It is these factors that we wish to exploit for energy storage. Phenyl azirine can be photo converted into its ylide counterpart with ultraviolet light and them the ylide can be converted back to the azirine form with longer wavelengths . With the phenyl azirine suspended in a cryogenic matrix of solid argon, it can be converted quantitatively to the ylide form as shown by the FTIR spectrum. A number of isotopically substituted phenyl azirines have been so studied in order to establish for the first time an unequivocal structure for the ylide. We have shown conclusively that the nitrogen atom occupies the central position in an allene-like zwitterion structure. The matrix reactions between Hg, Cd, and Zn atoms excited to the 3p state with halogenated olefins has been studied and compared to the photochemical products observed in absence of the metal atom with singlet excitation of the double bond. Photo induced metal atom insertion into a C-CI borld has been observed for the first time for 2-chloro-I,1-difluoroethene and for both cis and l,l-dichloroethenes. In addition, the dichloroethenes display Ch elimination but not HCI elimination when reaction is photo induced on· the triplet energy surface defined by the 3p metal atom.The data show that chemistry is different on the triplet surface v than on the singlet surface and that the results are not compatible with a simple energy transfer from MCSP) to the olefin. It is gratifying that the Ch elimination induced on the triplet surface stores about half of the photon energy, a significant improvement over the 15% stored in HCI ~I elimination on the singlet surface. The purpose of this program is to explore photosynthesis with near infrared quanta,hydroponic grow table with special attention to systems. which permit energy storage. The importance of chemistry with such long wavelength photons stems from the fact that more than half of the solar irradiance at ground level lies in the near infrared .

To illustrate the consequence of the abundance of near infrared quanta in the solar spectral distribution, one may consider the following: If maximum use of solar photon energy were to be attained by two separate photo driven chemical reactions, each with its’ own spectral sensitivity so as to optimize the combined use of the total solar irradiance, both systems would be required. to have their thresholds in the near infrared . However, photochemical reactions that can be initiated by continuous near infrared light are very sparse. It is the goal of this work to find reactions which permit efficient use of near infrared radiation for chemical synthesis, and to develop the concept of chemical storage of long lived electronically excited molecules to accomplish storage and conversion into useful energy of these long wavelength solar photons. We have concentrated our effort over the past few years on near infrared induced chemical reactions of singlet molecular oxygen. Singlet delta oxygen, O2 , carries 23 kcal electronic energy and is a reactive, long lived intermediate which plays a key role in many photo oxygenations. 02 can be chemically stored in the form of aromatic endoperoxides, and we have demonstrated earlier with cryogenic photochemical techniques that the . photon induced formation of such endoperoxides from O2 and parent hydrocarbon may proceed very efficiently with near infrared photons as long in wavelength as 1.3 micron.The long term ultimate solution of our needs for liquid fuels from renewable sources will be the construction of synthetic systems which will enable us to convert solar energy directly into useful chemical species, both as chemicals and for fuels. We are using what we know about the natural process of photosynthesis, insofar as it involves quantum conversion into stable chemical products, to guide us in the design of these totally synthetic systems. The principal factor which enables green plants to convert incoming visible quanta into some stable chemical form long enough to do secondary chemical reactions for storage involves the separation of charge across a phase boundary.

The positive charge is ultimately used to generate oxygen from water and the negative charge is used to reduce carbon dioxide. The phase boundaries under study are: the lipid bilayer walls of phospholipid vesicles which are used to keep separate the initial photoproducts; the surfaces of various polyelectrolytes; and the surfaces of polymeric colloids. Efforts have been made to find microheterogeneous systems that would involve photosensitizers active in the visible region. These would promote electron transfer from donors to acceptors, which would stabilize the charge separation long enough for suitable catalysts to make use of their separation. The particular systems which have been most useful have involved sensitizers with relatively long-lived triplet states. The two components of such systems can be examined separately by using irreversible electron acceptors on the oxygen-generating side to stabilize the hole and irreversible electron donors on the hydrogen side to· inhibit the back reaction of the initial charge separation. We are examining manganese porphyrin species as potential multi-electron oxidation catalyst for oxygen evolution from water and for other oxidation reaction. In photosynthesis some type of manganese complex is involved in the oxygen evolution process. Manganese porphyrin complexes exhibit a rich variety of oxidation states in which the porphyrin macrocycle is resistant to irreversible redox reactions. These properties make them promising oxidation catalysts, and, in addition, it has recently been shown that manganese porphyrin complexes catalyze the oxidation of olefinic hydrocarbons. Our research is directed at characterizing various highly oxidized manganese porphyrin species and studying their chemistry with the view of judging their potential usefulness in the oxidation cycle of an artificial photosynthesis assembly. The work has proceeded along two parallel pathways. The first is directed at water soluble manganese porphyrins and involves chemical, electrochemical and photochemical studies. However, isolation of intermediate species is frequently easier in organic solvents, and we are also investigating the redox chemistry of manganese tetraphenylporphyrin complexes in organic media.

Comparison of similarities and differences in the properties of oxidized manganese porphyrins in aqueous and nonaqueous systems has led to helpful insights and has suggested new experiments. We have continued to study the electrocatalytic reduction of carbon dioxide with cobalt and nickel macrocycles as catalysts in aqueous s~lution. We have found that of the various tetra-aza compounds tried as catalysts the ones that have given the best results in electrode reduction of CO2 have unsubstituted, ‘saturatedrihg structures. One of these [l,4,8,1l-tetraaza cyc10tetradecane nickel was found to be highly selective in producing CO rather than H2 , as well as giving. almost 100% current efficiency and high turnover numbers on Ni. After we were abl~ to repeat these results, we selected this catalyst as the basis for a threecomponent photochemical system for performing the CO2 reduction. Ruthenium tris-bipyridyl [Rua2+] was the sensitizer and ascorbate buffer the electron donor.We have continued our studies on the effect of charged interfaces on the photoelectron transfer reaction between the photosensitizer and the electron acceptor. After our initial results with the polyelectrolyte, polystyrene sulfonate ,flood tray showed that its presence not only inhibited the back reaction, as does colloidal silica, but also repressed the forward reaction and thus had little effect on the overall quantum yield, we began work with modified silica colloids. ,However, the, usefulness of silica is limited to pH regions above 8. If sodium aluminate is used to react with. the surface. of the sol, aluminum can be incorporated into the surface. The more acid aluminum sites make the colloid stable and usable down to pH 6 where it still retains all of its effectiveness in preventing back-reaction. In order to achieve photoelectron and hole separation we have proposed to use electron transferring membranes which will keep the oxidizing and reducing agents separated. We have been working with perfiuorinated ion exchange membrane obtained from duPont as well.as membranes from the Dow Chemical Company. The objective here is to load such a perfiuorinated cation exchange membrane with a cationic redox compound and so construct an electron transfer membrane by virtue of electron hopping between the two states of the redox couple bound to the membrane. We have loaded the Nafion membrane with ruthenium trisbipyridyl by electroiyzihg the cation·through the membrane. Such a fully loaded membrane is placed between an oxidant” such as permanganate anion, and a reductant, such as ferrocyanide anion. Prior tests indicate that such a membrane is impermeable to both of these anions. However, electron transfer does occur between the permanganate and the ferrocyanide anion, producing ferricyanide. Photosynthetic light reactions constitute the principal biological energy source derived from sunlight. We are carrying out spectroscopic and other biophysical studies aimed at understanding the mechanism of photon capture and excitation transfer among photosynthetic pigments, the earliest steps in conversion to chemical potential by electron transfer in the reaction centers and the mechanism of water oxidation to O2 • Both kinetic and structural investigations are carried out using a variety of spectroscopic techniques, including optical absorption and fluorescence, electron paramagnetic resonance {EPR) and X -ray spectroscopy.

In related studies we are looking at the composition and organization of. the photosynthetic complexes and their arrangement in the thylakoid membranes. We have also investigated model compounds designed to simulate the light-induced electron transfer that lies at the heart of the photosynthetic’ energy conversion. Primary electron transfer is initiated in the photosynthetic reaction center. In higher plants, algae and cyanobacteria, there are two distinct types of reaction cen~!S, known as Photo systems I and II. In the recent past we have done detailed investigations of the kinetics of PS IT using picosecond to nanosecond time-resolved fluorescence decay, and microsecond and longer EPR transient measurements. We have extended the studies on PS II and have begun analogous investigations of PS I. The use of cyanobacteria affords an opP9 unity to obtain enriched PS II reaction center complexes that retain important aspects of the primary electron transfer. These complexes exhibit significantly slower fluorescence decay components compared with those from the higher plant membranes that we had studied previously. The slow components from the cyanobacterial PS II complexes are sensitive to the open/closed state of the reaction centers and, therefore, may reflect charge recombination processes that have been altered by the isolation procedures. These studies’ will be pursued to map the origin of the several decay components that have been resolved. A new class of electron transfer inhibitors, including the unsaturated fatty aCids linolenic and linoleic, appear to act closer to the PS II reaction centers than any that had been previously observed. In collaboration With Prof. John Golbeck of Port1and_State._University_we~have __ investigated the effect of these inhibitors on the fluorescence decay kinetics and the formation of EPR-detectable triplets associated with PS II. The studies are consistent with the model that linolenic acid blocks electron transport between the primary and secondary electron acceptors; however, detailed studies of the effects on absorption and low temperature emission spectra indicate that LA at the low concentrations used does produce irreversible alterations’ of the reaction center pigment environments. The EPR studies indicate that the ability to form a radical-pair recombination triplet is retained in the presence of LA, but only when a strong reducing’ agent like dithionite is also present. The simplest interpretation of these results is that there is an additional electron acceptor in the· PS II reaction center that had not previously been detected. The evidence is conflicting, however, and further studies are needed be~ore a satisfactory:understanding of the situation will obtain. Electron .. donation to the PS II reaction center.comes ultimately from water oxidation. The successive storage of oxidizing equivalents. in this four-electron transfer process is reflected in the kinetics of intermediate carriers between the water-oxidation complex and PS II. Using kinetic EPR spectroscopy we can monitor Signal II, which we. have shown previously to be the primary electron donor to the PS II reaction center chlorophyll. Using a series of up to eight saturating, sub-microsecond flashes, we have monitored the kinetics of rereduction of the Signal II species and have seen oscillations of period 4 that correlate with storage of successive oxidizing equivalents in the water-splitting complex.