Photo-physical properties of 5,10,15-tri-n-pentyl-20-(1',1',3,3-tetramethylisoindolin-2'-yloxyl-5'-yl )porphyrinato zinc(11), 1, have been investigated using time-resolved EPR (TREPR) and transient absorption measurements. A formation of the excited doublet (D-1) and quartet (Q(1)) states constituted by excited triplet zinc porphyrin (ZnP) and doublet nitroxide is confirmed by TREPR. This is the first D-1 and Q(1) observation in a system where the nitroxide is directly substituted to a porphyrin ligand. Compound 1 exhibits the longest lifetime of any nitroxide-porphyrin systems in the lowest excited state, indicating a relatively weak electron exchange interaction between triplet ZnP and doublet nitroxide. (C) 2003 Elsevier Science B.V. All rights reserved.