We report the synthesis of a new 4-hydroxyazobenzene-appended bipyridine complex of copper, [Cu(oAB-2OF)(2)]BF4, which exhibits a reversible acid base responsive redox-active photoisomerization reaction. The acid base modulation of the photoisomerization reaction permits ON/OFF toggling of the photoelectric conversion in devices containing this complex by the addition of small quantities of acid or base in the presence of 4,4'-bis(ethoxycarbonyl)-2,2'-bipyridine, bpy-2COOEt.