Photo-oxidation of 1,3-cyclopentadiene using partially quaternized poly(1-vinylimidazole)-bound ruthenium(II) complexes

Photo-oxidation of cyclopenta-1,3-diene (CP) with singlet oxygen using tris (2,2'-bipyridine)ruthenium(II) [Ru(bpy)(3)(2+)] and polymer-bound ruthenium (II) complexes as photosensitizers was investigated in oxygen-saturated eth anol. The polymer-bound ruthenium(II) complexes consist of a bis(2,2'-bipyr idine)ruthenium(II) complex coordinated with two imidazolyl residues on par tially quaternized poly(1-vinylimidazole) with hexyl groups (C(6)RuQPIm) an d hexadecyl groups (C(16)RuQPIm) as the alkyl side chains. The photo-oxidat ion of CP using the polymer photosensitizers effectively occurred in a comp arable manner to the Ru(bpy)(3)(2+) system: the degree of reaction, being g iven by the ratio of reacted CP and initial CP concentrations, was high. In particular, all of the CP added was oxidized in the C(16)RuQPIm system eve n when the CP concentration was low. This was attributed to the concentrati on of CP species into the heterogeneous reaction field formed by the polyme r photosensitizers. The Ru(bpy)(3)(2+) photosensitizer showed excellent sta bility and was repeatedly able to be used for the photo-oxidation reaction. During the repeated experiments, the reaction activity for the polymer pho tosensitizer systems gradually decreased because the polymer photosensitize rs changed to monochloro complexes [CnRu(Cl)QPIm (n = 6 or 16)] in which on e imidazolyl residue was substituted by a chloride ion. However, these poly mer photosensitizers also had excellent stability. Compared with other phot osensitizers, such as Rose Bengal and zinc(II) phthalocyaninetetrasulfonic acid, the stability of the ruthenium(II) complex photosensitizers was excel lent.