The insoluble yellow powder of poly(p-phenylene) (PPP) prepared by nickel-catalyzed polycondensation of the Grignard reagent from 1,4-dibromobenzene shows photocatalytic activity under visible light toward water, carbonyl compounds, and olefins. Water is photoreduced to H2 in the presence of amines as sacrificial electron donors. The H2 evolution is enhanced 3-20 times by noble-metal deposition, in which Ru deposition is the most effective. Apparent quantum yields (4>('/2H2)) for Ru-loaded PPP-catalyzed H2 evolution depend on the irradiation wavelength, reaching a maximum value of 0.015 at 405 nm. On the other hand, nonmetallized PPP can more efficiently photocatalyze the reduction of carbonyls and electron-deficient olefins by triethylamine in methanol compared to Ru-loaded PPP, in cases where the reduction potentials of the substrates are more positive than -2.0 V vs Ag/0.01 M AgNO}. The carbonyls are reduced to the corresponding alcohols and/or pinacols, whereas the reduction of the olefins to the dihydro compounds is accompanied by rapid cis-trans photoisomerization. From the deuterium incorporation experiments for the photocatalyzed reduction of methyl 4-cyanocinnamate, 6j, in methanol-O-rf, disproportionation of one-electron-transfer reduction intermediates is suggested to be responsible for the eventual two-electron reductions and the cis-trans photoisomerization. The physical and spectral properties of PPP's are characterized, and the mechanism is discussed in terms of the energy structure.Since the photolysis of water on a Ti02 electrode (Honda-Fujishima effect) was reported,1 photoinduced charge separation on inorganic semiconductors has been widely investigated as a key step in the conversion of light to chemical potential energy.1 2 In order to achieve high efficiency in photochemical conversion or to utilize visible light much more effectively, integrated chemical systems using semiconductor/redox couple interfaces combined with metallic cocatalysts, electron relays, sensitizers, or polymers have been extensively studied.2'3 On the other hand, since polyacetylene film was synthesized and chemical doping effects on electric conductivity were discovered,4 a number of organic polymers with conjugated welectrons have been synthesized and some novel applications such as electrochromic polymers,5 organic batteries,6 sensing polymers,7 and solar batteries8 have been successfully proposed. Conjugated polymers called conducting polymers show electrical conductivity only when they are doped chemically with either electron donors or acceptors. Under undoped conditions, however, they are semiconducting and should be called polymeric organic semiconductors.9 Among such 7r-bond conjugated polymers, poly(pphenylene) (PPP) polymers are resistant to oxidation, thermal degradation, and radiation under aerobic conditions10 and are reported to have band gaps in the visible-light region.11 Evolution

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Stereogradient polymers, a fundamentally new type of polymers, were prepared by the stereospecific living radical copolymerization of two monomers that have different stereospecificities and reactivities. The ruthenium-catalyzed living radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and the silyl-capped HEMA [(tert-butyldimethylsilyl)-HEMA] (SiHEMA) in (CF3)2C(Ph)OH afforded stereogradient poly(HEMA), in which the rr content gradually increased from 62 to 77% at 0 degrees C, due to the lower reactivity and the higher syndiospecificity of SiHEMA.

The stereospecific living radical polymerizations of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) were achieved with a combination of ruthenium‐catalyzed living radical and solvent‐mediated stereospecific radical polymerizations. Among a series of ruthenium complexes [RuCl2(PPh3)3, Ru(Ind)Cl(PPh3)2, and RuCp*Cl(PPh3)2], Cp*–ruthenium afforded poly(methyl methacrylate) with highly controlled molecular weights [weight‐average molecular weight/number‐average molecular weight (Mw/Mn) = 1.08] and high syndiotacticity (r = 88%) in a fluoroalcohol such as (CF3)2C(Ph)OH at 0 °C. On the other hand, a hydroxy‐functionalized monomer, HEMA, was polymerized with RuCp*Cl(PPh3)2 in N,N‐dimethylformamide and N,N‐dimethylacetamide (DMA) to give syndiotactic polymers (r = 87–88%) with controlled molecular weights (Mw/Mn = 1.12–1.16). This was the first example of the syndiospecific living radical polymerization of HEMA. A fluoroalcohol [(CF3)2C(Ph)OH], which induced the syndiospecific radical polymerization of MMA, reduced the syndiospecificity in the HEMA polymerization to result in more or less atactic polymers (mm/mr/rr = 7.2/40.9/51.9%) with controlled molecular weights in the presence of RuCp*Cl(PPh3)2 at 80 °C. A successive living radical polymerization of HEMA in two solvents, first DMA followed by (CF3)2C(Ph)OH, resulted in stereoblock poly(2‐hydroxyethyl methacrylate) with syndiotactic–atactic segments. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3609–3615, 2006

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Compton scattering of short and ultra short (sub-cycle) laser pulses off mildly relativistic electrons is considered within a QED framework. The temporal shape of the pulse is essential for the differential cross section as a function of the energy of the scattered photon at fixed observation angle. The partly integrated cross section is sensitive to the non-linear dynamics resulting in a large enhancement of the cross section for short and, in particular, for ultra-short flat-top pulse envelopes which can reach several orders of magnitude, as compared with the case of a long pulse. Such effects can be studied experimentally and must be taken into account in Monte-Carlo/transport simulations of the interaction of electrons and photons in a strong laser field.

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