Structural Modulation of TpPa‑1 Covalent Organic Framework in Flow Synthesis Guided by Green Chemistry Principles

Here we present a solvent decision-making pathway for less hazardous and scalable synthesis of TpPa-1 covalent organic framework (COF) underpinned by environmental compatibility (CHEM21 framework), processability (Hansen solubility parameters), and thermodynamic suitability (free energy of solvation). Our analyses suggest that solvents with moderate solvation, such as 1,4-dioxane, propylene carbonate, and diacetin, hinder excessive reaction reversibility and promote crystallite growth. Balancing solvent greenness, compatibility, and thermodynamics, we find that diacetin is optimal for a continuous-flow synthesis. Compared with TpPa-1 COF synthesized in diacetin under batch conditions, the Brunauer-Emmett-Teller surface area of flow-derived TpPa-1 reached 418 m² g^-1, increasing CO₂ uptake by 50% at 298 K. The flow process achieved a 30-fold increase in space-time yield (STY), with excellent reproducibility and an 89% reduction in specific energy consumption. This solvent-thermodynamics-guided approach establishes a physically transparent and sustainable framework for optimizing COF synthesis under continuous-flow conditions.