Photosynthetic Water Splitting Research Articles

Mechanism of Water Splitting by Photosystem II

The light driven water splitting achieved in the oxygen evolving complex (OEC) of Photosystem II is a critical process that sustains our biosphere. Photosynthetic water splitting is fascinating in its complexity, inspiring due to its practical applications in designing artificial photosynthesis, and not yet understood. At the heart of the water splitting process is the Mn4Ca cluster embedded in a fine tuned protein environment.The electronic structure and geometry of this cluster were probed by X-ray spectroscopy at the functional room temperature state.1, 2 Detailed kinetic analysis of the X-ray induced damage was performed and allowed selection of undamaging conditions for experimentation. High-quality extended X-ray absorption fine structure (EXAFS) spectra of the OEC at room temperature will be presented and compared with XRD and DFT derived molecular models of the dark stable S1 state. The determined Debye-Waller factors, sensitive to dynamic processes, support the rigid structure of the Mn4Ca cluster at room temperature.Laser-pump X-ray probe time-resolved X-ray emission measurements (XES) allowed monitoring of changes in the electronic structure of the OEC in real time during the catalysis. Using time-resolved XES we monitored the evolution of the electronic structure of the OEC of Photosystem II during the most critical S3 to S0 transition which results in O2 evolution. Our data show no oxidation but only a gradual reduction of the Mn centers after excitation of the complex past the S3 state. These observations allow us to propose a unique O-O bond formation and water splitting mechanism. Combined with DFT modeling, our analysis reveals the mechanism of catalytic water splitting.1. Davis et al. J. Phys. Chem. B 117, 9161-9169 (2013).2. Davis et al. J. Phys. Chem. Lett. 3, 1858-1864 (2012).

Dye-modification effects on water splitting activity of GaN:ZnO photocatalyst

Photocatalytic water splitting activities of GaN:ZnO modified with various porphyrins were investigated. Tetraphenylporphyrinato-chromium(III) chloride (Cr-TPPCl) showed the most positive effect on the photocatalytic activity of GaN:ZnO, and worked without decomposition in the photocatalytic water splitting for 24 h. Fluorescence spectra measurements revealed that photoluminescence intensity of GaN:ZnO was decreased by Cr-TPPCl modification and by loading RhOX and NiO cocatalysts. It suggests that charge or energy transfer occurs from GaN:ZnO to Cr-TPPCl and from Cr-TPPCl to RhOX-NiO cocatalysts. Fluorescence lifetime measurement showed electron transfer occurred from GaN:ZnO to Cr-TPPCl, and thus artificial photosynthetic water splitting was achieved on GaN:ZnO photocatalyst modified with various porphyrins under visible light. The apparent quantum efficiency of the dye-modified GaN:ZnO photocatalyst (RhOX (0.1 wt%), NiO (0.1 wt%)/Dye (0.5 wt%)/IrO2 (0.1 wt%)–GaN:ZnO) was 2.73% at 410 nm.

Electronic structure of S2 state of the oxygen-evolving complex of photosystem II studied by PELDOR

Photosynthetic water splitting is catalyzed by a Mn4CaO5 cluster in photosystem II, whose structure was recently determined at a resolution of 1.9Å [Umena, Y. et al. 2011, Nature, 473:55–60]. To determine the electronic structure of the Mn4CaO5 cluster, pulsed electron–electron double resonance (PELDOR) measurements were performed for the tyrosine residue YD and S2 state signals with non-oriented and oriented photosystem II (PS II) samples. Based on these measurements, the spin density distributions were calculated by comparing with the experimental results. The best fitting parameters were obtained with a model in which Mn1 has a large positive projection, Mn3 has a small positive projection, and Mn2 and Mn4 have negative projections (the numbering of Mni (i=1–4) is based on the crystal structure at a 1.9Å resolution), which yielded spin projections of 1.97, −1.20, 1.19 and −0.96 for Mn1–4 ions. The results show that the Mn1 ion, which is coordinated by H332, D342 and E189, has a valence of Mn(III) in the S2 state. The sign of the exchange interactions J13 is positive, and the other signs are negative.

Sustained H(2) production driven by photosynthetic water splitting in a unicellular cyanobacterium.

ABSTRACTThe relationship between dinitrogenase-driven H2 production and oxygenic photosynthesis was investigated in a unicellular cyanobacterium, Cyanothece sp. ATCC 51142, using a novel custom-built photobioreactor equipped with advanced process control. Continuously illuminated nitrogen-deprived cells evolved H2 at rates up to 400 µmol ⋅ mg Chl−1 ⋅ h−1 in parallel with uninterrupted photosynthetic O2 production. Notably, sustained coproduction of H2 and O2 occurred over 100 h in the presence of CO2, with both gases displaying inverse oscillations which eventually dampened toward stable rates of 125 and 90 µmol ⋅ mg Chl−1 ⋅ h−1, respectively. Oscillations were not observed when CO2 was omitted, and instead H2 and O2 evolution rates were positively correlated. The sustainability of the process was further supported by stable chlorophyll content, maintenance of baseline protein and carbohydrate levels, and an enhanced capacity for linear electron transport as measured by chlorophyll fluorescence throughout the experiment. In situ light saturation analyses of H2 production displayed a strong dose dependence and lack of O2 inhibition. Inactivation of photosystem II had substantial long-term effects but did not affect short-term H2 production, indicating that the process is also supported by photosystem I activity and oxidation of endogenous glycogen. However, mass balance calculations suggest that carbohydrate consumption in the light may, at best, account for no more than 50% of the reductant required for the corresponding H2 production over that period. Collectively, our results demonstrate that uninterrupted H2 production in unicellular cyanobacteria can be fueled by water photolysis without the detrimental effects of O2 and have important implications for sustainable production of biofuels.

Interplay between Flavodiiron Proteins and Photorespiration in Synechocystis sp. PCC 6803

Flavodiiron (Flv) proteins are involved in detoxification of O(2) and NO in anaerobic bacteria and archaea. Cyanobacterial Flv proteins, on the contrary, function in oxygenic environment and possess an extra NAD(P)H:flavin oxidoreductase module. Synechocystis sp. PCC 6803 has four genes (sll1521, sll0219, sll0550, and sll0217) encoding Flv proteins (Flv1, Flv2, Flv3, and Flv4). Previous in vitro studies with recombinant Flv3 protein from Synechocystis provided evidence that it functions as a NAD(P)H:oxygen oxidoreductase, and subsequent in vivo studies with Synechocystis confirmed the role of Flv1 and Flv3 proteins in the Mehler reaction (photoreduction of O(2) to H(2)O). Interestingly, homologous proteins to Flv1 and Flv3 can be found also in green algae, mosses, and Selaginella. Here, we addressed the function of Flv1 and Flv3 in Synechocystis using the Δflv1, Δflv3, and Δflv1/Δflv3 mutants and applying inorganic carbon (C(i))-deprivation conditions. We propose that only the Flv1/Flv3 heterodimer form is functional in the Mehler reaction in vivo. (18)O(2) labeling was used to discriminate between O(2) evolution in photosynthetic water splitting and O(2) consumption. In wild type, ∼20% of electrons originated from water was targeted to O(2) under air level CO(2) conditions but increased up to 60% in severe limitation of C(i). Gas exchange experiments with Δflv1, Δflv3, and Δflv1/Δflv3 mutants demonstrated that a considerable amount of electrons in these mutants is directed to photorespiration under C(i) deprivation. This assumption is in line with increased transcript abundance of photorespiratory genes and accumulation of photorespiratory intermediates in the WT and to a higher extent in mutant cells under C(i) deprivation.

Photosynthetic electron partitioning between [FeFe]-hydrogenase and ferredoxin:NADP + -oxidoreductase (FNR) enzymes in vitro

Photosynthetic water splitting, coupled to hydrogenase-catalyzed hydrogen production, is considered a promising clean, renewable source of energy. It is widely accepted that the oxygen sensitivity of hydrogen production, combined with competition between hydrogenases and NADPH-dependent carbon dioxide fixation are the main limitations for its commercialization. Here we provide evidence that, under the anaerobic conditions that support hydrogen production, there is a significant loss of photosynthetic electrons toward NADPH production in vitro. To elucidate the basis for competition, we bioengineered a ferredoxin-hydrogenase fusion and characterized hydrogen production kinetics in the presence of Fd, ferredoxin:NADP(+)-oxidoreductase (FNR), and NADP(+). Replacing the hydrogenase with a ferredoxin-hydrogenase fusion switched the bias of electron transfer from FNR to hydrogenase and resulted in an increased rate of hydrogen photoproduction. These results suggest a new direction for improvement of biohydrogen production and a means to further resolve the mechanisms that control partitioning of photosynthetic electron transport.

1SL-02 光合成水分解を可能にする光化学系IIの原子構造(1SL 光合成研究で何が明らかにされ、これから何をできるか?～光合成研究の最先端とエネルギー創製研究の現状～,日本生物物理学会第49回年会(2011年度))

1SL-02 光合成水分解を可能にする光化学系IIの原子構造(1SL 光合成研究で何が明らかにされ、これから何をできるか?～光合成研究の最先端とエネルギー創製研究の現状～,日本生物物理学会第49回年会(2011年度))

Direct Detection of Oxygen Ligation to the Mn4Ca Cluster of Photosystem II by X‐ray Emission Spectroscopy

Seeing O: Mn Kβ2,5 and Kβ′′ X-ray emission spectra arise from transitions from the ligand 2s and 2p shells of the metal complexes to the metal 1s levels. In biological systems, it is difficult to specifically probe the O and N ligands. This spectroscopic technique is used to study the O ligands of the Mn4Ca cluster that catalyzes photosynthetic water splitting and allows direct detection for the first time of the bridging oxo groups of Mn.

Impact of dimeric organization of enzyme on its function: the case of photosynthetic water splitting

It is a question of whether the supramolecular organization of the protein complex has an impact on its function, or not. In the case of the photosystem II (PSII), water splitting might be influenced by cooperation of the PSIIs. Since PSII is the source of the atmospheric oxygen and because better understanding of the water splitting may contribute to the effective use of water as an alternative energy source, possible cooperation should be analyzed and discussed. We suggest that the dimeric organization of the PSII induces cooperation in the water splitting. We show that the model of monomeric PSII is unable to produce the oxygen after the second short flash (associated with the double turnover of the PSII), in contrast to the experimental data and model of dimeric PSII with considered cooperation. On the basis of this fact and partially from the support from other studies, we concluded that the double turnover of the PSII induced by short flashes might be caused by the cooperation in the water splitting. We further discuss a possibility that the known pathway of the electron transport through the PSII might be incomplete and besides D1-Y161, other cofactor which is able to oxidize the special chlorophyll pair (P680) must be considered in the monomeric PSII to explain the oxygen production after the second short flash. Commented SBML codes (.XML files) of the monomeric and dimeric PSII models will be available (at the time of publication) in the BioModels database (www.ebi.ac.uk/biomodels).

Photosystem II: The machinery of photosynthetic water splitting

This review summarizes our current state of knowledge on the structural organization and functional pattern of photosynthetic water splitting in the multimeric Photosystem II (PS II) complex, which acts as a light-driven water: plastoquinone-oxidoreductase. The overall process comprises three types of reaction sequences: (1) photon absorption and excited singlet state trapping by charge separation leading to the ion radical pair [Formula: see text] formation, (2) oxidative water splitting into four protons and molecular dioxygen at the water oxidizing complex (WOC) with P680+* as driving force and tyrosine Y(Z) as intermediary redox carrier, and (3) reduction of plastoquinone to plastoquinol at the special Q(B) binding site with Q(A)-* acting as reductant. Based on recent progress in structure analysis and using new theoretical approaches the mechanism of reaction sequence (1) is discussed with special emphasis on the excited energy transfer pathways and the sequence of charge transfer steps: [Formula: see text] where (1)(RC-PC)* denotes the excited singlet state (1)P680* of the reaction centre pigment complex. The structure of the catalytic Mn(4)O(X)Ca cluster of the WOC and the four step reaction sequence leading to oxidative water splitting are described and problems arising for the electronic configuration, in particular for the nature of redox state S(3), are discussed. The unravelling of the mode of O-O bond formation is of key relevance for understanding the mechanism of the process. This problem is not yet solved. A multistate model is proposed for S(3) and the functional role of proton shifts and hydrogen bond network(s) is emphasized. Analogously, the structure of the Q(B) site for PQ reduction to PQH(2) and the energetic and kinetics of the two step redox reaction sequence are described. Furthermore, the relevance of the protein dynamics and the role of water molecules for its flexibility are briefly outlined. We end this review by presenting future perspectives on the water oxidation process.

Effects of methanol on the S i -state transitions in photosynthetic water-splitting

From a chemical point of view methanol is one of the closest analogues of water. Consistent with this idea EPR spectroscopy studies have shown that methanol binds at-or at least very close to-the Mn(4)O(x)Ca cluster of photosystem II (PSII). In contrast, Clark-type oxygen rate measurements demonstrate that the O(2) evolving activity of PSII is surprisingly unaffected by methanol concentrations of up to 10%. Here we study for the first time in detail the effect of methanol on photosynthetic water-splitting by employing a Joliot-type bare platinum electrode. We demonstrate a linear dependence of the miss parameter for S( i ) state advancement on the methanol concentrations in the range of 0-10% (v/v). This finding is consistent with the idea that methanol binds in PSII with similar affinity as water to one or both substrate binding sites at the Mn(4)O(x)Ca cluster. The possibility is discussed that the two substrate water molecules bind at different stages of the cycle, one during the S(4) --> S(0) and the other during the S(2) --> S(3) transition.

Hydrogencarbonate is not a tightly bound constituent of the water-oxidizing complex in photosystem II

Since the end of the 1950s hydrogencarbonate (‘bicarbonate’) is discussed as a possible cofactor of photosynthetic water-splitting, and in a recent X-ray crystallography model of photosystem II (PSII) it was displayed as a ligand of the Mn 4O x Ca cluster. Employing membrane-inlet mass spectrometry (MIMS) and isotope labelling we confirm the release of less than one (≈ 0.3) HCO 3 − per PSII upon addition of formate. The same amount of HCO 3 − release is observed upon formate addition to Mn-depleted PSII samples. This suggests that formate does not replace HCO 3 − from the donor side, but only from the non-heme iron at the acceptor side of PSII. The absence of a firmly bound HCO 3 − is corroborated by showing that a reductive destruction of the Mn 4O x Ca cluster inside the MIMS cell by NH 2OH addition does not lead to any CO 2/HCO 3 − release. We note that even after an essentially complete HCO 3 −/CO 2 removal from the sample medium by extensive degassing in the MIMS cell the PSII samples retain ≥ 75% of their initial flash-induced O 2-evolving capacity. We therefore conclude that HCO 3 − has only ‘indirect’ effects on water-splitting in PSII, possibly by being part of a proton relay network and/or by participating in assembly and stabilization of the water-oxidizing complex.

The effect of hydration on protein flexibility in photosystem II of green plants studied by quasielastic neutron scattering

The effect of hydration on protein dynamics in photosystem II (PS II) membrane fragments from spinach has been investigated by using the method of quasielastic neutron scattering (QENS) at room temperature. The QENS data obtained indicate that the protein dynamics is strongly dependent on the extent of hydration. In particular, the hydration-induced activation of localized diffusive protein motions and QA- reoxidation by QB in PS II appear to be correlated in their onset at a hydration value of about 45% relative humidity (r.h.). These findings underline the crucial functional relevance of localized diffusive protein motions on the picosecond-timescale for the reactions of light-induced photosynthetic water splitting under formation of plastoquinol and molecular oxygen in PS II of green plants.

Structural changes in the Mn4Ca cluster and the mechanism of photosynthetic water splitting

Photosynthetic water oxidation, where water is oxidized to dioxygen, is a fundamental chemical reaction that sustains the biosphere. This reaction is catalyzed by a Mn4Ca complex in the photosystem II (PS II) oxygen-evolving complex (OEC): a multiprotein assembly embedded in the thylakoid membranes of green plants, cyanobacteria, and algae. The mechanism of photosynthetic water oxidation by the Mn4Ca cluster in photosystem II is the subject of much debate, although lacking structural characterization of the catalytic intermediates. Biosynthetically exchanged Ca/Sr-PS II preparations and x-ray spectroscopy, including extended x-ray absorption fine structure (EXAFS), allowed us to monitor Mn-Mn and Ca(Sr)-Mn distances in the four intermediate S states, S0 through S3, of the catalytic cycle that couples the one-electron photochemistry occurring at the PS II reaction center with the four-electron water-oxidation chemistry taking place at the Mn4Ca(Sr) cluster. We have detected significant changes in the structure of the complex, especially in the Mn-Mn and Ca(Sr)-Mn distances, on the S2-to-S3 and S3-to-S0 transitions. These results implicate the involvement of at least one common bridging oxygen atom between the Mn-Mn and Mn-Ca(Sr) atoms in the O-O bond formation. Because PS II cannot advance beyond the S2 state in preparations that lack Ca(Sr), these results show that Ca(Sr) is one of the critical components in the mechanism of the enzyme. The results also show that Ca is not just a spectator atom involved in providing a structural framework, but is actively involved in the mechanism of water oxidation and represents a rare example of a catalytically active Ca cofactor.

Oxidative photosynthetic water splitting: energetics, kinetics and mechanism

This minireview is an attempt to summarize our current knowledge on oxidative water splitting in photosynthesis. Based on the extended Kok model (Kok, Forbush, McGloin (1970) Photochem Photobiol 11:457-476) as a framework, the energetics and kinetics of two different types of reactions comprising the overall process are discussed: (i) P680+* reduction by the redox active tyrosine YZ of polypeptide D1 and (ii) Yz (ox) induced oxidation of the four step sequence in the water oxidizing complex (WOC) leading to the formation of molecular oxygen. The mode of coupling between electron transport (ET) and proton transfer (PT) is of key mechanistic relevance for the redox turnover of YZ and the reactions within the WOC. The peculiar energetics of the oxidation steps in the WOC assure that redox state S1 is thermodynamically most stable. This is a general feature in all oxygen evolving photosynthetic organisms and assumed to be of physiological relevance. The reaction coordinate of oxidative water splitting is discussed on the basis of the available information about the Gibbs energy differences between the individual redox states Si+1 and Si and the data reported for the activation energies of the individual oxidation steps in the WOC. Finally, an attempt is made to cast our current state of knowledge into a mechanism of oxidative water splitting with special emphasis on the formation of the essential O-O bond and on the active role of the protein in tuning the local proton activity that depends on time and redox state Si. The O-O linkage is assumed to take place at the level of a complexed peroxide.

Hydrogenases and Hydrogen Photoproduction in Oxygenic Photosynthetic Organisms

The photobiological production of H2 gas, using water as the only electron donor, is a property of two types of photosynthetic microorganisms: green algae and cyanobacteria. In these organisms, photosynthetic water splitting is functionally linked to H(2) production by the activity of hydrogenase enzymes. Interestingly, each of these organisms contains only one of two major types of hydrogenases, [FeFe] or [NiFe] enzymes, which are phylogenetically distinct but perform the same catalytic reaction, suggesting convergent evolution. This idea is supported by the observation that each of the two classes of hydrogenases has a different metallo-cluster, is encoded by entirely different sets of genes (apparently under the control of different promoter elements), and exhibits different maturation pathways. The genetics, biosynthesis, structure, function, and O2 sensitivity of these enzymes have been the focus of extensive research in recent years. Some of this effort is clearly driven by the potential for using these enzymes in future biological or biohybrid systems to produce renewable fuel or in fuel cell applications.

The mechanism of photosynthetic water splitting

Oxygenic photosynthesis, which provides the biosphere with most of its chemical energy, uses water as its source of electrons. Water is photochemically oxidized by the protein complex photosystem II (PSII), which is found, along with other proteins of the photosynthetic light reactions, in the thylakoid membranes of cyanobacteria and of green plant chloroplasts. Water splitting is catalyzed by the oxygen-evolving complex (OEC) of PSII, producing dioxygen gas, protons and electrons. O(2) is released into the atmosphere, sustaining all aerobic life on earth; product protons are released into the thylakoid lumen, augmenting a proton concentration gradient across the membrane; and photo-energized electrons pass to the rest of the electron-transfer pathway. The OEC contains four manganese ions, one calcium ion and (almost certainly) a chloride ion, but its precise structure and catalytic mechanism remain unclear. In this paper, we develop a chemically complete structure of the OEC and its environment by using molecular mechanics calculations to extend and slightly adjust the recently-obtained X-ray crystallographic model with reference to this structure and to some important recent experimental results.

Transition from hydrogen atom to hydride abstraction by Mn4O4(O2PPh2)6 versus [Mn4O4(O2PPh2)6]+: O-H bond dissociation energies and the formation of Mn4O3(OH)(O2PPh2)6.

Synthesis, characterization, and reactions of the novel manganese-oxo cubane complex [Mn(4)O(4)(O(2)PPh(2))(6)](ClO(4)), 1+ (ClO(4)(-)), are described. Cation 1+ is composed of the [Mn(4)O(4)](7+) core surrounded by six bidentate phosphinate ligands. The proton-coupled electron transfer (pcet) reactions of phenothiazine (pzH), the cation radical (pzH(.+)(ClO(4)(-)), and the neutral pz* radical with 1+ are reported and compared to Mn(4)O(4)(O(2)PPh(2))(6) (1). Compound 1+ (ClO(4)(-)) reacts with excess pzH via four sequential reduction steps that transfer a total of five electrons and four protons to 1+. This reaction forms the doubly dehydrated manganese cluster Mn(4)O(2)(O(2)PPh(2))(6) (2) and two water molecules derived from the corner oxygen atoms. The first pcet step forms the novel complex Mn(4)O(3)(OH)(O(2)PPh(2))(6) (1H) and 1 equiv of the pz+ cation by net hydride transfer from pzH. Spectroscopic characterization of isolated 1H is reported. Reduction of 1 by pzH or a series of para-substituted phenols also produces 1H via net H atom transfer. A lower limit to the homolytic bond dissociation energy (BDE) (1H --> 1 + H) was estimated to be >94 kcal/mol using solution phase BDEs for pzH and para-substituted phenols. The heterolytic BDE was estimated for the hydride transfer reaction 1H --> 1+ + H(-) (BDE approximately 127 kcal/mol). These comparisons reveal the O-H bond in 1H to be among the strongest of any Mn-hydroxo complex measured thus far. In three successive H atom transfer steps, 1H abstracts three hydrogen atoms from three pzH molecules to form complex 2. Complex 2 is shown to be identical to the "pinned butterfly" cluster produced by the reaction of 1 with pzH (Ruettinger, W. F.; Dismukes, G. C. Inorg. Chem. 2000, 39, 1021-1027). The Mn oxidation states in 2 are formally Mn(4)(2II,2III), and no further reduction occurs in excess pzH. By contrast, outer-sphere electron-only reductants such as cobaltacene reduce both 1+ and 1 to the all Mn(II) oxidation level and cause cluster fragmentation. The reaction of pzH(.+) with 1+ produces 1H and the pz+ cation by net hydrogen atom transfer, and terminates at 1 equiv of pzH(.+) with no further reaction at excess. By contrast, pz* does not react with 1+ at all, indicating that reduction of 1+ by electron transfer to form pz+ does not occur without a proton (pcet to 1+ is thermodynamically required). Experimental free energy changes are shown to account for these pcet reactions and the absence of electron transfer for any of the phenothiazine series. Hydrogen atom abstraction from substrates by 1 versus hydride abstraction by 1(+ )()illustrates the transition to two-electron one-proton pcet chemistry in the [Mn(4)O(4)](7+) core that is understood on the basis of free energy consideration. This transition provides a concrete example of the predicted lowest-energy pathway for the oxidation of two water molecules to H(2)O(2) as an intermediate within the photosynthetic water-oxidizing enzyme (vs sequential one-electron/proton steps). The implications for the mechanism of photosynthetic water splitting are discussed.

18O isotope effect in the photosynthetic water splitting process

In mass spectroscopic experiments of oxygen evolution in Photosystem II at 50% enrichment of H 2 18O, one expects equal signals of 18O 2 and 16O 2 unless one of the isotopes is favored by the oxygen evolving complex (OEC). We have observed a deviation from this expectation, being a clear indication of an isotope effect. We have measured the effect to be 1.14–1.30, which is higher than the theoretically predicted value of 1.014–1.06. This together with the strong temperature variation of the measured effect with a discontinuity at 11 °C observed for wild-type tobacco and at 9 °C for a yellow-green tobacco mutant suggest that an additional mechanism is responsible for the observed high isotope effect. The entry of a finite size of water clusters to the cleavage site of the OEC can explain the observation.

Initial steps of photosynthetic water splitting by associates of porphyrin

Photochemical and spectral properties of dimeric forms of meso-tetraphenylporphine (TPP), associated meso-tetra( p-aminophenyl)porphine (TAPP) and meso-tetra( N,N,N-trihexadecyl-4-aminophenyl)porphine (TTAP), which produce donor–acceptor complexes, are investigated by absorption, luminescence, and Raman spectroscopy. Three different protonated dimers of TPP observed in the ground state, according to fluorescence spectra, reveal only two different porphyrin dimers in the excited state and have maxima of emission bands at 693 and 730 nm. Low-temperature measurements of TPP dimers solutions at 77 K after illumination show EPR signal with g-factor of free electron and Δ H pp = 0.7 mT. The differential absorption spectrum of the solution is somewhat similar to spectrum of π-cation radical of TPP. Visible light illumination of associated TTAP in water containing small amount of dimethylformamide (DMF) produces irreversible changes at room temperature. The corresponding differential spectrum of the photoinduced changes exhibits mainly 692 nm band overlapping with broad band in the 460–800 nm region with the maximum at about 620 nm. According to fluorescence spectra of the TPP dimers, interaction between low- and high-energy dimeric forms of porphyrin (with the maxima of Soret bands at 465 and 403 nm, respectively), takes place in the excited state. Similar behavior can be possible for aminoporphyrins but interpretation of their spectra in this respect meets difficulties because of donor–acceptor interactions in the association complexes. Most probably the interactions bring about electron transfer photoreaction between TPP dimers and in the case of TTAP dimeric (or associated) similar forms too. It is proposed that the electron transfer photoreaction involves water and utilizes it as an electron donor in the case of TPP dimers and a sacrificial electron donor in the case of associated TTAP. Unordinary vibrational bands observed in the resonance Raman spectra of TAPP and TTAP support this unusual behavior of the aminoporphyrins.