Sunlight driven E–Z isomerization of liquid crystals based on hexahydroxytriphenylene nano-templates for enhanced solid-state solar thermal energy storage

Abstract

Solar thermal fuels (STFs) are increasingly pivotal in addressing global energy demands, yet their widespread adoption is hindered by challenges such as low energy density, short half-life, and inadequate sunlight photoconversion efficiency. To enable large-scale utilization of STFs, innovative material design is imperative for efficient light-to-heat conversion. This study presents a new approach for achieving high energy density STFs by employing a hexahydroxytriphenylene liquid crystal (LC) core as a nano-template, tethering six tetra-ortho-substituted azobenzene units. The resulting oligomers exhibit discotic nematic mesophases, demonstrating excellent photostability, photocyclability, and prolonged half-lives of metastable Z states. High E to Z isomer conversion of up to 79.4% and 75.2% is achieved under direct sunlight with and without a bandpass filter, respectively, with high solar conversion efficiencies of up to 1.87%. Upon discharging, infrared (IR) thermal imaging reveals remarkable heat release values of up to 9.64 °C. The present study introduces an innovative method for developing high-performance STFs using LC nano-templates, surpassing prior approaches utilizing carbon nanomaterials.