Microwave-assisted Fast Synthesis of a Donor-Acceptor Covalent Organic Framework towards Photooxidative Amidation Catalysis.

The synthesis of covalent organic frameworks (COFs) at bulk scale require robust, straightforward, and cost-effective techniques. However, the traditional solvothermal synthetic methods of COFs suffer low scalability as well as requirement of sensitive reaction environment and multiday reaction time (2-10 days) which greatly restricts their practical application. Here, we report  microwave assisted  rapid  and optimized synthesis of a donor-acceptor (D-A) based highly crystalline COF, TzPm-COF in second (10 sec) to minute (10 min) time scale. With the increasing of the time from seconds to minutes crystallinity, porosity and morphological changes are also observed for TzPm-COF. Owing to visible range light absorption, suitable band alignment, and low exciton binding energy (Eb=64.6 meV), TzPm-COF can efficaciously produce superoxide radical anion (O2•-) after activating molecular oxygen (O2) which eventually drives aerobic photooxidative amidation reaction with high recyclability. This photocatalytic approach works well with a variety of substituted aromatic aldehydes having electron-withdrawing or donating groups and cyclic, acyclic, primary or secondary amines with moderate to high yield. Furthermore, catalytic mechanism was established by monitoring the real-time reaction progress through in-situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study.