Electronic absorption spectral change

Figure 2. Electronic absorption spectral changes during 366-nm irradiation of an isooctane solution of [ReH5(PMe2Ph)s] under an Ht atmosphere.

Of these four properties, spectral shifts are the most sensitive to environmental changes and also the most readily measured. As a result the majority of investigations into electronic absorption spectral changes resulting from surface adsorption have been confined to measurements of spectral shifts. While the shift of the 0-0 bands is the most meaningful measurement to make, these 0-0 bands are not always discernible, especially when the molecules are adsorbed on polar surfaces, so it has become common practice simply to measure the shift of the absorption maximum. In most cases this measurement would correspond to the shift of the 0-0 band, in others, however, adsorption processes can produce unequal displacement of the ground and excited state potential curves, resulting in a different vibronic band shape. 

Figure 1. Electronic absorption spectral changes accompanying 366-nm photolysis of a 2.3 X 10 2M degassed CH2CI2 solution of [IrClH2(PPh J (27)...

Figure 3. Electronic absorption spectral changes resulting from 366-nm irradiation of a I0 3M CH2CI2 solution of [RuClH(CO)-(PPh)37 (35)...

Irradiation of a degassed benzene solution of [RuH2(CO)(PPh3)3] results in the electronic absorption spectral changes shown in Figure 4. As irradiation proceeds, the solutions change from colorless to yellow, and a shoulder appears... 

Figure 5. Electronic absorption spectral changes obtained during 366-nm irradiation of a 1.1 X 10 4M hexane solution of [Mo(r b-C H )2H2] and excess PPh ...

Figure 3. Electronic absorption spectral changes during 254-nm photolysis of [PttmntF]2 in CHCl3/MeCN (24 1 v/v) at 23 °C. Isosbestic points appear at 540, 435, 393, and 315 nm. Reproduced by permission from reference 81.

Fig. 8 Molecular structure of 8a (a). Electronic absorption spectral change of 8a upon self-assembly in THE (Imgml ) (b). SEM micrograph (c), proposed structure (d), and TEM micrograph (e) of tubularly assembled 8a. Proposed structure of the nanocoils of self-assembled 8a (f). TEM micrograph of a mixture of nanotuhes and nanocoUs formed by the self-assemhly of 8a in a mixture of THE and water (8/2 v/v) (1 mgml )...

Figure 2. Electronic Absorption Spectral Change of Amorphous BTPTC Film a) before photoirradiation,...

The CT state was found to decay rapidly (Figure 27c), with a lifetime of 50 ps, leaving a residual absorbance which was identified as the Au porphyrin neutral radical by virtue of its differential absorption spectrum. This latter species decayed relatively slowly, with a lifetime of 2.5 ns, to re-form the ground state of Cu.20. As above, the rapid deactivation of the CT state is ascribed to a combination of direct reverse electron transfer (Eq. 18) and oxidation of the central copper(I) complex by the Zn porphyrin 7r-radical cation (Eq. 19). The yield of the Au(III) porphyrin neutral radical which escaped direct electron transfer was estimated from the transient absorption spectral changes to be 90 %. Thus, direct reverse electron transfer (/ i8 = 2.0 X 10 s ) accounts for only 10 %, and electron abstraction from the central copper(I) complex k g = 1.8 x 10 s ) is the dominant decay route. The residual Au porphyrin neutral radical decays over several nanoseconds due to electron donation to the copper(II) complex (Eq. 20). 

The electronic spin-state crossover in [Fe(HB(pz)3)2] has also been observed in the fine structure of its fC-edge x-ray absorption spectrum [38]. The changes in the x-ray absorption spectra of [Fe(HB(pz)3)2] are especially apparent between 293 and 450 K at ca. 25 eV, as is shown in Fig. 5. The 293 K x-ray absorption spectral profile observed in Fig. 5 for [Fe(HB(pz)3)2] has been reproduced [39] by a multiple photoelectron scattering calculation, a calculation that indicated that up to 33 atoms at distances of up to 4.19 A are involved in the scattering. As expected, the extended x-ray absorption fine structure reveals [38] no change in the average low-spin iron(II)-nitro-gen bond distance of 1.97 A in [Fe(HB(pz)3)2] upon cooling from 295 to 77 K. 

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