Investigation of thiophene flanked diketopyrrolopyrrole monomers with straight and branched alkyl chains and their elect

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Sergei Manzhos Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, 9 Engineering DR 1, Singapore 117576, Singapore

Jennifer MacLeod School of Chemistry, Physics and Mechanical Engineering, Nanotechnology and Molecular Sciences Discipline, Queensland University of Technology (QUT), Brisbane, Australia

Henry J. Spratt Central Analytical Research Facility (CARF), Institute of Future Environments, Queensland University of Technology (QUT), Brisbane, Australia

Anthony P. O’Mullane and Prashant Sonarb) School of Chemistry, Physics and Mechanical Engineering, Nanotechnology and Molecular Sciences Discipline, Queensland University of Technology (QUT), Brisbane, Australia (Received 13 January 2017; accepted 7 April 2017)

Diketopyrrolopyrrole (DPP) is a critically important building block that has gained importance in the organic electronics community because of its wide applicability in various devices. In this work, the thiophene flanked DPP moiety attached to alkyl chains of various lengths (this includes straight octyl and branched ethyl hexyl units) has been used as the monomer for electropolymerization. This paper focuses on the study of optical, thermal, solid state ordering and electrochemical properties of these electron deficient monomers using various characterization techniques such as UV–Vis spectrometry (UV), photo-luminescence spectroscopy (PL), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), cyclic voltammetry (CV), as well as ab initio modeling. These monomers exhibit broad absorption spectra from the ultraviolet (280–400 nm) to visible (400–600 nm) regions and emission spectra between 560 and 610 nm. The band gaps of these monomers were calculated to be in the range of 2.00–2.20 eV. These monomers were electropolymerized by scanning the potential between 0.5 and 2.0 V versus ferrocene for up to 50 cycles on a glassy carbon electrode. I. INTRODUCTION

Diketopyrrolopyrrole (DPP) dyes have been widely used in many applications; for example, in inks, paints and plastics for coating purposes since they were first developed in the early 1970s.1,2 In subsequent decades, DPP-based organic semiconductors were extended into various applications such as opto–electronic devices including organic light emitting diodes (OLEDs),3 organic field effect transistors (OFETs),4,5 organic photovoltaics (OPVs),6,7 chemical sensors,8,9 and memory Contributing Editor: Linda S. Schadler Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2017.158

devices10 due to their excellent fluorescent, charge carrier mobility, and photo absorbance properties. In particular, OFETs and OPV devices fabricated using thin films of donor–acceptor (D–A) type organic semiconductors using an electron-accepting DPP moiety have received considerable attention and there are numerous publications on these applications.6,7,11 The backbone of DPP is unique because of its fused a