title: Tuning first molecular hyperpolarizabilities through the use of proaromatic spacers.
abstract: In this paper, we describe the second-order nonlinear optical properties of a series of 1,3-dithiole-based electron donor-acceptor systems incorporating proaromatic donor and spacer groups. Modification of the proaromaticity of the quinoid spacer gives rise to NLO-phores with mubeta values ranging from -2000 x 10(-)(48) esu to +3000 x 10(-)(48) esu. Quite surprisingly, compounds with a p-benzoquinoid spacer and a strong acceptor group show negative mubeta values, usually associated to zwitterionic ground states, and yet they are largely quinoid, as evidenced by crystallographic data and theoretical calculations. Progressive benzoannulation of the spacer and introduction of alkylsulfanyl substituents on the dithiole donor unit result in a shift to more positive mubeta values. DFT and ab initio calculations verify these empirical trends.
authors.affiliation: Departamento de Química Orgánica-ICMA, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Andreu
authors.forename: Maria Jesús
authors.initials: MJ
authors.lastname: Blesa
authors.forename: Laura
authors.initials: L
authors.lastname: Carrasquer
authors.forename: Javier
authors.initials: J
authors.lastname: Garín
authors.forename: Jesús
authors.initials: J
authors.lastname: Orduna
authors.forename: Belén
authors.initials: B
authors.lastname: Villacampa
authors.forename: Rafael
authors.initials: R
authors.lastname: Alcalá
authors.forename: Juan
authors.initials: J
authors.lastname: Casado
authors.forename: Mari Carmen
authors.initials: MC
authors.lastname: Ruiz Delgado
authors.forename: Juan T
authors.initials: JT
authors.lastname: López Navarrete
authors.forename: Magali
authors.initials: M
authors.lastname: Allain