New Second-Order NLO Chromophores Based on 3,3‘-Bipyridine: Tuning of Liquid Crystal and NLO Properties

Abstract

We report on the synthesis via a Knoevenagel condensation reaction of a new family of push−pull molecules based on 6,6‘-distyryl-3,3‘-bipyridine. These chromophores were characterized by spectroscopic methods (NMR, UV−vis, photoluminescence), their mesogenic behavior was investigated by DSC and optical microscopy, and their second-order NLO properties were evaluated by the electric field second harmonic (EFISH) technique. All the compounds are transparent at the second harmonic wavelength of typical laser sources (1.32 and 1.55 μm), and some of them exhibit a strong emission. By lateral substitutions of the π-conjugated bridge and by varying the nature of the acceptor/donor pair, we were able to tune both the mesogenic and NLO properties of the chromophores. For the mesogenic chromophores, first hyperpolarizabilities extrapolated to infinite wavelength, β0, between 16 × 10-30 and 85 × 10-30 esu were measured. These compounds exhibit enhanced hyperpolarizabilities compared to typical NLO liquid crystal chromophores reported in the literature.

New polyurethanes and polyesters for second‐order nonlinear optical applications

“…To our knowledge, only a few examples of LC polymers showing NLO properties have been described 33–35. For this reason, we believe that sufficient grounds are not available today for a systematic study of the influence of an LC phase on poling, and the following comments are simply speculative.…”

Symmetric and Asymmetric Conjugated 3,3′-Bipyridine Derivatives as a New Class of Third-Order NLO Chromophores with an Enhanced Non-resonant, Nonlinear Refractive Index in the Picosecond Range

“…Except for the chromophores bearing a nitro group, all the compounds exhibited intense fluorescence when excited at k max . [12,13] This has not been reported here, because it is outside the scope of this paper. Table 1.…”

Wavelength dependence and figures of merit of ultrafast third-order optical nonlinearity of a conjugated 3,3′-bipyridine derivative

“…6, and a new synthetic route 9 was developed by modification of the route reported in a previous paper. 10 The molecule exhibits a nondipolar donor-acceptor-acceptor-donor ͑D-A-A-D͒ structure in which the 3,3Ј-bipyridine core acts as the acceptor group ͑A-A͒ and the donor group ͑D͒ is a thiophene ring. In general there are two main peaks in the absorption spectrum, one near 225-260 nm and another, low energy, peak from 320 to 450 nm.…”