The interaction of the monomeric chlorophyll Q band electronic transition with solvents of differing physical-chemical properties is investigated through two-dimensional electronic spectroscopy (2DES). Chlorophyll constitutes the key chromophore molecule in light harvesting complexes. It is well known that the surrounding protein in the light harvesting complex fine tunes chlorophyll electronic transitions to optimize energy transfer. Therefore an understanding of the influence of the environment on the monomeric chlorophyll electronic transitions is important. The Q band 2DES are inhomogeneous at early times, particularly in hydrogen bonding polar solvents, but also in nonpolar solvents like cyclohexane. Interestingly this inhomogeneity persists for long times, even up to the nanosecond timescale in some solvents. The reshaping of the 2DES occurs over multiple timescales and was assigned mainly to spectral diffusion. At early times the reshaping is Gaussianlike, hinting at a strong solvent reorganization effect. The temporal evolution of the 2DES response was analysed in terms of a Brownian oscillator model. The spectral densities underpinning the Brownian oscillator fitting were recovered for the different solvents. The absorption spectra and Stokes shift were also properly described by this model. The extent and nature of inhomogeneous broadening was a strong function of solvent, being larger in H-bonding and viscous media and smaller in nonpolar solvents. The fastest spectral reshaping components were assigned to solvent dynamics, modified by interactions with the solute.

H (Rydberg) atom photofragment translational spectroscopy and ab initio electronic structure calculations are used to explore ways in which ring substituents affect the photofragmentation dynamics of gas phase pyrroles. S 1 S 0 (*π) excitation in bare pyrrole is electric dipole forbidden, but gains transition probability by vibronic mixing with higher electronic states.The S 1 state is dissociative with respect to N-H bond extension, and the resulting pyrrolyl radicals are formed in a limited number of (non-totally symmetric) vibrational levels (Cronin et al. Phys. Chem. Chem. Phys. 2004, 6, 5031-5041). Introducing -perturbing groups (e.g. an ethyl group in the 2-position, or methyl groups in the 2-and 4-positions) lowers the molecular symmetry (to C s ), renders the S 1 -S 0 transition (weakly) allowed and causes some reduction in N-H bond strength; the radical products are again formed in a select sub-set of the many possible vibrational levels, but all involve in-plane (a) ring-breathing motions as expected (by Franck-Condon arguments) given the changes in equilibrium geometry upon *π excitation. The effects of π-perturbers are explored computationally only. Relative to bare pyrrole, introducing an electron donating group like methoxy (at the 3-or, particularly, the 2-position) is calculated to cause a ~10% reduction in N-H bond strength, while CN substitution (in either position) is predicted to cause a substantial (~3000 cm -1 ) increase in the S 1 -S 0 energy separation but only a modest (~2%) increase in N-H bond strength.3

We report a new experimental scheme for two-dimensional electronic spectroscopy (2D-ES) based solely on conventional optical components and fast data acquisition. This is accomplished by working with two choppers synchronized to a 10 kHz repetition rate amplified laser system. We demonstrate how scattering and pump-probe contributions can be removed during 2D measurements and how the pump probe and local oscillator (LO) spectra can be generated and saved simultaneously with each population time measurement. As an example the 2D ES spectra for cresyl violet were obtained. The resulting 2D spectra show a significant oscillating signal during population evolution time which can be assigned to an intramolecular vibrational mode.