A Solution-Processable Porphyrin-Based Hydrogen-Bonded Organic Framework for Photoelectrochemical Sensing of Carbon Dioxide

Detecting CO₂ in complex gas mixtures is challenging due to the presence of competitive gases in the ambient atmosphere. Photoelectrochemical (PEC) techniques offer a solution, but material selection and specificity remain limiting. Here, we constructed a hydrogen-bonded organic framework material based on a porphyrin tecton decorated with diaminotriazine (DAT) moieties. The DAT moieties on the porphyrin molecules not only facilitate the formation of complementary hydrogen bonds between the tectons but also function as recognition sites in the resulting porous HOF materials for the selective adsorption of CO₂. In addition, the in-plane growth of FDU-HOF-2 into anisotropic molecular sheets with large areas of up to 23000 μm² and controllable thickness between 0.298 and 2.407 μm were realized in yields of over 89 % by a simple solution-processing method. The FDU-HOF-2 can be directly grown and deposited onto different substrates including silica, carbon, and metal oxides by self-assembly in situ in formic acid. As a proof of concept, a screen-printing electrode deposited with FDU-HOF-2 was fabricate as a label-free photoelectrochemical (PEC) sensor for CO₂ detection. Such a signal-off PEC sensor exhibits low detection limit for CO₂ (2.3 ppm), reusability (at least 30 cycles), and long-term working stability (at least 30 days).