Design, Synthesis, and Ultrafast Carrier Dynamics of Core-Substituted Naphthalene Diimide-Based Covalent Organic Frameworks

A series of two-dimensional polyimide covalent organic frameworks (2D COF) based on core-substituted naphthalene diimides (cNDIs) were designed and synthesized with the characteristic of tunable bandgap without global structural changes. Cyclic voltammetry (CV) and DFT calculations indicated that COFcNDI-OEt and COF(cNDI-SEt )possess higher HOMO/LUMO levels and narrower bandgaps than COFNDI-H. Further investigation indicated that the COF bandgaps are not only related to the electron-donating substituents but also varied with respect to the interlayer distances. Moreover, the femtosecond transient absorption (TA) spectra manifested that the electron donor substituents are beneficial to the charge delocalization in the pi-columnar unit, resulting in a longer lifetime of charge recombination, which is one of the pivotal prerequisites for high-performance solar cells and photocatalysis.

Automated summary

A series of 2D covalent organic frameworks (COF) based on core-substituted naphthalene diimides (cNDIs) were designed and synthesized, with tunable bandgap without global structural changes. The bandgaps of the COFs were found to be related to the electron-donating substituents and varied with respect to the interlayer distances. The presence of electron donor substituents promoted charge delocalization and resulted in a longer charge recombination lifetime.