| This study presents the effects of 26 different solvents on the absorption and emission characteristics of a set of six new dialkylamino-substituted styrylpyrazine (DEASP) dyes. DFT computations and linear and nonlinear spectroscopy are employed to derive structure-nonlinear optical property relationships. The solvatochromic comparison method is evoked to discuss the effects of solvent on this set of chromophores. The asymmetric D-pi-A molecular architecture of the molecules discussed in part I provides for the study of the effect of systematic variation of relative numbers and orientations of electron donor arms to the acceptor nuclei. This variation has significant impact on multipole moment and two-photon absorbance cross sections. Increases in the number of donor arms and in the molecular multipole moment are found to affect two-photon activities.; The symmetric, nondipolar D-pi-A-pi-D molecular architecture of the molecules discussed in part II is shown to disrupt the degeneracy of excited states and increase one- and two-photon transition probabilities. The coupling of strong electron donors to strong electron acceptors with symmetric, nondipolar molecular architecture produces fluorophores with exceptional two-photon activities. The solvatochromic behaviors of the DEASP dyes are compared with common single parameter scales of solvent polarity. Finally, a discussion of the nature and origin of intermolecular forces and the makings of an expanded theory of solvatochromism is presented. |
