Femtosecond non-degenerate four wave mixing spectroscopy: The two color photon echo peak shift

The couplings between multiple electronic states and electronic and nuclear coordinates are examined for condensed phase systems by femtosecond degenerate and non-degenerate four wave mixing. The two-color photon echo peak shift experiment is developed which allows measurement of the correlation between transition frequencies in two different spectral regions.; Two-color photon echo peak shift (2C3PEPS) experiments are used to study coupling between electronic states in the lutetium bisphthalocyanine anion, LuPc2-. Electronically induced mixing between exciton and charge resonance states leads to correlations in transition energies for the two observed transitions. This correlation generates non-zero 2C3PEPS which, when compared with 1C3PEPS, allows experimental determination of the degree of mixing, which was in good agreement with theoretical predictions.; By exploiting a coherently excited nuclear wavepacket, the nuclear dependence on the electronic mixing between exciton and charge resonance states is observed for LuPc2- along the excited nuclear coordinate. The change in mixing is manifested in pump probe spectroscopy as anti-correlated wave packet dynamics for the two dipole allowed states, and the nuclear coordinate dependence of the transition moment. Within the limit that all the dipole strength is derived from the exciton state, the change in mixing can be estimated.; 2C3PEPS is used to probe correlation between two different regions of the electronic spectrum of a chromophore. No correlation between the two spectral regions is observed at short times, but correlation appears owing to ultrafast solvent motion and the accompanying Stokes shift. A model for the spectral shift is proposed that incorporates a conditional probability distribution for transition frequencies in the two spectral regions. These results show that memory is partially conserved during the spectral diffusion process from the pump to the probe region.; Additional 2C3PEPS experiments exploring many spectral regions within the electronic transition band revealed that strongly coupled intramolecular vibrations generated correlations between different spectral regions. A single correlation function description of the solvation dynamics was insufficient to quantitatively describe the dynamics at all probe wavelengths indicating different dynamics in the ground and excited states, which implies a nonlinear dependence of the transition energy gap on the solvation coordinate.