| This thesis reports on the time-resolved excited state dynamics in regioregular poly(3-hexylthiophene), one of the most used conjugated polymers in organic-based photovoltaic devices. The dynamics are interpreted in terms of an excitonic description of the electronic excitation. Specific experiments include time and energy resolved fluorescence, using femtosecond optical gating (upconversion), on a set of poly(3-hexylthiophene) samples spanning an average size of 39-168 monomers. The sub 300 fs dynamics were explored using two-color 3 pulse photon echo peak shift spectroscopy (2C-3PEPS). The 2C-3PEPS experiments demonstrate the first experimental observation of the hot exciton relaxation mechanism in conjugated polymers. Hot exciton relaxation was shown to occur by transferring electronic energy into two specific phonons (vibrational modes) of the polymer. The results also demonstrate that the electronic to vibrational energy transfer processes causes the electronic energy gap to shrink by ca. 0.5 eV in a coherent and not, as previously postulated, stochastic fashion.; The remainder of this thesis explores two additional systems that undergo electronnuclear coupling upon electronic excitation: the mixed intermolecular solvent-solute coupling and intramolecular phonon coupling of betaine-30, as well as the intermolecular hydrogen bond disruption between water and coumarin 102 in acetonitrile-water binary mixtures. All the results demonstrate the rich complexity of dynamics governing chemical reactions occurring in condensed phase environments. |
