title: Antiparallel-aligned neutral-ground-state and zwitterionic chromophores as a nonlinear optical material.
abstract: Efficient noncentrosymmetric arrangement of nonlinear optical (NLO) chromophores with high first-order hyperpolarizability (beta) for increased electro-optical (EO) efficiency has proven challenging as strong dipolar interactions between the chromophores encourage antiparallel alignment, attenuating the macroscopic EO effect. This work explores a novel approach to simultaneously achieve large beta values while providing an adjustable dipole moment by linking a strong neutral-ground-state (NGS) NLO chromophore with positive beta to a zwitterionic (ZWI) chromophore with negative beta in an antiparallel fashion. It is proposed that the overall beta of such a structure will be the sum of the absolute values of the two types of chromophores while the dipole moment will be the difference. Molecules 1-3 were synthesized to test the feasibility of this approach. Molecular dynamics calculations and NMR data supported that the NGS chromophore component and the ZWI chromophore component self-assemble to an antiparallel conformation in chloroform. Calculations showed that the dipole moment of 1 is close to the difference of the two component chromophores. Hyper-Rayleigh scattering (HRS) studies confirmed that the first hyperpolarizability of 1 is close to the sum of the two component chromophores. These results support the idea that an antiparallel-aligned neutral-ground-state chromophore and a zwitterionic chromophore can simultaneously achieve an increase in beta and a decrease of the dipole moment.
authors.affiliation: Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Liao
authors.forename: Sanchali
authors.initials: S
authors.lastname: Bhattacharjee
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Firestone
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Eichinger
authors.forename: Rajan
authors.initials: R
authors.lastname: Paranji
authors.forename: Cyrus A
authors.initials: CA
authors.lastname: Anderson
authors.forename: Bruce H
authors.initials: BH
authors.lastname: Robinson
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Reid
authors.forename: Larry R
authors.initials: LR
authors.lastname: Dalton