Exceptionally high charge mobility in phthalocyanine-based poly(benzimidazoben­zophenanthroli­ne)-ladder-type two-dimensional conjugated polymers

Two-dimensional conjugated polymers (2D CPs), composed of multi-strands of linear CPs with extended in-plane π-conjugation, are emerging crystalline semiconducting polymers for organic (opto-)electronics. They are represented by 2D p-conjugated covalent organic frameworks, which typically suffer from poor p-conjugation and thus low charge carrier mobilities. In order to overcome this limitation, researchers from the group of Prof. Xinliang Feng and collaborators have demonstrated the first examples of poly(benzimidazobenzophenanthroline) (BBL)-ladder-type crystalline 2D CPs (based on phthalocyanine, termed as 2DCP-MPc, with M = Cu or Ni) showing unique band transport and outstanding charge carrier mobilities. To optimize the conjugation degree in 2D CPs, they investigate various conjugated linkages by theoretical computations on representative model compounds, and find that the BBL-ladder-type structure exhibits delocalized p-electrons with a narrow HOMO-LUMO  gap. 2DCP-MPcs are synthesized via an acid-modulated polycondensation between octaaminophthalocyaninato metal(II) and naphthalenetetracarboxylic dianhydride under solvothermal conditions. 2DCP-MPcs display narrow optical bandgaps of ~1.3 eV. Density functional theory calculations unveil strongly dispersive energy bands with small electron–hole reduced effective masses of ~0.15 m₀ for the layer-stacked 2DCP-MPcs. Terahertz spectroscopy reveals the band transport of Drude-type free carriers in 2DCP-MPcs with exceptionally high sum mobility of electrons and holes of ~970 cm²V^-1s^-1 at 298 K (and ~1390 cm²V^-1s^-1 at 78 K), which significantly exceeds that of linear and 2D CPs.

Reference: Mingchao Wang, Shuai Fu, Petko St. Petkov, Yubin Fu, Zhitao Zhang, Yannan Liu, Ji Ma, Guangbo Chen, Sai Manoj Gali, Lei Gao, Yang Lu, Silvia Paasch, Haixia Zhong, Hans-Peter Steinrück, Enrique Cánovas, Eike Brunner, David Beljonne, Mischa Bonn, Hai I. Wang*, Renhao Dong*, Xinliang Feng*. Exceptionally high charge mobility in phthalocyanine-based poly(benzimidazobenzophenanthroline)-ladder-type two-dimensional conjugated polymers. Nat. Mater. 2023, DOI: 10.1038/s41563-023-01581-6.

Acknowledgements: This work was financially supported by ERC Grants (T2DCP, no. 819698; FC2DMOF, no. 852909), DFG projects (CRC 1415, no. 417590517; SPP 2248, RACOF-MMIS), EU Graphene Flagship (Core3, no. 881603) and Center for Advancing Electronics Dresden. S.F. acknowledges fellowship support from the Chinese Scholarship Council (CSC). We thank Dresden Center for Nanoanalysis (DCN) and P. Formanek (IPF, Dresden) for the use of facilities. A portion of this work was performed on the Steady High Magnetic Field Facilities, High Magnetic Field Laboratory, CAS. We appreciate C. Naisa, S. Xing, W. Niu, S. Park, J. Liu, Z. Zhang, P. Zhang, B. Zhang and S. Revueta for helpful discussions and measurements. M.W. specially acknowledges J. Cui. R.D. thanks Taishan Scholars Program of Shandong Province (tsqn201909047) and National Natural Science Foundation of China (22272092). E.C. acknowledges financial support from MCIN/AEI grant PID2019-107808RA-I00 and Comunidad de Madrid grants 2021-5A/AMB-20942 and P2018/NMT-451. P.S.P. and Y.F. acknowledge the Center for Information Services and High Performance Computing (ZIH) at TU Dresden for providing the high-performance computing resources.