Comparison study on the influence of the central metal ions in palladium(II)- and gadolinium(III)-porphyrins for phosphorescence-based oxygen sensing

Lixin Zang, Huimin Zhao, Jianyu Hua, Wenwu Cao, Feng Qin, Jianting Yao, Ye Tian, Yangdong Zheng, Zhiguo Zhang

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

The luminescence and oxygen sensing properties of a series of palladium(ii)- and gadolinium(iii)-porphyrins were evaluated and compared. Spectral analysis indicates that absorption and luminescence of Gd-porphyrins are red-shifted compared to those of Pd-porphyrins. This demonstrates that the energy levels of excited states in Gd-porphyrins are lower than those in the corresponding Pd-porphyrins. Phosphorescence quantum yield of Pd-hematoporphyrin monomethyl ether (HMME) was about 3-fold higher than that of Gd-HMME due to the decreased non-radiative decay rate of triplet states in Pd-HMME, which was confirmed by the longer phosphorescence lifetime of Pd-HMME. This is attributed to the higher first excited triplet state (T1) in Pd-HMME as compared to that of Gd-HMME. However, the phosphorescence intensity and lifetime responses of Gd-HMME to oxygen were larger than those of Pd-HMME. To understand this difference, oxygen quenching constants (kq) of Gd- and Pd-HMME were evaluated and were found to be 4972.9 and 26.4 s-1, respectively. The huge difference in kq between the two species is responsible for their disparate oxygen responses. We suggest that the greater kq of Gd-HMME results from the better energy matching between its T1 (12&658-14&006 cm-1) and the second excited state (13&123 cm-1) of oxygen, which was demonstrated by the higher singlet oxygen quantum yield of Gd-HMME. The same phenomena (spectral red-shifts, lower phosphorescence quantum yields, shorter lifetimes, and larger oxygen responses) were also observed upon substituting Pd(ii) by Gd(iii) in other porphyrins studied in this work.

Original languageEnglish (US)
Pages (from-to)9581-9587
Number of pages7
JournalJournal of Materials Chemistry C
Volume4
Issue number40
DOIs
StatePublished - Jan 1 2016

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Materials Chemistry

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