Toward multi-addressable molecular systems: Efficient synthesis and photochromic performance of unsymmetrical bisthienylethenes
Introduction
Multi-addressable organic materials stimulated by light is currently a very active research topic and such systems are expected to be of great importance for optical computing as logic gates, field-effect transistors and high density data storage systems. [1], [2], [3], [4], [5] The design and synthesis for functional molecules that could serve as molecular devices for sensing, switching, and signal transduction from optical inputs are areas of intense activity and tremendous potential significance. The goal is a miniaturization of functional elements down to the molecular level, which could result in a markedly increased performance as a consequence of ultra-high density of the functional elements compared to current devices and in that regard organic photochromic compounds are targeted candidates because of the light-induced reversible isomerization between two isomers having different absorption spectra acting as a binary system. Several attempts to prepare multi-photochromic switches have been reported recently. [6], [7], [8], [9], [10] In the course of our programme to prepare photoinduced NLO-phores [11], [12], [13] we demonstrated that 1,2-bisthienylethenes [14] hereafter named BTE for convenience bearing an electronically withdrawing group are key intermediates to the route for covalently linked BTE to indolinoxazolidines which exhibit promising tunable hyperpolarisabilities. In this article, we describe the synthesis along the photochromic performance of four unsymmetrical bisthienylethenes 1–4 (Scheme 1) bearing a formyl group on position 5 as a strong electro-withdrawing group that can be used as intermediates for the preparation of multi-addressable systems based on bisthienylethene–indolinooxazolidine hybrid [15] or azacrown and bisthienylethene. [16]
Section snippets
Synthesis
As a synthetic route to prepare an unsymmetrical substituted BTE containing one aldehyde function from a symmetrical compound has been reported to proceed efficiently [17], we tried to synthesize the targeted unsymmetrical BTE starting from the diiodinated dithienylethene 5. This latter compound was selected as a common intermediate since iodine is a suitable prerequisite for either a carbon–carbon coupling reaction, following Sonogashira or Suzuki procedures, or a formylation using
Conclusion
Unsymmetrical 1,2-bisthienylperfluorocyclopentenes bearing a formyl group as an electro-withdrawing group on one side and various π-conjugated extended susbtituents on the other side were prepared using a sequential synthetic strategy. This versatile approach would allow the design of photocontrolled push-pull NLO-phores. The photochromic performance has been investigated and it has been demonstrated that the π-conjugated susbtituents deeply modify the absorption spectra of the both isomeric
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