Packing Polymorphism Affecting the Optoelectronic Properties of a π-Conjugated Organic Compound

[1]Benzothieno[3,2-b]benzothiophene (BTBT) derivatives are widely employed as hole transport materials in organic field-effect transistors. The electronic properties of these depend critically on the crystal packing, which turn depends choice attached functional group. With symmetrically alcohol chains, structure may display different packing modes depending number CH2 groups alkyl chain. dipentanol BTBT derivative has two polymorphs I and II, crystallizing from solvents, with distinct consequently properties. Whereas conformational changes very small between II hydrogen bonding networks structures identical, adjacent cores differently shifted oriented respect to each other. It is shown by density theory that polymorph having unfavorable slightly more stable than II. This caused much attractive cross stacking C5OH chains originates rather electrostatic interactions cores. differences similarities dibutanol dihexanol discussed. Both polymorphic forms negative uniaxial thermal expansion, but directions molecules. Different scanning calorimetry measurements suggest exist.