The influence of the excitation pulse carrier frequency on the ultrafast charge recombination dynamics of excited donor-acceptor complexes has been explored both theoretically and experimentally. The theoretical description involves the explicit treatment of both the optical formation of the nuclear wave packet on the excited free energy surface and its ensuing dynamics. The wave packet motion and the electronic transition are described within the framework of the stochastic point-transition approach. It is shown that the variation of the pulse carrier frequency within the absorption band can significantly change the effective charge recombination dynamics. The mechanism of this phenomenon is analyzed and a semiquantitative interpretation is suggested. The role of the vibrational coherence in the recombination dynamics is discussed. An experimental investigation of the ultrafast charge recombination dynamics of two donor-acceptor complexes in valeronitrile also is presented. The decays of the excited state population were found to be highly nonexponential, the degree of non-exponentiality depending on the excitation frequency. For one complex, the charge recombination dynamics was found to slow down upon increasing the excitation frequency, while the opposite behavior was observed with the other complex. These experimental observations follow qualitatively the predictions of the simulations.

The dependence of the ultrafast photoinduced electron transfer dynamics in donor-acceptor complexes on the excitation pulse carrier frequency (spectral effect) has been investigated in the framework of a model involving three electronic state. The spectral effect has been shown to strongly depend on the angle θ between the reaction coordinate directions corresponding to optical and charge transfer transitions. Describing the solvent as a linear homogenous polar medium and accounting for Coulombic interaction of the transferred charge with the medium polarization fluctuations, the angle θ has been found out to be typically in the area 40°–85°. Exactly in this area of θ the spectral effect is predicted to be most pronounced.

Quantum chemical calculations (CASSCF and XMCQDPT level of theory, IMCP-SR1 and SBKJC basis sets) of the structures and electronic absorption spectra of the Os^IVCl₅(H₂O)⁻ and Os^IVCl₅(OH)²⁻ complexes, which are the products of Os^IVCl₆ ²⁻ photoaquation, were performed. The satisfactory agreement between the experimental and calculated spectra was achieved using both triplet and quintet manifolds. The dissociation of the aquacomplex with the formation of the hydroxocomplex was explained by the thermochemical data.