J-Aggregates of zinc tetraphenylporphyrin: a new pathway to excellent electrochemiluminescence emitters

Low-potential electrochemiluminescence (ECL) luminophores with excellent ECL behavior have attracted considerable interest in biological analysis. Herein, we explored the ECL behavior of ZnTPP with different aggregates for the first time. In this work, we used the mixed solvent method to prepare the H- and J-aggregates of zinc tetraphenylporphyrin (ZnTPP). This resulted in a completely disparate morphology, such as nanoparticles and rod-aggregates, which were observed by recording atomic force microscopy (AFM) images. Characteristic changes in the optical properties and electrochemical properties of ZnTPP appeared when it underwent H- and J-aggregation. Significantly, the measured ECL behavior varied for the same ZnTPP molecules when they were in the form of H- and J-aggregates; and the ECL intensity of the J-aggregates was more than ten times that of the H-aggregates due to a narrower band gap and the formation advantages in J-aggregates. The narrower band gap of J-aggregates not only facilitates the electron-hole pair recombination, but also facilitates the electron injection into the J-aggregates. The formation advantage of the J-aggregates is likely to contribute to the strong ECL intensity of the J-aggregates. Maybe the big number of ZnTPP molecules in a J-aggregate unit increases the opportunity of generating excited states and light from excited state radiation. The ECL property could be regulated with the different aggregation of ZnTPP, which led to a decline of ECL cathode potential in the J-aggregates (191 mV) compared with the H-aggregates. This work provides an effective and novel strategy for developing ECL emitters with low potential and high ECL emission intensity via adjusting aggregation motifs.