Stereoisomerism-controlled Packing in Ladder-type Indacenodithieno[3,2-b]thiophene Crystals

Abstract

Stereochemistry is a potent way to direct the molecular packing in condensed phases. Here, we synthesized the enantiopure, racemic, and achiral isomers of p-type small molecule, that is, indacenodithieno[3,2-b]thiophene, to understand the impact of stereochemistry on molecular packing and solid-state properties. In the solution state, the optical properties remain nearly identical among the isomers; however, a significant difference was observed in the condensed phase. X-ray diffraction pattern revealed enantiopure isomers were more tightly packed and exhibited strong π-stacking relative to their racemic and achiral counterparts. Two-dimensional arrangement of the stacked enantiopure isomers gives more dense-packed crystalline phases than an achiral analog, which is unusual anti-Wallach type condensed phases. The enantiopure one exhibited two times higher photoconductivity than its achiral or racemic analogues, as well as showing high electron spin polarizability (∼75%) with electrical current throughput (100 nA). The result highlights the role of stereochemistry as a key strategy to direct the condensed phase packing and properties in conjugated crystals.