Solution and solid-state properties of highly fluorescent dithieno[3,2-b:2′,3′-d]pyrrole-based oligothiophenes

Abstract

Dithieno[3,2-b:2′,3′-d]pyrrole-based terthiophene and quaterthiophene analogues have been prepared from N-functionalized dithieno[3,2-b:2′,3′-d]pyrroles (DTPs) via Stille coupling. In order to thoroughly study the structure–function property relationships within these DTP-based oligothiophenes, an oligomer series was prepared that allows for the investigation of a number of structural effects including chain length, thiophene functionalization, and pyrrole N-functionalization. As pyrrole N-functionalization allows the incorporation of solubilizing side chains without the unwanted steric interactions that typically reduce backbone planarity, the effect of the bulk of these side chains on the optical properties in both solution and the solid state has been carefully investigated. The DTP-based quaterthiophene, N-tert-butyl-2,6-bis(2′-thienyl)dithieno[3,2-b:2′,3′-d]pyrrole was characterized via X-ray crystallography and was found to crystallize in the monoclinic space group P2₁/c with a = 17.489(4) Å, b = 7.8855(16) Å, c = 14.540(3) Å, β = 108.37(3)°, and Z = 4. The effect of side chains on the solid-state packing of the DTP-based quaterthiophenes was further investigated through X-ray diffraction of solution processed thin films. In comparison to the parent oligothiophenes, the resulting DTP-based systems exhibit enhanced fluorescence efficiencies in solution (up to 66%) and measurable solid-state emission from thin films.