Asymmetric zinc porphyrin derivatives bearing three pseudo-pyrimidine meso-position substituents and their photosensitization for H2 evolution?

New Journal of Chemistry Pub Date: 2020-06-11 DOI: 10.1039/D0NJ02056G

Abstract

Novel asymmetric zinc porphyrin derivatives (ZnPy-5 and ZnPy-6) with meso-positions bearing one benzoic acid and three pseudo-pyrimidines with two N atoms located at different positions were synthesized and utilized as sensitizers for Pt-loaded g-C3N4 (PCN). Compared to the analogue (ZnPy-1 bearing one benzoic acid and three phenyl meso-position substituents), ZnPy-5 and ZnPy-6 exhibit significantly enhanced photosensitization on PCN under visible light (λ ≥ 420 nm) illumination. In particular, ZnPy-5/PCN and ZnPy-6/PCN exhibit H2 evolution activities of 418 and 585 μmol h?1, corresponding to turnover numbers (TON) of 8845 and 12?381 h?1, respectively. Both of these values are much better that (316 μmol h?1) of ZnPy-1/PCN, which has a TON of 6687 h?1. In addition, ZnPy-5/PCN and ZnPy-6/PCN show apparent quantum yields of 32.6% and 33.1% at 420 nm monochromatic light, and these are much higher than that (10.6%) for ZnPy-1/PCN. Compared with ZnPy-5, the two N atoms of the pseudo-pyrimidines in ZnPy-6 are further away from the porphyrin macrocycle, which can more effectively combine with the sacrificial reagent and g-C3N4, thus promoting dye regeneration and the photoexcited charge transfer for delivering better photocatalytic performance. The present results demonstrate that the number and positions of the N atoms in the peripheral substituents of the porphyrin derivatives have a great influence on the photosensitization, and that the fine-tuning of molecular structures is crucial for improving the H2 evolution activity of the dye-sensitized semiconductors.

Graphical abstract: Asymmetric zinc porphyrin derivatives bearing three pseudo-pyrimidine meso-position substituents and their photosensitization for H2 evolution
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