Solid state a.c. conductivity and FT-IR spectral analyses for the conflicting effects of proton mobility and association in some azophenol derivatives of cyclic phosphazene

Variable strength H-bonding affects the mobility and so electric conduction of protons differently. Also, variable extent mesomerism modifies electric conduction with varying dielectric features. Both these molecular modifiers are properly cited using azophenol derivatives as model compounds for discussion of their consequences in the varying features of electric conduction. The electric permittivity shows low-frequency dispersion characteristic of ionic conduction over mobile charge carries; the mobility shifts at a critical temperature T _c, being structure dependent. The frequency-dependent Z′′-Z′ layout changes with temperature from linear at low temperatures to semicircular above T _c within a frame of temperature-sensitive dipole-ionic mediated conduction. The a.c. conductivity, σ_ac, increases with frequency and temperature and becomes frequency insensitive, like d.c. conductivity, σ_dc, above the T _c because of the escalating contribution from the d.c. conduction. The mesomeric structure seems to prompt a dipole-based electric conduction of high relaxation energy over the strongly associated phenolic protons that may be thermally activated above the T _c into a much lower relaxation energy protonic conduction of up to two orders higher conductivity. The protonic conduction emerges at a T _c that falls with a drop in the relaxation energy following a similar order of increasing proton mobility and mesomerism in the azophenol derivatives: azocatechol>azoquinol>azoresorcinol. On the molecular level, variable temperature infrared spectroscopy reveals higher proton mobility and mesomerism for the azocatechol derivative that demonstrates its higher protonic conductivity at lower T _c and relaxation energy, compared to the azoquinol and azoresorcinol derivatives. This is well verified in the light of conflicting intramolecular H-bonding that assists the proton mobility in azocatechol whereas it associates the protons in azoresorcinol more than in azoquinol. Electronic Publication