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

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 (EHOMO) among these derivatives. Moreover, it demonstrated strong intermolecular interactions and tight pi-pi 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).