Excited relaxation

Three of the four photophores, listed in Scheme 3, eliminate nitrogen upon excitation while the biradicaloid triplet state of benzophenone can be reversibly activated, and creates covalent linkage upon excitation-relaxation cycling. This fact and their extremely low reactivity towards protic solvents make them very efficient in the majority of the cases. [7, 19, 20]. Unsaturated ketones can be activated by a similar mechanism, although the secondary processes are much more complex [21]. That mechanism is mainly utilized in steroid hormones possessing unsaturated ketones as intrinsic photophores. 

Fig. 8.1 Laser distillation control scenario discussed in detail in Section 8.3. Two ljtsfi with pulse envelopes ,(0 and e2(0 couple, by virtue of the dipole operator, the states and L enantiomers to two vibrotational states 1) and 2) (denoted If ,) and E2) in the.t i the excited electronic manifold. A third laser pulse with envelope r.0(i) couples the ex E)) and E2) states to one another. The system is allowed to absorb a photon and relax hack the ground state. After many such excitation-relaxation cycles, a significant cnantionneh excess is obtained, as explained in Section 8.3. ...

Fig. 8.10 Control over dimethylallene enantiomer populations as a function of detuning A i1 for various laser powers. First column corresponds to probabilities of L (dot-dash curves) and" D (solid curves) after a single laser pulse, assuming that the initial state is all L. Second column is similar, but for an initial state, which is all D. Rightmost column corresponds toy probabilities of L and D after repeated excitation-relaxation cycles, as described in the text (This is a corrected version of Fig. 2, Ref. [260].) i g...

In Section I, the spectra of e"(ai) consist of Dirac 5 peaks (1.79). In a real crystal these peaks are broadened by static disorder, thermal fluctuations, and excitation-relaxation processes. Discarding for the moment the static disorder, we focus our attention on broadening processes due to lattice phonons, which may be described alternatively in terms of fluctuations of the local energies of the sites, or in terms of exciton relaxation by emission and absorption of phonons. These two complementary aspects of the fluctuation-dissipation theorem64 will allow us to treat the exciton-phonon coupling in the so-called strong and weak cases. The extraordinary (polariton) 0-0 transition of the anthracene crystal will be analyzed on the basis of these theoretical considerations and the semiexperimental data of the Kramers-Kronig analysis. 

In order to avoid the need to cycle repeatedly the excitation-relaxation process, we present in Sec. VII an alternative approach to the laser distillation scheme of Sec. IV in which one can affect enantioselectivity of the sample by a single laser pulse. The method exploits the coexistence, owing to the lack of an inversion center, of one- and two-photon transitions between the same chiral... 

Rather than going through many excitation-relaxation cycles as in the laser dis lation scenario, described in Sec. IV, it is possible to affect the enantio-selectiv... 

Spectra of both CS and SO could be observed. Surprisingly, for it is the old bond in this reaction, the CS vibration was appreciably excited. Relaxation ofCSf was quite slow [214, 215] and the initial distribution could be determined it was roughly Boltzmann with rvib-1775°K, corresponding to 9% of the reaction energy entering this mode. It was more difficult to measure the relative vibrational concentrations of SO, since the reaction... 

NMR measurements of the spin relaxation time have identified a small concentration of molecular hydrogen contained within the a-Si H material. The nuclear spin excitation relaxes to the ground state by transferring its energy to the lattice with a time constant denoted by 2. The temperature dependence of 7 is shown in Fig. 2.19 and has a minimum value at a temperature of about 30 K (Carlos and Taylor... 

In Figure 16.3, the excitation / relaxation electric fields that can interact with organic semiconductor are from the incident light field (E) and metal field (Em) for excitation and near metal surface quenching of non-radiative decay rates the radiative decay rate (F), metal radiative rate (F,), and metal radiative decay rate... 

Kovalevskij, V. Gulbinas, V. Piskarskas, A. Hines, M. A. Scholes, G. D., Surface passivation in CdSe nanocrystal-polymer films revealed by ultrafast excitation relaxation dynamics, Phys. Stat. Sol. B 2004, 241, 1986-1993... 

Since the development of ultrashort lasers, nudear wavepacket dynamics of various matters have attracted continuing attention [1,2]. The research targets extend from gas phase molecules [3, 4] to molecules in solution [5, 6], and solids [7]. In general, an excitation of matter by an ultrashort pulse with sufficient bandwidth leads to the creation of coherence between vibrational (or vibronic) eigenstates [1]. The induced nuclear wavepacket then starts to evolve on a certain potential energy surface and the dynamics is probed by a suitable pump-probe spectroscopy. The direct time-domain observation of the nudear motion provides us with valuable information on photochemical reaction dynamics, vibrational excitation/relaxation mechanisms, electron-vibration (phonon) coupling, and so on. 

Fig. 7.27 Excitation, relaxation and electron transfer during illumination...

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