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

Article abstract of DOI:10.1021/ic049902h

The highly electron-deficient, β-octafluorinated meso-tetrakis(pentafluorophenyl)-porphyrin (H₂F₂₈TPP) was metalated with platinum to afford the oxidatively robust luminophore [PtF ₂₈TPP], and its X-ray structure shows that the porphyrin core exists in a slightly saddle-shaped conformation. The absorption spectrum of [PtF ₂₈TPP] in CH₂Cl₂ displays a near-UV Soret band (B) at 383 nm (ε = 2.85 × 10⁸ 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 E_K and Φ 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{(C₅H ₄N)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/AgNO ₃, demonstrating that [PtF₂₈TPP] 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 ₂₈TPP] 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 [PtF ₂₀TPP] and [PtTPP], respectively; hence, [PtF₂₈TPP] exhibits superior photostability. Quenching of the emission of [PtF ₂₈TPP] by oxygen, alcohol, catechol, and butylamine reveals that [PtF₂₈TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties.

Full text of DOI:10.1021/ic049902h

Inorg. Chem. 2004, 43, 3724−3732
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,§ and
Nianyong Zhu†
Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular
Technology for Drug DiscoVery and Synthesis, The UniVersity of Hong Kong, Pokfulam Road,
Hong Kong SAR, China, Department of Applied Biology and Chemical Technology,
The Hong Kong Polytechnic UniVersity, Hunghom, Kowloon, Hong Kong SAR, China, and
Department of Chemistry, Hong Kong UniVersity of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong SAR, China
Received January 25, 2004
The highly electron-deficient, â-octafluorinated meso-tetrakis(pentafluorophenyl)-porphyrin (H F TPP) was metalated
2
28
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 CH Cl2 displays a
2
3
near-UV Soret band (B) at 383 nm (ꢀ ) 2.85 × 105 dm mol-1 cm-1) and two visible Q(1,0) and Q(0,0) bands at
3
3
501 (ꢀ ) 1.45 × 104 dm mol-1 cm-1) and 533 (ꢀ ) 1.36 × 104 dm mol-1 cm-1) nm, respectively. These
absorption bands of [PtF TPP] are blue-shifted from those in [PtF TPP] (390, 504, and 538 nm, respectively) and
28
20
[PtTPP] (401, 509, and 539 nm, respectively). Excitation of [PtF TPP] (complex concentration ) 1.5 × 10-6 mol
28
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{(C H N)HCdNCH C H }]
5
4
2 6 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 TPP] by cyclic voltammetry showed no porphyrin-centered oxidation at
28
potential e 1.5 V versus Ag/AgNO , demonstrating that [PtF TPP] is more resistant toward oxidation than [PtF -
3
28
20
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 [PtF TPP], and −1.51 V in [PtTPP],
20
respectively. The excited-state reduction potential of [PtF28TPP] is estimated to be 1.49 V versus Ag/AgNO . Over
3
97% of the emission intensity of [PtF TPP] was retained after irradiation with a high power mercury arc lamp (500
28
W) for 14 h, compared to 90% and 12% for [PtF TPP] and [PtTPP], respectively; hence, [PtF TPP] exhibits
20
28
superior photostability. Quenching of the emission of [PtF TPP] by oxygen, alcohol, catechol, and butylamine
28
reveals that [PtF TPP] is an oxidatively robust material with medium-sensitive photoluminescence properties.
28
Introduction
electron-withdrawing substituents at the meso-aryl1 and/or
â-pyrrolic2 positions; for example, the redox potentials of
metalloporphyrins3 are anodically shifted upon incorporation
Halogenated metalloporphyrins are well documented to
be robust toward oxidative degradation. The reactivities and
properties of this class of compounds can be modulated by
(1) (a) Chang, C. K.; Ebina, F. J. Chem. Soc., Chem. Commun. 1981,
778-779. (b) Traylor, P. S.; Dolphin, D.; Traylor, T. G. J. Chem.
Soc., Chem. Commun. 1984, 279-280. (c) Dicken, C. M.; Woon, T.
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1316.
* To whom correspondence should be addressed. E-mail: cmche@hku.hk.
† The University of Hong Kong.
‡ The Hong Kong Polytechnic University.
§ Hong Kong University of Science and Technology.
3724 Inorganic Chemistry, Vol. 43, No. 12, 2004
10.1021/ic049902h CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/15/2004

Perfluorinated Platinum Porphyrin
of halogen substituents. Previous studies showed that direct
substitution at the pyrrolic positions with electron-withdraw-
ing groups has a more pronounced effect on the electro-
chemical properties of porphyrin rings than derivatization
at the meso-aryl periphery.2b,4 â-Pyrrolic substitution also
imparts significant perturbation upon the electronic properties
of the porphyrin ring, which subsequently affects the HOMO
(highest occupied molecular orbital) and LUMO (lowest
occupied molecular orbital) levels of the corresponding
metalloporphyrins.5 The increase in redox potentials for
metalloporphyrins bearing halogenated substituents can lead
to significant changes in the spectroscopic and photochemical
properties, including improved stability toward oxidative
decomposition which can be useful for application studies
in materials science.6,7
bromo-substituted metalloporphyrins is known to induce red
shifts of the porphyrin absorptions12 due to a decrease in
the HOMO-LUMO energy gap, whereas incorporation of
strongly electron-withdrawing fluorine substituents can de-
stabilize the HOMOs effectively to afford blue-shifted
absorptions.13,14
We now describe the structure and photophysical and
electrochemical properties of the [â-octafluoro-meso-tetrakis-
(pentafluorophenyl)porphyrinato]platinum(II) complex [PtF28-
TPP], and comparisons with [meso-tetrakis(pentafluorophenyl)-
porphyrinato]platinum(II) [PtF20TPP]15 and the nonfluorinated
congener [PtTPP] (H2TPP ) 5,10,15,20-tetraphenylporphy-
rin) are presented. The [PtF28TPP] complex is demonstrated
to be an extremely oxidatively robust phosphorescent mate-
rial with medium-sensitive emission properties.
The perfluorinated 2,3,7,8,12,13,17,18-octafluoro-5,10,15,20-
tetrakis(pentafluorophenyl)porphyrin (H2F28TPP) is of par-
ticular interest in the context of its exceptional stability
toward oxidative degradation and the substantial anodic shift
in oxidation potential for the porphyrinato ring.8 Previous
works on halogenated metalloporphyrins have mainly fo-
cused on structural, electronic and electrochemical properties,
and catalytic activities.9-11 Structural deviation from planarity
in the saddle-shaped molecular structures of chloro- and
Experimental Section
Synthesis and General Procedures. H2F28TPP8 and [PtCl2-
(NCPh)2]16 were prepared by literature methods. [PtF28TPP] was
synthesized by a procedure similar to that for [PtF20TPP].15 H2F28-
TPP (0.50 g, 0.45 mmol) and [PtCl2(NCPh)2] (0.26 g, 0.55 mmol)
were suspended in anhydrous degassed benzonitrile (100 mL). The
mixture was heated at 190 °C under a nitrogen atmosphere for 12
h, and then cooled to room temperature. The solvent was removed
by vacuum distillation, and the crude product was purified by
column chromatography using CH2Cl2 as eluent (0.48 g, 81% yield).
19F NMR (400 MHz, CDCl3): δ -138.31 (8F, m, ortho-C6F5),
-145.03 (8F, s, â-F), -149.65 (4F, t, 3JF-F ) 20.6 Hz, para-C6F5),
-161.10 (8F, m, meta-C6F5). FAB-MS: m/z 1311 [M+], 1293 [M+
- F], 1275 [M+ - 2F]. Anal. Calcd for C44F28N4Pt: C, 40.29; N,
4.27. Found: C, 40.35; N, 4.73.
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S.; Kalsbeck, W. A.; Seth, J.; Lindsey, J. S.; Holten, D.; Bocian, D.
F. J. Mater. Chem. 1997, 7, 1245-1262. (c) Strachan, J.-P.; Gente-
mann, S.; Seth, J.; Kalsbeck, W. A.; Lindsey, J. S.; Holten, D.; Bocian,
D. F. Inorg. Chem. 1998, 37, 1191-1201.
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F.; Yu, S.-C.; Che, C.-M.; Lai, P. T. Appl. Phys. Lett. 2003, 83, 1518-
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Fast atom bombardment (FAB) mass spectra were obtained on
a Finnigan Mat 95 mass spectrometer. 19F (376 MHz) NMR spectra
were recorded on a Bruker Avance 400 FT-NMR spectrometer with
chemical shift (in ppm) relative to trifluoroacetic acid. Elemental
analyses were performed by the Institute of Chemistry at the
Chinese Academy of Sciences, Beijing. Cyclic voltammetry was
performed using a Bioanalytical Systems (BAS) model 100 B/W
electrochemical analyzer. The electrochemical cell was a conven-
tional two-compartment cell with a glassy carbon disk as the
working electrode, a Ag|AgNO3 (0.1 M) electrode as the reference
electrode, and a platinum wire as the counter electrode. Tetra-
butylammonium hexafluorophosphate (0.1 M) was used as the
supporting electrolyte. The ferrocenium/ferrocene was used as
internal reference and was observed at 0.19 V versus the Ag/AgNO3
electrode. The E1/2 values were taken as the average of the cathodic
and anionic peak potentials for the oxidative and reductive waves.
(11) (a) Hodge, J. A.; Hill, M. G.; Gray, H. B. Inorg. Chem. 1995, 34,
809-812. (b) Grinstaff, M. W.; Hill, M. G.; Birnbaum, E. R.; Schaefer,
W. P.; Labinger, J. A.; Gray, H. B. Inorg. Chem. 1995, 34, 4896-
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1997, 62, 1588-1593. (c) Smirnov, V. V.; Woller, E. K.; DiMagno,
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S. G. J. Am. Chem. Soc. 2000, 122, 8569-8570. (e) Smirnov, V. V.;
Woller, E. K.; Tatman, D.; DiMagno, S. G. Inorg. Chem. 2001, 40,
2614-2619.
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Dalton Trans. 1993, 3575-3580. (b) Takeuchi, T.; Gray, H. B.;
Goddard, W. A., III. J. Am. Chem. Soc. 1994, 116, 9730-9732. (c)
Ochsenbein, P.; Ayougou, K.; Mandon, D.; Fischer, J.; Weiss, R.;
Austin, R. N.; Jayaraj, K.; Gold, A.; Terner, J.; Fajer, J. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 348-350.
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(14) (a) Spellane, P. J.; Gouterman, M.; Antipas, A.; Kim, S.; Liu, Y. C.
Inorg. Chem. 1980, 19, 386-391. (b) DiMagno, S. G.; Wertsching, A.
K.; Ross, C. R., II. J. Am. Chem. Soc. 1995, 117, 8279-8280. (c)
Leroy, J.; Bondon, A.; Toupet, L.; Rolando, C. Chem. Eur. J. 1997,
3, 1890-1893.
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J. Mater. Chem. 2003, 13, 1362-1366.
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(9) (a) Mandon, D.; Ochsenbein, P.; Fischer, J.; Weiss, R.; Jayaraj, K.;
Austin, R. N.; Gold, A.; White, P. S.; Brigaud, O.; Battioni, P.;
Mansuy, D. Inorg. Chem. 1992, 31, 2044-2049. (b) Birnbaum, E.
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Inorganic Chemistry, Vol. 43, No. 12, 2004 3725

Lai et al.
Table 1. Crystal Data
Photophysical Measurements. Absorption spectra were re-
corded on a Hewlett-Packard HP8453 spectrophotometer. Lumi-
nescence spectra were collected by a Spex Fluorolog-double
spectrophotometer with a Xe arc lamp excitation source and a
Hamamatsu R928P photomultiplier tube. Solution samples for
measurements were degassed with at least four freeze-pump-thaw
cycles. Luminescence quantum yield of [PtF28TPP] was referenced
to [ZnTPP] in benzene (Φ ) 0.033) and calculated according to
the following equation:17
[PtF28TPP]
C44F28N4Pt
1311.57
0.50 × 0.15 × 0.03
monoclinic
P21/c
formula
fw
cryst size, mm3
cryst syst
space group
a, Å
15.402(3)
10.341(2)
28.085(6)
92.07(3)
4470.2(16)
4
1.949
3.295
51.12
5657
3337
694
0.050, 0.15
0.97
+0.89, -1.21
b, Å
c, Å
â, deg
V, Å3
2
Iunk Astd nunk
Φunk ) Φstd
Z
(
)(I )(n
)
Aunk
Dc, g cm-3
µ, mm-1
2θmax, deg
no. unique data
std
std
where Φunk is the radiative quantum yield of the sample, Φstd is
the radiative quantum yield of the standard, Iunk and Istd are the
integrated emission intensities of the sample and standard, Aunk and
no. obsd data (I g 2σ(I))
no. variables
b
R,a Rw
A
std are the absorbances of the sample and standard at the excitation
wavelength, and nunk and nstd are the refractive indexes of the sample
and standard solutions (pure solvents were assumed).
GOF
residual F, eÅ-3
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
2
The emission lifetimes were measured by a quanta ray DCR-3
pulsed Nd:YAG laser system (pulse output 355 nm, 6 ns). The
emission signals were collected by Hamamatsu R928 photomulti-
plier tube. Time-resolved difference absorption spectra were
recorded after excitation of the sample in a degassed solution with
a 8 ns laser pulse at λ ) 355 nm. The monitoring beam provided
by a 300 W continuous-wave xenon lamp was oriented perpen-
dicular to the direction of the laser pulse. The absorption signal at
each wavelength was collected with a SpectraPro-275 monochro-
mator operating with 2 mm slits, with the signal recorded to a
Tektronix TDS 350 oscilloscope. The optical difference spectrum
was generated point-by-point by monitoring at individual wave-
lengths.
data and details of data collection and refinement are summarized
in Table 1. Diffraction data of [PtF28TPP] were collected on a MAR
diffractometer with graphite monochromatized Mo KR radiation
(λ ) 0.71073 Å). The images were interpreted and intensities
integrated using the program DENZO.21 The structure was solved
by direct methods employing the SHELXS-9722 program. The Pt
atom was located according to direct methods. The positions of
the other non-hydrogen atoms were found after successful refine-
ment by full-matrix least-squares using the program SHELXL-9723
on PC. One crystallographic asymmetric unit consists of one
formula unit.
Luminescent Sensing Films. A series of solutions of [PtF28-
TPP] with concentrations ranging from 1.67 × 10-5 to 1.67 × 10-4
mol dm-3 were prepared from their stock solutions (5 × 10-4 mol
dm-3) in tetrahydrofuran (THF) by transferring the required volume
of complex solution and making up to a total of 1.5 mL with THF.
Silicone rubber (0.2 g) was added to a solution, and the mixture
was sonicated for 1 h. The resulting homogeneous paste (0.3 mL)
was pipetted into a glass cell, which contained short glass tubing
(11 mm in diameter × 10 mm in height) placed on the top of a
glass slide. The cell was allowed to stand for 24 h for evaporation
of solvent and completion of polymerization to give a film of about
0.2 mm in thickness. The complex concentration in each film was
calculated by dividing the amount (in molar quantity) of the
complex with the final volume of the sensing film.
For oxygen sensing experiments, the above glass cell with the
platinum-porphyrin-containing film was mounted to a flow cell,
and the oxygen concentration in the gas stream to the flow cell
was regulated by controlling the relative flow rate of oxygen to
nitrogen gas as previously described.18 The film was aligned at 45°
with respect to the excitation light source in the spectrofluorimeter.
For alcohol sensing experiments, alcohol vapor of various concen-
trations in nitrogen gas stream were produced by diffusion tube
method.19 The experimental setup had been reported previously.20
X-ray Crystallography. Crystals of [PtF28TPP] were obtained
by slow diffusion of hexane into a dichloromethane solution. Crystal
Results
Synthesis and Characterization. The H2F28TPP porphy-
rin was prepared8 according to Lindsey’s method,24 by acid-
catalyzed condensation of 3,4-difluoropyrrole25 with pen-
tafluorobenzaldehyde followed by oxidation with 2,3-dichloro-
5,6-dicyano-1,4-benzoquinone (DDQ). A solution of H2F28TPP
and [PtCl2(NCPh)2] in benzonitrile was heated at reflux to
afford [PtF28TPP] in ca. 80% yield as a dark red crystalline
solid, which exhibits good solubility in common organic
solvents including hexane, benzene, acetonitrile, and ethanol.
The 19F NMR spectrum of [PtF28TPP] in CDCl3 shows peaks
in the -138.31 to -161.10 ppm range, comparable to the
related values for H2F28TPP and [ZnF28TPP].8b,e The fluorine
resonances from all four meso-aryl rings appear to be
equivalent in the 19F NMR spectra, whereas the eight
â-pyrrolic fluorine atoms appear as one singlet signal, thus
suggesting that the structure of [PtF28TPP] contains a high
degree of symmetry.
(21) Otwinowski, Z.; Minor, W. In Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Carter, C. W., Jr., Sweet, R. M., Eds.;
Methods in Enzymology Vol. 276, Macromolecular Crystallography
part A; Academic Press: New York, 1997; pp 307-326.
(22) SHELXS97: Sheldrick, G. M. SHELX97, Programs for Crystal
Structure Analysis; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(17) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991-1024.
(18) Lee, W. W.-S.; Wong, K.-Y.; Li, X.-M.; Leung, Y.-B.; Chan, C.-S.;
Chan, K. S. J. Mater. Chem. 1993, 3, 1031-1035.
(19) Altshuller, A. P.; Cohen, I. R. Anal. Chem. 1960, 32, 802-810.
(20) Lu, W.; Chan, M. C. W.; Zhu, N.; Che, C.-M.; He, Z.; Wong, K.-Y.
Chem. Eur. J. 2003, 9, 6155-6166.
(23) SHELXL97: Sheldrick, G. M. SHELX97, Programs for Crystal
Structure Analysis; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(24) Lindsey, J. S.; Schreiman, I. C.; Hsu, H. C.; Kearney, P. C.;
Marguerettaz, A. M. J. Org. Chem. 1987, 52, 827-836.
(25) Leroy, J.; Wakselman, C. Tetrahedron Lett. 1994, 35, 8605-8608.
3726 Inorganic Chemistry, Vol. 43, No. 12, 2004

Perfluorinated Platinum Porphyrin
Figure 1. (a) Perspective view of [PtF28TPP] (30% probability ellipsoids). Average bond lengths (Å) and angles (deg): Pt-N 2.008, N-CR 1.398, CR-Câ
1.423, Câ-Câ 1.337, CR-Cmeso 1.363; CR-Ν-CR 109.0, N-CR-Câ 106.2, N-CR-Cmeso 126.6, CR-Câ-Câ 109.3, CR-Cmeso-CR 123.6, N(1)-Pt(1)-
N(3) 174.8, N(3)-Pt(1)-N(4) 90.7. Views of (b) [PtF28TPP] and (c) [PtF20TPP]15 (30% thermal ellipsoids) along the porphyrin plane.
Perspective views of [PtF28TPP] orthogonal to and along
the porphyrin plane are shown in part a of Figure 1 and parts
b and c in Figure 1, respectively. The platinum atom is nearly
coplanar with the plane of the porphyrin ring with a slight
displacement of 0.0119 Å. The mean platinum-nitrogen
distance is 2.008 Å, which is comparable to the metal-
nitrogen distances reported for [MF20TPP] analogues (1.996,
2.036, and 2.018 Å for M ) Cu,9b Zn,9b and Pt,15 respec-
Inorganic Chemistry, Vol. 43, No. 12, 2004 3727

Lai et al.
Figure 2. Cyclic voltammograms of [PtF28TPP], [PtF20TPP], and [PtTPP]
(10-4 mol dm-3) in CH2Cl2 containing 0.1 M nBu4NPF6 as supporting
electrolyte. Scan rate: 50 mV s-1
.
Figure 3. UV-vis absorption spectra of [PtF28TPP] (s), [PtF20TPP]
(- - -), and [PtTPP] (‚‚‚) in CH2Cl2 at 298 K. Inset: the low-energy Q(1,0)
and Q(0,0) bands.
tively) and that of 2.059 Å in [ZnF28TPP].8b The molecular
structure reveals a slightly saddle-shaped conformation,
whereby the fluorinated pyrrole rings, which are essentially
planar, lie alternately above and below the porphyrin mean
plane. The largest average deviations of 0.49 Å from the
porphyrin mean plane occur at the â-pyrrolic carbon atoms
(Câ). This is in stark contrast to the virtually planar porphyrin
core reported for [PtF20TPP]15 (Figure 1c), in which case
the platinum atom is located at the crystallographic inversion
center of the molecule. The meso-pentafluorophenyl rings
in [PtF28TPP] are essentially orthogonal to the porphyrin core,
like those in [PtF20TPP].15 In the crystal lattice of [PtF28-
TPP], intermolecular nonbonded C‚‚‚F contacts between
meso-aryl fluorine atoms and R- or â-pyrrolic carbon
(average 3.09 Å, shortest 3.02 Å) and between adjacent meso-
pentafluorophenyl rings (average 3.1 Å) are observed above
and below the porphyrin plane.
-1.55 V). For [PtTPP], the first reduction wave occurs at
an E1/2 value of -1.51 V.
Absorption Spectroscopy. The UV-vis absorption data
of [PtF28TPP], [PtF20TPP], and [PtTPP] in various solvents
are listed in Table 2, and their spectra in dichloromethane
are shown in Figure 3. The [PtF28TPP] complex exhibits a
near-UV Soret band (B) at 383 nm and two Q(1,0) and
Q(0,0) bands at 501 and 533 nm, respectively, in dichlo-
romethane. The relative extinction coefficients for the Q(0,0)
and Q(1,0) transitions of the three complexes are listed in
Table 2 and portrayed in Figure 3 (inset). The ratio of the ꢀ
values for [PtF28TPP] (0.94) is slightly smaller than that of
[PtF20TPP] (1.27), while both are significantly larger than
that of [PtTPP] (0.30) in CH2Cl2 solution. This is consistent
with the Gouterman four-orbital parameters26 and Shelnutt
and Oritz’s27 quantitative method of analysis, which rational-
ize the substituent effect upon the π-π* transitions of
metalloporphyrins. The B(0,0)-Q(0,0) spectral splitting
decreases in the order [PtF28TPP] > [PtF20TPP] > [PtTPP].
The solvent effect on the absorption spectrum of [PtF28-
TPP] has been examined (Table 2). When the solvent is
changed from dichloromethane to pyridine, the Soret band
absorption red-shifts by 270 cm-1, but the shift in the Q-band
energies is negligible. The ꢀ values for the Soret absorption
recorded in various solvents lie between 2.5 × 105 and 3.1
× 105 dm3 mol-1 cm-1, whereas the Q-band absorption bands
The electrochemical properties of [PtF28TPP], [PtF20TPP],
and [PtTPP] in CH2Cl2 solution have been investigated by
n
cyclic voltammetry at 298 K using 0.1 M Bu4NPF6 as
supporting electrolyte, and are depicted in Figure 2. For
[PtF28TPP], there is no oxidation peak even up to a potential
of 1.5 V, whereas for [PtF20TPP] and [PtTPP], there is a
reversible oxidation wave at E1/2 ) 1.33 and 0.97 V,
respectively. The two porphyrinato ring-centered reduction
waves of [PtF28TPP] (-0.75 and -1.18 V) occur at potentials
anodically shifted from those of [PtF20TPP] (-1.06 and
Table 2. Absorption Data of [PtF28TPP], [PtF20TPP], and [PtTPP] in Various Solvents
λ
max/nm (ꢀ/dm3 mol-1 cm-1
)
Q(0,0)/Q(1,0)
B(0,0)-Q(0,0)
splitting ν/cm-1
complex
solvent
hexane
Soret (B band)
Q(1,0) and Q(0,0) bands
ꢀ ratio
[PtF28TPP]
382 (312 000)
384 (295 000)
383 (285 000)
386 (260 000)
383 (292 000)
381 (286 000)
381 (289 000)
382 (256 000)
387 (250 000)
390 (323 000)
394 (220 000)
401 (329 000)
500 (16 400), 532 (14 400)
501 (18 900), 532 (17 600)
501 (14 500), 533 (13 600)
502 (14 300), 533 (12 900)
502 (24 200), 535 (22 300)
501 (14 000), 533 (12 700)
500 (14 200), 532 (12 800)
500 (12 300), 534 (10 800)
502 (14 600), 535 (13 100)
504 (23 200), 538 (29 400)
509 (13 400), 540 (18 100)
509 (33 600), 539 (9960)
0.88
0.93
0.94
0.90
0.92
0.91
0.90
0.88
0.90
1.27
1.35
0.30
7381
7245
7348
7145
7418
7485
7450
7451
7148
7054
6862
6385
CCl4
CH2Cl2
benzene
THF
acetonitrile
MeOH
EtOH
pyridine
CH2Cl2
Benzene
CH2Cl2
[PtF20TPP]
[PtTPP]
3728 Inorganic Chemistry, Vol. 43, No. 12, 2004

Perfluorinated Platinum Porphyrin
Table 3. Solution Emission Data for [PtF28TPP], [PtF20TPP], and
[PtTPP] in Various Solvents (Concentration 1.5 × 10-6 mol dm-3
)
complex
solvent
λ
em/nm
Φ
τb/µs
EK
[PtF28TPP]
hexane
651, 715 (sh)
648, 705 (sh)
650, 712 (sh)
651, 704 (sh)
650, 715 (sh)
651, 718 (sh)
650, 715 (sh)a
652, 717 (sh)a
nonemissive
647, 705 (sh)
647, 710 (sh)
649, 710 (sh)
647, 705 (sh)
647, 705 (sh)
665, 730 (sh)
0.076
0.047
0.043
0.033
0.028
0.012
0.0003
0.0002
9.3
6.2
48.9
49.9
53.9
53.4
55.4
59.0
56.3
55.3
57.0
48.9
53.9
53.4
59.0
56.3
53.9
CCl4
CH2Cl2
benzene
THF
acetonitrile
MeOH
EtOH
pyridine
hexane
CH2Cl2
benzene
acetonitrile
MeOH
CH2Cl2
5.8
5.3
4.4
1.3
<0.1c
<0.1c
[PtF20TPP]
[PtTPP]
0.081
0.088
0.070
0.084
0.045
0.046
52
60
26
55
26
50
a Weakly emissive. b Measured at λmax
.
c Estimated lifetime due to weak
emission.
Figure 5. Plot of emission lifetime (a) and quantum yield (b) for [PtF28-
TPP] against the EK scale.
performed in the concentration range 1.98 × 10-6 to 3.96
× 10-5 mol dm-3 in CH2Cl2 at 298 K, but no detectable
quenching effect was found. The 77 K glassy emission of
[PtF28TPP] in MeOH/EtOH (1:4) shows blue-shifted emis-
sion with an intense peak maximum at λmax 639 nm (τ ) 56
µs) and two weaker bands at 691 and 708 nm. In deoxy-
genated hexane solution, the emission lifetime and quantum
yield of [PtF28TPP] are 9.3 µs and 0.076, which decrease to
0.4 µs and 0.004, respectively, under aerated conditions.
The effect of solvent upon the emission of [PtF28TPP] and
[PtF20TPP] (complex concentration ) 1.5 × 10-6 mol dm-3)
has been examined (Table 3; see Supporting Information for
spectra). Although the emission maxima for both complexes
are insensitive to solvent polarity, the emission quantum yield
(Φ) for [PtF28TPP] decreases from 0.076 in hexane to <0.001
in methanol and ethanol, while that for [PtF20TPP] shows
only minor solvent dependence (from 0.088 in CH2Cl2 to
0.045 in methanol). In addition, the emission lifetime of
[PtF28TPP] at 298 K exhibits a pronounced solvent depen-
dence and varies from 9.3 µs in hexane to <0.1 µs in
methanol, whereas the emission lifetime of [PtF20TPP] shows
only a slight variation with solvent polarity (range 26-60
µs). We note that a linear correlation is evident between the
polarity of solvent, defined by the EK value (where solvent
polarities are classified with respect to the hypsochromic shift
of the longest wavelength absorption of the [Mo(CO)4-
{(C5H4N)HCdNCH2C6H5}] complex28), and the lifetime or
quantum yield of [PtF28TPP], as depicted in Figure 5a,b.
Excited-State Properties. The triplet excited-state absorp-
tion spectrum of [PtF28TPP] (1.5 × 10-6 mol dm-3) in
Figure 4. Excitation and emission spectra of [PtF28TPP] in dichlo-
romethane at 298 K (concentration 1.5 × 10-6 mol dm-3, λex 390 nm;
emission spectra of [PtF20TPP] and [PtTPP] also shown).
exhibit ꢀ values ranging from 1.0 × 104 to 2.4 × 104 dm3
mol-1 cm-1. The relative Q(0,0)/Q(1,0) intensity ratios vary
in the range 0.88-0.94, and the B(0,0)-Q(0,0) spectral
splitting occurs between 7145 and 7485 cm-1.
Luminescence Spectroscopy. The complexes [PtF28TPP],
[PtF20TPP], and [PtTPP] show intense phosphorescence in
solutions at room temperature; their photophysical data are
listed in Table 3. Figure 4 shows the excitation and emission
spectra of [PtF28TPP] in CH2Cl2 at 298 K. The emission
profile of [PtF28TPP] is nearly identical to that of [PtF20-
TPP]. With reference to previous work,15 the narrow peak
at 650 nm (680 cm-1 full width at half-maximum intensity)
and weak band at 712 nm are attributed to the excited triplet
states of the Q-bands. When monitoring the emission
wavelength at 650 nm, the excitation spectrum exhibits an
intense Soret band at 382 nm and the Q(1,0) and Q(0,0)
bands at 500 and 532 nm, respectively, which correspond
to the ground-state absorption spectrum in Figure 3. A self-
quenching experiment on the emission of [PtF28TPP] was
(26) Gouterman, M. In The Porphyrins; Dolphin, D., Ed.; Academic: New
York, 1978; Vol. III, pp 1-165.
(27) Shelnutt, J. A.; Ortiz, V. J. Phys. Chem. 1985, 89, 4733-4739.
Inorganic Chemistry, Vol. 43, No. 12, 2004 3729

Lai et al.
Table 4. Rate Constants for the Quenching of [PtF28TPP] by Various
Substrates in Dichloromethane unless Otherwise Stated
quencher
kq/dm3 mol-1 s-1
methanol
N,N-dimethylformamide
cyclohexene
deuterated cyclohexene (C6D10)
pyridine
1.34 × 106
7.56 × 106
3.16 × 107
3.19 × 107
2.33 × 108
1.30 × 109
2.39 × 109
2.61 × 109
5.64 × 108
3.32 × 109
triphenylphosphine
tetrahydrothiophene
1,2,4-trimethoxybenzene
butylaminea
catechola
a Measured in acetonitrile.
which can be attributed to the formation of the 1,2,4-
trimethoxybenzene radical cation.30 Using Stern-Volmer
analysis, the quenching rate constant of [PtF28TPP] by 1,2,4-
trimethoxybenzene was determined to be 2.61 × 109 dm3
mol-1 s-1.
Figure 6. Time-resolved differential absorption spectra of [PtF28TPP] (1.5
× 10-6 mol dm-3) monitored at 3.5-20 µs after pulsed excitation at λ )
355 nm in degassed hexane.
The emission of [PtF28TPP] in solution is sensitive to the
presence of substrates. Quenching experiments were per-
formed in dichloromethane or acetonitrile solutions upon
addition of different substrates at 298 K and linear Stern-
Volmer plots of 1/τ of [PtF28TPP] against substrate concen-
tration have been obtained (quenching rate constants, kq/dm3
mol-1 s-1 determined in the Supporting Information). The
results of quenching rate constants (kq) are listed in Table 4.
The kq value for deuterated cyclohexene (C6D10) in dichlo-
romethane is 3.19 × 107 dm3 mol-1 s-1, which is nearly
identical to that of 3.16 × 107 dm3 mol-1 s-1 for cyclohexene
(C6H10), suggesting no C-H isotope effect for the quenching
process. The kq values for the emission of [PtF28TPP] and
[PtF20TPP] (∼2 × 10-6 mol dm-3) by pyridine in dichlo-
romethane solution were found to be 2.33 × 108 and 2.17
× 107 dm3 mol-1 s-1, respectively.
deoxygenated hexane was recorded 3.5-20 µs after laser
flash photolysis of the solution at 355 nm. As depicted in
Figure 6, the difference absorption spectrum shows an
absorption maximum at 410 nm, which decays with a half-
life of 8.9 µs. The solvent effect on the triplet excited-state
absorption spectrum has been examined: the peak maximum
remains at ∼410 nm, while the decay half-life was found to
be 5.1 and 1.5 µs in CH2Cl2 and CH3CN solution, respec-
tively (see Supporting Information). These decay lifetimes
closely match the corresponding emission lifetimes (Table
3; 9.3 µs in hexane, 5.8 µs in CH2Cl2, and 1.3 µs in CH3-
CN). We attribute the 410 nm band to the intraligand 3(π,π*)
excited state of [PtF28TPP].29 In aerated dichloromethane
solution (2.5 × 10-6 mol dm-3), the differential absorption
spectrum remains the same except that the 410 nm band
decays with a shorter half-life (1.1 µs) due to quenching of
the [PtF28TPP] emission by oxygen (see later).
The excited-state potential of [PtF28TPP] can be estimated
using the spectroscopic and electrochemical data. The 0-0
transition energy E0-0, which can be approximated from the
overlap of the emission and excitation spectra, occurs at ca.
2.24 eV, and E1/2 for [PtF28TPP + e- f (PtF28TPP)-] is
-0.75 V versus Ag/AgNO3. Thus, the triplet excited state
of [PtF28TPP] is a powerful oxidant with the E1/2 for [(PtF28-
TPP)* + e- f (PtF28TPP)-] estimated to be ca. 1.49 V
versus Ag/AgNO3. The powerful oxidizing nature of [PtF28-
TPP]* has been demonstrated by the quenching of the
emission by 1,2,4-trimethoxybenzene, and the quenching
mechanism was found to occur via an electron-transfer
pathway. The differential absorption spectrum of a degassed
acetonitrile solution of [PtF28TPP] (1.5 × 10-6 mol dm-3)
and 1,2,4-trimethoxybenzene (5 mol dm-3), recorded after
excitation, shows a prominent absorption band at 450 nm,
Photostability and Luminescent Quenching Studies.
The photostabilities of [PtF28TPP], [PtF20TPP], and [PtTPP]
in thin silicone film were examined by broad-band irradiation
with a high-power mercury arc lamp (500 W) for 14 h under
aerobic conditions (Figure 7). Both [PtF28TPP] and [PtF20-
TPP] exhibited high photostability with 97% and 90%,
respectively, of their emission intensities retained after
irradiation. In contrast, only 12% of the emission intensity
remained for the nonfluorinated congener [PtTPP] under
identical irradiation conditions.
The sensitivity of the emission of [PtF28TPP] encapsulated
in silicone film toward dioxygen was examined by recording
the relative emission intensity at λmax 645 nm before (I0) and
after (I) purging oxygen (% in vol/vol) into the system
(Figure 8). First, a series of films containing different
concentrations of [PtF28TPP] were used, and the optimal
complex concentration of [PtF28TPP] which gave the highest
sensitivity (highest I0/I ratio) was found to be 0.24 mM. A
linear correlation between the relative emission intensity (I0/
I) of [PtF28TPP] recorded at 645 nm and the concentration
of oxygen (% vol/vol) purged into the system is observed
(Figure 8). Although the Stern-Volmer plots for most
(28) (a) Walther, D. J. Prakt. Chem. 1974, 316, 604-614. (b) Kamlet, M.
J.; Abboud, J. L. M.; Taft, R. W. In Progress in Physical Organic
Chemistry; Taft, R. W., Ed.; Wiley: New York, 1981; Vol. 13, pp
485-630. (c) Reichardt, C. SolVents and SolVent Effects in Organic
Chemistry; Wiley-VCH: Weinheim, 2003; Chapter 7, pp 389-469.
(29) Rodriguez, J.; Kirmaier, C.; Holten, D. J. Am. Chem. Soc. 1989, 111,
6500-6506.
(30) O’Neill, P.; Steenken, S.; Schulte-Frohlinde, D. J. Phys. Chem. 1975,
79, 2773-2779.
3730 Inorganic Chemistry, Vol. 43, No. 12, 2004

Perfluorinated Platinum Porphyrin
Figure 7. Photostability studies on silicone films of [PtF28TPP], [PtF20-
TPP], and [PtTPP]: plot of relative emission intensity versus time of
irradiation.
Figure 9. Alcohol sensitivity of silicone-encapsulated [PtF28TPP]: plot
of relative emission intensity (I0/I) at λmax 645 nm versus exposure to (a)
methanol and (b) ethanol (in ppm).
the [PtF28TPP] film was found to be 36 ppm for methanol
and 13 ppm for ethanol.
Figure 8. Oxygen sensitivity of silicone-encapsulated [PtF28TPP]: plot
of relative emission intensity (I0/I) at λmax 645 nm versus exposure of oxygen
(% in vol/vol).
Discussion
Structural, Photophysical, and Electrochemical Fea-
tures. In the molecular structure of [PtF28TPP], the meso-
pentafluorophenyl substituents are orthogonal to the por-
phyrin core to relieve steric encumbrance between the C6F5
rings and â-pyrrolic fluorine atoms at the porphyrin periph-
ery. The electronic effect of fluorine-substituted phenyl rings
can be inductively transmitted to the porphyrin ring. The
saddle-shaped distortion of the porphyrin core in [PtF28TPP]
(Figure 1b), in contrast to the planar geometry of [PtF20-
TPP] (Figure 1c), implies the presence of additional steric
congestion between the â-pyrrolic fluorine atoms and the
pentafluorophenyl moieties, while the strong σ electron-
withdrawing effect of the eight â-fluorine substituents may
also play a part. This structural distortion is similarly
observed in the [â-octabromo-meso-tetrakis(pentafluorophen-
yl)porphyrinato]zinc(II) complex,34 but only slight ruffling
is present in the structure of [ZnF28TPP].8b
oxygen sensors based on polymer-embedded luminophores
are nonlinear,31 linear calibration plots (I0/I versus concentra-
tion) have previously been reported for platinum porphyrins
encapsulated in silicone rubber32 and PVC matrix.33 The
linear Stern-Volmer plot for [PtF28TPP] can be attributed
to a better mixing of the hydrophobic platinum porphyrin
with silicone rubber, resulting in a more homogeneous
matrix. The I0/I100 ratio for [PtF28TPP] reaches 69 in the
presence of 100% oxygen, which is comparable to those
values reported for other platinum porphyrins.18
Similar studies on the sensitivity of the emission of
silicone-encapsulated [PtF28TPP] film toward methanol or
ethanol were also undertaken. The [PtF28TPP] complex
exhibited a decrease in emission intensity recorded at 645
nm upon exposure to these two alcohols. As depicted in
Figure 9, the plots of relative emission intensities (I0/I)
against the concentration of alcohol vapor (in ppm) are linear
up to alcohol concentrations of 200 and 140 ppm for
methanol and ethanol, respectively. The detection limit of
The Soret absorption at 26110 cm-1 (383 nm) of [PtF28-
TPP] in dichloromethane occurs at a higher energy compared
to that of 25 641 cm-1 (390 nm) for [PtF20TPP] and 24 938
cm-1 (401 nm) for [PtTPP] (Figure 3). Fluorination at
â-pyrrolic positions of the porphyrin macrocycle apparently
induces a significant electron-withdrawing effect, which
(31) Demas, J. N.; DeGraff, B. A.; Coleman, P. B. Anal. Chem. 1999, 71,
793A-800A.
(32) Kavandi, J.; Callis, J.; Gouterman, M.; Khalil, G.; Wright, D.; Green,
E.; Burns, D.; McLachlan, B. ReV. Sci. Instrum. 1990, 61, 3340-
3347.
(34) Marsh, R. E.; Schaefer, W. P.; Hodge, J. A.; Hughes, M. E.; Gray, H.
(33) Hartmann, P.; Trettnak, W. Anal. Chem. 1996, 68, 2615-2620.
B. Acta Crystallogr. 1993, C49, 1339-1342.
Inorganic Chemistry, Vol. 43, No. 12, 2004 3731

Lai et al.
propagates through the macrocyclic ring and substantially
modulates the a2u/a1u orbital energies, resulting in a blue-
shifted Soret absorption. The B(0,0)-Q(0,0) spectral splitting
decreases in the order [PtF28TPP] > [PtF20TPP] > [PtTPP],
which also suggests that the meso-C6F5 rings and â-fluorine
substituents are effective in removing electron density from
the porphyrinato nitrogen atoms, thereby widening the
HOMO-LUMO gap in the chromophores. The hypsochro-
mic shift in the absorption spectrum of [PtF28TPP] signifies
that the inductive effect of the eight â-fluorine atoms
outweighs the expected bathochromic shift arising from
distortion of the porphyrin core from planarity.
The one-electron redox potentials of porphyrins often
reflect the energy levels of their HOMOs and LUMOs.35
Compared to [PtF20TPP], the cyclic voltammogram of [PtF28-
TPP] shows an anodic shift (Figure 2) in potentials for both
the porphyrinato oxidation and reduction, implying that
â-pyrrolic fluorination removes electron density from the
porphyrin ring. Hence, the [PtF28TPP] complex is easily
reduced and resistant to oxidation relative to its [PtF20TPP]
and [PtTPP] analogues. The estimated excited-state potential
(ca. 1.49 V vs Ag/AgNO3) also signifies that [PtF28TPP] is
a powerful one-electron photo-oxidant.
solvent polarity is intriguing in the development of lumi-
nescent sensing and signaling probes.37 Indeed, quenching
experiments performed in this work revealed relatively high
quenching rate constants for soft and/or electron-rich donors
such as triphenylphosphine (1.30 × 109 dm3 mol-1 s-1),
tetrahydrothiophene (2.39 × 109 dm3 mol-1 s-1), catechol
(3.32 × 109 dm3 mol-1 s-1), and butylamine (5.64 × 108
dm3 mol-1 s-1), which approach the diffusion-controlled
limit.
Superior photostability has been observed for [PtF28TPP],
and 97% of emission intensity was retained after 14 h of
broad-band irradiation with a high power mercury arc lamp
(Figure 7). The â-fluorination of the porphyrin core evidently
confers improved photostability. Studies on the sensitivity
of the emission of [PtF28TPP]-incorporated silicone film
toward dioxygen, methanol, or ethanol revealed that, over a
wide concentration range of these substrates, linear calibra-
tion curves of the emission intensity ratio (I0/I) versus
concentration can be obtained (Figures 8 and 9). The I0/I100
ratio of [PtF28TPP] film recorded at 645 nm reached a
maximum value of 69 in the presence of pure oxygen (Figure
8), suggesting the potential use of [PtF28TPP] as a robust
luminescent sensory material for detection of dioxygen.
The emission spectrum of [PtF28TPP] is similar to that of
[PtF20TPP] (Figure 4) with the peak maximum at ∼650 nm
attributed to the excited Q(0,0) triplet state. The emission
lifetime and quantum yield (τ ranges from <0.1 to 9.3 µs
and Φ from <0.001 to 0.076) of [PtF28TPP] decrease notably
from those observed for [PtF20TPP] (τ ) 26-60 µs; Φ )
0.045-0.088) in various solvents. Interestingly, both the
emission lifetime and quantum yield of [PtF28TPP] decrease
in a linear fashion with an increase in solvent polarity
expressed as EK values (Figure 5), while [PtF20TPP] shows
no such correlation. A comparison between the quenching
rate constants by pyridine on the emission of [PtF28TPP] and
[PtF20TPP] (2.33 × 108 and 2.17 × 107 dm3 mol-1 s-1,
respectively) shows that the former is more prone to
quenching by nitrogen donors. This suggests the structural
and electronic differences of [PtF28TPP] from [PtF20TPP] (as
discussed above) promote its solvent-induced nonradiative
decay rates. First, the incorporation of fluorine atoms at both
meso-phenyl and â-pyrrolic carbons in [PtF28TPP] causes
deviation of the porphyrin core from planarity; this structural
change may increase the dipole moment in the excited state,
resulting in a more pronounced effect with change of
solvent.36 Second, the fluorine substituents at the â-pyrrolic
positions of [PtF28TPP] can confer electron-withdrawing
effects upon the porphyrinato ring, which in turn promote
porphyrin-solvent/substrate interactions in the excited state.
Also, specific solvation might induce variations in the degree
of ruffling for the structure of [PtF28TPP] in the solvent.
Emission Quenching Studies of [PtF28TPP]. The notice-
ably higher sensitivity of the emission of [PtF28TPP] toward
Conclusion
Spectroscopic and electrochemical studies on the perflu-
orinated [PtF28TPP] complex indicate that the incorporation
of fluorine atoms at the â-positions of the porphyrin ring
has a modest effect upon the electronic properties, but the
oxidation potentials are markedly increased for both the
ground and excited states, which enhances the resistance
toward oxidative degradation. The triplet excited state of
[PtF28TPP] is a powerful oxidant. The â-fluoro substituents
in [PtF28TPP] render blue-shifts for the Soret and Q-bands
in the absorption spectrum. Good photostability and remark-
able solvent dependence of emission lifetime and quantum
yield for [PtF28TPP] have been observed. Finally, the
emission quenching of [PtF28TPP] has been demonstrated
by diminution of the emission intensity upon exposure to
oxygen and alcohol. Employment of platinum-porphyrin
derivatives immobilized in polymer or Nafion as oxygen
sensors was documented previously.38
Acknowledgment. We are grateful for financial support
from The University of Hong Kong, Research Grants Council
of the Hong Kong SAR, China [HKU 7039/03P], and Area
of Excellence Scheme (AoE/P-10/01) of the University
Grants Committee of the Hong Kong SAR, China.
Supporting Information Available: Crystal data for [PtF28-
TPP] (CIF), emission spectra of [PtF28TPP] and [PtF20TPP] in
various solvents, Stern-Volmer plots of [PtF28TPP] using different
electron-donating quenchers, and time-resolved differential absorp-
tion spectra of [PtF28TPP]. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC049902H
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