A Tetracyanobutadiene Spirobifluorene: Synthesis, Enantiomeric Resolution and Chiroptical Properties

Abstract

Push-pull organic compounds with π-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 1,1,4,4tetracyanobutadiene (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.

A computational study of two promising tweezers

“…The analysis of the molecular orbitals involved in the main electronic transitions is of great interest when analyzing the system's possibility of presenting important optical properties. Thus, several studies [28,29] have postulated the relationship between nonlinear optical responses and intramolecular charge transfer, ICT. For this reason, Figures S2 collect the molecular orbitals involved in rsts electronic transitions for both tweezers, showing that some transitions can be involved in process of ICT.…”

Development of robust chiroptical systems through spirobifluorenes

“…F I G U R E 9 Representation of a TCBD-SBF. 29 F I G U R E 1 0 Representation of SBF and energy levels of spirobonding and spiro-antibonding generated by spiroconjugation. The ON/OFF switch stands for the presence or absence of spiroconjugation depending on the functionalization over the SBF unit.…”

“…Therefore, in order to modulate the optical and chiroptical properties of SBFs, we have developed the synthesis of TCBD-SBFs stable up to 200 C and predicted high NLO properties (Figure 9). 29 While the UV/Vis and ECD spectra of the acetylene bearing precursor is restricted to the UV region of the spectrum, the TCBD derivative absorption reaches the near infrared region.…”

Optical and electrochemical properties of spirobifluorene iridanaphthalene complexes

“…14,15 These characteristics together with their high polarizability grant them second-order NLO properties which are of great interest for applications in optical and electro-optical devices, photodynamic therapy or biological imaging. [16][17][18][19][20][21] In this regards, our group developed the synthesis of the first spirobifluorene metallaaromatic complex which showed aromaticity, high thermal stability and UV-Vis absorptivity. 22 However, studies on NLO and electrochemical properties were not performed.…”

“…14,15 These characteristics together with their high polarizability grant them second-order NLO properties which are of great interest for applications in optical and electro-optical devices, photodynamic therapy or biological imaging. 16–21…”