posted on 2024-03-04, 22:24authored byGeorgina E. Shillito, Dan Preston, James D. Crowley, Pawel Wagner, Samuel J. Harris, Keith C. Gordon, Stephan Kupfer
A series of photosensitizers
comprised of both an inorganic
and
an organic chromophore are investigated in a joint synthetic, spectroscopic,
and theoretical study. This bichromophoric design strategy provides
a means by which to significantly increase the excited state lifetime
by isolating the excited state away from the metal center following
intersystem crossing. A variable bridging group is incorporated between
the donor and acceptor units of the organic chromophore, and its influence
on the excited state properties is explored. The Franck–Condon
(FC) photophysics and subsequent excited state relaxation pathways
are investigated with a suite of steady-state and time-resolved spectroscopic
techniques in combination with scalar-relativistic quantum chemical
calculations. It is demonstrated that the presence of an electronically
conducting bridge that facilitates donor–acceptor communication
is vital to generate long-lived (32 to 45 μs), charge-separated
states with organic character. In contrast, when an insulating 1,2,3-triazole
bridge is used, the excited state properties are dominated by the
inorganic chromophore, with a notably shorter lifetime of 60 ns. This
method of extending the lifetime of a molecular photosensitizer is,
therefore, of interest for a range of molecular electronic devices
and photophysical applications.