Alkyl–π Functional Molecular Gels: Control of Elastic Modulus and Improvement of Electret Performance

The development of optoelectronically-active soft materials is drawing attention to the application of soft electronics. A room-temperature solvent-free liquid obtained by modifying a π-conjugated moiety with flexible yet bulky alkyl chains is a promising functional soft material. Tuning the elastic modulus (G′) is essential for employing optoelectronically-active alkyl–π liquids in deformable devices. However, the range of G′ achieved through the molecular design of alkyl–π liquids is limited. We report herein a method for controlling G′ of alkyl–π liquids by gelation. Adding 1 wt% low-molecular-weight gelator formed the alkyl–π functional molecular gel (FMG) and increased G′ of alkyl–π liquids by up to seven orders of magnitude while retaining the optical properties. Because alkyl–π FMGs have functional π-moieties in the gel medium, this new class of gels has a much higher content of π-moieties of up to 59 wt% compared to conventional π-gels of only a few wt%. More importantly, the gel state has a 23% higher charge-retention capacity than the liquid, providing better performance in deformable mechanoelectric generator-electret devices. The strategy used in this study is a novel approach for developing next-generation optoelectronically-active FMG materials.