Photosensitizers for H₂ Evolution Based on Charged or Neutral Zn and Sn Porphyrins

Abstract

We report a comparison between a series of zinc and tin porphyrins as photosensitizers for photochemical hydrogen evolution using cobaloxime complexes as molecular catalysts. Among all the chromophores tested, only the positively charged zinc porphyrin, [ZnTMePyP4+]­Cl4, and the neutral tin porphyrin derivatives, Sn­(OH)2TPyP, Sn­(Cl2)­TPP-[COOMe]4, and Sn­(Cl2)­TPP-[PO­(OEt)2]4, were photocatalytically active. Hydrogen evolution was strongly affected by the pH value as well as the different concentrations of both the sensitizer and the catalyst. A comprehensive photophysical and electrochemical investigation was conducted in order to examine the mechanism of photocatalysis. The results derived from this study establish fundamental criteria with respect to the design and synthesis of porphyrin derivatives for their application as photosensitizers in photoinduced hydrogen evolution.

Self-Assembly of Porphyrin Dipeptide Conjugates toward Hydrogen Production

“…Potentially, the SnPy 3 P-FF−Co mixture, following formation of the porphyrin triplet, undergoes an electron transfer (with an electron being transferred to the cobaloxime catalyst) producing a charge separated state (CSS) (Figure 9). 42,44,55 This fact is in support of the assumption that the porphyrin triplet participates in the hydrogen production pathway demonstrated with SnPy 3 P-FF−Co.…”

“…This might be attributed to fact that the later nanospheres were more well defined and had a bigger diameter (Figures and ). Our system exhibits similar and in some cases improved efficiency compared to analogous homogeneous photocatalytic systems, which utilize cobaloxime catalysts and porphyrin photosensitizers. , …”

“…Our system exhibits similar and in some cases improved efficiency compared to analogous homogeneous photocatalytic systems, which utilize cobaloxime catalysts and porphyrin photosensitizers. 42,44 In order to examine why H 2 production stops after 120 h of irradiation, we added extra SnPy 3 P-FF in the photocatalytic experiment after it reached a plateau and we observed the regeneration of the photocatalytic system. However, when an additional amount of the cobaloxime catalyst was inserted, no regeneration was observed.…”

“…Energy diagram depicting the fundamental photophysical processes of porphyrins following excitation in the Soret band (λ exc = 395 nm). Energy values of singlet and triplet states are based on experimental and computational studies. , …”

“…In the present paper, we synthesized a porphyrin-peptide conjugate via the amide coupling of diphenylalanine to a tris­(pyridyl)­porphyrin porphyrin macrocycle in order to convey self-assembling properties to the resulting hybrid. The pyridyl groups were selected because previous reports from our group showed that pyridyl substitution exhibited superior photocatalytic activity. , Two different non-noble metals were introduced inside the porphyrin core with the intention of studying their influence on the formation of supramolecular architectures. To the best of our knowledge, there has been no report so far that examines the effect of the metal inside the porphyrin macrocycle in the self-assembling ability of the porphyrin.…”