Chromophores, cooperative effect

In these molecular type lattices the structure of the CuN402 chromophore is independent of the structure of the host lattice, and the effect is referred to as the noncooperative Jahn-Teller effect.514 It applies to the vast majority of low symmetry copper(II) complexes involving organic type ligands, but even here cooperative effects that influence the ESR properties, such... 

Such fluctuations of the photon flux, emitted from a molecule, have been predicted to be due to cooperative effects (21.22). The theory is based on an idea of Prigogine and coworkers (s. e.g.(22)) who treated the irreversible part of a physical process by transforming the wavefunctions of a dissipative system into another space using a "dynamical" non-unitary representation D = exp(-iVT /fI) with a "star-Hermitian" time operator 3 and V describing the interaction of a relevant local system Hq, e.g. the complex chromophore, and the total system H, i.e. our crystal. In the new representation y>=D Y no additional time dependence is introduced, dD/dt = 0, any expectation value of an operator M=DMD should be unchanged = M> and the total Hamiltonian is transformed by 1T=DHD 1 = Hq to the local system Hamiltonian (21.22). To describe the time development in the new representation, the electron density... 

The paper is organized as follows. Section 2 shortly introduces the exciton model and its approximations. Section 3 reviews calculations of ground state properties (mainly the polarization and polarizability) paying special attention to the mean-field approximation. Push-pull chromophores, the special family of polar and polarizable molecules studied in this contribution, are presented in Section 4, with a brief discussion of their properties in solution and of relevant models. In Section 5 we present a model for interacting push-pull chromophores that will be the basis for the discussion of collective and cooperative effects in relevant materials. Static susceptibilities of clusters of push-pull chromophores are discussed in Section 6, focusing attention on cooperative effects in tlie ground state. Excited state properties are addressed in Section 7, with special emphasis to systems where intermolecular interactions lead to extreme consequences. Section 8 finally summarizes main results. 

In order to prove the microphase separation of both blocks, which is required to maintain the cooperative effect of the azobenzene chromophores, thin films of la (cyanoazobenzene content 27.4 wt%) were investigated by transmission electron microscopy (TEM see Fig. 7) and small angle X-ray scattering (SAXS). The... 

In spite of the large spacing of the fluorescent residues, an intense excimer emission was observed (48). The In/L ratio increased with concentration beyond a sharply defined point, corresponding presumably to the onset of chain interpenetration. However, the lifetime of monomer emission was concentration independent and it was concluded that a cooperative effect of evenly spaced chromophores favored chromophore dimer formation even in the ground state. The high intensity of excimer emission observed even in very dilute solutions seemed to imply a folded chain conformation. 

Two contributions from the Cooper group in 2006 focused on the delocalization of the triplet excitons in Pt-acetylides [86, 87], They investigated the effect of symmetry within the complexes by comparing chromophores with either one pendant acetylide or two symmetric acetylides trans disposed to each other. Similar to earlier... 

UV absorption spectra, fluorescence emission spectra and photostabilization effect of 2-(2-hydroxy-4-acryloyloxyphenyl)-2/7-benzotriazole and of its polymer bound forms were studied in poly-CK-l,4-polybutadiene [337]. The following activity series was found copolymer with methyl methacrylate > homopolymer > monomer. It seems that chromophoric units incorporated into a macromolecule behave cooperatively (causing self-absorbance of the emitted radiation). 

The effect of a combination of photochromic azobenzene with mesogenic units within the same polymer on cooperative motion and anisotropic enhancement is exemplified by the CPI and K1 polymer systems of Zilker et al. [53] shown in Fig. 6.16. In the CPI-50 polymer, a clear distinction between chromophore and cooperative mesogen (CPI-50 polymer) existed. There was no apparent distinction between chromophore and mesogen in the Kl-40 polymer because mesogen also contained a photoactive azo linkage. The boundary between fast-chromophore and slow-mesogen reorientation is blurred and an effective enhancement of reorientation occurs. 

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