrH2 by TolSQH(+) and PQH(+) was directly detected by using a stopped-flow technique. 相似文献
The Sr–Ge–O system has an earth‐scientific importance as a potentially good low‐pressure analog of the Ca–Si–O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3 high‐pressure perovskite phase is the first Ge‐based transparent electronic conductor make the Sr–Ge–O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high‐pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co‐existent phase with SrGeO3 perovskite single crystals in the sample recovered in the compression experiment of SrGeO3 pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium–oxygen framework layers stacked along [001], with Sr atoms located at the 12‐coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6 octahedra and between GeO6 octahedra and GeO4 tetrahedra. The present SrGe2O5 is thus isostructural with the high‐pressure phases of SrSi2O5 and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6 and GeO4 polyhedra to cation substitution at the Sr site are much less than that of the SrO12 cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature. 相似文献
Dilute aqueous dispersions of charged colloidal silica (particle volume fraction = approximately 0.03-0.04, particle diameter = 110 nm) exhibit unidirectional crystal growth due to the diffusion of a weak base, pyridine (Py). Similar diffusion-crystallization is enabled by a salt of a weak acid and a strong base, sodium hydrogen carbonate (NaHCO3). The resulting crystals consist of columnar (or cubic) crystal grains with a maximum height of a few centimeters and a maximum width of 1 cm. The crystal growth process is attributed to a combination of (i) the diffusion of Py or NaHCO3 accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. Theoretical growth curves based on the reaction-diffusion model for the case of Py were in good agreement with the observed curves. We also report the immobilization of the resulting large crystals by using a polymer hydrogel matrix. 相似文献