Photoredox Properties Research Articles

Comparison of the photoredox properties of polyoxometallates and semiconducting particles

We demonstrate that two large categories of compounds, namely, polyoxometallates (produced by acid condensation of mainly tungstates and/or molybdates) and aggregates of various metal oxides (formed by stirring, sonication etc) have similar properties. Emphasis is given to the photocatalytic properties of the two systems. The various steps in the photocatalytic cycles are described and several examples, from both systems, have been used to demonstrate that their photocatalytic performance is similar in terms of the overall mechanism of photodecomposition of organic compounds, the intermediate species involved and the final photodegradation products (i.e., CO2, H2O and inorganic anions).

Redox and photo-redox properties of isolated Mo5+ ions in MoH-ZSM-5 and MoH-beta zeolites : in situ ESR study

Redox and photo‐redox properties of isolated Mo5+ ions stabilized in H‐ZSM‐5 and H‐beta zeolites are studied by in situ ESR in flowing O2, NO, H2, and C3H6. Upon oxidation of pre‐reduced samples at 20 °C, NO demonstrates a higher oxidative ability, as compared with O2. Interaction of Mo5+ ions with propene at 20 °C results in formation of a chemisorption complex with enhanced reactivity of Mo(V) toward NO. Illumination of the Mo5+/HZSM‐5 sample with UV‐visible light causes measurable acceleration of Mo(V) oxidation by NO at 20 °C. Therefore, photochemical activation of the oxidation step could be realized, in principle, for Mo/zeolite catalysts. At 500 °C in the reaction mixture NO + H2, the step of the catalytic site reduction is fast, and the dynamic equilibrium of the redox reaction Mo(VI) ↔ Mo(V) for MoH‐ZSM‐5 and MoH‐beta seems to be strongly shifted to Mo5+.

Comparison of Electrochemically and Photochemically Induced Electron-Transfer Processes of a Series of Copper(II) Schiff Base Complexes with Thiolate Coordination

The electrochemical and photoredox properties of copper(II) thiopyrazolone Schiff base complexes 1–9 with imine and thiolate coordination, showing variable degrees of tetrahedral distortion, were investigated by means of combined electrochemical and spectroscopic techniques in the temperature range of 193–293 K. The cyclic voltammograms of 1–9 in butyronitrile revealed that the reduction and oxidation paths are strongly dependent on the geometry of the CuN2S2 moiety. Due to the strong delocalization of the singly occupied redox orbital (SOMO) the oxidations and reductions occur in a narrow potential range. The one-electron-reduced 1(r)–9(r) and oxidized 1(o)–9(o) products were electrogenerated and stabilized inside optically transparent thin-layer electrochemical (OTTLE) cells at variable temperatures and could be characterized for the first time by UV/Vis spectroscopy. The reduced formal d10 copper(I) species absorb only weakly in the visible region. The oxidized products 1(o)–9(o) show several strong absorptions in the visible region due to the presence of formal d8 copper(III) species. The spectral information allowed assignment of the initial photoproducts. Irradiations in donor media such as THF or EtOH initially produces 1(r)–9(r). No photoreduction was observed in tBuOH which cannot liberate reducing Hα. The primary oxidized species 1(o)–9(o) were formed in chlorinated acceptor solvents (CHCl3) on UV irradation. Fast relaxation to the ground state prevents the photoredox reactions from CT or LF excited states.

Comparison of Electrochemically and Photochemically Induced Electron-Transfer Processes of a Series of Copper(II) Schiff Base Complexes with Thiolate Coordination

The electrochemical and photoredox properties of copper(II) cells at variable temperatures and could be characterized for the first time by UV/Vis spectroscopy. The reduced formal thiopyrazolone Schiff base complexes 1–9 with imine and thiolate coordination, showing variable degrees of d10 copper(I) species absorb only weakly in the visible region. The oxidized products 1(o)–9(o) show several strong tetrahedral distortion, were investigated by means of combined electrochemical and spectroscopic techniques in absorptions in the visible region due to the presence of formal d8 copper(III) species. The spectral information the temperature range of 1932293 K. The cyclic voltammograms of 1–9 in butyronitrile revealed that the allowed assignment of the initial photoproducts. Irradiations in donor media such as THF or EtOH initially produces 1(r)– reduction and oxidation paths are strongly dependent on the geometry of the CuN2S2 moiety. Due to the strong 9(r). No photoreduction was observed in tBuOH which cannot liberate reducing Hα. The primary oxidized species delocalization of the singly occupied redox orbital (SOMO) the oxidations and reductions occur in a narrow potential 1(o)–9(o) were formed in chlorinated acceptor solvents (CHCl3) on UV irradation. Fast relaxation to the ground state range. The one-electron-reduced 1(r)–9(r) and oxidized 1(o)– 9(o) products were electrogenerated and stabilized inside prevents the photoredox reactions from CT or LF excited states. optically transparent thin-layer electrochemical (OTTLE)

Photochemistry and photophysical properties of novel, unsymmetrically substituted metallophthalocyanines.

A series of novel, unsymmetrically substituted metallo-phthalocyanines was synthesized, along with their symmetrically substituted analogs, and the effects of structure and metal substitution on their photophysical and photoredox properties were investigated. The macrocycles were synthesized using a mixed-condensation method followed by chromatographic separation of the resulting soluble products. They possess a catechol "active site" and three tert-butyl groups for enhanced solubility. The ground- and excited-state photophysical properties of the free-base, Zn(II) and Pd(II) macrocycles were measured and compared with their symmetrically substituted (tetra[tert-butyl]) analogs. The efficiency with which these macrocycles sensitize the formation of singlet oxygen was determined and discussed in the context of the excited-state photophysical properties. Several examples of photoinduced electron transfer reactions with one- and two-electron acceptors are demonstrated and discussed. These soluble molecules can be tuned to optimize their photochemical and redox properties by varying the central metal, axial ligands and other substituents, thereby providing a series of molecules for the investigation of photodynamic therapy and photoinduced electron transfer mechanisms.

Photophysical and redox properties of a series of phthalocyanines: relation with their photodynamic activities on TF-1 and Daudi leukemic cells.

The photodynamic therapy (PDT) efficiency of five phthalocyanines, chloroaluminum phthalocyanine (AlPc), dichlorosilicon phthalocyanine (SiPc), bis(tri-n-hexylsiloxy)silicon phthalocyanine (PcHEX), bis(triphenylsiloxy)silicon phthalocyanine (PcPHE) and nickel phthalocyanine (NiPc), was assessed on two leukemic cell lines TF-1 and erythroleukemic and B lymphoblastic cell lines, Daudi, respectively. AlPc showed the best photocytotoxicity leading to 0.008 surviving fraction at 2 x 10(-9) M for TF-1 and 4 x 10(-9) M for Daudi. A1 5 x 10(-7) M, SiPc and PcHEX induced a significant photokilling, whereas NiPc and PcPHE were inactive. Laser flash photolysis and photoredox properties of the phthalocyanines were investigated to try to relate these parameters with the biological effects. AlPc showed the longest triplet life-time: 484 microseconds in dimethyl sulfoxide/H2O. This value was increased up to 820 microseconds when AlPc was complexed with human serum albumin used as a membrane model. Such an enhancement was not observed with the silicon phthalocyanines. Upon irradiation, all the phthalocyanines generated singlet oxygen with 0.29-0.37 quantum yield values. The reduction potentials of the excited states obtained from measurement in the ground state and energy of the excited triplets show that AlPc is the best electron acceptor. The in vitro photocytotoxicity observed and the measured parameters are in agreement with a key role of electron transfer in PDT assays involving these phthalocyanines.

Photophysical properties and crystal structures of luminescent phenylethynylgold(I) complexes of alkyl and aryl isocyanides

Several phenylethynylgold(I) complexes were prepared by treating [{Au(CC–Ph)}∞] with 2,5-diisocyano-2,5-dimethylhexane (L1), (1,8-diisocyano-p-menthane (L2) and 2,6-dimethylphenyl isocyanide in dichloromethane. The intermolecular Au ⋯ Au separations established by X-ray crystal analyses are 3.329(4), 3.565(2) and 3.485(3)A for the crystals of [(Au(CCPh)(CNC6H3Me2-2,6)], [{Au(CCPh)}2L1] and [{Au(CCPh)}2L2] respectively. These gold(I) complexes have long-lived and emissive 3(ππ*) excited states in fluid solutions at room temperature. The photoredox properties of [Au(CCPh)(CNC6H3Me2-2,6)] have been studied by Stern–Volmer quenching experiments, and its excited-state redox potential E°(Au+–Au0*) is –1.62(1) V vs. saturated sodium chloride calomel electrode.

Photoredox properties of Kojic acid and its derivatives complexed to Iron(III)

Iron(III) complexes of the formcis-[Fe(SB(X - K)] in whichSB2− are open-chain tetradentateSchiff base N2O2-ligands ofacacen,benacen orsalen type, andX - K− are bidentate anions of kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one) or other γ-pyranones undergo photoredox transformations when being irradiated in methanol into intraligand orLMCT bands. The quantum yields of the photoredox reactions depend on the peripheral constitution of the N2O2 ligands, the substituentsA andB of the ligandsX - K−, and the wavelength of irradiation λirr. The proposed mechanism involves the population of photoredox reactiveLMCT states by photophysical deactivation steps, primary photoredox formation ofX - K radicals and Fe(II), and subsequent “dark” redox processes giving back the anionsX - K− and the final products Fe(II) and formaldehyde formed in the molar ratio 2:1.

Photochemical and photophysical studies of tetranuclear copper(I) halide clusters: an overview

This presentation will summarize recent studies in these laboratories of the rich luminescence and photoredox properties of tetranuclear copper(I) clusters of the type Cu 4X 4L 4.

Widely varying photophysical properties of ligand-nitrated bis(.mu.-chloro)tetrakis(2-phenylpyridinato)diiridium(III)

The photophysical properties of three cyclometalated bis([mu]-chloro)tetrakis(2-(4-R[prime]-phenyl)-5-R-pyridinato)diiridium(III) complexes are reported. The R = R[prime] = H complex is a strong photoreducing agent. The R = NO[sub 2], R[prime] = H complex is a strong photooxidant. With the NO[sub 2] group on the phenyl ring (R = H, R[prime] = NO[sub 2]), the complex displays intermediate photoredox properties and can act as a moderately photooxidizing or photoreducing agent.

Photophysical properties and X-ray crystal structure of a luminescent platinum(II) dimer [Pt2(2,2′ : 6′,2″-terpyridine)2(Gua)](CIO4)3·H2O (Gua = guanidine anion)

A new luminescent d8–d8 dinuclear PtII polypyridyl complex [Pt2(2,2′: 6′,2″-terpyridine)2(Gua)]3+ is synthesised and characterized by X-ray crystallography; its spectroscopic and photoredox properties are investigated.

Spectroscopy, photoredox properties and X-ray crystal structures of triangular gold(I) and silver(I) phosphine complexes

The reaction of HC(PPh2)3 with K[AuCl4] in the presence of 2,2′-thiodiethanol in methanol yielded [Au3{HC(PPh2)3}2Cl]2+. The related [Ag3{HC(PPh2)3}2]3+ was prepared by the reaction of HC(PPh2)3 with Ag(CF3SO3) in dichloromethane. Both complex cations were isolated as perchlorate salts. The X-ray structures of [Au3{HC(PPh2)3}2Cl][ClO4]2 and [Ag3{HC(PPh2)3}2][ClO4]3 have been determined: [Au3{HC(PPh2)3}2Cl][ClO4]2·2MeCN, monoclinic, space group C2/c(no. 15), a= 26.466(3), b= 12.741(2), c= 23.012(5)A, β= 98.89(1)° and Z= 4; [Ag3{HC(PPh2)3}2][ClO4]3·2MeCN, monoclinic, space group, P21/n, a= 14.597(4), b= 23.047(2), c= 22.485(3)A, β= 91.49(2)° and Z= 4. Both [Au3{HC(PPh2)3}2Cl]2+ and [Ag3{HC(PPh2)3}2]3+ consist of three metal atoms arranged in a nearly equilateral triangle with the M–M–M angles close to 60°. The measured intramolecular Ag–Ag and Au–Au distances of 3.1618(5)–3.2228(9) and 2.9220(8)–3.0889(8)A respectively, indicate that the Au–Au bonding interaction is much stronger than that for Ag–Ag. The UV/VIS spectrum of an acetonitrile solution of [Au3{HC(PPh2)3}2Cl]2+ exhibits intense absorption bands at 270 and 290 nm, assignable to the dσ·→ pσ transitions. For [Ag3{HC(PPh2)3}2]3+ the UV/VIS spectrum is virtually identical to that of the free HC(PPh2)3. Excitation of a degassed acetonitrile solution of [Au3{HC(PPh2)3}2Cl]2+ at 300–400 nm at room temperature leads to an observed photoluminescence centred at ca. 537 nm with a lifetime of 11 µs [ϕ=(1.0 ± 0.1)× 10–3]. The excited-state redox potential, [Au3{HC(PPh2)3}2Cl]3++ e–→[Au3{HC(PPh2)3}2Cl]2+*, determined by quenching studies with a series of pyridinium acceptors, is –1.6(2) V vs. saturated sodium chloride calomel electrode (SSCE).

Photoredox properties of [OsN(NH3)4]3+ and mechanism of formation of [{Os(NH3)4(CH3CN)}2N2]5+ through a nitrido-coupling reaction

The oxidation of [Os(NH3)5Cl]2+ by CeIV in water gave [OsN(NH3)4]3+ quantitatively. Excitation of [OsN(NH3)4]3+ in the solid state or in solution at 300–400 nm resulted in room-temperature photoluminescence. The low-lying spin orbital E sublevel of the 3E {3[(dxy)1(dπ*)1]} state was assigned as the emission state. The excited state of [OsN(NH3)4]3+ was quenched by electron donors such as aromatic hydrocarbons, alkoxybenzenes, amines and alcohols. A photoinduced electron-transfer mechanism is proposed for the quenching processes. The emission lifetime of [OsN(NH3)4]3+ depended on the complex concentration. An excited-state bimolecular self-quenching mechanism ([OsVIN]*+[OsVIN]→ product) is likely. Photolysis of [OsN(NH3)4]3+ in the presence of an electron donor such as 1,4-dimethoxybenzene or C6Me6 in acetonitrile led to the formation of the µ-dinitrogen product [{Os(NH3)4(CH3CN)}2N2]5+. The coupling reaction obeyed the kinetics rate =k2[OsVI][OsV] where k2 was estimated to be (3.75 ± 0.30)× 105 dm3 mol–1 s–1 at 298 K. Oxidation of [{Os(NH3)4–(CH3CN)}2N2]5+ by CeIV in water followed by precipitation with 2 mol dm–3 HCl gave the product [OsN(NH3)4]Cl3 in detectable yield.

Photoredox properties of luminescent trinuclear copper(I) complexes with a bridging phosphine ligand and crystal structure of [Cu3(dpmp)2(MeCN)2(µ-Cl)2]ClO4[dpmp = bis(diphenylphosphinomethyl)phenylphosphine

The complexes [Cu3(dpmp)2(MeCN)2(µ-X)2]ClO4 were prepared by the reaction of CuX (X = Cl or I) with bis(diphenylphosphinomethyl)phenylphosphine (dpmp) in methanol followed by recrystallisation from acetonitrile. The complex cation [Cu3(dpmp)2(MeCN)2(µ-Cl)2]+[triclinic, space group P(no. 2), a= 12.839(1), b= 13.582(3), c= 21.510(3)A, α= 84.06(1), β= 72.71(1), γ= 78.00(1)°, Z= 2, R= 0.083 for 11 520 unique Mo-Kα data] consists of three copper(I) ions bridged by two chloride ions on the same side and by two dpmp ligands. The intramolecular, Cu ⋯ Cu separations are 3.26 and 3.30 A indicating no metal–metal interaction. Both [Cu3(dpmp)2(MeCN)2(µ-Cl)2]ClO4 and [Cu3(dpmp)2(MeCN)2(µ-I)2]ClO4 display room-temperature photoluminescence at 530 and 560 nm respectively. The photoredox properties of [Cu3(dpmp)2(MeCN)2(µ-Cl)2]+ have been investigated by flash photolysis and Stern–Volmer quenching experiments.

Polymer‐bound porphyrins and their precursors, 10. Syntheses and photoredox properties of water‐soluble polymers with covalently bonded zinc tetraphenylporphyrin

AbstractPositively or negatively charged as well as uncharged water‐soluble polymers 2a – d, 6a – c, 7a – e and positively charged crosslinked polymers 3a, b containing covalently bonded moieties of the substituted zinc tetraphenylporphyrin 1a were prepared. In addition, positively charged polymers 4a – c with covalently bonded viologen, and 5 with covalently bonded 1a and viologen at one and the same polymer chain were obtained. The triplet lifetimes in water of different 1a‐ bonded linear polymers 2a – d, 6a – c, and 7a – e are not influenced by the kind of polymer environment. The photoredox activites in water of the polymers containing moieties of 1a in the presence of methylviologen and 2‐mercaptoethanol under irradiation with visible light are higher as compared with low‐molecular‐weight, positively or negatively charged porphyrins 1b, c. The influence of the amount of polymer‐bonded porphyrin and the molecular weight of a polymer on the photoredox activity is exemplarily described. Polymers 4a – c with viologen moieties as acceptor are more efficient than the low‐moleular‐weight methylviologen. The highest photoredox activities were observed with polymer 5 containing moieties of 1a and viologen. In the presence of the enzyme hydrogenase formation of hydrogen occurs.

Photophysics and photochemistry of hexachlororhenate(IV) and hexabromorhenate(IV)

A study of the solution photophysical and photoredox properties of ReCl 6 2− and ReBr 6 2− is reported. The solutions are phosphorescent at room temperature, with emission maxima of 1340 nm (80 ns) and 1380 nm (40 ns) for (Bu 4 N) 2 [ReCl 6 ] and (Bu 4 N) 2 [ReBr 6 ], respectively, in CH 3 CN

Inorganic excimer. Spectroscopy, photoredox properties and excimeric emission of dicyano(4,4′-di-tert-butyl-2,2′-bipyridine)platinum(II)

The complex [Pt(dtbipy)(CN)2](dtbipy = 4,4′-di-tert-butyl-2,2′-bipyridine) has a long-lived intra-ligand (ππ*)3 excited state in fluid solutions (room-temperature lifetime at infinite dilution 3 µs in 1,2-dichloroethane). Excimer emission (maximum 565 nm) and photoinduced cligomerisation have been found for this platinum complex. The measured rate constant for the process [Pt(dtbipy)(CN)2]*+[Pt(dtbipy)(CN)2]→[{Pt(dtbipy)(CN)2}2]* is 9.0 × 108 dm3 mol–1 s–1 in 1,2-dichloroethane at room temperature. The photophysics and photoredox properties of the excited monomer and dimer are discussed.

Luminescent and coordinatively unsaturated heterobimetallic d10–d8complexes. Photoredox properties and X-ray crystal structure of [AuPt(µ-dppm)2(CN)2]+[dppm = bis(diphenylphosphino)methane

The X-ray structure and photoredox properties of [AuPt(µ-dppm)2(CN)2]+ which has a long-lived (18 µs in acetonitrile at room temperature) and emissive excited state are described.

Equatorial‐axial interactions of ligands and Photoredox Properties of Iron(III) Complexes containing tetradentate ligands of N2O2‐type

AbstractIron(III) complexes with a non‐cyclic tetradentate N2O2‐ligand of the type of “acacen” and “benacen” forming their equatorial plane undergo a photoreduction of FeIII to FeII when being irradiated in methanol by ultraviolet light. Quantum yields of the photoreduction of FeIII and the oxidation of an axial ligand depend on the wavelength of excitation light and on the peripheral groups of the equatorial ligands, but they correlate neither with Taft nor Hammett parameters of the peripheral groups.

Photoredox properties of free and caged iron(III) cytochrome c

Chemistry of horse-heart cytochrome c in two differents forms: a free solvated complex and a complex caged in a phospholipid liposome bilayer or in sodium dodecylsulfate micelles.