Tuning Optical Properties of Covalent Organic Multicycles via Linkage Variation.

Tuning the optical properties of cyclic organic architectures is typically achieved through skeleton design, while the role of linkage chemistry remains largely unexplored. Herein, we demonstrate that linkage variation-vinylene versus imine-provides an effective strategy to modulate the optoelectronic properties of covalent organic multicycles (COMs). Two vinylene-linked COMs and two imine-linked COMs were rationally designed and efficiently synthesized via Knoevenagel and Schiff-base condensation, respectively. Compared with imine-linked COMs, the vinylene-linked analogues exhibit narrower optical bandgaps, lowered HOMO levels, longer fluorescence lifetimes, and higher photoluminescence quantum yields in solid and solution states. The femtosecond-transient absorption analysis and photocurrent response revealed that vinylene-linked COMs exhibit superior charge separation and transfer efficiency, thereby enhancing carrier transport and fluorescence properties.