Functionalized thienoacridines: Synthesis, optoelectronic, and structural properties

Abstract

The preparation and characterization of hexylated, brominated, and 5-hexyl-2-thienyl-substituted tetrathienoacridine (TTAc) is described. Comparative electrochemical, optical, computational, and solid-state studies with their thienoanthracene (TTAn) analogs demonstrate that replacement of CH with nitrogen leads to an overall lowering of the frontier molecular energy levels and decrease in the HOMO-LUMO energy gap. While the brominated TTAc and TTAn derivatives are isostructural, as indicated by X-ray diffraction studies, the lower sublimation temperature and thermochromic behaviour exhibited by bromo-TTAc is attributed to an additional dipole-dipole interaction resulting from the dipole moment afforded by carbon/nitrogen substitution in the core aromatic ring. This work represents a fundamental study of heteroatom substitution in 2-D conjugated small molecules and investigates how inclusion of an electron deficient aromatic ring into the molecular framework (i.e., acridine versus anthracene) can influence the physical properties.