Electric-field-induced switching of circularly polarized luminescence in a multicomponent emissive liquid-crystal system.

Abstract

Chiral liquid crystals (LCs) are indispensable functional materials for advanced optoelectronic devices. However, their integration with metal-based emitters remains largely unexplored, limiting the understanding of the influence of external electric fields on different photophysical regimes. In this study, we prepared emissive chiral LC materials by doping two achiral platinum(II) complexes-<i>trans</i>-bis(<i>N</i>-isopropyl-5-iminomethyl-1<i>H</i>-pyrazolato)platinum(II) and <i>cis</i>-bis(<i>N</i>-methyl-5-iminomethyl-1<i>H</i>-pyrazolato)platinum(II)-into a chiral nematic LC host (N* LC) composed of achiral 4'-pentyl-4-biphenylcarbonitrile and chiral 2-octyl-4-[4-(hexyloxy)benzoyloxy]benzoate (2OHBB). Although both platinum complexes are intrinsically achiral luminophores, the resulting N* LC materials exhibited pronounced circularly polarized luminescence (CPL). Remarkably, these CPL-active chiral LC systems demonstrated continuous and fully reversible modulation of their CPL characteristics upon application or removal of a direct-current (DC) electric field. In addition to the chiral induction originating from 2OHBB, the handedness of CPL emission could be reversibly switched by toggling the DC field (ON-OFF-ON). This behaviour is attributable to a reversible phase transition between distinct ordered helical structures within the chiral nematic phase. By combining organic platinum emitters and N* LC matrices, this work broadens the design space for CPL control and advances the materials science underpinning electrically switchable CPL devices.