Facile Synthesis and Chain-Length Dependence of the Optical and Structural Properties of Diketopyrrolopyrrole-Based Oligomers

Abstract

Here we report the synthesis, optical properties and solid-state packing of monodisperse oligomers of DPP up to five repeating units. Optical properties of DPP-oligomers in solution and solid state were investigated by a combination of steady-state, and transient spectroscopy. Transient absorption spectroscopy and time-correlated single photon counting (TCSPC) measurements show that the fluorescence lifetime decreases with increase in the oligomer size from monomer to trimer, thereby reaching saturation for pentameric DPP oligomer. The solid-state packing and crystallinity were probed using advanced techniques which included grazing incidence small-angle X-ray scattering (GISAXS) and X-ray diffraction (XRD) to elucidate the structure-property trend. Collectively, our chain-length dependent studies establish the fundamental correlation and provide a comprehensive understanding between structure-property correlation and solid-state properties in DPP-DPP based conjugated systems.