Visualizing molecular weights differences in supramolecular polymers

Qingyun Li; Hanwei Zhang; Kai Lou; Yabi Yang; Xiaofan Ji; Jintao Zhu; Jonathan L Sessler

doi:10.1073/pnas.2121746119

Visualizing molecular weights differences in supramolecular polymers

Proc Natl Acad Sci U S A. 2022 Mar 1;119(9):e2121746119. doi: 10.1073/pnas.2121746119.

Authors

Qingyun Li¹, Hanwei Zhang¹, Kai Lou¹, Yabi Yang¹, Xiaofan Ji², Jintao Zhu², Jonathan L Sessler³

Affiliations

¹ Key Laboratory of Materials Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
² Key Laboratory of Materials Chemistry for Energy Conversion and Storage, Ministry of Education, Hubei Key Laboratory of Materials Chemistry and Service Failure, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China; xiaofanji@hust.edu.cn jtzhu@mail.hust.edu.cn sessler@cm.utexas.edu.
³ Department of Chemistry, The University of Texas at Austin, Austin, TX 78712 xiaofanji@hust.edu.cn jtzhu@mail.hust.edu.cn sessler@cm.utexas.edu.

Abstract

Issues of molecular weight determination have been central to the development of supramolecular polymer chemistry. Whereas relationships between concentration and optical features are established for well-behaved absorptive and emissive species, for most supramolecular polymeric systems no simple correlation exists between optical performance and number-average molecular weight (M_n). As such, the M_n of supramolecular polymers have to be inferred from various measurements. Herein, we report an anion-responsive supramolecular polymer [M1·Zn(OTf)₂]_n that exhibits monotonic changes in the fluorescence color as a function of M_n Based on theoretical estimates, the calculated average degree of polymerization (DP_cal) increases from 16.9 to 84.5 as the monomer concentration increases from 0.08 mM to 2.00 mM. Meanwhile, the fluorescent colors of M1 + Zn(OTf)₂ solutions were found to pass from green to yellow and to orange, corresponding to a red shift in the maximum emission band (λ_max ). Therefore, a relationship between DP_cal and λ_max could be established. Additionally, the anion-responsive nature of the present system meant that the extent of supramolecular polymerization could be regulated by introducing anions, with the resulting change in M_n being readily monitored via changes in the fluorescent emission features.

Keywords: J-aggregate; fluorescence; molecular weight; self-assembly; supramolecular polymers.