Solvent, acceptor number viscosity

Table 3 contains the physical properties of solvents that are used for dissolving alkali metals. Besides boiling point (b.p.) and viscosity (the data enable one to judge on the experimental potentialities inherent in a solvent) the Table contains values of dielectric constant and of donor and acceptor numbers (DN, AN). It is hard to notice any correlation between the macroscopic properties of the solvents, on the one hand, and their ability to dissolve alkali metals and the possibility of electrochemical generation of solvated electrons, on the other hand. 

Exciplexes are complexes of the excited fluorophore molecule (which can be electron donor or acceptor) with the solvent molecule. Like many bimolecular processes, the formation of excimers and exciplexes are diffusion controlled processes. The fluorescence of these complexes is detected at relatively high concentrations of excited species, so a sufficient number of contacts should occur during the excited state lifetime and, hence, the characteristics of the dual emission depend strongly on the temperature and viscosity of solvents. A well-known example of exciplex is an excited state complex of anthracene and /V,/V-diethylaniline resulting from the transfer of an electron from an amine molecule to an excited anthracene. Molecules of anthracene in toluene fluoresce at 400 nm with contour having vibronic structure. An addition to the same solution of diethylaniline reveals quenching of anthracene accompanied by appearance of a broad, structureless fluorescence band of the exciplex near 500 nm (Fig. 2 )... 

Viscosity of polyester solutions depends on several variables molecular weight, molecular weight distribution, Tg of the resin, and the number of functional groups per molecule. Intermolecular hydrogen bonding can be minimized by using hydrogen-bond acceptor solvents such as ketones. Synthesis of low... 

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