Excited Slate

J. B. Foresman and H. B. Schlegel, Application of the Cl-Singles Method in Predicting the Energy, Properties and Reactivity of Molecules in Their Excited Slates in Molecular Spectroscopy Recent Experimental and Computational Advances, ed. R. Fausto, NATO-ASI Series C, Kluwer Academic, The Netherlands, 1993. 

In contrast with the thermal process, photochemical [2 + 2] cycloadditions me observed. Irradiation of an alkene with UV light excites an electron from i /, the ground-slate HOMO, to which becomes the excited-slate HOMO. Interaction between the excited-state HOMO of one alkene and the LUMO of the second alkene allows a photochemical [2 + 2j cycloaddition reaction to occur by a suprafacial pathway (Figure 30.10b). 

Figure 4-13. Evolution with the size of the sexithienyl cluster of the excitation energies from the ground stale to the lowest excited state (open circles), to the high-lying excited slate strongly coupled to the ground state (open squares), and to the lowest charge transfer-excited stale (open triangles). In all cases, only inlralayer interactions have been considered.

Table 6-1. C2(l molecular poinl group. The electronic stales of the flat T6 molecule are classified according lo the lwo-1 old screw axis (C2). inversion (/). and glide plane reflection (o ) symmetry operations. The A and lt excited slates transform like translations Oi along the molecular axes and are optically allowed. The Ag and Bg stales arc isoniorphous with the polarizability tensor components (u), being therefore one-photon forbidden and Iwo-pholon allowed.

Significant stimulated emission is only found for the pristine side of the sample. From these results it was concluded that the photoinduccd absorption that suppresses die stimulated emission is directly or indirectly caused by the presence of oxygen-related defects. It was shown earlier that the effect of photooxidation on the emission properties of PPV can be explained by the formation of carbonyl-groups that act as sLrong electron acceptors leading to an efficient dissociation of the plioh excited slate 29). It can be concluded that the dissociated pair near the defcci leads to the strong photoinduccd absorption. The observation that... 

Figure 12. Splitting the excited slate into two energy levels by exciton interactions between the two chromophores i and j. Reprinted with permission from N. Harada, K. Nakanishi, Circular Dichroic Spectroscopy - Exciton Coupling in Organic Stereochemistry, University Science Books, Mill Valley, California, 1983.

Compound Nature of excited Slate Singlet energy kj 1001- Triplet energy/ kj moH... 

Coherent nutbir motion of reacting excited-slate molecules in soluEinn observed b> ultrafast two color pump-prok spectroscopy... 

Chemical structure effect on the excited-slate relaxation dynamics of the PYP chromnphore... 

Fast excited-slate reaction in the photoreceptor pigment-protein complex of the eiliaie fitephiirismu faptmicum... 

Earlier vve used M to indicate a radioactive isotope. Here vve use M to indicate an excited slate. 

Similarities between [Ru(bpy),]2+ (discussed in Chapter 13) and [Pt,(pop)J4 are apparent. Reactive excited states are produced in each when it is subjected to visible light. The excited state ruthenium cation, [Ru(bpy)3]" +, can catalytically convert water to hydrogen and oxygen. The excited slate platinum anion, [Pt,(pop)J 4-, can catalytically convert secondary alcohols to hydrogen and ketones. An important difference, however, is that the ruthenium excited stale species results from (he transfer of an electron from the metal to a bpy ligand, while in the platinum excited state species the two unpaired electrons are metal centered. As a consequence, platinum reactions can occur by inner sphere mechanisms (an axial coordination site is available), a mode of reaction rot readily available to the 18-clectron ruthenium complex.-03... 

Energy of the singlel excited slate of anthracene moiety. bExciplex emission not included. 

The term has been used in atotnie physics for various excited stales, hut its most general usage today is for an excited slate form which all possible quantum transitions lu lower states are forbidden transitions hy ihe appropriate selection rules. 

To the extent that the electronic structure is describable in terms of independent atoms, the properties of inert-gas solids are easily understandable and not so interesting. There are, however, one or two points that should be made. The optical absorption spectra of isolated atoms consists of sharp lines that correspond to transitions of the atom to excited slates, and to a continuous spectrum of absorption beginning at the ionization energy and continuing to higher energy. The experimental absorption spectra of inert-gas solids (Baldini, 1962) also show fairly sharp lines corresponding to transitions from the valence p states to excited s... 

Fig. 11. a Example of a positively solvatokinetic ground state isomerization reaction (the activation barrier decreases with increasing solvent polarity) for an aza-dervative of a donor-acceptor stilbene [94], As outlined above, related donor-acceptor-stilbenes exhibit negative solvatokinetic behavior for the excited-state reaction, b For the merocyanine dye shown, the ground state trans-cis-isomerization across the central bond shows negative solvatokinetic behavior [95], the expectation for the excited slate reaction is positive solvatokinetic behavior... 

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