Photoactivated dyes

Sensitized photo-oxidation reactions are an example of such photoactivated catalysis (Section 4.5) in which C would be a dye which absorbs light and forms excited oxygen molecules (P) through energy transfer these excited oxygen molecules then lead to various oxidation reactions. There are other important examples of photoactivated catalysis in photoelectrochemistry (section 4.5.1). 

Photochemical preparation of stable dyes by irradiation of aminotriarylacetonitriles Photosensitive leucocyanide compositions Photoactivation of leucocyanides Solid photosensitive compositions Purification of triarylrnethane leucocyanides Fuchsine cyanide... 

Photoactivation of auric triarylmethanecyanide dyes with amine activator... 

For solution phase photopolymerization, photosensitive solutions must be prepared immediately before use. In film-based compositions, stability and sensitivity are lost in 2-5 days (compare Tables 6, 10). The lack of stability is directly related to the nature of the activator, although not in a way that necessarily parallels photosensitivity. The photoactivated reaction, dye-activator redox chemistry, is a go/no-go process and does not contribute to the dark reaction. Rather, dark reactions are in general a consequence of the basicity of most common activators, for example, amines, sulfinates, or enolates. Deprotonation of active methylene groups on some dyes (e.g.,... 

It should, however, be remembered that fixed cells cannot be stained with propidium iodide for live/dead discrimination. Fixed cells are, in fact, all dead and will therefore all take up propidium iodide even if some were alive and some dead before fixation. Ethi-dium monoazide offers an alternative to propidium iodide if cells will be fixed before flow analysis. It is a dye that, like propidium iodide, only enters dead cells. It has, however, the added advantage of forming permanent cross-links with DNA when photoactivated. Therefore, cells can be stained for surface proteins, incubated with ethidium monoazide under a desk lamp, washed, and then fixed. At the time of acquisition of data on the flow cytometer, red fluorescence will mark the cells that were dead before fixation. 

Adsorption of dyes onto a semiconductor surface allows for another mode of photoactivation [44-48]. The dye adsorbs a photon, generating an excited state in which a sufficiently higher-energy orbital is populated to allow direct injection of an electron into the conduction band edge [1]. The dye thus becomes oxidized and can either react chemically with nucleophiles by bond formation or can be restored to its original oxidation level by electron transfer. In the latter case, the reaction partner is oxidized, regenerating the ground state of the sensitizer ready to participate in... 

For practical photoinduced synthetic biocatalyzed transformations, it is important to integrate biocatalysts in immobilized matrices that allow the recycling of the photosystems. The fact that bipyridinium sites act as electron mediators for various redox enzymes was used to develop two paradigms for the electrical contacting and photoactivation of the biocatalyst (Figure 39). By one approach, the bipyridinium electron relays are tethered by covalent bonds to the protein backbone (Figure 39A). These electron relays act as oxidative quenchers of the excited state of the dye and, upon photoreduction of the electron acceptor units, they act as electron carriers that activate the reductive functions of the enzyme. As an example, the... 

A. Andreoni (1987). Two-step photoactivation of hematoporphyrin by excimer-pumped dye-laser pulses. J. Photochem. PhotobioL B, 1, 181-193. 

PO can be made degradable by means of additives. The types of additives include aromatic ketones (benzo-phenone and substituted benzophenones [47], qui-none), aromatic amines (trisphenylamine), polycyclic aromatic hydrocarbons (anthracene, certain dyes such as xanthene dyes), or transition metal organic compounds. The transition metal compounds of Fe, Co, Ni, Cr, Mn are widely used. Organo-soluble acetyl acetonates of many transition metals are photooxidants and transition metal carboxylates are also thermal pro-oxidants. Co acetylacetonate appears to be an effective catalyst for chemical degradation of PP in the marine environment. The preferred photoactivator system is ferric dibutyldithiocarbamate with a concentration range of 0.01. 1%. Scott has patented the use of organometallic compounds hke iron (ferric) dibutyldithiocarbamate or Ni-dibutyl-dithiocarbamate [48]. Cerium carboxylate [49] and carbon black are also used in such materials [50]. 

In addition to transferring excitation energy to molecular oxygen to generate singlet oxygen 2) (cf section 7.3), the photoactivated dye molecule (D )... 

The photoactivated dye molecule (D ) may also abstract a hydrogen atom from a polymer (PH) molecule and produce a polymer alkyl radical (P ), which may react further with molecular oxygen and form a polymer peroxy radical (POO ) ... 

K. V. Reddy and M. J. Berry, Intracavity CW dye laser photoactivation of unimolecular reactants Isomerization of state-selected methyl isocyanide, Chem. Phys. Lett. 52 111 (1977). 

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