title: Ultrafast photoinduced energy and electron transfer in multi-modular donor-acceptor conjugates.
abstract: New multi-modular donor-acceptor conjugates featuring zinc porphyrin (ZnP), catechol-chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C(60)), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction-center mimics. The X-ray structure of triphenylamine-BDP is also reported. The wide-band capturing polyad revealed ultrafast energy-transfer (k(ENT) =1.0 × 10(12) s(-1)) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA-BDP-ZnP triad through metal-ligand axial coordination resulted in electron donor-acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron-transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion-pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non-polar toluene were in the range of 5.0 × 10(9)-3.5 × 10(10) s(-1). Stabilization of the charge-separated state in these multi-modular donor-acceptor polyads is also observed to certain level.
authors.affiliation: Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Japan.
authors.forename: Mohamed E
authors.initials: ME
authors.lastname: El-Khouly
authors.forename: Channa A
authors.initials: CA
authors.lastname: Wijesinghe
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Nesterov
authors.forename: Melvin E
authors.initials: ME
authors.lastname: Zandler
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza