Influence of poly(diketopyrrolopyrrole) chain length and chemical structure on photocatalytic hydrogen evolution in composites with TiO 2 Teresa Mauerer 1 , Julian Hungenberg 2 , Mukundan Thelakkat 2 , Roland Marschall 1 1 Physical Chemistry III, University of Bayreuth, 95447 Bayreuth, Germany, 2 Applied Functional Polymers, University of Bayreuth, 95447 Bayreuth, Germany To meet the effects and threats of climate change, it is essential to reduce greenhouse gas emissions and transition to renewable energy sources. Solar energy and hydrogen technologies are promising in this regard, such as photocatalytic water splitting and hydrogen evolution. [1] Mostly, inorganic semiconductors are investigated for this reaction. [2] In the last years, organic photocatalysts have emerged as promising candidates for the hydrogen evolution reaction (HER). [3–6] Polymer semiconductors provide diverse synthetic modularity and the possibility to tailor the electronic and photophysical properties, as well as earth abundance and activity without noble metal co-catalysts. One strategy to influence the band gap is the copolymerisation of an electron-rich (donor) and an electron-poor (acceptor) moiety. [7,8] A promising approach is the combination of both inorganic and organic semiconductors to overcome the limitations of, e.g. TiO 2 , such as low quantum yield and lacking absorption in visible light. [9] By combination, the photocatalytic activity can be augmented by combining both attributes. We synthesized two hydrophilic conjugated donor-acceptor poly(diketopyrrolopyrrole) copolymers with fluorene or carbazole as comonomers with different chain lengths. To increase its compatibility with water, the diketopyrrolopyrrole core was modified with triethylene glycol side chains. We were able to form hybrid materials as composites of the individual polymers with anatase TiO 2 . The formed composite materials were characterized by their structural and optical properties as well as the frontier orbitals energy levels. Depending on the used comonomer, the optical properties of the polymers are tunable. The composite materials were tested for the HER and showed an eightfold enhancement in comparison to pristine TiO 2 . The stability of the organic part of the composite materials was characterized by solid-state NMR, UV-Vis, and DRIFT. A further influence on the activity towards hydrogen evolution is the chain length. With increasing chain length, the activity increases, while the active site of the process remains the inorganic semiconductor. References 1. S. Chu, A. Majumdar, Nature 2012 , 488 , 294–303. 2. R. Marschall, Adv. Funct. Mater. 2014 , 24 , 2421–2440. 3. Y. Wang, A. Vogel, M. Sachs, R. S. Sprick, L. Wilbraham, S. J. A. Moniz, R. Godin, M. A. Zwijnenburg, J. R. Durrant, A. I. Cooper, J. Tang, Nat. Energy 2019 , 4 , 746–760. 4. C. M. Aitchison, M. Sachs, M. A. Little, L. Wilbraham, N. J. Brownbill, C. M. Kane, F. Blanc, M. A. Zwijnenburg, J. R. Durrant, R. S. Sprick, A. I. Cooper, Chem. Sci. 2020 , 11 , 8744–8756. 5. X. Chen, K. Geng, R. Liu, K. T. Tan, Y. Gong, Z. Li, S. Tao, Q. Jiang, D. Jiang, Angew. Chemie - Int. Ed. 2020 , 59 , 5050– 5091. 6. J. Kosco, F. Moruzzi, B. Willner, I. McCulloch, Adv. Energy Mater. 2020 , 10 , DOI 10.1002/aenm.202001935. 7. M. Goel, C. D. Heinrich, G. Krauss, M. Thelakkat, Macromol. Rapid Commun. 2019 , 40 , 1–31. 8. J. A. Schneider, D. F. Perepichka, in Adv. Mater. (Eds.: T. van de Ven, A. Soldera), De Gruyter, Berlin, Boston, 2020 , pp. 1–50. 9. Y. Ma, X. Wang, Y. Jia, X. Chen, H. Han, C. Li, Chem. Rev. 2014 , 114 , 9987–10043.
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