title: Influence of pi-stacking on the resonant enhancement of the second-order nonlinear optical response of dipolar chromophores.
abstract: The wavelength-dependent second-harmonic generation (SHG) efficiency of two simple dipolar chromophores, 4-NO2C6H4N(H)Bun (1) and 4-NO2C6H4SN(H)But (2), was compared in solution and in the solid state. Hyper-Rayleigh scattering measurements at 532 nm provided comparable molecular first hyperpolarizabilities. Both compounds crystallize in non-centrosymmetric space groups, but a more efficient arrangement of dipole moments results in a significantly larger deff value for 2. Kurtz-Perry experiments from 450 to 700 nm revealed an important difference in the resonant component of the nonlinear optical responses of these compounds; the SHG efficiency of crystalline 1 depends more strongly on the incident wavelength than that of 2. This would be in contradiction with the TD-DFT excitation energies calculated for these molecules, but the observation can be explained by the resonant contribution from low-energy interchromophore excitations enabled by pi-stacking in the crystal of 1.
authors.affiliation: Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Anthony F
authors.initials: AF
authors.lastname: Cozzolino
authors.forename: Amir H
authors.initials: AH
authors.lastname: Mahmoudkhani
authors.forename: Mark
authors.initials: M
authors.lastname: Tulumello
authors.forename: Sarah
authors.initials: S
authors.lastname: Mansour
authors.forename: Ignacio
authors.initials: I
authors.lastname: Vargas-Baca