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The conversion of carbon dioxide and water to fuel in artificial systems requires efficient coupling of light absorbers and catalysts, and assembly of the components into hierarchical structures to close the photocatalytic cycle. Recent breakthroughs in the embodiment of molecular photoactive components in ultrathin oxide layers, and the introduction of new materials approaches for interfacial charge transfer have led to substantially improved coupling of chromophores and catalysts. These advances are accelerating the exploration of novel architectures for reducing CO2 by H2O in scalable, single integrated photosystems to reach the high power efficiencies recently demonstrated with photovoltaic-assisted approaches.

Water oxidation, as a mandatory reaction of solar fuels conversion systems, requires the use of light absorbers with electronic properties that are well matched with those of the multi-electron catalyst in order to achieve high efficiency. Molecular light absorbers offer flexibility in fine tuning of orbital energetics, and metal oxide nanoparticles have emerged as robust oxygen evolving catalysts. Hence, these material choices offer a promising approach for the development of photocatalytic systems for water oxidation. However, efficient charge transfer coupling of molecular light absorbers and metal oxide nanoparticle catalysts has proven a challenge. Recent new approaches toward the efficient coupling of these components based on synthetic design improvements combined with direct spectroscopic observation and kinetic evaluation of charge transfer processes are discussed.

Les sites binucleaires redox de Ti ou Zr oxopontes a un centre Cu(I) ou Sn(II) ont ete ancres de maniere covalente a la surface des pores d'un tamis de silice MCM-41 par un procede de greffage en uneseule etape. Les sites binucleaires illustrent un transfert de charge metal-metal (MMCT) induit par une absorption profonde dans le visible. L'ancrage covalent se manifeste par des modes infrarouge de basse frequence. L'illumination du chromophore MMCT de ZrCu(I)-MCM41 en presence d'un atmosphere de CO 2 a temperature ambiante conduit a l'apparition de pics a des frequences de 2150 et 1600 cm - 1 , dus respectivement au CO et a H 2 O. Les experiences de photolyse utilisant des molecules marquees 1 3 CO 2 et C 1 8 O 2 montrent que le monoxyde de carbone et l'atome d'oxygene de l'eau proviennent du CO 2 , indiquant que la decomposition du CO 2 procede de l'excitation de l'entite MMCT. Il s'agit de la premiere observation de la reduction du CO 2 a un site binucleaire MMCT, a une interface solide-gaz.

Photoisomerization of acetyl methyl iminoxy radical produced from NO2 and 2-butyne in low-temperature argon matrices has been studied by density functional theory (DFT) calculation. The infrared bands observed upon 585 nm irradiation are assigned, using the spectral patterns predicted by DFT, to the trans–trans, cis–trans, and cis–cis conformers, where the former and latter conformations refer to the CO–CN and CN bond axes, respectively. Conformational isomerization around the CN bond is found to occur upon 515 nm irradiation. The isomerization mechanism is discussed with the aid of the DFT calculation.

Loading of acetaldehyde from the gas phase into transition metal substituted aluminophosphate sieves of AFI structure resulted in mainly physisorbed CH3CHO in the case of FeAlPO4-5. By contrast, FT-IR spectroscopy revealed extensive chemical reaction upon loading into metal-free AlPO4-5 and CoAlPO4-5 materials at temperatures as low as −100°C. The low temperature product is identified as acetaldol, which dehydrates to crotonaldehyde upon warm-up to room temperature. The reactive sites are proposed to be Lewis acid sites in the aluminophosphate framework. Using FT-IR monitoring of acetaldehyde in the pores of aluminophosphate sieves as a sensitive method for the detection of Lewis acid sites, we find that their abundance varies substantially with metal substitution. Interestingly, isomorphous Fe substitution of the aluminophosphate framework seems to suppress the formation of such defect sites.

A new concept of room temperature selective oxidation of olefins, alkyl substituted benzenes and alkanes by electron transfer from the hydrocarbon to the oxygen molecule induced by irradiation with visible light is shown. The hydrocarbon radical cation–O2 charge-transfer pair is generated inside the cavities of alkali or alkaline-earth ion-exchanged zeolites, in which the large electrostatic field stabilizes the highly polar charge-transfer states of hydrocarbon–O2 collisional pair and allows to control the pathways of further transformation. High selectivities to useful products are obtained using this approach.

Time-resolved step-scan FT-IR spectroscopy with 20 ns resolution has been used to investigate the conformational transformation from cZt-1,3,5-hexatriene to tZt-1,3,5-hexatriene following the photochemical ring opening of 1,3-cyclohexadiene. The step-scan FT-IR spectrometer and an IR flow-cell system for performing UV pump, IR probe experiments with 20 ns time resolution are described. At the earliest measurable time points, only features of the final tZt-hexatriene product were observed in the time resolved spectra. Therefore the time constant for this transformation must be faster than 20 ns.

Electronic absorption spectra of cis- and trans-2-butyl, cyclopentyl, and cyclohexyl nitrite radical are reported. These new species were generated photochemically in an Ar matrix at 12 K. All alkyl nitrite radicals exhibit a long wavelength absorption that extends into the red spectral region. It is assigned to excitation of a charge transfer state involving transfer of the electron on the C radical center to the nitrite group. The 300–400 nm region shows a vibronic progression similar to the well known S1(n(N)π*)→S0 system of closed shell alkyl nitrites.

O 2 ( 1 Σ g + ) has been detected in solution for the first time through observation of 1 Σ g + → 1 Δ g emission at 1.93 μm. In a search for direct evidence of singlet molecular oxygen expelled upon decomposition of 1,4-dimethylnaphthalene endoperoxide, we found O 2 1 Δ g → 3 Σ g − chemiluminescence at 1.27 μm during thermolysis at room temperature and upon excitation of the S 2 excited state at 266 nm. No chemiluminescence was observed upon excitation of the S 1 state at 355 nm.

1 Δ g → 3 Σ g − near infrared chemiluminescence of molecular oxygen eliminated from3,3'-(1,4-naphthylidene)dipropionate endoperoxide in aqueous and methanol solution upon thermal or electronic excitation has been observed. A UV laser flash-chemilununescence study of the decay of the expelled singlet oxygen in H 2 O, D 2 O, and CH 3 OH revealed lifetimes identical with those measured upon photosensitization of singlet O 2 , in these solvents. No shortening of the lifetime of the photochemically eliminated O 2 ( 1 Δ g ) by interaction with the product hydrocarbon was found, in contrast to our previously studied case of singlet oxygen expelled from 1,4-dimethylnaphthalene endoperoxide in CCl 4 .