A Tetracyanobutadiene Spirobifluorene: Synthesis, Enantiomeric Resolution and Chiroptical Properties

Push-pull organic compounds with pi-conjugated backbones are attracting considerable interest in terms of their highly efficient (NLO) non-linear optical effects. In this respect, cyano groups constitute one of the strongest electron acceptors suitable for NLO materials. We herein report the first 1,1,4,4-tetracyanobutadiene (TCBD) spirobifluorene (SBF) through a double [2+2] cycloaddition-retroelectrocyclization. Enantiomeric resolution by HPLC using a chiral stationary phase (CSP) and theoretical calculations unveiled not only the nature of the potential energy surface, but also the absolute configuration of each enantiomer. Since both the presence of strong donor and acceptor, as well as the intrinsic non-centrosymmetric character of chiral compounds are a prerequisite for the development of NLO properties, the first hyperpolarizability of the developed system was theoretically calculated. The results suggested a strong dependence on the conformation and an intensity enhancement for certain conformers of 1 as compared to its allenic TCBD analogue. Therefore, the present study opens a new class of SBF compounds suitable for NLO applications.

Automated summary

This study reports the synthesis and characterization of the first TCBD-SBF compound and provides information on its chiral configuration and potential energy surface through experiments and calculations. The calculated first hyperpolarizability suggests that this compound has potential nonlinear optical properties suitable for NLO applications.