Optical and crystalline properties of benzo[1,2-b:4,5-b′]dithiophene derivatives†

Abstract

When designing solution-processable semiconducting molecules and polymers, benzo[1,2-b:4,5-b′]dithiophene (BDT) derivatives are widely used because of their planar structures, superior optical properties, ease of synthesis and ease of modification. In this work, four BDT derivatives—BDTT, BDTT–Et, BDTT–OMe and BDTT–CH₂–OMe—were designed and synthesized with different side chains, considering the important roles of side chains in the performance of organic semiconductors. Especially for BDTT–CH₂–OMe, with a new methoxymethyl chain, it exhibited excellent optical properties and the deepest highest occupied molecular orbital energy level (E_HOMO) among these derivatives. Moreover, it demonstrated strong intermolecular interactions and tight π–π stacking. The optical, electrochemical and crystalline properties suggested that BDTT–CH₂–OMe could be further modified as a potential building block for the design of electron-donating small molecules (SMs) or polymers when used in organic electronics, such as bulk heterojunction organic solar cells (BHJ-OSCs).