Time profiles of the transient absorbance A

The triplet and singlet radical pairs are represented by [A B ] and [A B ], respectively, and ki shows the respective rate constant. It is noteworthy that the MFEs and MIEs on Trp and Te can be measured with ns-lasers for the reactions in such confined systems as radical pairs in micelles as shown in Fig. 7-1. In this figure, the time profiles of the transient absorbance (A(t) curves) are observed for the generated ketyl radicals (XC OH). The Trp value can be obtained from the initial decay of the A(f) curve and the Fe one from the nearly constant component observed after the initial decay. 

Fig. 7-1. The time profiles of the transient absorbance (A(t) curves) observed at 525 nm for a micellar SDS solution of (A) BP, (B) BP-cfio, and (C) BP- C (a) in the absence of a magnetic field in the presence of a magnetic field of (b) 10 mT, (c) 20 mT, (d) 40 mT, and (e) 70 mT. (Reproduced from Ref. [lb] by permission from The American Chemical Society)...

Figure 4. Main figure, transient absorbance spectra recorded at three-times (5, 59, and 180 ps) post-355-nm excitation of a solution of bis(tribexylsiloxy) phthalocyaninato-Sn" in toluene solution. Inset, the time profile of the absorption decay at 520 nm.

Figure 26. (a, b) Transient differential absorption spectra recorded after excitation of Cu.20 in DMF with a 0.5-ps laser pulse at 586 ntn delay times are given on the traces, (c) Growth of the transient absorbance at 660 nm attributed to the charge-transfer state, (d) Decay profile recorded for the above experiment at 660 nm. Note its clear biphasic nature. 

Fig. 18. Time profiles of transient absorbance at 602 nm due to MV+ for the poly (A/St/Phen)-MV2+ system [Phen](residue) = 0.66 mM [MV2+] = 5mM ( ), 10mM (a). The solid lines represent the best-fit curves calculated from Eq. 10 with the use of the parameters given in Table 6 [120]...

Immediately upon excitation of an IPCT band with a fs laser at 400 nm, transient absorption was observed for both salts in solutions with a peak at about 600 nm, characteristic of 4,4/-bipyridinium radical cations. Figure 20 shows the transient absorption spectra of PV2+(I )2 in methanol solution. A marked increase in the absorbance of the 4,4/-bipyridinium radical cations took place within 1 ps after excitation. 4,4/-Bipyridinium radical cations were thus formed in a fs time scale by the photoinduced electron transfer from a donor I- to an acceptor 4,4/-bipyridinium upon IPCT excitation [48], The time profiles of transient absorption at 600 nm are shown in Fig. 21 for (a) PV2+(I )2 in a film cast from DME and (b) PV2+(TFPB )2 in DME solutions. Both of them showed a very rapid rise in about 0.3 ps, which was almost the same as the time resolution of our fs Ti sapphire laser measurement system with a regenerative amplifier. Similar extremely rapid formation of 4,4/-bipyridinium radical cations was observed for PV2+(I )2 salts in methanol and dimethylsulfoxide solutions upon IPCT excitation, respectively. These results demonstrated that the charge separated 4,4/-bipyridinium radical cations were formed directly upon IPCT excitation because of the nature of IPCT absorption bands (that the electrons correlated with the IPCT band are transferred partially at the ground state and completely at the excited state). Such a situation is very different from usual photochromism which is caused by various changes of chemical bonds mainly via the excited singlet state. No transient absorption was observed for PV2+(I )2... 

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