PHOTOCHROMIC, ELECTROCHEMICAL, AND PHOTOELECTROCHEMICAL PROPERTIES OFNOVEL AZOPYRIDINIUM DERIVATIVES

Organic photochrome azopyridiniums were systematically prepared by qua ternizing azopyridines with either dimethyl sulfate or 1,3-propanesult one. photochemical, electrochemical, and photoelectrochemical studies on the azopyridiniums as methyl sulfate, hexafluorophosphate, and zwit terionic compounds were carried out in aprotic solvents and in aqueous solutions. The azopyridiniums, which have 3-located quaternized nitro gens to the azo group, exhibited photochemical activity of trans rever sible arrow cis isomerization. Quaternization of the pyridine moiety d ecreased the photochemical conversion between the trans and cis forms. The photochromic properties were influenced by an electronic effect o f quaternized nitrogens and an electrostatic interaction of counter an ions. In electrochemical studies, new redox-active azopyridiniums were found by using cyclic voltammetry and an electrochemical technique co upled with UV-vis spectroscopy. By the quaternization of azopyridines, the formal reduction potentials were shifted to a positive region up to -0.27 V vs. Fc/Fc(+). The reversibility of the electrochemical reac tions was strongly dependent on the location of quaternized nitrogen. The trans reversible arrow cia photoisomerization of electroactive azo pyridiniums influenced their electrochemical properties. The photochro mic molecules exhibited a photoelectric effect, which was a change in the cathodic limiting currents of azopyridiniums, reversibly modulated by ultraviolet light of an external stimulation.