Platinum octaethylporphyrin

Platinum porphyrin complexes can be prepared by reaction with PtCl2(PhCN)2. Purification of the final complex is by medium pressure liquid chromatography on alumina. The strongly phosphorescent platinum(II) porphyrin complexes are efficient sensitizers for stilbene isomerization. The quantum yields for the cis to trans process are greater than unity because of a quantum chain process in which the metalloporphyrin serves both as an energy donor and an acceptor.1110 Picosecond laser spectroscopy has been used to obtain time-resolved excited-state spectra of platinum octaethylporphyrin complexes, and to probe the excited-state energy levels.1111 Tetrabenzoporphyrin complexes have been prepared for platinum in both the divalent and tetravalent oxidation states. The divalent complex shows strong phosphorescence at 745 nm.1112... 

Another promising example of a metal-based sensor can be seen in the work of Lee and Okura (239) who used entrapped platinum octaethylporphyrin complexes to form photostable devices. In their study, they found by adding the surfactant Triton X-100 to the sol-gel mixture, they could improve homogeneity and phosphorescence of the dye-containing glass. Encapsulated porphyrin molecules have also been used successfully in the sensing of nitrogen dioxide (240) and, as will be discussed below, can be used to sense metal ions. 

Fig. 15.3 (a) Room-temperature phosphorescence spectra of platinum-octaethylporphyrin (PtOEP)-doped sol-gel glass under different atmospheric conditions top), ambient conditions (middle), and bottom). Excitation wavelength, 535 nm. (b) Response time, relative intensity change, and reproducibility of sensor response on switching between 100 % nitrogen (a) and 100 % oxygen (Reprinted with permission from Lee and Okura 1997, Copyright 1997 Royal Society of Chemistry)... 

With their preference for square planar coordination, palladium(II) and platinum(II) are well suited to binding to porphyrins and related N4 donor macrocycles. Therefore, Pd(octaethylporphyrin) is readily synthesized starting from the labile PhCN complex (like the platinum analogue) [92]... 

Wu et al. [31] have recently presented a novel concept of designing oxygen nanosensors. They used the precipitation method to obtain polyfluorene beads (0 25 nm) doped with the oxygen indicator platinum(II) octaethylporphyrin. Poly (9,9-dihexylfluorene) belongs to materials widely used in OLEDs and has a bright blue emission when excited in the UV region. In beads, FRET-mediated red emission... 

Table 8 Half-wave Potentials (E)) (in V vs. see) of Octaethylporphyrins, using Cyclic Voltammetry with a Platinum Button Electrode3...

Ru(bipy)i Ru(II)-tris-2,2,bipyridiyne Ru(phen) Ru(II)-tris-l,10-phenanthroline Ru(dpp) Ru(II)-tris(4,7-diphenyl)-l,10-phenanthroline PtOEP platinum(II)-octaethylporphyrin PdOEP palladium(II)-octaethylporphyrin PdTPFFP palladium(II)-tetra(pentafluoro-phenyl)porphyrin L 2,4,7,9-tetraphenyl-l,10-phenanthroline py pyridine MP 3-methyl-pentane... 

Similarly, octaethylporphyrin iron (lll)-(r-bonded pyrrole [(OEP)FePy], either adsorbed on a glassy carbon electrode, or buried in a polypyrrole film of different thickness (from 0.9 to 60 pm), deposited on a GC electrode, displays an excellent activity towards oxygen reduction leading to water production efficiencies of nearly 90% [150]. These [(OEP)FePy] electrodes buried into a PPy film are remarkably stable leading to a catalytic activity similar to that obtained with platinum electrodes and limited by the diffusion of dioxygen in the solution phase. 

Besides hard inorganic metal templates, lipid molecules are used in the synthesis of foam-like nanostructures. Shelnutt and coworkers synthesized foam-like Pt nanospheres with a 2 nm-thick shell and diameters of up to 200 nm in the presence of liposomes, through either a chemical or photochemical reduction process (Figure 10.14c) [57-59]. Here, ascorbic acid was used as the chemical reducer for the platinum precursor. Alternatively, hydrophobic Sn(lV) octaethylporphyrin (SnOEP) could be used as the photocatalyst molecule under white light irradiation. 

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