Stepwise fluorescence

In stepwise fluorescence, the upper levels of the exciting and the emitted lines are different. In the normal case, the excited atoms lose part of their energy by collisional deactivation (by collision with flame molecules) and then return to the original (usually ground) state by radiational deactivation. Sodium, for example, is excited at the 330.3-nm line and undergoes stepwise fluorescence to emit a line at... 

In the case of the stepwise line fluorescence, the effect is divided into Stokes and anti-Stokes stepwise fluorescence depending on the wavelength (energy) relationships. A thermally assisted process may take place, if after radiation excitation, further collisional excitation occurs. 

Note Primary amines yield fluorescent chromatogram zones even before the application of reagent 3. Secondary amines do not yield fluorescent derivatives until they have been treated with reagent 3. Hence, the reagent sequence allows the stepwise detection of primary and secondary amines. Taurine is preferred as the essential component of reagent 3 over the multiplicity of other possibilities because it produces intense fluorescence it is also not very volatile and is readily available. Amides and substances with peptide linkages, eg. hippuric acid, are not detected, neither are secondary amines that are volatile at high temperatures. 

The NIR femtosecond laser microscope realized higher order multi photon excitation for aromatic compounds interferometric autocorrelation detection of the fluorescence from the microcrystals of the aromatic molecules confirmed that their excited states were produced not via stepwise multiphoton absorption but by simultaneous absorption of several photons. The microscope enabled us to obtain three-dimensional multiphoton fluorescence images with higher spatial resolution than that limited by the diffraction theory for one-photon excitation. 

Alternatively, arene displacement can also be photo- rather than thermally-induced. In this respect, we studied the photoactivation of the dinuclear ruthenium-arene complex [ RuCl (rj6-indane) 2(p-2,3-dpp)]2+ (2,3-dpp, 2,3-bis(2-pyridyl)pyrazine) (21). The thermal reactivity of this compound is limited to the stepwise double aquation (which shows biexponential kinetics), but irradiation of the sample results in photoinduced loss of the arene. This photoactivation pathway produces ruthenium species that are more active than their ruthenium-arene precursors (Fig. 18). At the same time, free indane fluoresces 40 times more strongly than bound indane, opening up possibilities to use the arene as a fluorescent marker for imaging purposes. The photoactivation pathway is different from those previously discussed for photoactivated Pt(IV) diazido complexes, as it involves photosubstitution rather than photoreduction. Importantly, the photoactivation mechanism is independent of oxygen (see Section II on photoactivatable platinum drugs) (83). 

S2 - Sq fluorescence and radiationless transitions from the state of porphyrins have been studied in order to reveal photodynaunics of porphyrins. The S2 state fluorescence of zinc(II)-tetraphenylporphin is caused even by the excitation to the state. Two-photon absorption and optical-optical double resonance studies show that a stepwise two-photon absorption through the state is a main process populating the S2 state. 

Monitoring the formation of Na atoms by laser induced fluorescence spectroscopy (at another wavelength) as a function of time shows a stepwise growth in the Na atom intensity, following the implications of the periodic vibration of the [Na—I] species exactly. Thus product formation depends on both a vibrational mode and a curve crossing both play a role along the reaction coordinate. 

Thermally assisted fluorescence is the converse of stepwise line fluorescence. It occurs as a result of a stepwise absorption of energy by... 

Another interesting system that was studied for two-photon 3D data storage in our group is based on the modulation of fluorescent properties of 2PA chromophores by protonation [95]. For example, due to differences in basicity (pKb), fluorene 3 undergoes selective, stepwise protonation, first by proto-... 

Fig. 16.8 Schematic illustration of the magnetic resonance technique used to measure the Rb nf fine structure intervals. The Rb atoms in the n2F states are populated by spontaneous decay of the n D5/2 states, which are populated by stepwise excitation of the ground state atoms. The rf transitions, induced among the magnetic sublevels of the n2F states, are detected as a change in the intensity of the polarized n2F — 42D fluorescence. The lower part of the figure shows a sketch of the experimental arrangement (from ref. 36).

Access to nucleic acid dendrimers is initiated by a zip-fastener like dissociation of the DNA double strand by heating. The double strand separates into the two individual strands by thermal motion (denaturation). Subsequent association, hybridisation of complementary sequences, is followed by stepwise cross-linking to form DNA dendrimers, which can contain up to two million oligonucleotide-end group strands (Fig. 8.19). The latter can be labelled with fluorescence or radioactive markers. 

The present analysis relies on - and extends - the comprehensive theoretical study of Refs. [23,24] on the multi-state interactions in the manifold of the X — E states of Bz+. Like this recent work, it utilizes an ab initio quantum-dynamical approach. In Refs. [23,24] we have, in addition, identified strong coupling effects between the B — C and B — D electronic states, caused by additional conical intersections between their potential energy surfaces. A whole sequence of stepwise femtosecond internal conversion processes results [24]. Such sequential internal conversion processes are of general importance as is evidenced indirectly by the fluorescence and fragmentation dynamics of organic closed-shell molecules and radical cations [49,50]. It is therefore to be expected that the present approach and results may be of relevance for many other medium-sized molecular systems. 

The characteristics of electrokinetically controlled fluid flow in microchannel manifolds has been studied in a systematic way by Harrison and coworkers [28, 30]. An illustrative demonstration of the potential of this approach is shown in Fig. 2 for the controlled dilution of a fluorescein solution under voltage control. In parallel with a stepwise decrease of the potential applied to the fluorescein reservoir, a decrease of fluorescence signal downstream after the junction is visible in Fig. 2. As long as the ionic strength and pH in each supply channel is the same (same jieo), mass balance is automatically fulfilled, and the incoming flows at the intersection will be exactly balanced by the outgoing flow of the mixed components (otherwise, mass balance would be enforced by additional hydrodynamic or secondary internal flows). This way of mixing fluids was also... 

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