SIZE-SELECTIVE DIFFUSION OF FERROCENES THROUGH MOLECULAR VOIDS CREATED BY PHOTOLYSIS OF COPOLYMERIC FILMS

Photolysis of the copolymeric films poly(x)[Ru(Me(1)bpy)(2)(vpy)(2)](PF6)(2x), (1 - X)[Ru(vbpy)(3)](PF6)(2-2x) formed by reductive electropolymerization on Pt electrodes (surface coverage Gamma = 2 x 10(-9) to 6 x 10(-9) mol/cm(2)) results in loss of the fragment -[-Ru(Me(4)bpy)(2)](PF6)(2). For x = 0.4-0.6 electrochemical and angle-resolved XPS measurements before and after photolysis show that film thickness is unaffected by photolysis. Diffusion of ferrocene and substituted ferrocenes through the films was studied by rotated disk voltammetry, from which values for PDs,pol were derived. D-s,D-pol is the diffusion coefficient of ferrocene through the film, and P is the partition coefficient within the film. Removal of -[-Ru(Me(4)bpy)(2)](PF6)(2) by photolysis creates molecular sized voids and increases PDs,pol by factors of 10-20. The photolyzed films act as size-selective membranes with PDs,pol, decreasing by as much as 16 as the volume of the ferrocene increases from 150 to 500 Angstrom(3). The diffusional properties of the films can be varied somewhat by adding substituents to the bpy rings of the leaving group or by partly filling the molecular voids by coordination to pyridyl groups released in the photolysis step.