The
use of multiple chromophores as photosensitizers for catalysts
involved in energy-demanding redox reactions is often complicated
by electronic interactions between the chromophores. These interchromophore
interactions can lead to processes, such as excimer formation and
symmetry-breaking charge separation (SB-CS), that compete with efficient
electron transfer to or from the catalyst. Here, two dimers of perylene
bound either directly or through a xylyl spacer to a xanthene backbone
were synthesized to probe the effects of interchromophore electronic
coupling on excimer formation and SB-CS using ultrafast transient
absorption spectroscopy. Two time constants for excimer formation
in the 1–25 ps range were observed in each dimer due to the
presence of rotational isomers having different degrees of interchromophore
coupling. In highly polar acetonitrile, SB-CS competes with excimer
formation in the more weakly coupled isomers followed by charge recombination
with τ<sub>CR</sub> = 72–85 ps to yield the excimer.
The results of this study of perylene molecular dimers can inform
the design of chromophore–catalyst systems for solar fuel production
that utilize multiple perylene chromophores