Absorption spectra transient

Several of the aforementioned compounds have now been examined by femtoseconds and nanoseconds, transient absorption spectroscopy in THF solutions. From the decay of the transients, the lifetimes of the photoexcited states SI and T1 have been determined. Representative compounds that have been examined in this manner are given in Table 6.3. 

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The one-electron reduction of thiazole in aqueous solution has been studied by the technique of pulse radiolysis and kinetic absorption spectrophotometry (514). The acetone ketyl radical (CH ljCOH and the solvated electron e were used as one-electron reducing agents. The reaction rate constant of with thiazole determined at pH 8.0 is fe = 2.1 X 10 mole sec in agreement with 2.5 x 10 mole sec" , the value given by the National Bureau of Standards (513). It is considerably higher than that for thiophene (6.5 x 10" mole" sec" ) (513) and pyrrole (6.0 X10 mole sec ) (513). The reaction rate constant of acetone ketyl radical with thiazolium ion determined at pH 0.8 is lc = 6.2=10 mole sec" . Relatively strong transient absorption spectra are observed from these one-electron reactions they show (nm) and e... 

Data on duorescence, phosphorescence, excited-state lifetimes, transient absorption spectra, and dye lasers are tabulated in Ref. 16. The main nonduorescent process in cyanine dyes is the radiationless deactivation Sj — Sg. Maximum singlet-triplet interconversion ( 52 ) methanol for carbocyanines is about 3% (maxLgrp > 0.03), and the sum [Lpj + st] I than 0.10. 

Fig. 16. Time-resolved transient absorption spectra for poly(A/St/Phen) (29) in aqueous solution in the presence of 5 mM MV2 + [Phen] (residue) = 0.66 mM. Delay times after the laser pulse are indicated [102]...

Transient absorption spectra were measured with PBS in dioxane solution. In aerated solution the absorption decayed by two processes, a rapid one with f 1/2 50 /rs and a slow one with fj/2 20ms. In argon-saturated solution, a relatively weak absorption which decayed with f1/2 20ms was observed. The rate of the rapid decrease in the optical density agrees with that of the decrease in the intensity of the scattered light. 

Fig. 1. a) UV-Vis absorption and fluorescence emission spectra of riboflavin (RF, 20 pM) and Gum Arabic aqueous solutions at pH 7 (phosphate buffer 100 mM). b) Transient absorption spectra of RF (35 pM) in N2-saturated MeOH-Water (1 1) solution. The insets show the transient decay at 720 nm for the RF species and the Stern-Volmer plot for the quenching of 3RF by GA, eqn 11. 

Figure lb shows the transient absorption spectra of RF (i.e. the difference between the ground singlet and excited triplet states) obtained by laser-flash photolysis using a Nd Yag pulsed laser operating at 355 nm (10 ns pulse width) as excitation source. At short times after the laser pulse, the transient spectrum shows the characteristic absorption of the lowest vibrational triplet state transitions (0 <— 0) and (1 <— 0) at approximately 715 and 660 nm, respectively. In the absence of GA, the initial triplet state decays with a lifetime around 27 ps in deoxygenated solutions by dismutation reaction to form semi oxidized and semi reduced forms with characteristic absorption bands at 360 nm and 500-600 nm and (Melo et al., 1999). However, in the presence of GA, the SRF is efficiently quenched by the gum with a bimolecular rate constant = 1.6x10 M-is-i calculated... 

Transient absorption spectra of the CeoN cluster (C6oN" ) -MePH system following laser excitation at 355 nm indicate that the photoinduced intermolecular electron-transfer from the triplet excited state of PH to the QqN cluster (CfioN) occurs as shown in Figure 15.9a. 

Using nanosecond laser flash photolysis techniques, Leigh80 observed transient absorption spectra which he attributed to the silenes derived from photolysis of various methylphenyldisilylbenzenes. Thus the silenes 52,53, and 54 were found to absorb at 425,460, and 490 nm, respectively, in isooctane, and 55 was also found to absorb at 490 nm.75 In other studies, the silene Ph2Si=CH2 derived by laser flash photolysis was found to absorb at 323 nm.111... 

Fig. 3 Transient absorption spectra of hairpin 3G obtained at increasing delay times following 340 nm excitation with a laser system having a 150 fs instrument response function...

Fig.2 Transient absorption spectra of PyODN 1 observed several times after the electron pulse. The inset shows the time profile of the transient absorption peak of Py + at 470 nm, which corresponds to the direct oxidation of Py with S04 (Scheme 3, path a)...

Fig. 5 Transient absorption spectra of PtzODNl obtained at 1 f.is, 5 f.is, and 50 f.is during pulse radiolysis of N20-saturated aqueous solution containing 0.2 mM PtzODNl (strand cone.), 20 mM pH 7.0 Na phosphate buffer, and 1 mM T12S04... 

Transient absorption spectra changes and time profiles observed during pulse radiolysis of PtzPy-n are shown in Fig. 10. When Ptz was separated... 

Fig. 10 Transient absorption spectra observed at 5 and 100 /is after the electron pulse during pulse radiolyses of a PtzPy-1 and b PtzPy-3. Also shown are time profiles of the transient absorption of Py + and Ptz + observed at 470 and 520 nm for c PtzPy-1 and d PtzPy-3, respectively...

FIGURE 8.7 Transient absorption spectra recorded 3ps following excitation for zeaxanthin (a) and ACOA (b). The spectra were measured with excitation at 400 nm (H-aggregates), 485 nm (monomers), and 525 nm (J-aggregates). 

FIGURE 14.7 Transient absorption spectra observed following pulse radiolysis of CAN and formate in argon-saturated aqueous 2% TX-100 (pH = 7.1). Inset Kinetic traces of CANH at 570 nm and CAN " at 720 nm, showing the decay of the radical anion and concomitant formation of the neutral radical. 

FIGURE 14.10 Transient absorption spectra observed following pulse radiolysis of 1 x 10-4 M ASTA with 1 x 10-5 M LYC in argon flushed benzene. 

Figure 4. Transient absorption spectra of 2-hydroxyphenyl benzotriazole and its...

Laser Flash Photolysis at 248 nm of TDI-PU. MDI-PUE. and Model Compounds. Figures 1 and 2 show the transient absorption spectra of MDI-PUE (5.5 X lO-3 g/dL) and TDI-PU (2.3 X 10 3 g/dL) in THF at a 2.0 ns delay after pulsing with a krypton fluoride excimer laser (Xex=248 nm) in air and nitrogen saturated samples. Both spectra have common peaks in nitrogen saturated solutions (shown by arrows) at 310 nm, 330-360 nm (broad), and above 400 nm (broad, diffuse absorbance).. The MDI-PUE sample has an additional and quite distinctive peak at 370 nm. In the presence of air, the peak at 370 nm for MDI-PUE is completely extinguished, while the sharp peaks at 310 nm for TDI-PU and MDI-PUE and the broad band above 400 nm are only marginally quenched by oxygen. 

Figure 1. Transient absorption spectra (2.0 ms) of 5.5 X 10 3 MDI-PUE in THF (a) Nitrogen saturated (b) Air saturated (xex 248 nm) (Reproduced from Ref. 13. Copyright 1988 ACS).

In kinetic spectroscopy a continuous liglit source is used. The transient signal at a fixed wavelength is detected with a photomultiplier and displayed on a storage oscilloscope. Repeating the kinetic experiments at several wavelength positions again allows us to determine transient absorption spectra. 

Figure 2 Time-resolved transient absorption spectra obtained by flash photolysis of phenyl acetate in methylcyclohexane (266 nm excitation). Delay times 50, 100, 200, and 400 msec. (Adapted from Ref. 41.)...

Figure 11 Transient absorption spectra observed in photoinduced electron Uansfer from Cso (1-1 X 10 " M) to CI4Q (4.0 X 10 M) in the presence of Sc (0.11 M) after laser irradiation at X = 532 nm in deaerated PhCN at 298 K (black circles = 5 p.sec, black square = 25 xsec and black triangle = 100 (xsec). Inset Time profile of the absorption band at 740 nm and 980 nm due to Cso and Cso - (From Ref. 135.)...

Another explanation for their resonance Raman results could be a change in the zwitterionic nature of the merocyanine isomers in the different solvents which may result in changes in the Raman transition probabilities, or the spectral changes could be due to solvent shifts of the absorption spectrum, resulting in a change in the relative contribution of the different vibrational modes to each resonance Raman spectrum. We note that in the same article, the authors report the transient absorption spectra of the merocyanine forms, which clearly show that the BIPS spectrum in cyclohexane has more discrete vibrational modes than are observed in the polar solvents, which show more spectral broadening. Al-... 

Figure 6 (a) Transient absorption spectra for NOSI5 irradiated with 388-nm 180 fsec light in 1-butanol, (b) Transient rise kinetics for NOSI5 in 1-butanol. 

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