Butterfly-shaped π-extended benzothiadiazoles as promising emitting materials for white OLEDs

Abstract

A series of butterfly-shaped D–A–D and D–A–A compounds composed of a benzothiadiazole core and corresponding terminal alkynes were synthesized. Their photophysical properties in different states (solution, film, crystal, and powder) were investigated. Meanwhile, the linear-shaped compounds were prepared accordingly for the comparative investigation of their photophysical properties. Three phenomena (aggregation caused quenching, crystal induced emission, and aggregation induced emission enhancement) were all observed for the butterfly-shaped compounds. Although the linear-shaped compounds emitted brighter light in pristine powders with higher quantum yields, the butterfly-shaped compounds formed crystals and emitted colorful light from 473 nm to 622 nm in the crystalline state. Moreover, most of them exhibited a mechanochromic character. The color of 2POZ-56 could be reversibly tuned from yellow to red by grinding and fuming. Furthermore, polymorphism-dependent emission was observed for 2POZ-56, allowing for its use as an emissive layer in white organic light emitting diodes.