Comparison study on the influence of the central metal ions in palladium(ii)- and gadolinium(iii)-porphyrins for phosphorescence-based oxygen sensing. Issue 40 (3rd October 2016)

• Record Type: Journal Article
• Authors: Zang, Lixin; Zhao, Huimin; Hua, Jianyu; Cao, Wenwu; Qin, Feng; Yao, Jianting; Tian, Ye; Zheng, Yangdong; Zhang, Zhiguo
• Is Part Of: Journal of materials chemistry. Volume 4:Issue 40(2016)
• Page Start: 9581
• Page End: 9587
• Publication Date: 2016-10-03
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c6tc01762b
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Gd-porphyrins exhibit longer phosphorescence wavelength and greater oxygen sensitivity as compared to Pd-porphyrins. 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 ( k q ) of Gd- and Pd-HMME were evaluated and were found to be 4972.9 and 26.4 s −1, respectively. The huge difference in k q between the two species is responsible for their disparate oxygen responses. We suggest that the greater k q 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.