Enantiomeric Hydrogen-bonded Chains Driving Ferroelectric and Nonlinear Optical Behavior

Organic multiferroic materials have been widely investigated due to their novel physical properties and broad applications. However, the discovery of organic small-molecular multiferroic compounds is still rare. Herein, based on the chemical design strategy of introducing homochirality, we present a pair of enantiomeric organic small-molecular compounds [HDABCO (1,4-diazabicyclo[2.2.2]octonium)][l- and d-MA (malic acid)], which displays high Curie temperatures (Tc) of 409/412 K, superior optoelectronic performance, and unique ferroelectric and ferroelastic nature. In comparison with the reported ferroelectrics with the [HDABCO]+ cation chain structure, the enantiomers show a neutral one-dimensional chain, where hydrogen bonds connect [HDABCO]+ cations and [MA]− anions. Strikingly, [HDABCO][l- and d-MA] exhibit a large second harmonic generation (SHG) intensity of about 2.46 and 2.53 times that of KH2PO4 (KDP), exceeding those of all the organic ferroelectrics (about 0.2–1 × KDP). With excellent SHG signal and ferroic properties, as well as the merit of low acoustic impedance z0 matching that of the body and easy processing, [HDABCO][l- and d-MA] are potential candidates for future biocompatible electronic devices with multi-functionality.