Synergistic enhancement of luminescence and ferroelectricity driven by (Z)-clipping of a tetraphenylethene†

Abstract

Synergistic enhancement of luminescence and ferroelectricity (SELF) was explored in a (Z)-isomer of tetraphenylethene derivatives containing two clipping units in (Z)-configuration (TPC2-(Z)). TPC2-(Z) was synthesized utilizing a ‘body core’ precursor, which exclusively afforded (Z)-configuration. High-resolution transmission electron microscopy measurements indicated that TPC2-(Z) formed a layered morphology in film, with well-ordered crystalline structures, which was ascribed to the (Z)-clipped self-assembled structures. The film exhibited good photoluminescence performances with 45.6% quantum yield. Simultaneously, the film exhibited high ferroelectricity as inferred from high remnant polarization (P_r = 2.54 μC cm⁻²) and saturated polarization (3.56 μC cm⁻²) along with a longitudinal piezoelectric coefficient (d₃₃ = −23.8 pm V⁻¹), indicating that TPC2-(Z) exhibits excellent SELF. Owing to its fluorescence and thermal stability, we fabricated light-emitting electrochemical cells (LEC) that exhibited maximum 890 cd m⁻² at V_on of 3.9 V. This was more than 40% enhanced performance compared to that of the (E)/(Z) mixture. A new self-powered, stimuli-sensitive electroluminescent device was demonstrated with TPC2-(Z), where the piezoelectrically tunable LECs effectively ‘switched on’ luminescence, showing 120-fold increased brightness after 254 bending at 1 Hz, compared to the ‘off’ state without bending. These results underscore that Z-clipping is an effective method for enhancing SELF and could create new self-powered, stimuli-sensitive electroluminescent devices.