Mode Coupling Pattern Changes Drastically Upon Photoisomerization in RuII Complex

Photoinduced isomerization in a bis(4,4'-dimethyl-2,2'-bipyridyl)(o-methylsulfinylbenzoate) ruthenium(11), (RuBzSO) complex is investigated using linear infrared absorption and dual-frequency two-dimensional infrared (2DIR) spectroscopies. The changes in the linear absorption spectrum associated with the photoisomerization were compared to the changes in the mode coupling pattern observed in the 2DIR spectra. The comparison indicates that the coupling of the SO and C=O stretching modes is much smaller in the photoisomerized compound compared to that in the ground-state isomer that has not been exposed to incident light (relaxed). Transition-dipole interaction estimations indicate a large decrease of the electric coupling contribution to the C=O/SO mode anharmonicity in the O-bonded versus S-bonded states thus supporting the formation of the O-bonded state upon photoisomerization of the RuBzSO compound.