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

A. Plaquet, B. Champagne, J. Kulhánek, F. Bureš, E. Bogdan, F. Castet, L. Ducasse, V. Rodriguez

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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.
Original languageEnglish
Pages (from-to)3245-3252
Number of pages8
JournalChemPhysChem
Volume12
Issue number17
DOIs
Publication statusPublished - 9 Dec 2011

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