Long-range photoinduced electron transfer dynamics in rigid media

Area of Science:

• Photochemistry
• Polymer Science
• Electron Transfer

Background:

• Ruthenium(II) tris(2,2'-bipyridine) ([Ru(bpy)3](2+)) is a key photosensitizer with a metal-to-ligand charge transfer excited state.
• Electron transfer quenching is a crucial process for understanding excited state dynamics in various media.
• Poly(ethylene glycol) diacrylate (PEG-DMA) films offer a semi-rigid matrix for studying molecular interactions.

Purpose of the Study:

• To investigate the mechanisms of electron transfer quenching of [Ru(bpy)3](2+) in semi-rigid PEG-DMA550 films.
• To differentiate between fixed-site and diffusional quenching processes.
• To analyze the influence of medium viscosity and quencher incorporation on electron transfer kinetics.

Main Methods:

• Utilized [Ru(bpy)3](2+) as a photosensitizer and reductive quenchers in PEG-DMA550 films.
• Employed Stern-Volmer analysis to study diffusional quenching kinetics.
• Investigated electron tunneling for fixed-site quenching and analyzed distance dependence.

Main Results:

• Observed both rapid, fixed-site, and slow, diffusional, electron transfer quenching processes.
• Diffusional quenching was diffusion-controlled in both fluid and film states, but significantly inhibited by film viscosity.
• Fixed-site quenching data supported electron tunneling with a distance attenuation factor (β) of ~0.47 Å(-1), decreasing to 0.16 Å(-1) when the quencher was incorporated into the polymer backbone.

Conclusions:

• Electron transfer in PEG-DMA550 films involves distinct fixed-site and diffusional pathways.
• The high viscosity of the polymer matrix plays a critical role in inhibiting diffusional electron transfer.
• Long-range electron transfer is feasible via tunneling, with the polymer backbone structure influencing its efficiency.