Porphyrins were covalently linked to modified Merrifield polymers by chlorosulphonation activation of the porphyrin nucleus. These supported porphyrins were used as photosensitizers to promote singlet oxygen oxidation of monoterpenes with an efficiency that depends on porphyrin structure and the spacer used to link it to the polymer structure. The performance of these photosensitizers was studied. Citronellol and alpha-terpinene gave the expected singlet oxygen ene addition products. alpha-Pinene and P-pinene also gave products from non-ene reactions, which is explained by the existence of an alternative radical pathway. (c) 2008 Elsevier Inc. All rights reserved.