Nanosecond transient absorption spectroscop

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. 

Results of nanosecond and miaosecond transient absorption spectroscopic experiments on the photolysis of the complex (r -dfepe)Cr(CO)4 [dfepe = (C2F5)2PCH2CH2P(C2F5)2l in hexane and cyclohexane solvents indicated the formation of alkane complexes of the type (Ti -dfepe)Cr(CO)3(Alkane) and (t] -dfepe)Cr(CO)4(Alkane) [22], The rearrangement of the silane complex CpMn- CO)2(HSiEt3> has been studied by photoacoustic calorimetry [23],... 

Capellos and Suryanarayanan (Ref 28) described a ruby laser nanosecond flash photolysis system to study the chemical reactivity of electrically excited state of aromatic nitrocompds. The system was capable of recording absorption spectra of transient species with half-lives in the range of 20 nanoseconds (20 x lO sec) to 1 millisecond (1 O 3sec). Kinetic data pertaining to the lifetime of electronically excited states could be recorded by following the transient absorption as a function of time. Preliminary data on the spectroscopic and kinetic behavior of 1,4-dinitronaphthalene triplet excited state were obtained with this equipment... 

Nanosecond flash photolysis of 1,4-dinitro-naphthalene in aerated and deaerated solvents showed a transient species with absorption maximum at 545nm. The maximum of the transient absorption was independent of solvent polarity and its lifetime seemed to be a function of the hydrogen donor efficiency of the solvent. The transient absorption was attributed to the lowest excited triplet state of 1,4-dinitronaphthalene. Based on spectroscopic and kinetic evidence, the triplet state of 1,4-dinitronaphthalene behaved as an n - Tt state in nonpolar solvents,... 

The photophysical properties of [Ru(TBP)(CO)(EtOH)], [Ru(TBP)(pyz)2], [Ru(TBP)(pyz)] (Fl2TBP = 5,10,15,20-tetra(3,5-tert-butyl-4-hydroxyphenyl)porphyrin) have been investigated by steady-state and time-resolved absorption and emission spectroscopies. The complexes are weakly luminescent, and the origins of this behavior is discussed.Transient Raman spectroscopic data have been reported for [Ru(TPP)(py)2], [Ru(TPP)(CO)(py), and [Ru(TPP)(pip)2] (pip = piperidine),and nanosecond time-resolved resonance Raman spectroscopy has been used to examine the CT excited states of [Ru(0EP)(py)2] and [Ru(TPP)(py)2]. " ... 

To study the excited state one may use transient absorption or time-resolved fluorescence techniques. In both cases, DNA poses many problems. Its steady-state spectra are situated in the near ultraviolet spectral region which is not easily accessible by standard spectroscopic methods. Moreover, DNA and its constituents are characterised by extremely low fluorescence quantum yields (<10 4) which renders fluorescence studies particularly difficult. Based on steady-state measurements, it was estimated that the excited state lifetimes of the monomeric constituents are very short, about a picosecond [1]. Indeed, such an ultrafast deactivation of their excited states may reduce their reactivity something which has been referred to as a "natural protection against photodamage. To what extent the situation is the same for the polymeric DNA molecule is not clear, but longer excited state lifetimes on the nanosecond time scale, possibly of excimer like origin, have been reported [2-4],... 

Photoinduced electron injection is by no means a new development. This process has already been applied in areas such as silver halide photography. In this discussion, only sensitized TiC>2 surfaces will be considered. Many experiments have shown that the charge injection into the semiconductor surface is very fast. In order to study these processes, fast spectroscopic techniques are preferred. Whether or not charge injection takes place can be studied conveniently on the nanosecond time-scale by using transient absorption spectroscopy. However, to address the injection process directly, experiments are carried out on the femtosecond time-scale, while recombination and charge separation require the nanosecond to microsecond range. 

Nanosecond laser flash photolyses of 77a under TCNB- and NMQ BF -sensitized conditions provide strong spectroscopic evidence not only for the intermediacy of cation radical 82a in the SET-sensitized photoreactions but also for the trimethylenemethane biradical intermediate 82a. Laser excitation (308 nm) of TCNB with 77a in acetonitrile gives rise to two intense transient absorptions with maxima at 350 and 500 nm whereas in dichloromethane only the shorter wavelength transient absorption is observed. In contrast, under the NMQ BF -sensitized conditions in acetonitrile the longer wavelength transient absorption predominates but the shorter wavelength band is extremely weak (Table 5). 

As in all potentiostatic techniques, the double layer charging is a parallel process to the faradaic reaction that can substantially attenuate the photocurrent signal at short-time scale (see Section 5.3)" . This element introduces another important difference between fully spectroscopic and electrochemical techniques. Commercially available optical instrumentation can currently deliver time resolution of 50 fs or less for conventional techniques such as transient absorption. On the other hand, the resistance between the two reference electrodes commonly employed in electrochemical measurements at the liquid/liquid interfaces and the interfacial double layer capacitance provide time constants of the order of hundreds of microseconds. Consequently, direct information on the rate of heterogeneous electron injection from/to the excited state is not accessible from photocurrent measurements. These techniques do allow sensitive measurements of the ratio between electron injection and decay of the excited state under pho-tostationary conditions. Other approaches such as photopotential measurements, i.e. relative changes in the Fermi levels in both phases, can provide kinetic information in the nanosecond regime. 

Although the transient spectrum of a radical-ion pair was recorded in a picosecond-nanosecond time domain in the flash photolysis of Co(III) alkylcobalamins,123 there has been no direct spectroscopic observation of the LMCT excited states. The observed photochemical behavior may be simply described by the following sequence of events (1) absorption of radiation produces a Franck-Condon excited state, which (2) rapidly loses its excess vibrational energy (k > 10ns ) to form the thermalized excited state, followed by (3) product formation and internal conversion to the ground state. The existence of LMCT excited states with a finite lifetime in the... 

We summarize here two time-resolved spectroscopic methods, giving direct information on picosecond and nanosecond photodynamics of solid surface. One is a fluorescence spectroscopy which analyzes fluorescence behavior of the surface area excited by the evanescent laser pulse. The other is to get transient UV-visible absorption spectra by using the evanescent light as a probe beam. 

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