Low‐band gap copolymers containing thienothiadiazole units: Synthesis, optical, and electrochemical properties

Abstract

Novel low‐band gap alternating copolymers consisting of 9,9‐bis(2‐ethylhexyl)fluorene and 4,6‐di(2‐thienyl)thieno[3,4‐c][1,2,5]thiadiazole and its 3,3″‐dialkyl derivatives were synthesized by Suzuki copolymerization reaction, and their photophysical and electrochemical properties were studied. The copolymers possess small optical band gap 1.3–1.4 eV. The absorption covers the whole visible spectral region. The long‐wavelength absorption maxima in thin films located at approximately 750–785 nm are significantly red shifted compared with those in solution, indicating strong intermolecular interactions. The introduction of alkyl chains to the thiophene units increases the molecular weights of soluble fractions and solubility of the final copolymers, leading to the improved processability of thin films. Polymer solutions exhibited solvatochromism and thermochromism, which is strongly supported by the involvement of the alkyl chains. The copolymers exhibited ambipolar redox properties and reversible electrochromic behavior. The electronic properties are influenced only slightly by alkyl substituents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2743–2756, 2010

Raman Microspectroscopy of Thienothiadiazole‐Fluorene Copolymer and its Blends with Fullerene

“…Copolymer CDTF was prepared by the Suzuki coupling reaction of 9,9‐bis(2‐ethylhexyl)‐2,7‐bis(1,3,2‐dioxaborinan‐2‐yl)fluorene with 4,6‐bis(5‐bromo‐3‐dodecylthien‐2‐yl)thieno[3,4‐ c ][1,2,5]thiadiazole. The details of the synthesis are described in our previous paper . The molecular weight was M n = 31000 and M w = 42000.…”

“…does not influence ICT, and it also does not prevent strong intermolecular interactions between polymer chains leading to the aggregate formation in thin films. The strong aggregation in the CDTF thin films was shown in our previous papers from the comparison of absorption in solution and thin films. In thin film absorption spectra the low‐energy absorption maxima are significantly red‐shifted compared to those in its solution spectra.…”

“…[1][2][3] Recently, we have prepared a novel series of low-band gap copolymers with electron accepting thienothiadiazole-based units, which are promising for photovoltaic applications due to the low-band gap, high electron affinity and reversible redox properties. [4][5][6][7][8][9] The quality of the blend film is important for the PV device performance. [10][11][12][13] Raman spectroscopy is a useful tool to monitor local polymer order and particularly, Raman microspectroscopy enable us to study the chemical composition of blends used in bulk-heterojunction structure.…”

New two-step synthesis ofN-(2-ethylhexyl)-2,7-diiodocarbazole as a monomer for conjugated polymers

“…Short alkyl side chains are inconvenient from the solubility viewpoint for the final conjugated material. Monomers with longer or branched alkyl chains are required for syntheses of conjugated polymers in order to obtain soluble and high-molar-weight polymers [18,19].…”

Low Band Gap Polymers for Roll-to-Roll Coated Organic Photovoltaics – Design, Synthesis and Characterization

“…nitrile, thiazole) are attached. Examples of fused ring systems used as acceptors in low band gap polymers are benzothiadiazole [24] and thieno-thiadiazole [25]. Donors.…”