Photoactive complex

It is important to emphasize the role of the solid state in providing a medium for the formation of the molecular assembly 2(resorcinol) 2(4,4 -bpe). Indeed, that 2(resorcinol) 2(4,4 -bpe) is stabilized by weak forces (i.e. hydrogen bonds) comparable in strength to structure effects of solvent and entropy of the liquid phase [13] means that the components of 2(resorcinol)-2(4,4 -bpe) may assemble in solution to produce multiple equilibria involving individual molecules and undesirable (photostable) complexes. In effect, the solid state was used to sequester [23] 2(resorcinol) 2(4,4 -bpe) from the liquid phase, facilitating the formation of the desired photoactive complex and construction of the cyclobutane product. 

Although not necessarily involving photoactive complexes, a variety of approaches have been used to design radiopharmaceuticals for imaging central nervous system receptors. Ultimately, such studies are an important extension of photochemical applications of Re complexes since the design of radiopharmaceuticals that luminescence (for detection) and are therapeutic (by radiation) is a topic of current interest [19]. Re complexes are usually studied prior to the preparation of Tc derivatives since their chemistries are so similar, although the use of Re isotopes for therapy is also possible. 

Excited state lifetime tq is another important parameter to be controlled, especially if the photoactive complex is intended for bimolecular photochemical electron transfer. MLCT excited states of most polypyridine complexes decay both radia-tively and non-radiatively, with the respective rate constants and k r. The inherent excited state lifetime is defined as tq = l/( r + nr)- The non-radiative decay pathway in most cases prevails k r K. Hence To = 1 /km- Non-radiative decay of MLCT excited states can be treated as intramolecular electron transfer in the Marcus inverted region ... 

One other feature of the data in Table 3 and elsewhere [56,79, 82] relates to the pressure effects on the nonradiative pathways from the LF excited states of the Rhm complexes. For these photoactive complexes, the pressure dependence of kn generally has the same sign as that for the major photoreaction pathway but a smaller absolute value. This finding may indicate the parallel character of ks and a strong-coupling contribution [88] to ka. Such a pattern would be consistent with a reaction coordinate, which approaches the GS surface in a manner that allows partitioning between reactive deactivation and nonradiative deactivation. 

N-acetylated derivatives leads to the formation of Fe(II) porphyrins together with the acyloxy radical which undergoes decarboxylation to give ammonio-alkyl or amidoalkyl radicals. Large differences in the observed rates of Fe(II) porphyrin formation can be accounted for in terms of two factors, the binding affinity of the carboxyl to form a photoactive complex, and competitive reactions of acyloxy radicals following photolysis. 

The structural and spectroscopic features of the photoactive complex are preserved inside the polymeric film, as confirmed by UV-vis spectra. In addition, SEM analysis of both the film surface and cross-section highlight a well-dispersed, homogeneous distribution of the catalyst domains, which appear as spherical particles of approximately 1-2 xm in diameter. The structural similarity of (RfN)4Wio032 with other surfactant encapsulated polyoxometalates (SEPs) suggests the formation of organized domains, similar to spherical onion-like vesicles. ... 

It is obvious from the three examples studied that the formation of the photoactive complex parallels the complexing ability of the substrate and one may speculate that formation of this species requires photodissociation of at least one phosphine ligand in addition to CO. However, the exact nature of one and the other species remains obscure. Moreover, in the hydrogenation study of acrylate the most effective wavelength, 407 nm, does not coincide with an absorption band of the starting complex but rather with an MLCT band of the hydride Ir(Cl)H2(CO)(P(j-prop)3)2. 

Bipyridyl complexes of Ru(II) can be used for the production and storage of multiple photochemical redox equivalents by attachment to a soluble polymer. The photoactive complexes have been bound to a styrene/chloromethylstyrene copolymer by nucleophilic displacement of the chloro groups from the chloromethyl-styrene. Because the excited state properties are relatively unaffected in the mixed-valence polymers, it is possible to build up a chain of approximately 30 oxidative equivalents with a (bpy)2Ru or a (bpy)20s moiety bonded to each strand of the polyma . Excited state donors and acceptors can also be immobilized using a sol-gel technique. Such a technique has been s plied to the 1,4-dimethoxyl-benzene mediated photoinduced electron transfer between bipyridyl complexes of ruthenium and iridium. Metallopolymeric films have also been used for energy... 

The initiating radicals are assumed to be SCN, ONO or N3 free radicals. Tris oxalate-ferrate-amine anion salt complexes have been studied as photoinitiators (A = 436 nm) of acrylamide polymer [48]. In this initiating system it is proposed that the CO2 radical anion found in the primary photolytic process reacts with iodonium salt (usually diphenyl iodonium chloride salt) by an electron transfer mechanism to give photoactive initiating phenyl radicals by the following reaction machanism ... 

Silver nitrate and/or cuppric nitrate [50] can photoinitiate the polymerization of acrylonitrile in a dimethyl formamide (DMF) medium. The photoactive species is the complex formed between the monomer and salt molecules ... 

A novel type of grafting process was developed using a new photosensitive polymer containing vanadium (V) chelates. These polymers were generally synthesized by the condensation of a VOQ2OH complex and a hydroxy-containing polymer to produce photoactive polymer (red in color) with pendant vanadium (V) chelate. 

No structural studies have been reported on these complexes, but detailed study of their vibrational spectra permits the assignments shown in Table 2.13. Like the rhodium analogues, iridium ammines are photoactive therefore, on excitation of ligand-field bands, solutions of [Ir(NH3)6]3+ or [Ir(NH3)5Cl]+ afford [Ir(NH3)5(H20)]3+. 

The cathodic approach has been investigated actively as a method for the production of thin film CdS, in particular for the fabrication of heterojunction cells. Photoactive CdS films could be grown in alkaline NH3/NH4Cl-buffered aqueous solutions containing thiosulfate as sulfur source and complexed Cd (EDTA+NH3), on Ti substrates [41]. The electroreduction of thiosulfate was considered to proceed as... 

The [Co(phen)3]3+ complex is photoactive and a powerful oxidant in its excited state. The ion has no H-bonding groups and hence is considerably more hydrophobic1279 than hexaamine relatives. These properties have proven particularly useful. Aryl and alkyl substituted [Co(phen)3]3+ complexes have received a great deal of attention due to their ability to intercalate within the helical structure of DNA through a combination of electrostatic and hydrophobic forces. The chirality of the tris-chelate complex is crucial in determining the degree of association between the complex and... 

The X-ray structure of zinc naphthalocyanate has been determined with Zn—N bond lengths of 1.983(4) A.829 Pentanuclear complexes with a zinc phthalocyanine core and four ruthenium subunits linked via a terpyridyl ligand demonstrate interaction between the photoactive and the redox active components of the molecule. The absorbance and fluorescence spectra showed considerable variation with the ruthenium subunits in place.830 Tetra-t-butylphthalocyaninato zinc coordinated by nitroxide radicals form excited-state phthalocyanine complexes and have been studied by time-resolved electron paramagnetic resonance.831... 

The mechanism of this reaction was studied in detail, using high-pressure UV and IR spectroscopy. The first step is a fast thermal reaction of cobalt acetate with syn-gas and phosphine to from the ionic complex 7. The yellow cation is the photoactive species. 

A methanofullerene derivative possessing an ammonium subunit has been prepared and subsequently shown to form a supramolecular complex with a porphyrin-crown ether conjugate <06T1979>. The synthesis and study of these fullerene-containing supramolecular photoactive devices have also been reported <06CRC1022>. 

Fig. 3. Photoactivation of Pt(IV) complexes as a prodrug strategy for metallochemotherapeutics (a) general scheme of prodrug activation by photoreduction (b) photosubstitution and photoisomerization are competing photoreaction pathways, which can result in different reactive species upon reduction (c) an example of a photoactive platinum(IV) diazido complex developed in our lab.

Pt(TV)-Iodido Complexes. The first photoactive Pt(IV) prodrugs were reported by Bednarski et al. in the 1990s (23). The complex... 

Fig. 4. Photoactive Pt(IV)-iodido complexes, (a) Molecular structures of complexes 1-3 (b) influence of visible light on CT DNA binding of 2 and cytotoxicity of 2 against a TCCSUP human bladder cell line (data from Ref. (23)) (c) NMR studies showed that photosubstitution precedes photoreduction in the reaction of 2 with 5 -GMP upon irradiation Ref. (25).

The iodido-Pt(IV) complexes thus provided a proof-of-principle being photoactive, but the complexes still suffered from slow photoreactions and, importantly, limited stability in the dark especially against biological reducing agents such as glutathione, which results in undesired toxicity of the anticancer agents in the dark. 

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