Electronic spectroscopy, photophysical properties, and emission quenching studies of an oxidatively robust perfluorinated platinum porphyrin

Siu Wai Lai, Yuan Jun Hou, Chi Ming Che, Hei Leung Pang, Kwok Yin Wong, Chi K. Chang, Nianyong Zhu

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Abstract

The highly electron-deficient, β-octafluorinated meso-tetrakis(pentafluorophenyl)-porphyrin (H2F28TPP) was metalated with platinum to afford the oxidatively robust luminophore [PtF28TPP], and its X-ray structure shows that the porphyrin core exists in a slightly saddle-shaped conformation. The absorption spectrum of [PtF28TPP] in CH2Cl2displays a near-UV Soret band (B) at 383 nm (ε = 2.85 × 108dm3mol-1cm-1) and two visible Q(1,0) and Q(0,0) bands at 501 (ε = 1.45 × 104dm3mol-1cm-1) and 533 (ε = 1.36 × 104dm3mol-1cm-1) nm, respectively. These absorption bands of [PtF28TPP] are blue-shifted from those in [PtF20TPP] (390, 504, and 538 nm, respectively) and [PtTPP] (401, 509, and 539 nm, respectively). Excitation of [PtF28TPP] (complex concentration = 1.5 × 10-6mol dm-3) in dichloromethane at the Soret or Q(1,0) or Q(0,0) band gave a phosphorescence with peak maximum at 650 nm (lifetime = 5.8 μs) and a weak shoulder at 712 nm. Both the emission lifetime and quantum yield vary with solvent polarity, and plots of τ versus EKand Φ versus EK(where EKis the empirical solvent polarity parameter based on the hypsochromic shift of the longest wavelength absorption of the [Mo(CO)4{(C5H4N)HC=NCH2C6H5}] complex with increasing solvent polarity; see: Kamlet, M. J.; Abboud, J. L. M.; Taft, R. W. Prog. Phys. Org. Chem. 1981, 13, pp 485-630) show linear correlation, indicating that the emission is sensitive to the local environment/ medium. Electrochemical studies on [PtF28TPP] by cyclic voltammetry showed no porphyrin-centered oxidation at potential ≤ 1.5 V versus Ag/AgNO3, demonstrating that [PtF28TPP] is more resistant toward oxidation than PtF20-TPP] (E1/2= 1.33 V) and [PtTPP] (E1/2= 0.97 V). The porphyrin-centered reduction of [PtF28TPP] occurs at -0.75 and -1.18 V, which is anodically shifted from those at -1.06 and -1.55 V in [PtF20TPP], and -1.51 V in [PtTPP], respectively. The excited-state reduction potential of [PtF28TPP] is estimated to be 1.49 V versus Ag/AgNO3. Over 97% of the emission intensity of [PtF28TPP] was retained after irradiation with a high power mercury arc lamp (500 W) for 14 h, compared to 90% and 12% for [PtF20TPP] and [PtTPP], respectively; hence, [PtF28TPP] exhibits superior photostability. Quenching of the emission of [PtF28TPP] by oxygen, alcohol, catechol, and butylamine reveals that [PtF28TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties.
Original languageEnglish
Pages (from-to)3724-3732
Number of pages9
JournalInorganic Chemistry
Volume43
Issue number12
DOIs
Publication statusPublished - 14 Jun 2004

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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