Determination of the Structural Features of a Long-Lived Electron-Transfer State of 9-Mesityl-10-methylacridinium Ion

Extensive efforts have been devoted to developing electron
donor–acceptor
systems that mimic the utilization of solar energy that occurs in
photosynthesis. X-ray crystallographic analysis shows how absorbed
photon energy is stabilized in those compounds by structural changes
upon photoinduced electron transfer (ET). In this study, structural
changes of a simple electron donor–acceptor dyad, 9-mesityl-10-methylacridinium
cation (Acr+–Mes), upon photoinduced ET were directly
observed by laser pump and X-ray probe crystallographic analysis.
The N-methyl group in Acr+ was bent, and
a weak electrostatic interaction between Mes and a counteranion in
the crystal (ClO4) was generated by photoinduced ET. These
structural changes correspond to reduction and oxidation due to photoinduced
ET and directly elucidate the mechanism in Acr+–Mes
for mimicking photosynthesis efficiently.