A comprehensive study of tetracyanobutadiene push-pull chromophores derived from γ-pyranylidene

• Published in: Tetrahedron chem Vol. 5; p. 100036
• Main Authors: Philippe, Clotilde, Melan, Johann, Barsella, Alberto, Vives, Thomas, Leroux, Yann R., Robin-Le Guen, Françoise, Lemiègre, Loïc, Jacquemin, Denis, Gauthier, Sébastien, Trolez, Yann
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-03-2023; Elsevier
• Subjects: Chemical Sciences; Cycloaddition-retroelectrocyclization; Nonlinear optics; Organic chemistry; TCBD; γ-Pyranylidene; Nonlinear optics; TCBD; γ-Pyranylidene; Cycloaddition-retroelectrocyclization
• ISSN: 2666-951X; 2666-951X
• DOI: 10.1016/j.tchem.2023.100036

A new class of push-pull 1,1,4,4-tetracyanobutadienes (TCBDs) chromophores bearing a γ-pyranylidene as a pro-aromatic donor group have been developed, characterized and studied for their electrochemical, photophysical and second-order nonlinear optical (NLO) properties. [2 ​+ ​2] Cycloaddition-retroelectrocyclizations (CA-RE) with tetracyanoethylene (TCNE) allowed the formation of new TCBDs by taking advantage of the electron-donating ability of γ-pyranylidene functional groups. The limits of the reaction between TCNE and the corresponding alkynes have been investigated, both in terms of reactivity and solubility. Electrochemical studies of pyranylidene-TCBD 1a-1j revealed two reversible reduction waves typical of TCBDs, and two oxidation waves originating from the γ-pyranylidene moiety. More complex electrochemical signals have been recorded when studying chromophores bearing multiple TCBD and/or γ-pyranylidene units. All pyranylidene-TCBDs showed panchromatic absorption properties, extending to the NIR in some cases. Changes made around the electron-withdrawing TCBD units significantly affected the ICT performance of the push-pull chromophores. Computational studies have been performed on this series of compounds to rationalize the origin of their optical properties. TD-DFT calculations confirmed that the synthesized pyranylidene-TCBDs are potential NLOphores. The second-order NLO properties of all chromophores were determined by the Electric Field-Induced Second Harmonic generation (EFISH) technique, and all systems exhibited valuable NLO properties with large μβEFISH values for purely organic compounds, up to 5700 10−48 ​esu.
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