Enhanced Electrochemiluminescence of Porphyrin-Based Hydrogen-Bonded Organic Frameworks at Low Positive Potential via Substituent-Induced Outer-Sphere Microenvironment Modulation

The porphyrin-based hydrogen-bonded organic framework (HOF) offers a superior platform for decoding electrochemiluminescence (ECL) via controlling charge transfer due to its higher solubility, chemical stability, and tunable framework behavior. In this research, three kinds of HOFs including TDPP-HOF, TCPP-HOF, and TCNPP-HOF are synthesized based on a porphyrin tectonic plate decorated with 2,4-diaminotriazinyl (DAT), carboxyl, and nitrile moieties to study their ECL performances. The hydrazine as the coreactant can trigger TDPP-HOF at the low-excited positive potential to generate 15.8- and 112.9-fold enhancement in ECL signal than TCNPP-HOF and TCPP-HOF. Experimental results and density functional theory calculations verify that TDPP-HOF with a lower bandgap and a larger binding energy (ΔE) between coreactant and HOF is beneficial to intrareticular charge transfer (ICT), facilitating the enhancement of ECL performance. These results indicate that the peripheral substituents can establish a specialized outer-sphere microenvironment around the porphyrin center to tune both the HOF activity and the ECL performance. As a proof of concept, a simple TDPP-HOF-based ECL sensor is constructed to sensitively detect phenolic compounds. This research provides a new avenue for improving the ECL performance via modulating the outer-sphere microenvironment of HOFs.