Relaxed excited state

The resulting PL intensity depends on the absorption of the incident light and the mechanism of coupling between the initial excited states and the relaxed excited states that take part in emission. The spectrum is similar to an absorption spectrum and is useful because it includes higher excited levels that normally do not appear in the thermalized PL emission spectra. Some transitions are apparent in PLE spectra from thin layers that would only be seen in absorption data if the sample thickness were orders of magnitude greater. 

Little is known about the fluorescence of the chla spectral forms. It was recently suggested, on the basis of gaussian curve analysis combined with band calculations, that each of the spectral forms of PSII antenna has a separate emission, with Stokes shifts between 2nm and 3nm [133]. These values are much smaller than those for chla in non-polar solvents (6-8 nm). This is due to the narrow band widths of the spectral forms, as the shift is determined by the absorption band width for thermally relaxed excited states [157]. The fluorescence rate constants are expected to be rather similar for the different forms as their gaussian band widths are similar [71], It is thought that the fluorescence yields are also probably rather similar as the emission of the sj tral forms is closely approximated by a Boltzmann distribution at room temperature for both LHCII and total PSII antenna [71, 133]. 

For vibrationally relaxed excited state in which initial and final states are weakly coupled through a dipole-dipole interaction, the rate constant for energy transfer is given by... 

The vibrationally excited singlet Si and triplet Tf, expected upon the annihilation of the lowest excited triplets Ti, have an energy below the autoionization threshold of typical aromatic crystals [26], thus, no intrinsic photoionization has been observed in these solids. However, the presence of intentional or non-intentional admixtures can allow the triplet-triplet interaction-induced photoionization forming a free carrier in the matrix and a trapped carrier on an admixture molecule. Also, such a process has been reported for the CT triplet states localized on the donor molecule, e.g. in polycrystalline samples of CT complex anthracene-tetracyanoben-zene, where the triplets are localized on the anthracene donor (3Di). Annihilation of 3Di results in the population of non-relaxed excited states of the complex 1(D+A ) and 3(D+A") , dissociation of which may lead to the formation of free charges D+ [214]. 

The emission properties of anions as for instance carbanions of indene [28], xanthene or thioxanthene [29], fluorene [30, 31], diphenyl propene or penta-diene [32] were also discussed. It was shown that in certain cases, important changes may occur between ground and excited states, increasing the percentage of SSIP when the relaxed excited state is reached [33], Two different types of... 

When stereogenic centers are introduced on the tether, a large asymme induction can also be observed, especially when the product results from an initi 1,5-ring closure. The relaxed excited state of the starting enone behav... 

In the case of tr > Ts the emission will occur before any rearrangement of solvent molecules in the solvation shell takes place. The initial state of the emission process is the Franck-Condon excited state and the final state is the equilibrium ground state. Hence, the wavenumber of emission will be equal to the wavenumber of the corresponding absorption. In the case of tr Te (c/ Fig. 6-7) , reorientation of the solvent molecules can take place after electronic excitation and a relaxed excited state is obtained in which another solvation equilibrium has been established. It is from this equilibrium state that fluorescence occurs at room temperature. By analogy, there is a... 

Keywords Triplets in organometallic compounds. Chemical tunability. Spin-lattice relaxation. Excited state binding properties, Vibronic coupling. Spatial extensions of electronic states, ODMR results... 

What happens after the absorption transition First we return to the lowest vibrational level of the excited state that is, the excited state relaxes to its equilibrium position, giving up the excess energy as heat to the lattice. The system of dopant ion and surroundings is then in the relaxed excited state. The emission transition can be described in exactly the same way as the absorption transition. This is indicated in Fig. 3 in the same way as for the absorption transition. Finally the system relaxes within the g parabola to the lowest vibrational level. 

Let us consider the configurational coordinate diagrams of Fig. 5 in order to understand the relevant physical processes. Figure 5a presents essentially the same information as Fig. 3. Absorption and emission transitions are quite possible and are Stokes-shifted relative to each other. The relaxed-excited state may, however, reach the crossing of the... 

If luminescent centers come closer together, they may show interaction with each other that results in new phenomena. Consider two centers, S and A, with a certain interaction. The relaxed-excited state of S may transfer its energy to A. This energy transfer has been treated by Forster and Dexter and is now well understood (8). 

Extremely remarkable is the case of YP04 Sb (177). In this lattice the ion shows two emissions from the relaxed excited state. This... 

In the case of thermal ET, which applies either to ground state ET or photo-intitiated ET from a vibrationally relaxed excited state (cf, [15d]), we now define the effective coupling T,f by employing the two-state approximation (TSA) introduced in Eqs. 14-15 ... 

The emission of [Ru(bipy)j] is quenched in the presence of [Co(NH3)5Br], and this process can be described by electron transfer from the excited state of [Ru(bipy)j]. Molecules that are poor reductants in their ground states can be converted by a photon into a species with a hole in a stable orbital that are oxidants this same excited-state molecule, with an electron in an unstable orbital, also will be a reductant. For [Ru(bipy)3] , the vibrationally relaxed excited state is ca. 200 kJ mol above the ground state hence combining ... 

---