Photosensitizer macrocyclic

Run/Nin heteronuclear complexes such as (653), in which a photosensitizer [Ru(bpy)3]2+ or [Ru(phen)3]2+ is covalently attached to the Ni1 cyclam complex, have been synthesized in order to improve the efficiency of electron transfer from the photoexcited photosensitizer to the catalytic site.1 44-1646 However, these complexes did not perform particularly well, either due to unfavorable configuration of the Nin-cyclam subunit and the resulting steric hindrance or due to short lifetime of the excited states of the Ru photosensitizer moieties. A stable catalytic system has been prepared by immobilizing macrocyclic Ni11 complexes and [Ru(bipy)3]2+ in a nafion membrane.164... 

Some Ni(II) macrocyclic complexes mediate electron transfer and produce CO during the photochemical reduction of C02. However, photochemical reduction of C02 using a photosensitizer, a sacrificial electron donor, and [Ni(cyclam)]2+ as the catalyst has been only moderately successful compared to the electrochemical reduction of C02 using [Ni(cyclam)]2+. 

In this section, the various transition metal complexes, macrocycles, and aromatic hydrocarbons which act as either photosensitizers or cocatalysts for the reduction of C02, will be described. 

Matsuoka used a different photosensitizer, p-terphenyl, with a cobalt(III) cyclam as the catalyst [37-39], In a C02-saturated acetonitrile/methanol solution with either TEOA or TEA as the sacrificial reductant, the quantum efficiencies for CO and formic acid production were 15% and 10%, respectively, under 313 nm illumination. Again, however, the TONs and production rates for macrocyclic complexes were low. 

Sessler, J.L. et al. (1991) Tripyrroledimethine-derived ("texaphyrin"-type) macrocycles potential photosensitizers which absorb in the far-red spectral region, Proc. SPIE-The International Society for Optical Engineering 1426, 318-329. 

Synytsya, A. et al. (2003) In vitro interaction of macrocyclic photosensitizers with intact mitochondria a spectroscopic study, Biochim. Biophys. Acta 1620, 85-96. 

Photosensitized generation of hydrido-metal complexes in aqueous media provides a general route for H2-evolution, hydrogenation of unsaturated substrates (i.e. olefins, acetylenes), or hydroformylation of double bonds, see Scheme 2. Co(II) complexes, i.e. Co (II)-fn s-bipyridine, Co(bpy) +, or the macrocyclic complex Co(II)-Me4[14]tetraene N4, act as homogeneous H2-evolution catalysts in photosystems composed of Ru(bpy) + (or other polypyridine (Ru(II) complexes) as photosensitizers and triethanolamine, TEOA, or ascorbic acid, HA-, as sacrificial electron donors [156,157], Reductive ET quenching of the excited photosensitizer... 

Other Co(II)-complexes that were applied in the photosensitized reduction of C02 to CO (and concomitant H2-evolution) include Co(II)-ethylene glycol dimethyl ether complexes [178], and different tetraaza-macrocyclic Co(II)-complexes such as 27,28. A closely related system, where Ni(II)-tetraaza macrocycle (29) substitutes the cobalt homogeneous complexes in the photosystem including Ru(bpy) + as photosensitizer and ascorbic acid as electron donor, has been reported by Tinnemans [181] and Calvin [182],... 

The chemical structures of [2]catenane 19 and the related [3]catenane 20 (Fig. 8) were conceived as an extension of their work on molecular shuttles. The larger macrocycle in 19 comprises two fumaramide stations with differing macro cycle binding affinities. In station B (red) the methyl groups on the fumaramide motif cause it to have lower affinity than the standard fumaramide station. The non-methylated fumaramide station (station A, green) is located next to a benzophenone unit. This allows selective, photosensitized isomerization of station A by irradiation at 350 nm. Station B (red) can be photoisomerized by direct irradiation at 254 nm. The third station, a succinic amide ester (station C, orange), is not photoactive and is intermediate in macrocycle binding affinity between the two fu-... 

The [2 + 2]-photocycloaddition of nonconjugated alkenes was described in Chapter 5. This strategy can be used for synthesizing macrocyclic rings by using a long linker between the two alkene moieties (Scheme 9.47). Thus, bicyclic cyclobutanes can be obtained starting from enol ethers and cinnamates by means of electron-transfer sensitizers, such as DCN or DCA [80], and triplet photosensitizers such as benzo-phenone (BP) [81]. 

Parker D, Senanayake PK, Williams JAG. Luminescent sensors for pH, 02, hahde and hydroxide ions using phenantrohne as a photosensitizer in macrocyclic europium and terbium complexes. J Chem Soc Perkin Trans 2 1998 2129-39. 

Selectivity. The selectivity of photosensitizers can be also affected by central metal ions and substituents at the macrocycle, eg tetrasulphonated chloroaluminium phthalocyanine [Al(pcS4)Cl] localizes well in the tumour, whereas tetrasulphonated zinc phthalocyanine [Zn(pcS4)] (and also disulphonated zinc phthalocyanine [Zn(pcS2)]) shows a relatively poor tumour localization [207],... 

Currently the singlet oxygen producing capability and general photosensitizing properties, of the macrocycle 287 along with its efificacity vis a vis the photodynamic... 

Ni macrocyclic complexes have also been investigated as covalent attachments to photosensitizers such as [Ru(bipy)3] +, and as interchelating agents for the cleavage ofDNA. ... 

These complexes, all of which contain cobalt within a macrocyclic ligand and an axial cobalt-carbon bond, have been found to be photosensitive and have been the subject of numerous photochemical studies. Space does not permit a detailed summary of all the studies which have been conducted on these classes of compounds, and we present here only a general summary of the various observations and discuss pertinent articles from the most recent literature. The reader is referred to an excellent review of the subject by Koerner von Gustorf et al. 108) which presents a detailed discussion of reports that appeared prior to 1975. 

Figure 14. Photocontrollable molecular machines based on pseudorotaxanes. In these second-generation systems the light-fueled motor (i.e., the photosensitizer, P) is part of the (a) wire-like [18] or (b) macrocyclic component [20], Red (triethanolamine) is a reductant scavenger. Conditions (a) EtOH, 298 K (b) H2O, 298 K.

The prototypical photochemical system for CO2 reduction contains a photosensitizer (or photocatalyst) to capture the photon energy, an electron relay catalyst (that might be the same species as the photosensitizer) to couple the photon energy to the chemical reduction, an oxidizable species to complete the redox cycle and CO2 as the substrate. Figure 1 shows a cartoon of the photochemical CO2 reduction system. An effective photocatalyst must absorb a significant part of the solar spectrum, have a long-lived excited state and promote the activation of small molecules. Both organic dyes and transition metal complexes have been used as photocatalysts for CO2 reduction. In this chapter, CO2 reduction systems mediated by cobalt and nickel macrocycles and rhenium complexes will be discussed. 

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