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

The high design flexibility of organic semiconductors should lead to diverse and complex electronic functions. However, currently available high-performance organic semiconductors are limited in variety; most of p-type materials are based on thienoacenes or related one-dimensionally (1D) extended pi- conjugated systems. In an effort to expand the diversity of organic semiconductors, we are working on the development of tetrabenzoporphyrin (BP) derivatives as active-layer components of organic electronic devices. BP is characterized by its large, rigid two-dimensionally (2D) extended pi-framework with high light absorptivity and therefore is promising as a core building unit of organic semiconductors for optoelectronic applications. Herein, we demonstrate that BP derivatives can afford field-effect hole mobilities of > 4 cm2 V-(-1) s(-1) upon careful tuning of substituents. Comparative analysis of a series of 5,15-bis(n- alkyldimethylsilylethynyl)tetrabenzoporphyrins reveals that linear alkyl substituents disrupt the pi-pi stacking of BP cores, unlike the widely observed fastener effect for 1D extended pi-systems. The n-octyl and n-dodecyl groups have the best balance between high solution processability and minimal pi-pi 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 ? 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 pi-frameworks and thus for increasing the structural or functional diversities of high-performance organic semiconductors.

Automated summary

The high design flexibility of organic semiconductors allows for diverse and complex electronic functions. However, the current variety of high-performance organic semiconductors is limited, with most p-type materials being based on one-dimensionally extended pi-conjugated systems. To expand the diversity, researchers are developing tetrabenzoporphyrin (BP) derivatives as active-layer components for organic electronic devices. BP derivatives have a large, rigid two-dimensionally extended pi-framework with high light absorptivity, making them promising as core building units for organic semiconductors in optoelectronic applications. By carefully tuning substituents, BP derivatives can achieve field-effect hole mobilities of over 4 cm2 V-1 s-1. Linear alkyl substituents disrupt the pi-pi stacking of BP cores, unlike the commonly observed fastener effect in 1D extended pi-systems. The n-octyl and n-dodecyl groups have the best balance between high solution processability and minimal pi-pi stacking disruption, leading to superior hole mobilities in solution-processed thin films. These findings provide a basis for exploring the full potential of two-dimensionally extended pi-frameworks and increasing the structural or functional diversities of high-performance organic semiconductors.