title: Effects of the nature and length of the π-conjugated bridge on the second-order nonlinear optical responses of push-pull molecules including 4,5-dicyanoimidazole and their protonated forms.
abstract: Theoretical and experimental methods of characterization have been employed to investigate a series of six push-pull molecules containing a 4,5-dicyanoimidazole acceptor (A) unit, a N,N-dimethylamino donor (D) group, and systematically enlarged π-conjugated linkers (π) with the view of assessing their first hyperpolarizabilities (β) as well as their variations upon protonation. The results demonstrated that protonation occurred at the N,N-dimethylamino function, which led to disruption of the electronic charge-transfer delocalization: the A-π-D pattern of the neutral species with large β values was transformed into an A-π-A' pattern, which displayed much smaller β values. This feature makes these systems applicable as pH-triggered nonlinear optics (NLO) switches. In particular, protonation led to a decrease of the hyper-Rayleigh scattering first hyperpolarizabilities by at least one order of magnitude as well as to a decrease of the depolarization ratio, from about five for neutral species, which also supported the 1D-like NLO-phore nature, to about two for the protonated ones.
authors.affiliation: Laboratoire de Chimie Théorique (LCT), Unité de Chimie Physique Théorique et Structurale, Facultés Universitaires Notre-Dame de la Paix (FUNDP), Rue de Bruxelles, 61, B-5000 Namur, Belgium.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Plaquet
authors.forename: Benoît
authors.initials: B
authors.lastname: Champagne
authors.forename: Jiří
authors.initials: J
authors.lastname: Kulhánek
authors.forename: Filip
authors.initials: F
authors.lastname: Bureš
authors.forename: Elena
authors.initials: E
authors.lastname: Bogdan
authors.forename: Frédéric
authors.initials: F
authors.lastname: Castet
authors.forename: Laurent
authors.initials: L
authors.lastname: Ducasse
authors.forename: Vincent
authors.initials: V
authors.lastname: Rodriguez