Tuning Photoexcited Charge Transfer in Imine-Linked Two-Dimensional Covalent Organic Frameworks

• Published in: The journal of physical chemistry letters 2022-02, Vol.13 (6), p.1398-1405
• Main Authors: Feng, Tiantian, Streater, Daniel, Sun, Bing, Duisenova, Korlan, Wang, Dong, Liu, Yi, Huang, Jier, Zhang, Jian
• Format: Article
• Language: English
• Subjects: Physical Insights into Materials and Molecular Properties
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.1c04163

The generation of a long-lived charge-separated state in versatile π-conjugated two-dimensional covalent organic frameworks (2D COFs), a process essential to extending their great potentials in advanced semiconducting applications, is yet fully elucidated. Herein, we report a systematic investigation of the photophysical properties of three highly crystalline imine-linked 2D COFs using steady-state and transient absorption spectroscopy accompanied by time-dependent density functional theory (TDDFT) calculations. The different electron affinity between 5,5′,5″-(1,3,5-benzenetriyl)­tris­(2-pyridine­carboxaldehyde) (BTPA) and three tunable electron-donating/accepting triamine monomers dominated the formation of the excited-state, charge-transfer direction, and lifetime. A prominent charge transfer from electron-rich 4,4′,4″-triamino­triphenylamine (TAPA) to BTPA in COFTAPA‑BTPA led to the long-lived charge-separated state, which was attributed to a greater degree of delocalization compared to the two other COFs. These results provide fundamental insight into the importance of structure–property correlation for designing advanced photoactive 2D COF materials with the efficient charge transfer and long-lived charge-separated state.