Geometric Influence on Intramolecular Photoinduced Electron Transfer in Platinum(II) Acetylide-Linked Donor-Acceptor Assemblies

A new donor-acceptor system, in which the electron donor triphenylamine (TPA) and the electron acceptor C-60 are bridged through a cis- or trans-platinum(II) acetylide spacer have been prepared. Ground-state studies were conducted using electrochemistry and UV/Vis spectroscopy. Fluorescence studies suggested that charge transfer is the deactivation mechanism for the singlet excited state, and this was verified by transient absorption spectroscopy. Selective photoexcitation of 1 and 2 at 387 nm leads to a fast charge transfer between the TPA and C-60, which gives rise to a radical ion-pair state (TPA(center dot+)-Pt-C-60(center dot)). Our results suggest that charge transfer is favored for the cis configuration while the presence of the trans configuration in the Pt-II diacetylide results in a longer-lived charge separated states.