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

Abstract

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 COF TAPA-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.

Boosting Reactive Oxygen Species Generation by Regulating Excitonic Effects in Porphyrinic Covalent Organic Frameworks

“…Since the fluorescence in the system is mainly generated by the radiative decay of the singlet exciton, the significant shortening of the singlet exciton lifetime again proves the dissociation of the singlet exciton in the system. 4,21 In conclusion, the low exciton concentration (singlet state and triplet state) will reduce the interaction between excitons, thereby increasing the quantum yield of excited species.…”

“…The worldwide energy and environmental concerns are stimulating people’s unprecedented research interests to pursue more efficient conversion and utilization of green solar energy. Recently, as a typical solar energy conversion technology, semiconductor-based photocatalysis has shown great potential in many fields such as fuel manufacturing, organic synthesis, dye degradation, and antibacterial medicine. − It is well-accepted that the photocatalytic processes mainly involve three steps, i.e., the excitation of carriers in catalysts by appropriate irradiation, the separation and transfer of the photogenerated carriers, and the redox reactions at the material interface . However, these steps neglect an important excitonic effect during optical excitation processes.…”

Emissive Substoichiometric Covalent Organic Frameworks for Water Sensing and Harvesting

“…These observations, along with the earlier discussed steady-state fluorescence results in various solvents suggest charge transfer in COF-SMU-1. [12,28] Cyclic voltammetry was carried out to gauge the redox properties of COF-SMU-1. As shown in Figure S7 (Supporting Information), the oxidation corresponding to pyrene moiety was quasireversible, while the reduction corresponding to triazine moiety was irreversible.…”

Connecting the dots for fundamental understanding of structure–photophysics–property relationships of COFs, MOFs, and perovskites using a Multiparticle Holstein Formalism

“…Moreover, electron-phonon coupling and different forms of electronic and conformational defects play fundamental roles in determining the photophysical response and, consequently, the transport properties of most organic and hybrid materials. Although, LR-TDDFT/BSE approaches have been successfully employed to investigate the photophysical response of MOFs, [167][168][169][170][171] COFs, 141,[172][173][174] and perovskites, 130,142,[175][176][177][178][179][180][181][182] to the best of our knowledge, none of the existing methodologies simultaneously take into account aggregation, electronic coupling, strong electron-phonon coupling, and crystalline disorder on equal footing.…”