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Laser photolysis triplet-state probes

The use of excited triplet states as probes occurred in concert with the development of fluorescent probe methodologies but have not been employed to the same extent. Phosphorescence quantum yields in solution are generally much lower than fluorescence quantum yields, and when the emission of triplet states is measured, the signal-to-noise advantage of the fluorescent probes is lost. In most cases, triplet excited states are followed by their absorption spectra using laser flash photolysis. A second reason for the scarcer reports on the use of excited triplet states probes in supramolecular systems is the fact that the laser flash photolysis technique has not been as widespread as fluorescence techniques. This situation has changed over the past decade and we expect that the number of smdies which employ excited triplet states will increase. [Pg.433]

Boxer s group [2] first made a ns-laser photolysis apparatus with a super-conducting magnet. The sample was excited at 532 or 600 nm with a frequency-doubled YAG pumped dye laser (8ns, fwhm) and was probed at 860 nm with a laser diode. The maximum field of their magnet was 5 T. With this apparatus, they measured the quantum yield of triplet states (detected optically in quinone-depleted photosynthetic reaction centers (RCs) from R. spheroids, R-26 mutant, as a function of applied magnetic strength and temperature. The reaction scheme for qinone-depleted RCs is shown in Fig. 12.1. Here, the singlet and triplet radical-ion pair (RIP) are represented by [D" A ] and [D A ], respectively, and the rate constants of the S-T conversion of RIP, the recombination from [D A ], and the recombination from [D A ] are denoted by hsT, ks, and kj, respectively. [Pg.179]

Since the lowest triplet state of nitrostilbenes at room temperature can be probed by laser flash photolysis, quenching rate constants could be measured directly [188,200], Values for kq are close to the diffusion-controlled limit (Table 17). Comparable results have been obtained for naphthyl-[410] and 2-anthrylethylenes [433] and for ADBs [33, 143, 145-147, 232, 411], For substituted 1-NPEs, conclusions about the position of the triplet equilibrium were drawn on the basis of rate constants for quenching by ferrocene and oxygen [441]. [Pg.68]

The most widely used vibrational spectroscopic technique is time-resolved resonance Raman spectroscopy (TR ) [65]. This has been used successfully to obtain structural information about organic excited states in SCCO2. McGar-vey and co-workers probed the excited triplet state of anthracene in SCCO2 [66]. However, TR experiments involve data collection over many laser pulses, with all of the problems associated with secondary photolysis. These problems have prevented TR being used effectively to follow chemical reactions apart from highly photoreversible processes. To our knowledge, TR has not yet been used to follow chemical reactions in SCFs. Recently, however. [Pg.156]

The use of triplet excited states as probes to study the surface properties of many solids is particulary interesting, due to the fact that they usually exhibit long lifetimes which in most cases come closer to those obtained for rigid matrices. These long lifetimes increase in many cases the efficiency of several photochemical processes. Therefore spectroscopic and kinetic studies can be performed in a wide and interesting variety of situations. As we said before, the development of the diffuse reflectance laser flash photolysis technique [1,10] by Wilkinson et al. was crucial for the development of these studies on surfaces. [Pg.298]


See other pages where Laser photolysis triplet-state probes is mentioned: [Pg.921]    [Pg.204]    [Pg.305]    [Pg.112]    [Pg.219]    [Pg.90]    [Pg.306]    [Pg.312]    [Pg.147]    [Pg.61]    [Pg.110]    [Pg.319]    [Pg.322]    [Pg.331]    [Pg.1694]   


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