Transient absorption traces

Except as indicated, all laser flash data are averages from 10 laser shots on one spot of an aerated film. In the fitting routines using the model, k.co was fixed to the values derived from the rise portions of transient absorption traces. 

Transient absorption traces are most often fitted with a sum of exponentials, and the decay rates are related to the processes taking place. When a range of wavelengths is probed, all the decay curves can be fitted simultaneously to a minimum number of decay parameters in a global analysis according to... 

Figure B2.1.8 Dynamic absorption trace obtained with the dye IR144 in methanol, showing oscillations arising from coherent wavepacket motion (a) transient observed at 775 mn (b) frequency analysis of the oscillations obtained using a linear prediction, smgular-value-decomposition method.

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. 

A broad transient absorption in the visible region is observed when a solution of Cr(CO)6 is photolyzed with a uv flash. The position of the absorption and its decay rate are very sensitive to trace impurities in the solution 30,31). 

Figure 4 Transient absorption spectra of radical anions (a) and radical cations (b) of pol5nnetliyl-phenylsilane at 15,100, and 250 nsec after a pulse. Superimposed figures indicate the kinetics traces of transient absorption.

Figure 1 Transient absorption spectra of c-S and t-S (S = r -4 ) recorded at time t after eT during PR of c-S and t-S (S = 1-4) with [S] = 5.0 x 10 M in DCE at r.t. Insets kinetic traces illustrating the time profiles of the D2 band at 1 as a function of t. Both t and the observed decay rate constant (kobs) and are mentioned in the figure.

Figure 13 Transient absorption spectra recorded before hvs i (O) and immediately after ( ) and 200 nsec (A) and 1 ps (A) after hvs32 during PR-LFP of c-St (5x10 M) in DCE (a). Kinetic traces illustrating time profiles of AO.D.480 (b) and AO.D.515 (c) as a function of time after e. ...

Fig. 1. a) Normalized transient absorption time profiles for benzene ( ) in the gas phase (4 bar, T = 408 K) for = 1670 nm and kp,, = 275 nm. Also shown is a fit using the model described in the text (—). b) Normalized transient absorption time profiles for toluene ( ) in the gas phase (4 bar, T = 421 K) for = 1678 nm and = 280 nm. The solid line is a fit using the model described in the text. Residuals show the quality of the fits. The insets display the traces on a shorter timescale, the cross correlation of the experiment, and the comparison with the solution experiment in Fig. 3 (grey line). 

The strong dependence of the Si/ICT lifetime on solvent polarity revealed first by transient absorption experiments in the visible region by Bautista et al. [8] was further confirmed by measurement of Si/ICT fluorescence using a streak-camera [11]. The Si/ICT state fluorescence kinetics of peridinin taken at 730 nm in solvents of different polarity are shown in Fig. 2b. The lifetime changes more than one order of magnitude, from 156 ps in n-hexane to 10.5 ps in methanol. In the middle-polarity solvents tetrahydrofuran and 2-propanol, the observed lifetimes are 77 and 54 ps, respectively. In all solvents, kinetic traces could be fitted by a single exponential decay independent of detection wavelength over nearly the entire fluorescence band (650 - 850 nm). The same decay times were also observed in transient absorption [11,12]. 

Figure 2 Transient absorption spectrum observed 200 ns after 355 nm laser excitation of benzophenone in supercritical CO2 at 117 bar and 33°C compared with that obtained in N2-saturated CH3CN. Insert Typical benzophenone triplet decay trace observed at 525 nm in supercritical CO2.

Fig. 5.10. The theoretical calculation of the time trace of transient absorption (TRABS) for a one-mode system. The energy gap is 20 cm-1 and the vibrational mode is 420 cm-1. The dark curve is the reactant TRABS and the light-gray curve is the product TRABS. The probing frequency is set at respective peak positions of the induced absorption spectra of both reactant state and product state. For discussion see text.

Fig. 7. Transient absorption (980 nm) of ca 1 x 10-4 M solutions of 40 (upper trace), 41 (lower trace) and 42 (middle trace) in dichloromethane at ambient temperature following pulsed laser excitation with 590 nm light. The curves have been normalized so that relative transient absorption reflects relative quantum yield...

This tunable source was used to investigate the transient absorption kinetics of hypericin in DMSO as a function of pump wavelength (Fig. 1.10). The startling result is that using pump wavelengths from 495 to 600 nm, the data can be fit globally by a sum of two exponentials, which except for two traces exhibits the 10-ps component characteristic of H-atom transfer. Fit results are compiled in Table 1.1. 

Fig. 7 Transient absorption difference spectra of 3.7 (a), 3.8 (b), and [( Bu3)tpyPtC=CPh]+ (c) measured in deaerated CH2C12 following a 475 nm, 5-7 ns fwhm, 2-mJ laser pulse. Single wavelength kinetic traces and residuals are inset in each panel. Adapted from [20]...

Figure 15-28. (a) Transient absorption spectra of DMABN in cyclohexane at room temperature. The spectra were observed at lOOps delay time from the exciting pulse. The assignments inset are based on the calculation from Table 15-2 (Reprinted with permission from Ref. [49]), (b) 15cosecond Kerrgated time-resolved resonance Raman spectra of DMABN in hexane (upper trace) with 267 nm pump and 460 nm probe wavelength at 50 ps delay time, and that of DMABN in cyclohexane (lower trace) with 267 nm pump and 600 nm probe wavelength at 50 ps delay time. (Reprinted with permission from Ref. [63].)... 

Figure 24. (a) Transient absorption spectra recorded after excitation of 19 in DMF with a 30-ps laser pulse at 598 nm delay times are given on the traces, (b) Typical kinetic trace observed for the conditions as in (a), (c) Transient absorption spectra recorded after excitation of 19 in DMF with a 30-ps laser pulse at 532 nm. (d) Typical kinetic trace observed for the conditions as in (c). 

Figure 30. Transient absorption spectrum of pyrene-TEA in an acetonitrile-ethyl acetate solution. Delay time after the laser pulse A) 500 ns, B) 6 ps. Inset typical first-order decay trace monitored at 488 nm (data from Figure 1, Ref. [154]).

The kinetics of the oxidation of iodide by the oxidized state of c -[Ru (dcbpy)2-(NCS)2] sensitizer adsorbed on nanocrystalline Ti02 films was measured by transient laser spectroscopy [92]. Figure 16 shows the transient absorption kinetics recorded in propylene carbonate with various electrolytes added. In all cases, the recovery of the ground-state absorption of the dye, after the fast electron injection into the solid, does not follow a simple kinetic law. In the absence of any electrolyte (trace a), the time needed to reach half of the initial absorbance (/1/2) through back electron transfer is 2 ps. Total recovery of the initial absorption, however, requires several hundreds of microseconds to milliseconds. Traces b, c, and d were recorded after addition of a common concentration of 0.1 m of iodide in the form of tetra-butylammonium (TBA+), Li+, and Mg + salts, respectively. Addition of the electrolyte in all three cases led to a considerable acceleration of the dye regeneration with ti/2 < 200 ns and complete suppression of the slow kinetic tail. 

Figure 10. Transient absorption at 980nm of — 1 x 10" M solutions of C-P-Qa-Qb tetrad 15 (upper trace), and model compounds 16 (C-P-Qa, lower trace) and 17 (C-P-QA(OMe)2-QB, middle trace) in dichloromethane following 590-nm excitation with a 15 ns laser pulse. The results have been normalized to the same absorption of the parent species at the excitation wavelength so that the relative transient absorption reflects the relative quantum yield.

Figure 2.6. (a) Transient absorption spectra recorded before the laser flash (open circles) and immediately after (filled circles) and 200 ns (open triangles) and 1 ps (filled triangles) after the laser flash during pulse radiolysis-laser flash photolysis of c-St (5 x 10-3 M) in Ar-saturated 1,2-dichloroethane. (b, c) Kinetic traces of AO.D.480 and AO.D.515, respectively, as a function of time after the electron pulse. 

Figure 2.14. Transient absorption spectra obtained during two-laser (first 355-nm and second 425-nm) excitation (filled circles) and one-laser (355-nm) excitation (open circles) of BP (7.0x10 3M) with 1-methoxynaphthalene (7.0xl0-3M) in Ar-saturated acetonitrile in the presence of CCI4 (1.0M) at room temperature. The second laser was irradiated at 200 ns after the first laser pulse. Inset Kinetic traces of AO.D. at 440 (a) and 702 nm (b) with and without the second 425-nm laser irradiation. The initial growth of AO.D in the 50-ns time scale corresponds to the formation of NpDlTj) by the ENT from...

Figure 2.18. (a) Transient absorption spectra observed at 40 ps before and 20 and 150 ps after the laser flash during two-color two-laser flash photolysis of 4T in toluene employing a nanosecond YAG laser (355 nm, FWHM 5 ns, 7 mJ pulse-1) and a picosecond YAG laser (532 nm, FWHM 30 ps, 21 mJ pulse-1), (b) Difference spectra of transient absorption spectra at 20 and 150 ps. (c) Kinetic traces of AO.D. at 650 and 600 nm. Thick lines are fitted curves. 

The full experimental details are given elsewhere [13,14]. A typical transient absorption, due to the triplet-triplet absorption from a microcrystalline sample of benzil [16], is illustrated in figure 3, also included in this figure are the emission and baseline experimental traces which are employed in the subsequent correction of the data. 

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