Controlling electron transfer in donor-bridge-acceptor molecules using cross-conjugated bridges

Area of Science:

• Photochemistry
• Molecular Electronics
• Organic Chemistry

Background:

• Donor-bridge-acceptor (D-B-A) molecules are crucial for understanding charge separation (CS) and recombination (CR).
• The electronic properties of the bridge significantly influence the efficiency of CS and CR processes.

Purpose of the Study:

• To compare and contrast photoinitiated CS and CR in D-B-A molecules with varying bridge conjugation (cross-conjugated, linearly conjugated, saturated).
• To investigate the role of bridge structure on electron transfer rates and electronic coupling.

Main Methods:

• Time-resolved spectroscopy was employed to study CS and CR dynamics.
• Molecular conductance calculations were performed to analyze through-bridge electronic coupling.

Main Results:

• CS through a cross-conjugated 1,1-diphenylethene bridge was 30 times slower than through its linear trans-stilbene counterpart, comparable to a saturated diphenylmethane bridge.
• CS through a cross-conjugated xanthone bridge showed rates similar to its linear trans-stilbene counterpart.
• Molecular conductance calculations revealed quantum interference effects in cross-conjugated systems, altering electronic coupling.

Conclusions:

• Cross-conjugation significantly reduces the pi orbital contribution to donor-acceptor electronic coupling, favoring sigma pathways for CS.
• Quantum interference effects in cross-conjugated bridges modulate electronic coupling, aligning with experimental electron transfer rate trends.