Exploration of Alkyl Group Effects on the Molecular Packing of 5,15-Disubstituted Tetrabenzoporphyrins Toward Efficient Charge-Carrier Transport

Abstract

In an effort to expand the diversity of organic semiconductors, tetrabenzoporphyrin (BP) derivatives were developed as active-layer components of organic electronic devices. BP is characterized by its large, rigid two-dimensionally (2D) extended π-framework and therefore is promising as a core building unit of organic semiconductors [1,2]. Herein, we demonstrate that BP derivatives can afford field-effect hole mobilities of >4 cm2 V−1 s−1 upon careful tuning of substituents [3]. Comparative analysis of a series of 5,15-bis(n-alkyldimethylsilylethynyl)tetrabenzoporphyrins reveals that linear alkyl substituents disrupt the π−π stacking of BP cores. The n-octyl and n-dodecyl groups have the best balance between high solution processability and minimal π−π stacking disruption, leading to superior hole mobilities in solution-processed thin films. The resulting thin films show high thermal stability wherein the field-effect hole mobility stays above 1 cm2 V−1 s−1 even after heating at 160 °C in air, reflecting the tight packing of large BP units. These findings will serve as a good basis for extracting the full potential of 2D extended π-frameworks and thus for increasing the structural or functional diversities of high-performance organic semiconductors.