Aromatic hydrocarbon absorption electron systems

Among the most common unsaturated units, there are mono (poly) cyclic aromatic hydrocarbons, heterocycles, benzofused systems, and olefinic and acetylenic groups, typically paired with various fullerene derivatives. The extent of conjugation/interaction between these units determine the polymer solution/solid-state electronic structure, which in turn control polymer properties, such as, optical absorption/emission, redox... 

The parallels observed between CM) solubility and electrophilic substitution products are regular if C6o dissolution in aromatic hydrocarbons is considered as acid-base relationships. According to the theoretical research and experimental results, double bonds of aromatic hydrocarbons with mobile Tt-electrons are Lewis base. Consequently, they react with acids and Lewis acids to form complexes. It has been established that these complexes cannot be to a marked extent electrostatic. It has been found that they are often colored. Complexes with iodine (Lewis acid) give absorption bands at 300 nm in the UV region. These complexes are not true chemical compounds. According to Dewar, all the above facts are due to the formation of Tt-complexcs between an acid or Lewis acid and the entire Ji-electron system of an unsaturated compound which should be considered as Lewis base. Because in these complexes a double bond is an electron donor and Lewis acid is an electron acceptor, they are known as donor-acceptor complexes. The decrease in energy in complexing is conditioned by quantum-mechanical reasons. 

The three electronic absorption bands of benzene are listed in Table 3.1, identified by two common systems of notation. Platt developed the perimeter or free-electron model of the absorption bands of polycyclic aromatic hydrocarbons... 

Spectroscopy in the ultraviolet and the visible region was one of the first physical methods applied to the studies of aromatic compounds in acid systems. By this method the first indications were obtained for arenium ions. In particular, V. Gold and F. Tye showed the solutions of anthracene and 1,1-diphenylethylene in concentrated sulphuric acid to have absorption maxima very close in position and intensity 422 and 431 nm, respectively). This similarity meant that the hydrocarbons are protonated to form, respectively, the 9-H-anthracenium ion and the di-phenylmethyl cation having similar 7t-electron systems ... 

PMDA is a well-known low molecular weight strong electron acceptor in a large number of studies on CTCs. Fig. 2 shows the plot of the peak wavenumber in CT absorption bands (Ami) vs the values 7p [11 -15] of the donor components in the PMD A-aromatic hydrocarbon systems reported in the literature [ 10,16-26]. A good linear relationship was observed according to Mulliken s theory for weak CTCs [27-29] ... 

In polar solvents, such as acetonitrile, organic donor-acceptor systems such as those listed in Table 6.2 show only the fluorescence due to A no new fluorescence appears as in exciplex formation. Flash spectroscopy shows absorption spectra characteristic of the hydrocarbon radical anion and the amine radical cation. The product in these solvents is either an ion-pair or two free ions, stabilised no doubt by solvation, and the reaction is a complete transfer of an electron from one molecule to another, rather than exciplex formation. The reaction goes effectively to completion, and so (with only one fluorescence lifetime to be considered) the kinetic equations for the intensity and lifetime reduce to the simple Stem-Volmer forms (Equations (6.16) and (6.19)). The rate constants for the reactions of aromatic hydrocarbons with various amines in acetonitrile are found to be correlated with the free-... 

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