Photoinduced electron transfer between mono-6-p-nitrobenzoyl-β-cyclodextrin and adamantanamine-Cn-porphyrins

A series of monotailed porphyrins, zinc 5-{4-[omega-(1-adamantaneamino)alkyloxy]phenyl}-10,15,20-triphenyl porphyrinate (ZnPC(n)A, n = 4, 5, 6), were synthesized in which the porphyrin moiety was connected to I-adamantanamine via a flexible hydrocarbon chain. It was found that photoinduced electron transfer could occur between these porphyrin compounds and mono-6-p-nitrobenzoyl-beta-cyclodextrin (NBCD) in aqueous solution. Detailed steady-state and time-resolved fluorescence measurements revealed two pathways of electron transfer, i.e., the electron transfer between the free donor and free acceptor in solution (dynamic quenching), and the electron transfer between the donor and acceptor bound in a supramolecular complex (static quenching). In these two pathways, the static quenching was found to be highly efficient and dominant in the presence of NBCD. The remarkably large electron-transfer rate (k(SET), ca. 1.0 x 10(9) s(-1)) of the static quenching was found to be very close to that of a covalently linked porphyrin-nitrobenzene dyad.