STUDIES OF THE ANTENNA EFFECT IN POLYMER-MOLECULES .24. SOLAR PHOTOSYNTHESIS OF PREVITAMIN-D3 IN AQUEOUS-SOLUTIONS OF POLY(SODIUM STYRENE-SULFONATE-CO-2-VINYLNAPHTHALENE)

The photochemical step in the synthesis of vitamin D3 in an aqueous so lution of poly(sodium styrenesulfonate-co-2-vinylnaphthalene) (PSSS-VN ) was studied using solar light. The photoisomerization of 7-dehydroch olesterol to previtamin D3 was found to be exceptionally clean and eff icient. The process was shown to be photosensitized by the pendant nap hthalene chromophores in the copolymer via singlet-singlet energy tran sfer. The lack of tachysterol, a major side product formed during phot oisomerization in organic solution, was explained by triplet-sensitize d isomerization of tachysterol to previtamin. Triplet-triplet energy t ransfer from excited polymeric naphthalene chromophores to tachysterol is efficient because of the high local concentration of tachysterol i n the vicinity of the energy donors.