Charge-Transfer Absorption Spectroscopy

Charge-Transfer Absorption Spectroscopy 245 7.2.3 The Analysis of Spectroscopic Absorption Bands... 

Blatter, F., Moreau, F. and Frei, H. (1994). Diffuse reflectance spectroscopy of visible alkene-02 charge transfer absorptions in zeolite Y and determination of photooxygenation quantum efficiencies. J. Phys. Chem, 98(50), 13403-13407... 

Figure 12 Vibrational enhancement selectivity available from resonance Raman spectroscopy. The UV-visible spectrum of a P. aeruginosa azurinis shown together with two different Raman spectra (frozen solution at 77 K) that derive from laser excitation within the S(Cys) — Cu(II) charge-transfer absorption band at 625run (647.1 nm) and away from the absorption (488.Onm). Excitation within resonance leads to dramatically increased Raman scattering from the Cu active site, whereas off-resonance excitation produces a spectrum dominated by bands of nonchromophoric ice...

Photoinitiated SET has been used to drive a molecular machine and absorption and fluorescence spectroscopy have been used to monitor it. A 1 1 pseudoro-taxane forms spontaneously in solution as a consequence of the donor-acceptor interactions between the electron-rich naphthalene moiety of the thread (380) and the electron-deficient bipyridinium units of the cyclophane (381). The threading process is monitored by the appearance of a charge transfer absorption band and disappearance of the naphthalene fluorescence. Excited state SET from 9-anthracenecarboxylic acid (9-ACA) reduces a bipyridinium moiety of the cyclophane, lessening the extent of interaction between the thread and the cyclophane and dethreading occurs. On addition of oxygen the reduced cyclophane is reoxidised and threading reoccurs. ... 

The CoSCN complex (7) is usually stable under neutral conditions and at ambient temperature, and separation from (8) is possible by fractional crystallization or by chromatographic methods. The two isomers can easily be distinguished spectrally, with (7) having extensive charge transfer absorptions in the near UV (< 400 nm), whereas (8) does not. Also IR spectroscopy can be used to distinguish these isomers. The most recent general account of thiocyanate coordination is that of Burmeister (7). 

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

Wang C, Mohney B K, Williams R, Hupp J T and Walker G C 1998 Solvent control of vibronic coupling upon intervalence charge transfer excitation of (NC)gFeCNRu(NH3)g- as revealed by resonance Raman and near-infrared absorption spectroscopies J. Am. Chem. Soc. 120 5848-9... 

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