Enhancing Chiroptical Responses in Helical Nanographenes via Geometric Engineering of Double [7]Helicenes

Wenhui Niu; Yubin Fu; Qingsong Deng; Zhen-Lin Qiu; Fupin Liu; Alexey A Popov; Hartmut Komber; Ji Ma; Xinliang Feng

doi:10.1002/anie.202319874

Enhancing Chiroptical Responses in Helical Nanographenes via Geometric Engineering of Double [7]Helicenes

Angew Chem Int Ed Engl. 2024 May 6;63(19):e202319874. doi: 10.1002/anie.202319874. Epub 2024 Mar 28.

Authors

Wenhui Niu^{1

2}, Yubin Fu^{1

2}, Qingsong Deng³, Zhen-Lin Qiu², Fupin Liu⁴, Alexey A Popov⁴, Hartmut Komber⁵, Ji Ma^{1

2

6}, Xinliang Feng^{1

2}

Affiliations

¹ Max Planck Institute of Microstructure Physics, Weinberg 2, Halle, 06120, Germany.
² Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062, Dresden, Germany.
³ State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China.
⁴ Leibniz Institute for Solid State and Materials Research, 01069, Dresden, Germany.
⁵ Leibniz-Institut für Polymerforschung Dresden e. V., Hohe Straße 6, 01069, Dresden, Germany.
⁶ College of Materials Science and Opto-Electronic Technology & Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Science, 100049, Beijing, P. R. China.

PMID: 38372180
DOI: 10.1002/anie.202319874

Abstract

Helical nanographenes with high quantum yields and strong chiroptical responses are pivotal for developing circularly polarized luminescence (CPL) materials. Here, we present the successful synthesis of novel π-extended double [7]helicenes (ED7Hs) where two helicene units are fused at the meta- or para-position of the middle benzene ring, respectively, as the structural isomers of the reported ortho-fused ED7H. The structural geometry of these ED7Hs is clearly characterized by single-crystal X-ray analysis. Notably, this class of ED7Hs exhibits bright luminescence with high quantum yields exceeding 40 %. Through geometric regulation of two embedded [7]helicene units from ortho-, meta- to para-position, these ED7Hs display exceptional amplification in chiroptical responses. This enhancement is evident in a remarkable approximate fivefold increase in the absorbance and luminescence dissymmetry factors (g_abs and g_lum), respectively, along with a boosted CPL brightness up to 176 M^-1 cm^-1, surpassing the performance of most helicene-based chiral NGs. Furthermore, DFT calculations elucidate that the geometric adjustment of two [7]helicene units allows the precise alignment of electric and magnetic transition dipole moments, leading to the observed enhancement of their chiroptical responses. This study offers an effective strategy for magnifying the CPL performance in chiral NGs, promoting their expanded application as CPL emitters.

Keywords: CPL Brightness; Chirality; Chiroptical Responses Amplification; Geometric Engineering; Helical Nanographenes.