Time-resolved absorption spectrum

Fig. 17. Time-resolved absorption spectra for APh-2 (8 with x = 2) in aqueous solution in the presence of 5raM MV2 + [Phen](residue) -- 0.66 mM. Delay times after the laser pulse are indicated [120]...

We emphasize that the critical ion pair stilbene+, CA in the two photoactivation methodologies (i.e., charge-transfer activation as well as chloranil activation) is the same, and the different multiplicities of the ion pairs control only the timescale of reaction sequences.14 Moreover, based on the detailed kinetic analysis of the time-resolved absorption spectra and the effect of solvent polarity (and added salt) on photochemical efficiencies for the oxetane formation, it is readily concluded that the initially formed ion pair undergoes a slow coupling (kc - 108 s-1). Thus competition to form solvent-separated ion pairs as well as back electron transfer limits the quantum yields of oxetane production. Such ion-pair dynamics are readily modulated by choosing a solvent of low polarity for the efficient production of oxetane. Also note that a similar electron-transfer mechanism was demonstrated for the cycloaddition of a variety of diarylacetylenes with a quinone via the [D, A] complex56 (Scheme 12). 

Figure 3 Subpicosecond time-resolved absorption spectra for the ring opening of NOSH in 1-butanol. (Data courtesy of N. Tamai [26].)...

Figure 22 Time-resolved absorption spectra measured at 30,220, and 2000 nsec (gate time 30 nsec) after e during PR of DMP (5.0 x 10 M) in DCE.

Experiments have been carried out on PS1 reaction centres, isolated from pea chloroplasts, with a chi/ P700 ratio of 50 (see Giorgi et al., 1987). P700 was chemically reduced in the dark by ascorbate and chemically oxidised by ferricyanide. The time-resolved absorption spectra obtained are shown in Fig.l. Two obvious spectral features occur, one centred at 690nm and one at 700nm. 

Figure 15-18. Picosecond time-resolved absorption spectra of p-CH3OOC-DPA (left), DPA (center), and /7-OCH3-DPA (MO-DPA) in n-hexane at room temperature, which illustrate the effects of electron-donating and electron-withdrawing substituents on the iter -state absorption of DPA at about 700 nm. The spectra were adapted from [38] with permission, and the assignments S, (tto- ), S2 (tt-jt ), and T, (tth ) are with reference to the bent geometry of DPA (from Ref. [37]). (Reprinted with permission from Ref. [44].)...

Figure 15-23. Picosecond time-resolved absorption spectra of / -(dimethylamino)-//-cyano DPA (DACN-DPA) (left) and DM ABN (right) in non-polar and polar solvents. The assignments of the lightabsorbing states are and S2( mr ). The spectra for DACN-DPA are adapted with permission...

When primary and secondary co-arylalkylamines are excited, exciplex fluorescence is not observed, but fluorescence quenching does take place (Shizuka et al., 1979). Presumably chemical reaction competes effectively with exciplex formation. However, by means of picosecond laser flash photolysis, the time-resolved absorption spectra of the species produced on reaction of pyrene with diphenylamine have been obtained (Okada et al., 1980b). It was shown that the reaction leads to neutral radicals via an exciplex. Although the formation of neutral radicals in such systems had been previously identified (Okada et al, 1976a) the role of exciplexes had been purely speculative. 

Figure 11. (a) Time-resolved absorption spectra of observed at 0.1 ps (O) and 1 ps ( ) after laser... 

The simplest picture of donation to P-680 is one in which a single component, Z, acts as a carrier for electrons between P-680 and the oxygen-evolving complex. Time-resolved absorption spectra of minus Z in Tris-inhibited [171,172] and in... 

Fig. 11. Time-resolved absorption spectra in neat methanol after two-photon absorption at 273 nm and energy level scheme used to account for the measmed dynamics during the generation of solvated electrons. [Reprinted ftom Ref. 94, Copyright 2003, with permission from Elsevier.]...

Fig. 4. (A) Time-resolved absorption spectra obtained from pulse radiolysis...

Fig. 3.2 Deca-picosecond time-resolved absorption spectra of the all-trans and cis isomers of retinal. The T, state was generated by direct excitation of isomeric retinal with the 355 nm, 20-25 ps pulses [5].

Figure 3.13 shows the time-resolved absorption spectra of isomeric sphero-idenes. In the all-trcws isomer, concomitant with the decay of a sharp peak on the shorter wavelength side due to the sensitizer anthracene, the rise and decay of the... 

Figure 16.6. Time-resolved absorption spectra of enzyme-bound FAD in pyruvate oxidase from Lactobacillus plantarum during the first turnover reduction by pyruvate under anaerobic...

Picosecond and nanosecond pulse methods have been used to measure the time-resolved absorption spectra of 9-nitroanthracene, 9-benzoyl-10-nitroanthracene, and 9-cyano-10-nitroanthracene. The long build-up time for triplet-triplet absorptions (72—86 ps) suggests that these do not represent the lifetimes of the singlet states but are the rates of internal conversion within the triplet manifold and that indirect intersystem crossing Si(n,n ) T (n,n ) - Ti(n,n ) is the most important process for populating Tj. 

Nickel.—Studies of the time-resolved absorption spectra of (14) following mode-locked laser photolysis have been reported.116 Spectra could be recorded down... 

Figure 7a presents the four traces needed to obtain a corrected transient absorption decay at a specific wavelength baseline, top-line, emission, and absorption. By taking into account the entire wavelength range where the excited species absorbs, and also by a suitable choice of the time scale, triplet-triplet time resolved absorption spectra can be obtained, such as the one presented in Figure 7b for benzophenone crystals. These spectra provide both spectroscopic and kinetic information regarding the powdered opaque sample. It is obvious that these spectra will enable one to study the occurrence of a chemical reaction on surfaces, pro-... 

Using high resolution time resolved absorption spectra we have been able to observe the time evolution of a nearly monoenergetic population of carriers in a semiconductor, excited with a short optical pulse, to a carrier distribution In which a temperature can be defined. 

Sj-Sn absorption spectra of meso and racemic A6 were reported by Masuhara et al. (1983). The growing in of a new absorption band at 880 nm in the time-resolved absorption spectra of meso A6 in THF corresponds to the growing in of the excimer emission at 460 nm. No large changes were observed in the time-resolved absorption spectra of racemic A6. 

Several combinations of pump and probe experiments are possible (i) UV-Vis pump/visible single wavelength probe, types of the data generated are absorption changes at a certain wavelength (ii) UV-Vis pump/white light probe, types of the data generated are time-resolved absorption spectra (Fig. 8.15). 

In these experiments the decay curve of transient absorbance at a given wavelength is studied in real time. It is also possible to obtain time-resolved absorption spectra of transients, recording their absorbance at pre-determined times (2. , f -... 

Time-resolved absorption spectra of samples of BZP/C12- 1700/EtOH and Cl 2-I5OO/H2O samples were obtained by the use of diffuse reflectance laser flash photolysis technique, developed by Wilkinson et al. [2-4]. In this study, the use of an intensified charge-coupled device as a detector allowed us to obtain time-resolved absorption spectra with nanometer spectral spacing (i.e., where the 200-900 scale is defined by the 512 pixels used for recording spectra in the array of the ICCD) [1,8-14]. 

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