Chromophore/chromophoric

Barium and strontium salts of polystyrene with two active end-groups per chain were prepared by Francois et al.82). Direct electron transfer from tiny metal particles deposited on a filter through which a THF solution of the monomer was percolated yields the required polymers 82). The A.max of the resulting solution depends on the DPn of the formed oligomers, being identical with that of the salt of polymers with one active end-group per chain for DPn > 10, but is red-shifted at lower DPn. Moreover, for low DPn, (<5), the absorption peak splits due to chromophor-chromophor interaction caused by the vicinity of the reactive benzyl type anions. 

The function of the bulky butyl groups on the thiophene ring of the chromophore is the prevention of unwanted chromophore-chromophore interactions. This and other design principles have led to the development of new materials, such as (5.12) and related chromophores, which when embedded in a polymer matrix give materials with dramatically improved performance. ... 

It was found that the quantum efficiency of the anodic photocurrent in the Chi a-DPL system was increased from 3-4% in the pure Chi a monolayer up to about 25% (65) in highly diluted mixed monolayers. This increase in efficiency was accompanied by red shifts of the photocurrent peak positions in the red and blue bands (e.g., in the red, from 675 nm (pure Chi a) to 665-670 nm (Chi atDPL 1/49)) and probably reflects the change in chromophore-chromophore interaction between Chi a molecules. 

The first term, Vs, accounts for the Coulomb-exchange direct interaction between D and A (see Eq.10), and the second, Vexpucit, describes a solvent-mediated chromophore-chromophore contribution between the transition densities. In addition to this explicit medium effect (VexpuCit), we note that another implicit effect of the environment is included in the Vs term, due to changes on the transition densities upon solvation. It is useful to define a screening factor s, conceptually equivalent to the 1/n2 term in the Forster equation, so that V = sVs ... 

In the first contribution, Huxter Scholes present a review of the recent evolution of theory of EET in condensed phase from their earliest and simple formulation, based on the Forster theory to the most recent advances of theoretical and computational methods based on continuum solvation models. In the second contribution, Curutchet reviews the recent developments of PCM towards accurate theoretical investigations of EET in solution. In particular, the modelization of the various contributions of solvent effects in the chromophore-chromophore electronic coupling is presented using quantum-mechanical approaches. 

Of course, for chromophores with dipole moments less than 6 Debye and corresponding small polarizability, chromophore-chromophore intermolecular electrostatic interactions are unimportant and independent particle analysis is completely appropriate. However, it is unlikely that such chromophores will ever have commercial relevance. 

Kaino and co-workers [255] have investigated the effect of polymer polydis-persity on electro-optic materials properties. No dependence on polydispersity was observed for guest host materials but for Disperse Red chromophores covalently attached to monodisperse polystyrene weaker absorption tails were observed. This result suggests that chromophore-chromophore interactions are modified by the polymer host. 

An interesting class of multi-chromophoric chromophores are the binaphthol derivatives. In this class of molecules, two naphthyl ether units are covalently attached to each other in the 1,1 -positions, as shown in Figure 4 [70-72]. 

From the small difference in the spectral width (vide supra), the assumption of an excited state excimer-like (or dimer) chromophore-chromophore interaction is possible but not conclusive. Better insight into the extent of excimer-like emission is obtained from the fluorescence decays, where only for the multichromophoric dendrimers is a long decay component of 7.4 ns observed along... 

TABLE 1.4 Fit Parameters of the Fluorescence Anisotropy Decays Measured for m-C1P (x —1-4) in Toluene with Xexc — 488 and /.nu = 600 nm at Which There Is Only Monomer Emission and Average Chromophore-Chromophore Distances (tfDA)... 

In order to reveal properties that are independent of potential chromophore-chromophore interactions, p-C lPj was investigated in a first series of measurements as a model compound, since it contains only one chromophore. Figure 1.17a shows a typical result for p-C 1 Pi at two different detection... 

Inherently chiral chromophores Chromophore itself is twisted and chiral and, therefore, the 7t—7t and/or n—it transitions become CD active, because both electric transition moment and magnetic transition moment < M 0> take nonzero values. The CD intensity of this group is stronger than that of group (a). 

The dicarbanionic nature of the ultimately produced oligomers was confirmed by their conversion into dicarboxylic adds. Moreover, their optical spectrum reveals splitting of the absorption band due to the chromophore-chromophore interaction (see, e.g. Ref. 465), and this phenomenon provides an additional argument for their dicarbanionic structure. Nevertheless, this writer is not convinced that the prepared solutions used for the kinetic studies of styrene propagation were rigorously free of the monocarbanionic oligomers. 

For a treatment of the ionization energies one has to refer to particular molecular orbitals (MOs), in case of electronic excitation energies one has to refer to chromophores, Chromophores also play the key role, if substituent effects on intensities of uv bands or cd bands in circular dichroism spectroscopy are considered. 

Harper, A.W., S. Sun, L.R. Dalton, S.M. Garner, A. Chen, S. Kalluri, W.H. Steier, and B.H. Robinson. 1998. Translating microscopic optical nonhnearity to macroscopic optical nonlinearity The role of chromophore-chromophore electrostatic interactions. / Opt Soc Amer B 15 329-337. 

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