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

Graphical Abstract

In chains: The total synthesis of diketopyrrolopyrrole (DPP) based conjugated polymers and DPP–DPP pentamers is reported. The novel synthetic route paves the way for the synthesis of DPP-based oligomers of desired chain lengths. As higher oligomers absorb in the near infrared (NIR) region, advanced optical characterization techniques such as transient absorption (TA) spectroscopy were used to establish the trends in optical properties and quantification of luminescence lifetimes.

Abstract

Here, we report the synthesis, optical properties, and solid-state packing of monodisperse oligomers of diketopyrrolopyrrole (DPP) up to five repeating units. The optical properties of DPP oligomers in solution and the 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 an increase in the oligomer size from monomer to trimer, thereby reaching saturation for pentameric DPP oligomers. The solid-state packing and crystallinity were probed by 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 between the structure and property and provide a comprehensive understanding of the solid-state properties in DPP–DPP based conjugated systems.