title: Photoinduced electron transfer between the interlocked components of porphyrin catenanes: effect of the presence of nonequivalent reduction sites on the charge recombination rate.
abstract: [2]Catenanes made up of several polyether-strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat-p-phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro-active subunits. The redox patterns represent useful "fingerprints" that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with tau=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge-separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41+/-4 ps. Comparison of the electron transfer rates CS and CR in the host-guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two-step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination.
authors.affiliation: Istituto ISOF-CNR, Via P. Gobetti 101, 40129 Bologna, Italy. flamigni@frae.bo.cnr.it
authors.forename: Lucia
authors.initials: L
authors.lastname: Flamigni
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Talarico
authors.forename: Scolastica
authors.initials: S
authors.lastname: Serroni
authors.forename: Fausto
authors.initials: F
authors.lastname: Puntoriero
authors.forename: Maxwell J
authors.initials: MJ
authors.lastname: Gunter
authors.forename: Martin R
authors.initials: MR
authors.lastname: Johnston
authors.forename: Tyrone P
authors.initials: TP
authors.lastname: Jeynes