F. C. Bailey

Linear free energy relationships—II : Synthesis and spectral characterization of some new solvatochromics: 5′-substituted-2′-hydroxy-4-stilbazole derivatives☆

Abstract A series of 5′-substituted-2′-hydroxy-4-stilbazolium methiodides was prepared by reaction of 5-substituted salicylaldehydes and 4-picoline methiodide. Reaction of these with base leads to the corresponding betaines, which are highly solvatochromic. In addition, 1 : 1 complexes of the methiodide salts and the betaines were isolated from the initial reaction. The energies of the long wavelength transitions of the salts, the betaines and the 1 : 1 complexes of these are directly proportional to the electrophilic substituent constants (σ+) and the slopes are positive. Hence, the transitions appear to involve electron transfer from the salicyl ring to the pyridyl moiety. The solvatochromisms of the betaines and the complexes are directly proportional to the solvent polarity parameter, ET. The slopes are positive, meaning the dipole moments decrease upon excitation, again consistent with the charge transfer transition mentioned above. The relative slopes are rationalized on the basis of substituent effects.

Linear free energy relationships. Triboelectric charging of poly(olefins)

Abstract The logarithm of cascade triboelectric charging of substituted polyethylenes and polypropylenes is linearly correlated by inductive substituent constants. The slope is positive as expected for injection of electrons from the metal (Ni) into the lowest unoccupied molecular orbitals of the organic. The logarithm of changing varies linearly with the gas phase ionization potentials of model monomers.

Space-charge effects of semiconductive coatings on triboelectric charge exchange

Abstract Triboelectric charge exchange studies have revealed a previously unreported “semiconductive” effect. A semiconductive film on a metal substrate acquires the opposite sign of charge when contacted with another body than that expected on the basis of energy level considerations for the two contacting materials. The effect is explained in terms of a space-charge region (depletion or accumulation layer) caused by charge exchange of the semiconductor film with the substance onto which it is coated. It is estimated from our measurements that the space-charge depth for poly(N-vinylcarbazole) is between 3 and 8 μm.

Chemical modification of polymers: 17. Dyeing of sulphonated polystyrene films by ion exchange with cationic dyes

Abstract Heterogeneous dyeing of free-standing films of surface sulphonated polystyrene by ion exchange with aqueous cationic dyes has been studied. Studies of (1) the optical density of films with a given extent of sulphonation as a function of dyeing times, (2) the optical density for constant dyeing time as a function of extent of sulphonation and (3) the thickness of dye sulphonate layers as a function of both dyeing time and extent of sulphonation have been used to establish times for complete dyeing. Using the thickness measurements, estimates of equivalent volumes of the dye sulphonates were made. Displacement of one dye by another was also studied; used of previously derived analytical techniques for this sort of displacement must be used with care due to differences in degree of aggregation, as demonstrated for methylene blue.

Linear free energy relationships. Part VI. Acidity of 4-(5-X-2-hydroxystyryl)-N-methylpyridinium iodides

The pKa values of the title compounds have been determined spectrophotometrically as a function of temperature in a number of buffer systems. In all cases pKa is a linear function of substituent constant. σx, and ranges from 5.8 to 8.7 at room temperature. From the pKa values of 4-(2-hydroxystyryl)-N-methylpyridinium iodide and the corresponding N-benzyl compound apparent ortho substituent constants, σ–ortho, for the 4-vinyl-N-alkylpyridinium groups were assigned (+0.61 ± 0.04 and +0.70 ± 0.01, respectively) and compared to the para-substituent constant (+0.61 ± 0.02) for the 4-vinyl-N-methylpyridinium group evaluated from published data. Differences between thermodynamic parameters (ΔH° and ΔS°) in borate-containing buffers and those in other buffers are attributed to specific interaction with boric acid. All the results are consistent with a significant contribution from quinonoid forms involving the pyridyl ring to the ground states for these compounds and their solvatochromic conjugate bases in aqueous solution: however, this contribution increases upon excitation.