High-temperature enantiomeric azobenzene-based photoisomerized piezoelectrics: 4-(phenyldiazenyl)anilinium) d- and l-tartrate

Abstract

Rochelle salt, as the initiator of piezoelectrics and ferroelectrics, has been a bridge between homochirality as well as piezoelectricity and ferroelectricity since the late 19th century. One can greatly increase the hit rate of constructing non-centrosymmetric or even polar materials by using enantiomeric components. It should be highlighted that the marriage of photoisomerization and piezoelectricity can endow molecular piezoelectrics with unique optical phenomena, which may realize multi-channel encryption and detection. However, it is still a great challenge to design a photoisomerized piezoelectric. Here, under the guideline of introducing homochirality, we have designed a pair of high-temperature enantiomeric azobenzene-based piezoelectrics, 4-(phenyldiazenyl)anilinium) D- and L-tartrate (D-1 and L-1), whose piezoelectric behaviors persist up to 460 K. Compared to the racemic compound 4-(phenyldiazenyl)anilinium) rac-tartrate (rac-1) which adopts the centrosymmetric space group P, the selection of homochiral anions makes the enantiomers crystallize in an enantiomeric-polar space group and thereby induce piezoelectricity and potential ferroelectricity. As piezoelectric materials, the enantiomers show relatively large piezoelectric responses of 7 pC per N, comparable to that of Rochelle salt. Besides, D-1 and L-1 possess the ability of photoisomerization; to our knowledge, this is the first azobenzene-based high-temperature enantiomeric piezoelectric which shows a photoisomerization phenomenon upon 450 nm irradiation. This combination of piezoelectricity and photoisomerization may support further exploration of optically-controlled smart devices for multi-channel information encryption and signal detection.