Nanosecond transient absorption

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

A similar supramolecular approach, in which both n-n stacking stacking of pyrene on the SWNT surface and alkyl ammonium-crown ether interactions were used in the self-assembly process of a fullerene derivative with SWNTs, was recently reported (Scheme 9.22).72 The nanohybrid integrity was probed with various spectroscopic techniques, , and electrochemical measurements. Nanosecond transient absorption studies confirmed electron transfer as the quenching mechanism of the singlet excited state of C60 in the nanohybrid resulting in the formation of SWNT"1"/ Pyr-NH3 + /crown- charge-separated state. 

Nanosecond transient absorption measurements provided a further indication of efficient mediator transport within the nanopores of the gel, showing basically no difference in dye regeneration using the liquid iodide/iodine precursor and the quasi-solid-state polymeric electrolyte. 

The UV-visible absorption and fluorescence spectra of NKX-2311 in solution are measured. The absorption and fluorescence maxima are located at 490 and 555 nm, respectively. The fluorescence spectrum is shown in Fig. 1. This figure also shows the transient absorption spectrum of NKX-2311 in deuterated methanol (CD3OD) solution measured by the nanosecond laser system. The spectrum is ascribed to the excited singlet state (dye ). The absorption spectrum of the oxidized form of NKX-2311 (dye+) was measured by nanosecond transient absorption spectroscopy after adding electron acceptor, 1,4-benzoquinone, in NKX-2311 solution of CD3OD. As shown in Fig. 1, there are two characteristic peaks at around 875 and 1010 nm. 

Additionally, in order to examine the charge-recombination dynamics we turned to complementary nanosecond transient absorption measurements. Once more, the spectral fingerprints of the radical ion pair state emerged immediately after the laser pulse and their decays yielded charge-recombination lifetimes in the order of 4.0 ps (Fig. 9.38). 

As has been shown by time-resolved flash photolysis measurements in colloidal titanium dioxide suspensions trapping is a very fast process. Rothenberger et al. performed picosecond and nanosecond transient absorption experiments on titanium dioxide and observed that the electron trapping time was faster than 30 ps, the time resolution of their laser system [4e]. The trapping time for holes was estimated to be < 250 ns. In a recent picosecond study by Serpone et al. on titanium dioxide colloids solutions of varying diameters it was observed that the spectra of trapped electrons as well as of trapped holes are fully developed after a laser... 

Nanosecond transient absorption experiments on 28a-f provide clear evidence for the charge separated state (26 in Scheme 12) that is the product of forward ET [101]. For example, Fig. 7 compares the transient absorption spectra... 

An attempt to clarify the first stages of the mechanism of carbene formation was undertaken in a nanosecond transient absorption study of 5-chloro-2-hydroxybenzonitrile (4-chloro-2-cyanophenol), based on the hypothesis... 

The triplet state decay kinetics of benzophenone has been monitored in fluorinated surfactants (sodium perfluorooctanoate, SPFO) where the surfactant does not quench the triplet40>. In this case, the excited benzophenone cannot react with the surfactant and the excited molecule escapes into the aqueous phase. When increasing amounts of SDS is added to solution, the observed triplet lifetime (by nanosecond transient absorption techniques) decreases indicating that hydrogen abstraction is occurring from the SDS (Fig. 17). 

Yan and Hupp used nanosecond transient absorption to probe charge recombination after selective excitation of a hexaphosphonated Ru(bpy)3 + derivative bound to DeGussa Ti02 as a function of pH [212]. They found that a fast first-order charge recombination process was insensitive to pH over 13 decades of H+ concentration. Assuming the sensitizer oxidation potential is independent of pH and... 

Nanosecond transient absorption measurements were carried out on 1 X 10" M solutions in air-saturated dichloromethane, chloroform, and benzoni-trile with excitation at 590 nm or 650 nm. The pump laser was a Continuum Surelite frequency-doubled Nd YAG laser with a pulse width of about 5 ns the spectrometer has been described previously (30). For each sample, absorption spectra were obtained before and after the experiment to rule out degradation of the compound. 

Nanosecond Flash Photolysis Measurements.—A computer-controlled ns flash photolysis spectrometer has been described. " The system was employed in a study of the photochemistry of xanthene dyes in solution. A nitrogen laser was used to provide 2—3 mJ excitation pulses at 337.1 nm for a ns flash photolysis study of electron-transfer reactions of phenolate ions with aromatic carbonyl triplets. " A PDP II computer was used to control the transient digitizer employed for detection, and to subsequently process the data. A nanosecond transient absorption spectrophotometer has been constructed using a tunable dye laser in a pulse-probe conflguration with up to 100 ns probe delayA method for reconstructing the time-resolved transient absorption was discussed and results presented for anthracene in acetonitrile solution. The time-resolution of ns flash photolysis may be greatly increased by consideration of the integral under the transient absorption spectrum. Decay times comparable to or shorter than the excitation flash may be determined by this method. 

Schaniel and coworkers studied the properties of the photoinduced ON and r/ -NO isomers in Na2[Fe(CN)5N0]-2H20 embedded in meso-pores of sihca xerogels by X-ray diffraction, steady-state low-temperature absorption, nanosecond transient absorption spectroscopy, and IR spectroscopy (34). They determined that the electronic structures and activation energies of these / -ON and tf -NO isomers were not dependent on the particle size (statistically distributed molecules or nanoparticles) and as such the isomers were essentially quasi-free inside the pores of the gel (34). 

The mechanism and dynamics of photoinduced charge separation and charge recombination have been investigated in synthetic DNA hairpins possessing donor and acceptor stilbenes (stilbene-4,4 -dicarboxylic acid, bis(3-hydroxypropyl)amide of stilbene-4,4 -dicarboxylic acid, bis(2-hydroxyethyl)stilbene 4,4 -diether) (Figure 11.1) using femtosecond broadband pump-probe spectroscopy, nanosecond transient absorption spectroscopy, and picosecond fluorescence decay measurements [11]. Nanosecond time-resolved spectra of stilbenes attached to DNA are shown in Figure 11.4. 

For the homoleptic compounds M02(O2CC6H4-p-X)4 (X=CsC-H or C=N), fs-TRIR studies showed that for the MLCT Si state the negative charge is delocalised over two tram ligands ligands. NIR emission and nanosecond transient absorption spectroscopy showed that the Ti states are MoMo88, with lifetimes of 56 (X = C=C-H) and 61 (X = C=N) ps. 

The photoinduced electron transfer reactions have also been studied with nanosecond transient absorption spectroscopy [67]. The transient absorption difference spectrum for the reaction of 12a and 4-(methoxycarbonyl)-A/-methylpyr-idinium is shown in Fig. 4. The difference spectrum is characterized by a sharp intense absorption at approximately 390 nm, a Iowa- intensity band at 484 nm, and an intense broad absorption band at approximately 693 nm. The sharp band at around 390 nm is characteristic of pyridinyl radical absorption. The reaction mechanism is depicted in Scheme 1. 

The photoinduced electron transfer behavior has also been confirmed by nanosecond transient absorption spectroscopy [102,103,108,111]. A representative transient absorption difference spectrum recorded 10 ps after laser flash excitation of 24a (0.05 mM) and 4-(methoxycarbonyl)-A[-methylpyridinium hexaflu-orophosphate (13 mM) in degassed acetonitrile (0.1 M "Bu4NPF6) is shown in... 

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