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Lai SW, Hou YJ, Che CM, Pang HL, Wong KY, Chang CK, Zhu N: Electronic spectroscopy, photophysical properties, and emission quenching studies of an oxidatively robust perfluorinated platinum porphyrin. Inorg Chem. 2004 Jun 14;43(12):3724-32.
The highly electron-deficient, beta-octafluorinated meso-tetrakis (pentafluorophenyl)-porphyrin (H (2) F (28) TPP) was metalated with platinum to afford the oxidatively robust luminophore [PtF (28) TPP], and its X-ray structure shows that the porphyrin core exists in a slightly saddle-shaped conformation. The absorption spectrum of [PtF (28) TPP] in CH (2) Cl (2) displays a near-UV Soret band (B) at 383 nm (epsilon = 2.85 x 10 (5) dm (3) mol (-1) cm (-1)) and two visible Q (1,0) and Q (0,0) bands at 501 (epsilon = 1.45 x 10 (4) dm (3) mol (-1) cm (-1)) and 533 (epsilon = 1.36 x 10 (4) dm (3) mol (-1) cm (-1)) nm, respectively. These absorption bands of [PtF (28) TPP] are blue-shifted from those in [PtF (20) TPP] (390, 504, and 538 nm, respectively) and [PtTPP] (401, 509, and 539 nm, respectively). Excitation of [PtF (28) TPP] (complex concentration = 1.5 x 10 (-6) mol 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 micros) and a weak shoulder at 712 nm. Both the emission lifetime and quantum yield vary with solvent polarity, and plots of tau versus E (K) and Phi versus E (K) (where E (K) is the empirical solvent polarity parameter based on the hypsochromic shift of the longest wavelength absorption of the [Mo (CO)(4)[(C (5) H (4) N) HC [double bond] NCH (2) C (6) H (5)]] 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 [PtF (28) TPP] by cyclic voltammetry showed no porphyrin-centered oxidation at potential < or = 1.5 V versus Ag/AgNO (3), demonstrating that [PtF (28) TPP] is more resistant toward oxidation than [PtF (20) TPP] (E (1/2) = 1.33 V) and [PtTPP] (E (1/2) = 0.97 V). The porphyrin-centered reduction of [PtF (28) TPP] occurs at -0.75 and -1.18 V, which is anodically shifted from those at -1.06 and -1.55 V in [PtF (20) TPP], and -1.51 V in [PtTPP], respectively. The excited-state reduction potential of [PtF (28) TPP] is estimated to be 1.49 V versus Ag/AgNO (3). Over 97% of the emission intensity of [PtF (28) TPP] was retained after irradiation with a high power mercury arc lamp (500 W) for 14 h, compared to 90% and 12% for [PtF (20) TPP] and [PtTPP], respectively; hence, [PtF (28) TPP] exhibits superior photostability. Quenching of the emission of [PtF (28) TPP] by oxygen, alcohol, catechol, and butylamine reveals that [PtF (28) TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties. |
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