Photoinduced Charge Transfer Processes along Triarylamine Redox Cascades

In this paper, we describe the synthesis and photophysical properties of a series of acridine−triarylamine redox cascades. These cascades were designed in order to promote photoinduced hole transfer
from an acridine fluorophore into an adjacent triarylamine. The excited dipolar state then injects a hole into
the triarylamine redox cascade. Subsequently, the hole migrates along the redox gradient which was tuned
by the substituents attached to the triarylamine redox centers. The rate of hole migration was determined
by fluorescence lifetime measurements and is in the ns regime and depends strongly on the solvent polarity.
The photophysical processes were also investigated by femtosecond broadband pump−probe spectroscopy.
Our studies reveal different dynamic processes in the cascades depending on the solvent polarity, e.g.,
direct charge separation after photoexcitation vs a two step hole transfer mechanism.