ic8b00093_si_001.pdf (698.5 kB)
Photochemistry of fac-[Re(CO)3(dcbH2)(trans-stpy)]+: New Insights on the Isomerization Mechanism of Coordinated Stilbene-like Ligands
journal contribution
posted on 2018-02-22, 19:24 authored by Leandro A. Faustino, Antonio Eduardo Hora Machado, Antonio Otavio T. PatrocinioIn
this work, a novel complex fac-[Re(CO)3(dcbH2)(trans-stpy)]+, (dcbH2 = 4,4′-dicarboxylic acid-2,2′-bipyridine; trans-stpy = trans-4-styrylpyridine) was
synthesized and characterized toward its spectroscopic, photochemical,
and photophysical properties. The experimental data provide new insights
on the mechanism of photochemical trans-to-cis isomerization of the stilbene-like ligand coordinated
to Re(I) polypyridyl complexes. The new complex exhibits an unusual
and strong dependence of the isomerization quantum yield (Φt→c) on the irradiation wavelength.
Φt→c was 0.81 ± 0.08
for irradiation at 365 nm and continuously decreased as the irradiation
wavelength is shifted to the visible. At 405 nm irradiation Φt→c is almost 2 orders of magnitude
lower (0.010 ± 0.005) than that observed at 365 nm excitation.
This behavior can be explained by the low-lying triplet metal-to-ligand
charge-transfer excited state (3MLCT) that hinders the
triplet photoreaction mechanism under visible light absorption. Under
UV irradiation, direct population of styrylpyridine-centered excited
state (1IL) leads to the occurrence of the photoisomerization
via a singlet mechanism. Further experiments were performed with the
complex immobilized on the surface of TiO2 and Al2O3 films. The nonoccurrence of isomerization at the oxide
surfaces even under UV excitation evidences the role of energy gap
between the 1IL/1MLCT states on the photochemical/photophysical
processes. The results establish important relationships between the
molecular structure and the photoelectrochemical behavior, which can
further contribute to the development of solid-state molecular switches
based on Re(I) polypyridyl complexes.