Irradiation W 2 9 0 nm) of an aqueous suspension of poly(p-phenylene) leads to photocatalytic H2 evolution in the presence of triethylamine or diethylamine.

Herein we report a detailed investigation of a highly robust hybrid system (sensitizer/TiO2/catalyst) for the visible-light reduction of CO2 to CO; the system comprises 5'-(4-[bis(4-methoxymethylphenyl)amino]phenyl-2,2'-dithiophen-5-yl)cyanoacrylic acid as the sensitizer and (4,4'-bis(methylphosphonic acid)-2,2'-bipyridine)Re(I)(CO)3Cl as the catalyst, both of which have been anchored on three different types of TiO2 particles (s-TiO2, h-TiO2, d-TiO2). It was found that remarkable enhancements in the CO2 conversion activity of the hybrid photocatalytic system can be achieved by addition of water or such other additives as Li(+), Na(+), and TEOA. The photocatalytic CO2 reduction efficiency was enhanced by approximately 300% upon addition of 3% (v/v) H2O, giving a turnover number of ≥570 for 30 h. A series of Mott-Schottky (MS) analyses on nanoparticle TiO2 films demonstrated that the flat-band potential (V(fb)) of TiO2 in dry DMF is substantially negative but positively shifts to considerable degrees in the presence of water or Li(+), indicating that the enhancement effects of the additives on the catalytic activity should mainly arise from optimal alignment of the TiO2 V(fb) with respect to the excited-state oxidation potential of the sensitizer and the reduction potential of the catalyst in our ternary system. The present results confirm that the TiO2 semiconductor in our heterogeneous hybrid system is an essential component that can effectively work as an electron reservoir and as an electron transporting mediator to play essential roles in the persistent photocatalysis activity of the hybrid system in the selective reduction of CO2 to CO.

A bright combination: a new type of donor-acceptor dyad, carbazolylaryl-substituted ortho-carboranes, which are conveniently prepared from the corresponding acetylenes and decaborane pathways, showed unique excited-state behavior associated with electron transfer unlike the meta- and para-counterparts.

4437MA-CVE sample. The technical assistance of Mrs. L. Mansuy in the synthesis of dialkyl viologens is also gratefully acknowledged. Registry No. di-C4 viologen, 36437-30-6; di-C, viologen, 6 159-05-3; di-C8 viologen, 32449-1 8-6; di-C4 viologen radical cation, 87922-26-7; di-C, viologen radical cation, 631 19-42-6; di-C8 viologen radical cation, 49765-26-6; PSSH, 50851-57-5; MA-CVE, 26935-44-4. have tried to interpret the data on semiquantitative grounds after having developed a kinetic model which takes very satisfactorily into account the disappearance of the reduced viologens in the absence of stabilizing agent. Acknowledgment.We are indebted to Dr. E. Pefferkorn (Institut Charles Sadron, Strasbourg) for providing us with the Photoreduction of C02 to formic acid (HCO,) and a small quantity of carbon monoxide (CO) can be achieved in nonaqueous polar solvent by using oligob-phenylenes) (OPP-n) as a photocatalyst and triethylamine (TEA) as a sacrificial electron donor under >290-nm irradiation, where the photocatalysis in N,N-dimethylformamide leads to the most effective formation of HC0,-and CO. Among OPP-n, OPP-3 and OPP-4 show high photocatalytic activity for the formation of HC02-, in which the apparent quantum yields of HCOT formation for OPP-3 and OPP-4 are 0.072 and 0.084, respectively. Although photocatalyst OPP-3 itself concurrently undergoes photo-Birch reduction during the photocatalysis, the turnover number for the formation of HC02-based on the reacted OPP-3 is calculated to be 4, implying a cyclic activity of the reduction system. The laser flash photolysis and pulse radiolysis studies reveal that the photocatalysis initially starts from the reductive quenching of the singlet state of OPP-n by TEA followed by the formation of the radical anion of OPP-n, OPP-n'-, resulting in direct electron transfer from OPP-n'-to C 0 2 molecules.

Visible-light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H evolving Co catalyst and a CO-producing Re catalyst on TiO have been found to produce both H and CO (syngas) in CO -saturated N,N-dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H /CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re and Co catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO to each of the CO -reduction and hydrogen-evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.