High energy and quantum efficiency in photoinduced charge separation

Area of Science:

• Supramolecular chemistry
• Photochemistry
• Materials science

Background:

• Trisbipyridine ruthenium(II) chromophore (C2+) based supramolecular triads with phenothiazine donors (D) and diquat acceptors (A2+) exhibit high quantum efficiency for photoinduced charge separated states (CSS).
• The underlying reasons for this consistently high efficiency across this class of molecules, unlike similar systems, remain poorly understood.

Purpose of the Study:

• To elucidate the mechanism behind the high quantum efficiency observed in D-C2+-A2+ supramolecular triads.
• To investigate the role of pre-photoexcitation interactions in charge separated states (CSS) formation.

Main Methods:

• Utilized a bimolecular system comprising a chromophore-acceptor diad (C2+-A2+) and an N-methylphenothiazine donor.
• Investigated ground-state association between the ruthenium(II) chromophore and the phenothiazine donor prior to photoexcitation.

Main Results:

• Demonstrated a significant ground-state association between the ruthenium(II) chromophore (RuL3(2+)) and the phenothiazine donor in the bimolecular system.
• This ground-state association was identified as the critical factor enabling efficient charge separated states (CSS) formation.

Conclusions:

• Ground-state association is essential for efficient charge separated states (CSS) formation in these supramolecular systems.
• This pre-assembly mechanism is inferred to be a key factor in the high efficiencies of intramolecular D-C2+-A2+ triads.