Charge relaxed state

Several base pairs of adenine-thymine, including the WC pair, have also been studied [238], It is found that a charge transfer state exists about 1.5 eV higher than the local nn states. Proton transfer between the bases stabilizes a charge transfer state which then crosses with the ground state facilitating radiationless relaxation. This mechanism is not energetically favorable for non WC pairs. 

In electron transfer reactions one studies the conversion of an electron state localized on A to one localized on B. One can also consider the relaxation of a charge localized state to the adiabatic delocalized state [366],... 

The efficient screening approximation means essentially that the final state of the core, containing a hole, is a completely relaxed state relative to its immediate surround-ing In the neighbourhood of the photoemission site, the conduction electron density of charge redistributes in such a way to suit the introduction of a core in which (differently from the normal ion cores of the metal) there is one hole in a deep bound state, and one valence electron more. The effect of a deep core hole (relative to the outer electrons), may be easily described as the addition of a positive nuclear charge (as, e.g. in P-radioactive decay). Therefore, the excited core can be described as an impurity in the metal. If the normal ion core has Z nuclear charges (Z atomic number) and v outer electrons (v metallic valence) the excited core is similar to an impurity having atomic number (Z + 1) and metalhc valence (v + 1) (e.g., for La ion core in lanthanum metal, the excited core is similar to a Ce impurity). 

Excimer may relax (i) by emission of characteristic structureless band shifted to about 6000 cm-1 to the red of the normal fluorescence, (ii) dissociate nonradiatively into original molecules, (iii) form a photodimer. Those systems which give rise to photodimers may not decay by excimer emission. The binoing energy for excimer formation is provided by interaction between charge transfer (CT) state A+A- A-A and charge resonance state AA s A A. 

A relevant result here is that the emissions of the relaxed and unrelaxed DMABN charge-transfer states have the same spectral shape the instantaneous spectral distributions deduced from the decays i( v, t) show no significant time dependence of their contours, which differ only slightly from that of the stationary distribution (Fig. 2.22). 

In Table II are reported the values of v0, and rR obtained for different temperatures as well as the experimental and calculated wavenumber v of the peak of the stationary spectrum. Figure 2.21, where the solid lines represent calculated decays, shows that the experimental results can well be accounted for by the expressions (2.37) and (2.38). These results indicate that the relaxation of the electronic energy of the TICT state of DMABN due to interaction with the polar medium can well be described by a single exponential law not only for the n-butyl chloride solution but also for the solutions in alcohols. This relaxation process, leading to final states having an electronic energy markedly lower than that of the unrelaxed charge-transfer states, is responsible for the presence of an intramolecular potential barrier for the reverse reaction to the locally excited B state the barrier is made evident by the... 

Because of the spectral relaxation due to the appearance of a high dipole moment in the charge-transfer state, the dynamics of the TICT state formation has been studied by following the fluorescence rise in the whole A band. In Fig. 5.6 are plotted, in the 10 ns time range, the experimental curve iA(t) at -110°C in propanol (tj = 1.5 x 103 cp) and the decay of the B emission at 350 nm. The solid curve representing the evolution of the TICT state expected in a constant reaction rate scheme shows a slower risetime with respect to that of the recorded A emission. To interpret the experimental iA(t) curves, the time dependence of the reaction rate kliA(t) should be taken into account. From the coupled differential equations for the populations nB(t) and nA(t) of the B and A states (remembering that the reverse reaction B <—A is negligible at low temperatures) ... 

The first example of e.t. controlled by solvent relaxation was probably the TICT state formation in DMABN and similar molecules [74]. The twisted intramolecular charge transfer state is, however, formed gradually the charge separation increases with the twist angle of the dimethylamino substituent... 

Ligand Solution conformation Charge/tautomeric state Solution dynamics Bound conformation Pharmacophore models 1D/2D NMR Chemical shift Line shape/relaxation analysis TrNOE All of the above, including 1D/2D of multiple ligands... 

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