Preparation and properties of porphyrin-modified hollow-fiber membranes for use as heterogeneous photosensitizers for singlet oxygen and for artificial photosynthesis

Commercially available cellulose acetate hollow fiber membranes have been modified to incorporate high concentrations of zinc tetraphenylporphyrin (ZnTPP). The modification procedure involves swelling the fibers in a tetrahydrofuran solution saturated with ZnTPP, followed by an aqueous rinse which contracts the fibers and entraps the ZnTPP. The modified membranes are dark purple, containing up to 3% ZnTPP by weight. The membranes remain sufficiently durable to sustain a flow system, and they are impermeable to ionic solutes. The membranes exhibit fluorescence with a short lifetime (<10 nsec) and a spectrum consistent with that of ZnTPP. The membranes are effective as a heterogeneous photosensitizer for the generation of singlet molecular oxygen, monitored by the oxygenation of aqueous 2-furylmethanol. Initial efforts to develop electrontransfer reactions photosensitized by these modified membranes are described. Novel polyether-substituted electron donor and acceptor molecules are effective at increasing photosensitized electron transfer from ZnTPP in nonionic Triton X-100 micelles, but offer only slight success from the ZnTPP-modified membranes.