Yi-Jyun Lien
428 – Chemistry
In the field of photochemistry and photophysics, a high interest in substituting for rare and
expensive ruthenium has risen in these years. With the goal in mind, iron seems to be a
propriate metal candidate due to its abundance in the earth crust.
1
Besides, low-spin (LS) iron(II)
polypyridyls have isoelectronic configuration to its ruthenium(II) polypyridyl analogues, which
leads to similar visible light absorption mechanism in terms of electron transfer process from
metal to ligand. However, the main reason regarding current failure of replacing ruthenium with
iron is majorly attribute to the extremely short metal-to-ligand charge transfer (MLCT) excited
state lifetime. Unlike the 2
nd
or 3
rd
row transitional metal complexes, metal-centered states such
as
3
T
1
,
5
T
2
serve as a channel for ultrafast deactivation from the MLCT excited state in LS iron(II)
polypyridyls.
2
Ideally, this short MLCT excited state lifetime for d
6
electron configuration LS
iron(II) polypyridyls is able to be effectively prolonged by either choosing to destabilize the
metalcenter states or stabilize the MLCT excited state. On the contrary, rather than adjusting
ligand field strength over iron(II) complexes, restricting corresponding vibrational motions
arising from the MLCT relaxation is a relatively uncharted strategy to extend the MLCT lifetime.
3
Although this idea is practical,
4
the most challenging portion is to quantify the relaxation
dynamics of the MLCT excited state because of
unthermalized property of the MLCT excited state
manifolds. Therefore, instead of directly probing the
MLCT deactivation, two primary constituting
components of the MLCT deactivation will be
investigated in this research: the MLCT formation as
well as ground state recovery processes. (Fig. 1) The
dynamics of the two specific transition processes will
reveal potential vibrational motions on
corresponding reaction coordinates may couple into
the MLCT deactivation. Besides, this fruitful
information can be also transformed into basis on
molecular design of iron(II) complexes in which
binding motifs is a critical factor that can affect
photophysical dynamics.
References:
1. Wenger, S. Chem. Eur. J. 2019, 25, 6043-6052.
2. Gawelda, W.; Cannizzo, A.; Pham, V.-T.; van Mourik, F.; Bressler, C.; Chergui, M. J. Am. Chem. Soc.
2007, 129, 8199-8296.
3. Paulus, B. C.; Adelman, S. L.; Jamula, L. L.; McCusker, J. K. Nature 2020, 582, 214-219.
4. Schrauben, J. N.; Dillman, K. L.; Beck, W. F.; McCusker, J. K. Chem. Sci. 2010, 1, 405-410.
