Electronic Spectroscopy, Photophysical Properties, and Emission Quenching Studies of an Oxidatively Robust Perfluorinated Platinum Porphyrin

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 CH2Cl2 displays a
near-UV Soret band (B) at 383 nm (ε = 2.85 × 105 dm3 mol-1 cm-1) and two visible Q(1,0) and Q(0,0) bands at
501 (ε = 1.45 × 104 dm3 mol-1 cm-1) and 533 (ε = 1.36 × 104 dm3 mol-1 cm-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 × 10-6 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 μs) and a weak shoulder at 712 nm. Both the emission lifetime and quantum yield vary with
solvent polarity, and plots of τ versus EK and Φ versus EK (where EK is 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 [PtF20TPP] (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.