Photoinduced spectrum

It appears that no absorption measurements of (S,Cu) in the near IR has been reported, but absorption measurements of the isoelectronic donor centres associated with Sa and Sb have been performed at lower energies under continuous photoexcitation with a Nd-YAG laser operated at 1.06 or 1.32pm (1.17 or 0.939eV) by Beckett et al. [18]. At LHeT, the creation in the triplet state is predominant and the ground state for the EM spectra is therefore, the triplet states Sa° and Sb°. The photoinduced spectrum so obtained is displayed in Fig. 6.39. 

Figure 1. Photoinduced absorption spectrum of Y-iBaaCusOy-j (5=0.75) at 15K (2.7 eV pump at 30 mW/cm ) inset shows photoinduced spectrum of La2Cu04 obtained at 15 K (2.56 eV at 50...

Next in the analysis are the photoinduced IR spectra. The pattern of the photoinduced spectrum is practically superimposable to the IR spectrum of the doped species, thus indicating that the photogenerated conjugational defect has a dimension of 5 "effective" units. The small differences in the frequencies reported in the literature may be ascribed to the chemical and /or structural inhomogeneity of the samples, i.e. to a different distribution of conjugation lengths. 

Sub-picosecond photoinduced absorption studies were employed to demonstrate the speed of the photoinduced electron transfer. Upon addition of C(M to P30T, the P1A spectrum, decay kinetics, and intensity dependence all change dramatically 36J. Already at 1 ps after photoexcitation by a 100 fs pump pulse at... 

The characteristic derivative-shaped feature at g 1.94 first observed in mitochondrial membranes has long been considered as the sole EPR fingerprint of iron-sulfur centers. The EPR spectrum exhibited by [4Fe-4S] centers generally reflects a ground state with S = I and is characterized by g values and a spectral shape similar to those displayed by [2Fe-2S] centers (Fig. 6c). Proteins containing [4Fe-4S] centers, which are sometimes called HIPIP, essentially act as electron carriers in the photoinduced cyclic electron transfer of purple bacteria (106), although they have also been discovered in nonphotosynthetic bacteria (107). Their EPR spectrum exhibits an axial shape that varies little from one protein to another with g// 2.11-2.14 and gi 2.03-2.04 (106-108), plus extra features indicative of some heterogeneous characteristics (Pig. 6d). 

Photoinduced oxidation of 1,4-dimethoxybenzene (DMB) and tetrahydrofuran (THF) by [Au(C N N-dpp)Cl]+ in acetonitrile upon UV/Vis irradiation have been observed. The time-resolved absorption spectrum recorded 12 (xs after excitation of [Au(C N N-dpp)Cl] with a laser pulse at 35 5 nm showed the absorption band of the DMB radical cation at 460nm, whereas upon excitation at 406 nm in the presence of THF, a broad emission characteristic of the protonated salt of 2,9-diphenyl-l,10-phenanthroline (Hdpp ) developed at 500 nm. 

In almost all applications, fluorescent pH indicators are employed in a pH range around the ground state pKa (even if the excited state pK is different). Therefore, the absorption (and excitation) spectrum depends on pH in the investigated range. These indicators can be divided into three classes (see formulae in Figure 10.2) on the basis of the elementary processes (photoinduced proton transfer or electron transfer) that are involved. 

Bifluorophores consisting of two different fluorescent dyes linked by a flexible spacer containing heteroatoms (oxygen, nitrogen or sulfur atoms) can bind cations. This results in a decrease of the distance between the two fluorophores and, consequently, to an increase in efficiency of photoinduced energy transfer between the two moieties (Figure 2.13) provided that the emission spectrum of the donor (D) overlaps the absorption spectrum of the acceptor (A).(36) The transfer efficiency depends on the distance according to Forster s theory ... 

Formation of the radical intermediate complex [Ceo CUQ -Sc " ] in Scheme 15 was also confirmed by the ESR spectrum observed in the Sc " -promoted photoinduced electron transfer from Ceo to CI4Q in frozen PhCN at... 

Figure 8. Absorption onset experiments for photoinduced conversion of compound 10 NH-tautomers in EPIP at 77 K (A) Initial spectrum (B,C) Monitored spectra after irradiation (At 30 min) by the polarized light (Xg = 638 nm). Conditions for polarized excitation and polarized monitoring are shown by arrows. The displacement of inner protons in tautomers conforms to experimental data. The direction of X-axis is chosen for tautomer 1 to be parallel to vector E of exciting light. (Reproduced with permission from Ref. 15. Copyright 1985 North-Holland Physics Publishing Company.)...

One of the properties of a class of materials known as chalcogenide glasses is that they exhibit a wide spectrum of photoinduced effects. Photoinduced phenomena have recently been extensively studied (see corresponding references in previous sections), partly as an interesting subject for fundamental research in the field of disordered sohds and partly due to the potential apphcation of these phenomena in opto(photo)electronics (xerography and xeroradiography, optical memories, optical circuits, photoresists, etc.). 

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