Water excitation

This reaction can be viewed as an internal hydrogen abstraction which takes place through a highly strained four-membered transition state instead of the usual six-mem bered one. The formation of the enol is wavelength dependent and is retarded by triplet quenchers.58-80 In water, excitation into the second excited singlet of biacetyl formed the enol with a quantum yield of 0.10, while excitation into the first excited singlet formed the enol with a quantum yield of 0.01, possibly via a higher excited state formed by a triplet-triplet reaction. Therefore, the authors conclude that the second excited triplet is the state that isomerizes to the enol. 

A biomimetic artificial photylase model was described by Wiest et al. [18] The model recognised pyrimidine dimers in both organic solvents and water. Excitation of the complex with visible light led to cycloreversion of the pyrimidine dimer through photoinduced electron-transfer catalysis (Scheme 21). 

As in isolated phenol and in phenol-ammonia/water clusters, the OH bond is broken homolytically in 7HQ-A3, resulting in the transfer of a hydrogen atom rather than proton transfer. As found for phenol-A /W and naphthol-A /W clusters, ammonia is a better hydrogen acceptor than water. Excited-state hydrogen transfer processes are thus strongly favoured in an ammonia environment. 

Fig. 5.4a,b. Susceptibility artifacts due to the vicinity of air in the sphenoid sinus the flow signal of ICA is lowered symmetrically on the TOF images (a), when a fat-signal suppressing water excitation pulse sequence was used. The conventional TOF/ TONE sequence shows no false vessel extinction, but a higher background signal from fat tissue (b)... 

Left side intrinsic fluorescence of waters excited at 330 nm. Right side fluorescence of water after treatment with fluo-rescamine regent, excited at 390 nm. Peaks at 372 nm and 450 nm in the left and right sets of curves, respectively, are from Raman emission. 

The MBSL of both aqueous and non-aqueous solutions is similar to the emission expected from high-temperature flames e.g., excited-state OH from water, excited states of C2 (d3IIg - a3IIu,) from hydrocarbons (these lines also give hydrocarbon flames their blue color), and CN excited... 

Figure 9. Emission spectrum of Ti02 particulate suspension in water. Excitation wavelength 320 nm.

A simple and sensitive in situ algae fluorosensor based on fiber optics was described by Lund [13]. It was used for in situ studies of natural sweet water. Excitation spectroscopy of four algae species revealed differences in their excitation spectra, which therefore may yield more specific and more accurate information than data obtained with single-wavelength excitation. 

Figure 5.10 shows the Ip and 7 components and calculated total intensities of fluorescein in water excited and measured through an oil immersion objective lens of NA = 1.3. Two-photon excitation by a femtosecond Ti Sapphire laser was used. The data were corrected for the sensitivity difference of the Ip and Is channels by matching the tails of the curves. The total intensity calculated by 7 = 7, 4- 27j is clearly not single-exponential, i.e. not entirely free of the anisotropy decay. However, the sum I = Ip + 1.07 is almost free of the anisotropy decay, i.e. the factor k is close to 1. 

Morestan Solid phase phosphorescence Natural, tap, sea, river, waste water Excitation 363 nm emission 520 nm... 

Sequences must be optimized to achieve a high spatial resolution and a fast acquisition time. As sequences must allow analysis of the cartilage with high contrast to the surrounding tissue, thin sliced 3D spoiled gradient echo sequences with spectral fat suppression (Eckstein et al. 1998) or with selective water excitation (Hyhlik-Durr et al. 2000) are usually performed. The water excitation protocol allows the water-bound protons in the cartilage to be excited selectively and directly. Therefore, no prepulse is required as in conventional fat-suppressed imaging protocols. 

Figure 8.14 (a) Fluorescence spectra of compound 30 (2.5 X 10" M) in TFIF after the addition of various amounts of water (excitation wavelength 430 nm). (b) Plots of the relative fluorescence enhancement of compound 30 versus the volume fraction... 

An example of an emission spectrum from a dissociating molecule is depicted in Figure 10. Shown is the intensity distribution for water excited in the first absorption band. 

Fig. 5.9 Emission scan of a dilute [Ru(bpy)3] solution in water, exciting at 260 nm, using (dashed line) or not (full line) a cut-off filter (T 50% at 385 nm)...

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