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  • Title: Influence of pi-stacking on the resonant enhancement of the second-order nonlinear optical response of dipolar chromophores.
    Author: Zhang W, Cozzolino AF, Mahmoudkhani AH, Tulumello M, Mansour S, Vargas-Baca I.
    Journal: J Phys Chem B; 2005 Oct 06; 109(39):18378-84. PubMed ID: 16853366.
    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.
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