▎ 摘　　要

Developing graphene-like two-dimensional materials naturally possessing a band gap has sparked enormous interest. Thanks to the inherent wide band gap and high mobility in the 2D plane, covalent organic frameworks containing triazine rings (t-COFs) hold great promise in this regard, whilst the synthesis of single-layer t-COFs remains highly challenging. Herein, we present the fabrication of a well-defined graphene-like t-COF on Au(111). Instead of single/ multiple-step single-type reactions commonly applied for onsurface synthesis, distinct stepwise on-surface reactions, including alkynyl cyclotrimerization, C-O bond cleavage, and CH bond activation, are triggered on demand, leading to product evolution in a controlled step-by-step manner. Aside from the precise control in sophisticated on-surface synthesis, this work proposes a single-atomic-layer organic semiconductor with a wide band gap of 3.41 eV.