Chemistry Department Seminar

"Light-Induced Transient Bonding: A Way To Control Charge Separation?"

Presented by Julia A. Weinstein, University of Sheffield, United Kingdom

Monday, January 29, 2007, 11:00 am — Hamilton Seminar Room, Bldg. 555

Photoinduced electron transfer plays a fundamental role in a variety of light-energy conversion processes, from photosynthesis to photocatalysis, with a charge-separated excited state being a key transient in many of those. Such states are formed as a result of photo-induced electron transfer in an essential Donor-Spacer-Acceptor component. In artificial systems, the charge-separated [D+-sp-Ai* state is often too short-lived due to facile back electron transfer. The fundamental challenge is how to block back electron transfer until the excited state becomes engaged into a desired chemical event.
+ — *

To explore light-induced formation of a transient three-electron S∴ S-bond on a metal template as a way to stabilize charge separation.
The formation of a new bond in the excited state, which is not present in the ground state, would create an activation barrier for back electron transfer.
A combination of pico-to-milli-second transient absorption, emission, and time-resolved resonance Raman (TR3) techniques is utilized in order to test and develop the “S∴ S” hypothesis. (Spectro)electrochemistry (UV-NIR, EPR) and pulse radiolysis methods are also used to obtain information on spectral signatures of the radical cations and anions supplementary to the excited state structure. Theoretical calculations into the structure of excited states are performed in collaborations.
The current model systems are Pt(II) diimine-dithiolates, show a 100-fold variation in the excited state lifetime and reactivity as a function of electron donor/acceptor properties of the “RS”-ligand.
Such “core” Pt(II) complexes are presently being incorporated into multi-component assemblies for long-distance electron transfer, in which an interplay between electron and energy transfer on the picosecond time scale offers great promise for a “switchable” excited state behaviour.

Hosted by: David Grills

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