Collect. Czech. Chem. Commun. 1998, 63, 1295-1308

Ab initio Hartree-Fock Investigation of π-Conjugated Compounds Presenting Large βve Ratio: Merocyanines

Benoît Champagne, Thierry Legrand, Eric A. Perpete, Olivier Quinet and Jean-Marie André

Laboratoire de Chimie Théorique Appliquée, Facultés Universitaires Notre-Dame de la Paix, rue de Bruxelles 61, B-5000 Namur, Belgium


CHF/6-311G* calculations of the first electronic and vibrational hyperpolarizabilities reveal that merocyanines present a substantial βve ratio under their quinonoid nonpolar form. It originates from a large vibrational first hyperpolarizability whereas its electronic counterpart is small for this class of push-pull π-conjugated molecules. The transition from the quinonoid to the aromatic configuration is accompanied by an increase of βe and a decrease of the βve ratio as well as by a ≈ 180° rotation in the plane of the molecule of βe and βv with respect to the molecular frame. Our results support the recent experimental discovery that antiparallel aggregation of aromatic and quinonoid forms of merocyanine is energetically favoured and that their first hyperpolarizabilities, which combine constructively, present both electronic and non purely electronic origins.

Keywords: Ab initio coupled Hartree-Fock; Electronic and vibrational first hyperpolarizabilities; Merocyanines; Ab initio calculations.