Electron conjugated chains

Toexaminetheeffectofir-electron conjugated chain length on singlet energy transfer, Frank et al. (1993b) and Farhoosh et al. (1994) incorporated 3,4,7,8-tetrahydrospheroidene, 3,4,5,6-tetrahydrospher-... 

Fig. 3.19 Stractural units of x-electron conjugated chains based on N-based ligands (a) from Ref. [95] (b) from Ref [94]...

Gas Phase to Solid State Evolution of the Electronic and Optical Properties of Conjugated Chains A Theoretical Investigation... 

According to a large number of experimental studies, the most stable phologen-erated species in the lowest excited stales of conjugated chains are electron-hole pairs bound by Coulomb attraction and associated to a local deformation of the backbone, i.e., polaron-excilons [18]. A good insight into the properties of these species can be provided by quantum-chemical calculations our recent theoretical... 

An increase in polarizability of the w-electron system in a PCS is expected to be followed by an easy transfer of the chemical behavior along the conjugation chain and by a decrease in the internal energy of the PCS, thus enhancing the thermal stability of the polymers and the rigidity of the main chain. 

In the process of radical polymerization a monomolecular short stop of the kinetic chain arises from the delocalization of the unpaired electron along the conjugated chain and from the competition of the developing polyconjugated system with the monomer for the delivery of rr-electrons to the nf-orbitals of a transition metal catalyst in the ionic coordination process. Such a deactivation of the active center may also be due to an interaction with the conjugated bonds of systems which have already been formed. 

The effects of metal-to-metal electronic coupling are observed for several complexes where a ferrocene moiety is bound to transition-metal complexes with a -conjugated chain, 68 (167), 69 (168), and 70 (169). Tertiary amine-ferrocene conjugated molecules, 71, show two-step le oxidation, and their monocationic forms exhibit strong LMCT bands at 600-700 nm (170). 

The electronic properties of these dyes can be tailored by changing the length of conjugation chain or by adding specific terminal groups Rj and R2. Due to their different electron affinities, these terminal groups can be classified into electron acceptor (A), and electron donor (D) groups. 

Appending different terminal groups to the ji-conjugated ends, the cyanine-like molecules may have the following molecular structures D-ji-D, D-ji-A, and A-ji-A. Additionally, electron acceptor/donor groups may be included into the main Ji-conjugation chain to form D-7i-A-ji-D or A-ji-D-ji-A quadrupolar structures. These basic structures are shown schematically in Fig. 4 and discussed in detail in Sect. 3. 

The addition of an electron acceptor group into the D-ti-D can further enhance the 2PA cross sections. A series of dyes, cationic PD 2630, and two neutral dyes, SD 2243 and TD 2765, are shown in Fig. 18a. Compared with the polymethine dye PD 2630, SD 2243 has a squaraine fragment and a strong electron acceptor inserted into the main conjugation chain, while TD 2765 contains a tetraone fragment and an... 

By extension one may say that the power laws (5-7) which determine the magnitude of the linear and nonlinear optical coefficients are consequences of this strong electron-lattice coupling. We now make the conjecture that the time response of these coefficients is severely affected by the dynamics of the electron-lattice coupling in conjugated chains when two or more resonant chemical structures can coexist this is the case for many of the organic chains of Figure 2. 

The prototypes of electronically active molecules are linear conjugated chains made from olefinic and aromatic repeat units (Scheme 1). 

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