Donor-acceptor complexes, optical

A theoretical formalism is available for understanding optical charge transfer processes in a variety of chemical systems (mixed-valence ions, donor-acceptor complexes, metal-ligand charge transfer chromophores, etc) where the extent of charge transfer is large and where electronic coupling between the electron donor and acceptor sites is relatively small. 

A poly(phenylquinoxaline) was prepared for electroluminescence applications <1996SM(76)105>. Crystallization of solution donor-acceptor complexes of 2,3-dimethylquinoxaline 1,4-dioxide or phenazine 5,10-dioxide with TCNE afforded two-component solids containing weakly bound 1-D donor-acceptor arrays <1997TL7665>. A pyrazine ladder polymer was constructed from two different pyrazine units, as an optical device <1999JA8783>. The new electron-deficient macrocycle tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine was prepared from l,2-di(2-pyridyl)ethanedione and 2,3-diaminomaleonitrile for a study of its electrochemical properties <2004IC8626>. 

The D-PS-A systems investigated for their ability to yield charge-separated states possess suitable features (see Section 8.2.3). Ion-dependent optical changes produced by indicator ligands [8.34-8.40] could lead to ion-selective control of nonlinear optical properties. Molecular electron donor-acceptor complexes may present NLO effects since they possess polarized ground states and undergo inter-... 

A more general definition of the FCWD includes overlap integrals of quantum nuclear modes. The definition given by Eq. [19] includes only classical solvent modes (superscript s ) for which these overlap integrals are identically equal to unity. An extension of Eq. [19] to the case of quantum intramolecular excitations of the donor-acceptor complex is given below in the section discussing optical Franck-Condon factors. 

As is easy to see from Eq. [80] and Figure 7, the Q model predicts the breaking of the symmetry between the absorption and emission widths (Eq. [11]) generated by a statistical distribution of solvent configurations around a donor-acceptor complex (inhomogeneous broadening). This fact may have a significant application to the band shape analysis of optical transitions since unequal absorption and emission width are often observed experimently. " ... 

Both electronic delocalization and polarizability of the donor-acceptor complex lead to a significant asymmetry between the absorption and emission optical lines as is often observed in experiment.The importance of this effect can be assessed by comparing the dependence of the observed spectral width on solvent polarity with the prediction of MH theory. Equations [6] and [12] can be combined to give... 

Ranjit, K. T, Marx-Tibbon, S., Ben-Dov, I., and Wilber, I. Formation of supramolecular donor-acceptor complexes between bis(pyridiniomethyl)azobenzenes and eosin in solutions and at solid interfaces Transduction into optical and microgravimetric signals. Angew/. Chem. Int. Ed. Engl. 1997, 36,147-150. 

Such a type of donor-acceptor complex represents an original class of 2D dipolar NLO chromophore, and EFISH and HRS experiments in combination with INDO/singles configuration interaction(SCI)-SOS theoretical calculations have been used to investigate the 2D character of the [3 response in 62 (A = C1) the 2D optical nonlinearity is related to the existence of various low-energy charge transfer states, and while... 

LB films of tetra-4-tert-butyl- and tetra-(3-nitro-5-tcrt-butyl)-substituted CoPcs were used to detect pyridine, primary aliphatic amines, and benzylamine, by means of microgravimetry, UV-Vis spectroscopy, and optic microscopy [59], The sorption occurs as stepwise intercalation of the sorbate molecules into the supramolecular 3D structure of the phthalocyanine assembly followed by formation of the donor-acceptor complexes. Both intercalation depth and stoichiometry of the complexes are determined by the molecular structure of amines. The supramolecular factor allows discrimination between amines in air but not in aqueous solutions because of concurrent intercalation of water. 

The two main nuclear modes affecting electronic energies of the donor and acceptor are intramolecular vibrations of the molecular skeleton of the donor-acceptor complex and molecular motions of the solvent. If these two nuclear modes are uncoupled, one can arrive at a set of simple relations between the two spectral moments of absorption and/or emission transitions and the activation parameters of ET. The most transparent representation is achieved when the quantum intramolecular vibrations are represented by a single, effective vibrational mode with the frequency vv (Einstein model).15-17 If both the forward (absorption) and backward (emission) optical transitions are available, their first spectral moments determine the reorganization energies of quantum vibrations, Xv, and of the classical nuclear motions of the donor-acceptor skeleton and the solvent, Xci ... 

In crystals which are composed of two different partner molecules, CT excitations and with them CT excitons are frequently the predominant lowest excitation states and are thus responsible for the lowest-energy transitions in the singlet system. We will illustrate this using the example of the weak donor-acceptor complex anthracene/pyromellitic acid dianhydride, (A/PMDA) (Fig. 6.14). The ground state is neutral and nonpolar, with only a small charge-transfer fraction. The lowest optical excitation starts from the ground state of the donor D, anthracene, (from its highest occupied orbital or HOMO) and leads to the lowest unoccupied orbital (LUMO) of the acceptors A, PMDA, within the mixed stack DADADA. A polar ex-... 

The power of chiroptical techniques has been further demonstrated by induced circular dichroism studies of donor-acceptor complexes of optically active low molecular weight carbazole derivatives 4-6 with chloranil and other electron accep-... 

The outstanding optical activities of conjugate OPV rods can be upgraded by adopting supramolecular concepts. As described in Sect. 2.6, fibrous aggregates of OPV rod molecules were able to enhance light-harvesting behavior, and fmther fine-tune emissive colors via donor-acceptor complexes. 

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