Homochirality-Induced Piezoelectricity in a Single-Component Molecular System

Abstract

Organic piezoelectric materials have recently garnered significant attention as potential alternatives to ceramics. However, there are only a handful of reports on single-component molecular crystals exhibiting piezoelectric properties. Introducing homochirality is one of the simplest approaches to achieving piezoelectricity in molecular crystals. Herein, we present an enantiomeric pair of compounds (R)-2-(((1-(p-tolyl)ethyl)imino)methyl)phenol (RPTIMP) and (S)-2-(((1-(p-tolyl)ethyl)imino)methyl)phenol (SPTIMP) crystallizing in the noncentrosymmetric P212121 space group making them suitable for piezoelectric studies In contrast, the racemic mixture of these compounds, Rac-2-(((1-(p-tolyl)ethyl)imino)methyl)phenol (RacPTIMP), crystallizes in the centrosymmetric P21/n space group. The noncentrosymmetry of both RPTIMP and SPTIMP was confirmed through second harmonic generation (SHG) measurements, showing the SHG efficiencies of 0.11 and 0.12, respectively, relative to standard potassium dihydrogen phosphate (KDP). Piezoelectric coefficient (d33) measurements on a powder-pressed pellet of SPTIMP resulted in a d33 value of 4.7 pC N–1. The piezoelectric energy harvesting experiments performed on the poled thermoplastic polyurethane (TPU) composite films of SPTIMP resulted in a maximum voltage output of 7.04 V for the 15 wt % SPTIMP-TPU composite device. The energy storage efficacy was also tested by successfully charging a 10 μF capacitor within 100 s using the best-performing 15 wt % SPTIMP-TPU device.