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A significant number of quadrupolar dyes with a D-$pi$-A-$pi$-D or A-$pi$-D-$pi$-A structure, where D and A are electron donor and acceptor groups, were shown to undergo symmetry breaking (SB) upon optical excitation. During this process, the electronic excitation, originally distributed evenly over the molecule, concentrates on one D-$pi$-A branch, and the molecule becomes dipolar. This process can be monitored by time resolved infra-red (TRIR) spectroscopy and causes significant spectral dynamics. A theoretical model of excited-state SB developed earlier ( extit{J. Phys. Chem. C}, extbf{2018}, extit{132}, 29165) is extended to account for the temporal changes taking place in the IR spectrum upon SB. This model can reproduce the IR spectral dynamics observed in the $-mathrm{C}equiv mathrm{C}-$ stretching region with a D-$pi$-A-$pi$-D dye in two polar solvents using a single set of molecular parameters. This approach allows estimating the degree of asymmetry of the excited state in different solvents as well as its change during SB. Additionally, the relative contribution of the different mechanisms responsible for the splitting of the symmetric and antisymmetric $-mathrm{C}equiv mathrm{C}-$ stretching bands, which are both IR active upon SB, can be determined.

In this article, regularities of ultrafast charge recombination (CR) kinetics in photoinduced intramolecular electron transfer in polar solvents are studied. The kinetics of charge separation and ensuing ultrafast CR are simulated within the framework of the multichannel stochastic model. This model accounts for the reorganization of both the solvent and a number of intramolecular high-frequency vibrational modes. The solvent relaxation is described in terms of two relaxation modes. For ultrafast CR, the free-energy-gap law strongly depends on the parameters: the electronic coupling, reorganization energy of intramolecular high-frequency vibrational modes, and the vibrational and solvent relaxation times. The semilog dependence of the CR rate constant on the free-energy gap varies from a parabolic shape to a nearly linear one with increasing the electronic coupling and decreasing the vibrational relaxation time. The dynamic solvent effect in CR is predicted to be large in the area of strong exergonicity and small in the area of weak exergonicity. This regularity is opposite to that observed for the thermal reactions.