Distance-Dependent Electron Transfer Kinetics in Axially Connected Silicon Phthalocyanine-Fullerene Conjugates

Area of Science:

• Materials Science
• Photochemistry
• Molecular Electronics

Background:

• Electron transfer processes are fundamental to many photochemical and electronic applications.
• Silicon phthalocyanine-C60 (SiPc-C60) dyads are promising systems for studying charge separation.
• The influence of molecular architecture on electron transfer dynamics requires further investigation.

Purpose of the Study:

• To synthesize and characterize novel SiPc-C60 dyads with varying donor-acceptor distances.
• To investigate the effect of these structural variations on electron transfer rates.
• To elucidate the mechanism and kinetics of charge separation and decay in these dyads.

Main Methods:

• Synthesis and characterization of two C60-SiPc-C60 dyads with phenyl and biphenyl spacers.
• Femtosecond transient absorption spectroscopy to monitor ultrafast electron transfer.
• Nanosecond transient absorption spectroscopy to study longer-lived excited states and decay pathways.

Main Results:

• Dyad 1 (phenyl spacer) exhibited faster electron transfer (kcs = 2.7×10^9 s^-1) compared to Dyad 2 (biphenyl spacer, kcs = 9.1×10^8 s^-1).
• Increased donor-acceptor distance (∼4.3 Å) in Dyad 2 resulted in a ∼3.7-fold slower electron transfer rate.
• The charge-separated state persisted for over 3 ns, with 3^3SiPc* identified as the end product, having a lifetime in the 3-20 ns range.

Conclusions:

• Donor-acceptor distance is a critical factor in controlling electron transfer rates in SiPc-C60 dyads.
• The observed trends are consistent with energy level diagrams, indicating population of lower-energy triplet states.
• These findings provide valuable insights for the rational design of molecular systems for optoelectronic applications.