Interacting chromophores

In the dipole—dipole approximation, the intensities of the long-wavelength, 1 —, and short-wavelength, 1 +, bands are related to the angle between the interacting chromophores, 5 (47) ... 

The application of exciton coupling between the benzoate and the s-trans-diene or -enoate chromophore in axially dissymmetric molecules derived from hydroxy-substituted adaman-tanone allowed determination of not only the absolute but also the relative configuration. All benzoates 2-5 of 4R configuration show negative exciton Cotton effects, with amplitudes lower for (2 )-adamantylidene compounds 2, 4 compared with 2Z-isomers 3, 5, in which the two interacting chromophores are at a closer distance143. 

The separation of the energy, Av, for two transitions with A and B symmetry in the interacting chromophores is ... 

Due to the subpicosecond lifetimes of the monomeric bases there is little time for significant geometric rearrangements that might be necessary to form an excimer from an excited state initially localized on a single base. This suggests that excimers in nucleic acid polymers are more properly described as static excimers [30] in which two or more interacting chromophores are already pre-associated at the time of absorption. This implies that excimer states depend sensitively on conformation at the time of excitation, as the results presented here demonstrate. 

Onfelt, B., Lincoln, P., Norden, B., Baskin, J. S., and Zewail, H. (2000) Femtosecond linear dichroism of DNA-interacting chromophores solvation and charge separation dynamics of [Ru(phen)2dppz]+2 systems, Proc. Natl. Acad. Sci. USA 97, 5708-5713. 

The Hamiltonian in Eq. (10) is very simple but describes a fairly rich physics. Indeed it encompasses both the mf and Are excitonic models for interacting chromophores. To demonstrate this Important point we rewrite the same Hamiltonian... 

In this contribution we discuss mm based on pp chromophores, a very interesting class of molecules for applications in molecular photonics and electronics. Push-pull chromophores are both polar and polarizable and this makes the role of intermolecular interactions particularly important. The toy model we propose for clusters of pp chromophores neglects intermolecular overlap, just accounting for classical electrostatic intermolecular interactions, and describes each pp chromophore based on a two state model. The two-state model for pp chromophores has been discussed and validated via an extensive comparison with the spectroscopic properties of several dyes in solution [74, 75, 90], The emerging picture is safe and led to the definition of a reliable set of molecular parameters for selected dyes. This analysis then offers valuable information to be inserted into models for clusters of interacting chromophores, in a the bottom-up modeling strategy that was nicely exemplified in Ref. [90]. 

Murrell described and illustrated the theory of weakly interacting chromophores. His approach may be used in a straightforward way for analysis of the electronic spectra of vdW systems. Unless the states of one subsystem are mixed by the field of the other subsystems (i.e. in the absence of the field effect), the decisive matrix elements of the total Hamiltonian between the ground state, the singly excited states and the doubly excited state are then (the symbols used by Murrell are employed) ... 

In the publications on excimer formation in polymers to date, the vast majority have concentrated on homopolymers or copolymers having pendant aromatic chromophores such as phenyl or naphthyl groups. Polymers and copolymers based on 1-vinylnaphthalene, styrene, 2-vinylnaphthalene and N-vinylcarbazole have probably received the most attention while polymers based on vinyltoluene, acenaphthalene, vinylpyrene, 2-naphthylmethacryl ate, and a number of other monomers have also been studied, but to a lesser extent. Excimer formation in such polymer systems is especially favorable when the interacting species are "nearest neighbors" pendant to the polymer backbone and separated by three carbon atoms. However, excimers have also been reported for copolymer systems where the interactive chromophores are separated by a larger number of atoms. 

Since any sample of polymer is characterised by a distribution of molecular weights and the fluorescence of a chromophore is in principle environmentally sensitive, even for non-interacting chromophores it would not be surprising if a distribution of decay... 

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