Phosphorescent platinum

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... 

Long-decay luminescent dyes and probes that are effectively quenched by molecular oxygen can be used for its quantitation. Examples of such probes include ruthe-nium(II)-rm(diphenyl phenanthroline) and phosphorescent platinum(II) porphyrins. Their long emission lifetimes facilitate quantitation by lifetime or intensity measurements. Other chemical specie, such as heavy-metal ions and heterocyclic compounds, can be quantified by luminescence quenching, according to Eq. 3. 

Two examples of such PPPs with on-chain phosphorescent units are presented here. In the first example phosphorescent palladium centers are incorporated into the LPPP backbone by accident, and in the second example, phosphorescent platinum-salen (Pt-salen) complexes are incorporated by design into the PF-type copolymers. 

Like the palladium(II) complexes, the platinum(II) porphyrins show appreciable phosphorescence even in aqueous media at room temperature in one study,169 singlet oxygen quantum yields ranged from 0.1 to 0.9 and were strongly influenced by dimerization/aggregation. Platinum(II) 5,10,15,20-tetrakis(/>-carboxyphenyl)porphyrin and platinum(II)coproporphyrin-I ((36) for Pd read Pt) have been studied as phosphorescent labels of antibodies for use in time-resolved microscopy.189... 

Baldo et al. [ 164] used the platinum complex of 2,3,7,8,12,13,17,18-octaethyl-21 //,23//-porphine (PtOEP, 66) as efficient phosphorescent material. This complex absorbs at 530 nm and exhibits weak fluorescence at 580 nm but strong phosphorescence from the triplet state at 650 nm. Triplet transfer from a host like Alq3 was assumed to follow the Dexter mechanism. Dexter-type excitation transfer is a short-range process involving the exchange of electrons. In contrast to Forster transfer, triplet exciton transfer is allowed. 

Platinum and palladium porphyrins in silicon rubber resins are typical oxygen sensors and carriers, respectively. An analysis of the characteristics of these types of polymer films to sense oxygen is given in Ref. 34. For the sake of simplicity the luminescence decay of most phosphorescence sensors may be fitted to a double exponential function. The first component gives the excited state lifetime of the sensor phosphorescence while the second component, with a zero lifetime, yields the excitation backscatter seen by the detector. The excitation backscatter is usually about three orders of magnitude more intense in small optical fibers (100 than the sensor luminescence. The use of interference filters reduce the excitation substantially but does not eliminate it. The sine and cosine Fourier transforms of/(f) yield the following results ... 

Edmond Becquerel (1820-1891) was the nineteenth-century scientist who studied the phosphorescence phenomenon most intensely. Continuing Stokes s research, he determined the excitation and emission spectra of diverse phosphors, determined the influence of temperature and other parameters, and measured the time between excitation and emission of phosphorescence and the duration time of this same phenomenon. For this purpose he constructed in 1858 the first phosphoroscope, with which he was capable of measuring lifetimes as short as 10-4 s. It was known that lifetimes considerably varied from one compound to the other, and he demonstrated in this sense that the phosphorescence of Iceland spar stayed visible for some seconds after irradiation, while that of the potassium platinum cyanide ended after 3.10 4 s. In 1861 Becquerel established an exponential law for the decay of phosphorescence, and postulated two different types of decay kinetics, i.e., exponential and hyperbolic, attributing them to monomolecular or bimolecular decay mechanisms. Becquerel criticized the use of the term fluorescence, a term introduced by Stokes, instead of employing the term phosphorescence, already assigned for this use [17, 19, 20], His son, Henri Becquerel (1852-1908), is assigned a special position in history because of his accidental discovery of radioactivity in 1896, when studying the luminescence of some uranium salts [17]. 

Recently we observed eel of the binuclear platinum complex tetra-kis(diphosphonato)diplatinate(II) (Pt (pop) ) (37). This anion has attracted much attention due to its intense green luminescence in room temperature solution (38-40) (excited state of this complex undergoes oxidative (42) and reductive quenching (41). From the quenching experiments the redox potentials were estimated to be E° = -1.4 V vs. SCE for the reduction and E° 1 V for the oxidation of Pt2(pop) - (41). The potential difference of 2.4 V almost matches the energy of the phosphorescing triplet ( 2.5 eV) of Pt -(pop) . Consequently, it should be possible to observe eel of this... 

For this particular complex, the only emission observed at room temperature was residual fluorescence emanating from the BODIPY fragment and at low temperature, the presence of the platinum center induces intersystem crossing and phosphorescence from the BODIPY was indeed observed at 1.6 eV. 

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