Excitons intramolecular

Packard, B. Z., Toptygin, D. D., Komoriya, A. and Brand, L. (1996). Profluorescent protease substrates intramolecular dimers described by the exciton model. Proc. Natl. Acad. Sci. USA. 93, 11640-11645. 

Particularly useful in such measurements are 4-dimethylaminobenzoates160 and 4-dimethylaminocinnamates161 as their intramolecular charge-transfer bands at 309 nm and 362 nm, respectively, are well separated from shorter wavelength bands and the exciton amplitudes are higher, compared with other benzoates or cinnamates. 

Rigorously, ORD and CD spectra are related through the Kronig-Kramers theorem, a well-known general relationship between refraction and absorption, i.e. nL - nR is determined by eL - % for A from zero to infinity [128], (The analogous relationship between refraction and reflection applies to cholesteric liquid crystals.) Hence, in order to maximize ORD in the transparent region, Cotton effects, associated with exciton coupling (both intramolecular and intermolecular), have... 

A comparison of the UV-vVis spectra of the ball-type, its precursor, and mono Pc 28, 29, and 30 in (Fig. 8) in THF shows characteristic absorptions between 610 and 710 nm in the Q band region for metal-free Pcs. Because of the lower symmetry of the metal-free Pcs, the Q band splits into two intense bands in that region. An additional third band at 636 nm and a fourth band/shoulder at 610 nm are exciton coupling and charge transfer bands, respectively. The intensity of the third band of the compound 30 clearly indicates the presence of strong intramolecular interactions between two Pc macrocycles [45]. 

The ZnPc-Cgo dyad 110 has a low fluorescence quantum yield (f = 0.01) in toluene due to the intramolecular electron-transfer deactivation. Addition of 108 leads to a further reduction in the fluorescence intensity (4>f = 0.002) and a slight blue shift of the emission maximum, suggesting the formation of the ensemble 108-110, in which the two components have strong excitonic coupling. The addition of 108 (i.e. the hetero-association) also stabilizes the radical ion pair ZnPc+-C6o, increasing the lifetime from 130 ns (for 110) to 475 ns (for 108-110) (measured in tetrahydrofuran). 

When the two dipoles occupy symmetrical positions in the cell, as for instance in the case of the anthracene crystal, (1.70) may be further simplified by introducing symmetric and antisymmetric states for all directions of K, with respect to the assumed symmetry. Then (1.70) reduces to 2 x 2 determinants for the two (symmetric and antisymmetric) transitions. The solution of (1.70) leads to four values of co for each wave vector K, i.e. to four excitonic branches. In general, the crystal field is assumed weak compared to intramolecular forces, so that coupling between excitonic branches may be neglected. To a first approximation, each of the excitonic branches, symmetric and antisymmetric, is given by the equation... 

Thus the hamiltonian (2.15) couples the electronic excitations to the vibrations by linear terms in and by quadratic terms in A. The molecular eigenstates of (2.15) are the vibronic states they are different from tensorial products of electronic excitations and undressed vibrations. Even for this simple intramolecular effect, we cannot, when moving to the crystal, consider excitonic and vibrational motions as independent. 

First, we envisage the weak exciton-photon coupling (which allows an intuitive description of the phonon effects on the nature of the secondary emissions). Therefore we write the hamiltonian of the total system as sums of free photons (Hy), free excitons (He), and free phonons (Hp), with the appropriate interactions Hey (Section I) and Hep (see Sections II, A, B, C.), including intramolecular vibrations too. 

The working substance of the ITEP-group /9 source was a doubly tritiated crystalline amino acid, DL-valine (Mallikarjunan and Rao, 1969), which is a molecular crystal. As a result of decay, during the time 10 18 sec the valine molecule transforms into the corresponding helium-containing ion (RHe)+. Since the translational symmetry of the crystal is disturbed, no exciton states are produced, and only molecular states of the complex (RHe)+ are excited. Since in molecular crystals the intermolecular interactions are considerably weaker than the intramolecular ones, one can neglect the influence of the valine crystalline surrounding on the /S-decay process and consider only an isolated valine molecule. 

Furo T, Mori T, Wada T, Inoue Y (2005) Absolute configuration of Chiral [2.2]paracyclo-phanes with intramolecular charge-transfer interaction. Failure of the exciton chirality method and use of the sector rule applied to the cotton effect of the CT transition. J Am Chem Soc 127 7995-8006 and 1638... 

Another significant source of variations in the local site energies of molecular ions and excitons in condensed media is the modulation of these energies by the thermal vibrations either of the medium (e.g., acoustical phonons and librons) or of the molecular ion (exciton) itself (intramolecular vibrations). A model Hamiltonian which incorporates electronic interactions with... 

The photoinduced creation of an ion or exciton in condensed molecular media causes greater relaxation than in isolated molecules because the induced charge redistribution generates electronic and atomic relaxation in the other constitutents of the medium as well as in the excited molecule itself. The associated intermolecular contributions to the relaxation energy are comparable in magnitude to the intramolecular ones from the molecule itself, i.e., E (inter)=l-2eV, E (inter)=0.leV (4, 6, 10). 

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