Oxygen-sensing properties of 5, 10, 15, 20-tetraphenylporphinato platinum(II) and palladium(II) covalently bound on poly(isobutyl-co-2,2,2-trifluoroethyl methacrylate)

Article abstract of DOI:10.1002/pola.23818

A novel methacrylate monomer bearing 5, 10, 15, 20tetraphenylporphyrinato palladium(II) (PdTPP) (monomer 1a) was synthesized and copolymerized with isobutyl methacrylate (IBM) and 2,2,2-trifluoroethyl methacrylate (TFEM) to give poly (IBM-co-TFEM) bearing PdTPP (copolymer 2a) as a dye-conjugated oxygen-permeable polymer for pressure-sensitive paint applications. The introduction of PdTPP into copolymer 2a was confirmed by UV-vis spectroscopy and extended X-ray absorption fine structure analysis. The Stern-Volmer plots of the copolymer 2a and a mixture of PdTPP and poly(IBM-co-TFEM) both showed downward curvature, unlike that of the platinum complex analogue (copolymer 2b) previously reported. The plots were successfully fitted with a two-site model to give two distinct Stern-Volmer constants (K_sv1 andK_sv2 and the partition ratio f₁. Interestingly, the f₁ values for the copolymer 2a were almost constant at about 0.98, whereas those of the mixture of PdTPP and poly(IBM-co-TFEM) increased from 0.889 to 0.967 as the temperature was increased. This finding suggests that there are two distinct microheterogeneities, one temperature-dependent and the other temperature-independent, in the mixture of PdTPP and poly(IBM-co-TFEM). The dye-conjugation approach effectively eliminates the temperature-dependent, but not the temperature-independent microheterogeneity. The luminescence decays of copolymers 2a and 2b and the corresponding mixtures in the absence of oxygen indicated that the temperature-dependent microheterogeneity involves an oxygen diffusion process, whereas the temperature-independent one appears to be inherent nature in PdTPP.

Full text of DOI:10.1002/pola.23818

Oxygen-Sensing Properties of 5,10,15,20-Tetraphenylporphinato
Platinum(II) and Palladium(II) Covalently Bound on
Poly(isobutyl-co-2,2,2-trifluoroethyl methacrylate)
MAKOTO OBATA,1 NORIKO MATSUURA,2 KAZUNORI MITSUO,3 HIROKI NAGAI,4 KEISUKE ASAI,4 MASAFUMI HARADA,5
SHIHO HIROHARA,6 MASAO TANIHARA,6 SHIGENOBU YANO7
1Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Kofu 400-8510, Japan
2Faculty of Science, Nara Women’s University, Nara 630-8506, Japan
3Japan Aerospace Exploration Agency, Tokyo 182-852, Japan
4Department of Aeronautics and Space Engineering, Tohoku University, Sendai 980-8579, Japan
5Faculty of Human Life and Environment, Nara Women’s University, Nara 630-8506, Japan
6Graduate School of Materials Science, Nara Institute of Science and Technology, Nara 630-0101, Japan
7Endowed Research Section, Photomedical Science, Innovative Collaboration Center, Kyoto University, Kyoto 615-8520, Japan
Received 4 July 2009; accepted 6 November 2009
DOI: 10.1002/pola.23818
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A novel methacrylate monomer bearing 5,10,15,20-
tetraphenylporphyrinato palladium(II) (PdTPP) (monomer 1a)
was synthesized and copolymerized with isobutyl methacrylate
(IBM) and 2,2,2-trifluoroethyl methacrylate (TFEM) to give poly
(IBM-co-TFEM) bearing PdTPP (copolymer 2a) as a dye-conju-
gated oxygen-permeable polymer for pressure-sensitive paint
applications. The introduction of PdTPP into copolymer 2a was
confirmed by UV–vis spectroscopy and extended X-ray absorp-
tion fine structure analysis. The Stern–Volmer plots of the co-
polymer 2a and a mixture of PdTPP and poly(IBM-co-TFEM)
both showed downward curvature, unlike that of the platinum
complex analogue (copolymer 2b) previously reported. The
plots were successfully fitted with a two-site model to give two
distinct Stern–Volmer constants (KSV1 and KSV2) and the parti-
tion ratio f1. Interestingly, the f1 values for the copolymer 2a
were almost constant at about 0.98, whereas those of the mix-
ture of PdTPP and poly(IBM-co-TFEM) increased from 0.889 to
0.967 as the temperature was increased. This finding suggests
that there are two distinct microheterogeneities, one tempera-
ture-dependent and the other temperature-independent, in the
mixture of PdTPP and poly(IBM-co-TFEM). The dye-conjugation
approach effectively eliminates the temperature-dependent, but
not the temperature-independent microheterogeneity. The lu-
minescence decays of copolymers 2a and 2b and the corre-
sponding mixtures in the absence of oxygen indicated that the
temperature-dependent microheterogeneity involves an oxy-
gen diffusion process, whereas the temperature-independent
C
V
one appears to be inherent nature in PdTPP.
2009 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 663–670,
2010
KEYWORDS: luminescence; metalloporphyrin; oxygen-sensing;
photochemistry; pressure-sensitive paint; radical polymeriza-
tion; sensors
INTRODUCTION Pressure-sensitive paint (PSP) is an emerg-
ing technology to visualize an air-pressure map on the sur-
face of a model placed in a wind tunnel.1–5 The principle of
PSP is based on luminescence quenching by oxygen molecule
(O2), whose ground state has a unique triplet character. Con-
ventional PSP consists of a luminescent dye embedded in a
film made of an oxygen-permeable polymer such as poly-
siloxane,6–10 fluorinated polymethacrylate,11,12 or poly(3-tri-
methylsilyl-1-propyne).13 When the luminescent dyes are
excited, the luminescence intensity or lifetime reflects the
local O2 concentration. The O2 concentration in the film is
proportional to the outer air-pressure, if Henry’s law holds.
Therefore, an air-pressure map on the surface can be calcu-
lated from luminescence intensity or lifetime images of a
PSP-coated model. The luminescence quenching behavior is
ideally described by a single Stern–Volmer equation. How-
ever, most PSPs show a downward curvature of the Stern–
Volmer plots, probably because of microheterogeneity of the
film. The downward deviation of the calibration curve results
in serious error in the pressure measurements.
One possible reason for the microheterogeneity is segrega-
tion and aggregation of dye molecules during the vaporiza-
tion process. Adopting this idea as a working hypothesis, we
previously synthesized a novel methacrylate monomer having
Correspondence to: M. Obata (E-mail: mobata@yamanashi.ac.jp)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 663–670 (2010) 2009 Wiley Periodicals, Inc.
PdTPP-PENDANT PSP, OBATA ET AL.
663

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
5,10,15,20-tetraphenylporphyrinato platinum(II) (PtTPP) and
copolymerized it with isobutyl methacrylate (IBM) and 2,2,2-
trifluoroethyl methacrylate (TFEM).14 The resulting copolymer,
which carries covalently bounded PtTPP dyes, showed a linear
Stern–Volmer plot, whereas a the mixture of PtTPP and poly
(IBM-co-TFEM) shows a downwardly curved plot. The conjuga-
tion of PtTPP to poly(IBM-co-TFEM) mainchain effectively elimi-
nates this microheterogeneity. This is a quite attractive method-
ology to improve the PSP performance. However, the reason
why the dye-conjugation approach reduces the microheteroge-
neity is not fully understood. The application and limitation of
this approach should be clarified to develop novel PSP system.
5-(4-Methoxycarbonylphenyl)-10,15,20-
triphenylporphinato Palladium(II)
5-(4-Methoxycarbonylphenyl)-10,15,20-triphenylporphyrin (690
mg, 1 mmol), PdCl2 (448 mg, 2.5 mmol), sodium acetate (1.7
g), acetic acid (40 mL), and chlorobenzene (50 mL) were
placed in a 300 mL flask equipped with a condenser. The flask
was evacuated and backfilled with nitrogen gas five times. The
mixture was heated at 135 ꢀC for 4 days. The crude product
was passed through a short plug of alumina, and the filtrate
was purified by silica gel column chromatography (CHCl3:hex-
ane ¼ 2:1) to give an orange powder (376 mg, yield 47%).
1H NMR (400 MHz, CDCl3, Si(CH3)4 ¼ 0 ppm): d (ppm) ¼
8.82 (d, 3J ¼ 4.9 Hz, 2H, pyrrole-bH), 8.80 (s, 4H, pyrrole-
bH), 8.74 (d, 3J ¼ 4.9 Hz, 2H, pyrrole-bH), 8.41 (d, 3J ¼ 8.4
Hz, 2H, 5-(3,5-PhH)), 8.24 (d, 3J ¼ 8.4 Hz, 2H, 5-(2,6-PhH),
8.16–8.14 (m, 6H, 10-, 15-, and 20-(2,6-PhH)), 7.76–7.69 (m,
9H, 10-, 15-, and 20-(3,4,5-PhH), 4.09 (s, 3H, CH3). 13C NMR
(100 MHz, CDCl3, CDCl3 ¼ 77 ppm): d (ppm) ¼ 167.07
(C¼¼O), 146.46 (C), 141.55 (C), 141.48 (C), 141.39 (C),
140.77 (C), 133.98 (CH), 133.93 (CH), 131.20 (CH), 131.03
(CH), 130.97 (CH), 130.37 (CH), 129.47 (C), 127.80 (CH),
127.68 (CH), 126.61 (CH), 121.96 (C), 121.84 (C), 120.13 (C),
52.47 (CH3). ESI-TOF HRMS: m/z for C46H30O2N4PdNa ([M þ
Na]þ) calcd. 799.13175, found 799.12882 (error ꢁ2.93
mmu, ꢁ3.67 ppm). Anal. calcd. for C46H30O2N4Pd: C, 71.09;
H, 3.89; N, 7.21. Found: C, 70.85; H, 3.82; N, 7.15. IR (KBr): m
(cmꢁ1) ¼ 1724 (mC¼O), 1609 (mC¼C). UV–vis (c ¼ 3.13 ꢂ 10ꢁ6
M, CHCl3, path length ¼ 1 cm): k/nm (e/Mꢁ1 cmꢁ1) ¼ 418
(3.19 ꢂ 105), 524 (2.82 ꢂ 104), 554 (2.94 ꢂ 103).
On the other hand, 5,10,15,20-tetraphenylporphyrinato palla-
dium(II) (PdTPP) is also a strong luminescence emitter,
showing a longer luminescence lifetime than that of PtTPP.
In addition, the longer luminescent wavelength of PdTPP
allows us to use another dye for the simultaneous tempera-
ture sensing. Therefore, PdTPP is also a promising lumines-
cent dye for PSP. In this article, we report the synthesis and
characterization of poly(IBM-co-TFEM) bearing PdTPP and
the results of an evaluation of its pressure-sensing properties
to examine the availability of the dye-conjugation approach.
EXPERIMENTAL
Measurements
1H NMR and 13C NMR spectra were recorded using a JEOL
AL-400 instrument (400 MHz). UV–vis spectra were recorded
on a JASCO V-570 spectrophotometer. IR spectra were
recorded on a Shimadzu FT-IR 8700. Electron-spray ioniza-
tion time-of-flight (ESI-TOF) mass spectra were recorded on
a JEOL JMS-T100LC. High-resolution mass spectra were
5-(4-Carboxyphenyl)-10,15,20-triphenylporphinato
Palladium(II)
5-(4-Carboxyphenyl)-10,15,20-triphenylporphinato palladiu-
m(II) was prepared by alkaline hydrolysis of 5-(4-methoxy-
carbonylphenyl)-10,15,20-triphenylporphinato palladium(II)
and was used without further purification.
measured using a-cyclodextrin (C36H60O30Na, [M þ Na]þ
¼
995.30671) as an internal standard. Elemental analyses were
performed on a Perkin-Elmer 2400 series II CHNS/O ele-
mental analyzer. The molecular weight of the resulting poly-
mers was measured by size exclusion chromatography (SEC)
in tetrahydrofuran with two polystyrene columns (Styragel
HR4 and Styragel HR3). The number-average molecular
weight (Mn) was calculated on the basis of polystyrene cali-
bration. Scanning electron microscope (SEM) images were
recorded on a JEOL JSM-6060LA analytical SEM using an
accelerating voltage of 15 keV.
5-[4-(2-Methacryloyloxyethoxycarbonyl)phenyl]-10,15,20-
triphenylporphinato palladium(II) (1a)
5-(4-Carboxyphenyl)-10,15,20-triphenylporphinato palladium(II)
(125 mg, 0.16 mmol), N-hydroxybenzotriazole (53 mg, 0.39
mmol), 2-hydroxyethyl methacrylate (544 mg, 4.18 mmol),
and dry DMF (1.5 mL) were placed in a Schlenk tube. The
tube was cooled on an ice-salt bath. To the solution was
added dropwise a dry DMF solution (2 mL) of dicyclohexyl-
carbodiimide (74 mg, 0.36 mmol). The mixture was stirred at
room temperature overnight, then washed with 1 M HCl, sat.
NaHCO3(aq), and brine, and dried over Na2SO4. The solvent
was removed under reduced pressure, and the crude product
was purified by column chromatography (silica gel, CH2Cl2)
followed by recrystallization from CHCl3-MeOH to give 1a as
a deep red solid (80 mg, yield 56%). TLC (silica gel, CH2Cl2):
Rf ¼ 0.53.
Materials
a,a0-Azobisisobutyronitrile (AIBN) and isobutyl methacrylate
(IBM) were purchased from Wako Pure Chemical Industries,
Ltd. 2,2,2-Trifluoroethyl methacrylate (TFEM) was purchased
from Aldrich. AIBN was recrystallized from methanol. IBM
and TFEM were distilled under reduced pressure just before
use. Dichloromethane was refluxed over calcium hydride and
distilled just before use. N,N-Dimethylformamide (DMF) was
distilled from anhydrous CaSO4 just before use. Toluene was
refluxed over sodium benzophenone ketyl and distilled just
before use. 5,10,15,20-Tetraphenylporphinato palladium(II)
(PdTPP) was prepared according to the literature.15 5-
(4-Methoxycarbonylphenyl)-10,15,20-triphenylporphyrin was
prepared as reported previously.16
1H NMR (400 MHz, CDCl3, Si(CH3)4 ¼ 0 ppm): d (ppm) ¼
8.82 (d, 3J ¼ 5.0 Hz, 2H, pyrrole-bH), 8.80 (s, 4H, pyrrole-
bH), 8.74 (d, 3J ¼ 5.0 Hz, 2H, pyrrole-bH), 8.42 (d, 3J ¼ 8.1
Hz, 2H, 5-(3,5-PhH)), 8.26 (d, 3J ¼ 8.1 Hz, 2H, 5-(2,6-PhH)),
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ARTICLE
8.15 (d, 3J ¼ 6.4 Hz, 6H, 10-, 15-, and 20-(2,6-PhH)), 7.78–
7.70 (m, 9H, 10-, 15-, and 20-(3,4,5-PhH), 6.24 (s, 1H, ¼¼CH2
(trans to CH3)), 5.65 (q, 4J ¼ 1 Hz, 1H, ¼¼CH2 (cis to CH3)),
4.75 (dd, 3J ¼ 5.7 and 3.8 Hz, 2H, ACH2A), 4.63 (dd, 2H, 3J
¼ 5.9 and 3.7 Hz, ACH2A), 2.02 (s, 3H, ACH3). 13C NMR
(100 MHz, CDCl3, CDCl3 ¼ 77 ppm): d (ppm) ¼ 167.06
(C¼¼O), 166.32 (C¼¼O), 146.77 (C), 141.60 (C), 141.53 (C),
141.50 (C), 141.48 (C), 141.43 (C), 140.77 (C), 134.06 (CH),
133.95 (CH), 131.18 (CH), 131.06 (CH), 130.99 (CH), 130.35
(CH), 129.18 (C) 127.93 (CH), 127.71 (CH), 126.62 (CH),
126.12 (¼¼CH2), 122.01 (C), 121.87(C), 120.06(C), 63.04
(CH2), 62.61 (CH2), 18.50 (CH3). ESI-TOF HRMS: m/z for
C
51H36O4N4PdNa ([M
897.16711 (error 1.57 mmu, 1.75 ppm). Anal. calcd. for
51H36O4N4Pd: C, 69.98; H, 4.15; N, 6.40. Found: C, 69.51; H,
þ
Na]þ) calcd 897.16868, found
FIGURE 1 1H NMR spectrum of monomer 1a in CDCl3.
C
3.98; N, 6.78. IR (KBr): m (cmꢁ1) ¼ 1720 (mC¼¼O), 1607 (mC¼C).
UV–vis (c ¼ 1.44 ꢂ 10ꢁ6 M, CHCl3, path length ¼ 1 cm): k/
nm (e/Mꢁ1 cmꢁ1) ¼ 417 (3.83 ꢂ 105), 523 (3.36 ꢂ 104),
555 (3.60 ꢂ 103).
where ri, Ni, Fi(k), Ui(k), and ri represent the interatomic dis-
tance, the coordination number, the back-scattering ampli-
tude, the phase shift, and the Debye–Waller factor of the i-th
coordination shell, respectively. k is the photoelectron wave-
vector, defined as k ¼ [(2m/h2)(E ꢁ E0)]1/2 with the thresh-
old energy E0. The back-scattering amplitude Fi(k) and the
phase shift Ui(k) functions for the corresponding shells, such
as those between Pd and N atoms and between Pd and C
atoms, were derived from the EXAFS oscillation of the BN
pellet of PdTPP, using NN and NC values fixed to 4 and 8,
respectively, as well as the interatomic distances rN and rC
fixed to 2.01 and 3.04 Å, respectively, derived from X-ray
crystallography.17 The Fourier-filtered method for each shell
was applied to avoid other strong parameter correlations. All
calculations were performed with REX2000 version 2.0.7
(Rigaku Co.).
Radical Copolymerization
IBM (0.925 g, 6.51 mmol), TFEM (1.127 g, 6.70 mmol), mono-
mer 1a (21.5 mg, 0.025 mmol), AIBN (165.8 mg, 1.01 mmol),
and dry toluene (3.5 mL) were placed in a Schlenk tube. The
tube was evacuated and backfilled with nitrogen gas five
times, then heated at 60 ꢀC for 24 h. The crude mixture was
poured into methanol, and the precipitate was collected by fil-
tration. The resulting powder was purified by reprecipitation
with CHCl3-MeOH to give an orange powder (0.9 g, 45%).
Extended X-Ray Absorption Fine Structure
Measurements
Extended X-ray absorption fine structure (EXAFS) measure-
ments were performed at beam line 10B of the Photon Fac-
tory of the High-Energy Acceleration Research Organization
(KEK-PF; Tsukuba, Japan). A channel-cut Si(311) monochro-
mator was used. The ring current was 300–450 mA, and the
storage ring was operated with electron energy of 2.5 GeV.
The experiments at the Pd K edge (23,348 eV) were carried
out at room temperature in the transmission mode on a bo-
ron nitrate (BN) pellet containing powdered PdTPP and a
cell (path length is 2 cm) filled with powdered copolymer
2a. The k3v(k) values for the case of single scattering are
theoretically given by eq 1:
Test of Pressure-Sensing Ability
Luminescence images of films made from the copolymer 2a
and from the mixture of PdTPP and poly(IBM-co-TFEM) were
taken in the air pressure range from 5 to 100 kPa and in the
ꢀ
temperature range from 0 to 60 C. The copolymer 2a or the
mixture of PdTPP and poly(IBM-co-TFEM) was dissolved in
toluene (25 g Lꢁ1) and sprayed onto an aluminum plate (15
ꢂ 15 mm2) with a conventional air-brush. The plate was
then mounted in a temperature-controlled pressure chamber.
Excitation was provided with a 300 W xenon lamp (C4338,
Hamamatsu Photonics) equipped with a bandpass filter of
380–530 nm. The emission from the sample was detected
with a cooled CCD camera (C4880-50-26W, Hamamatsu
ꢀ
ꢁ
k2Ni
ri2
X
k3vðkÞ ¼
FiðkÞ expðꢁ2r2i k2Þ sinð2kri þ UiðkÞÞ (1)
i
FIGURE 2 UV–vis spectra of monomer 1a (a), PdTPP (b), and copolymer 2a (c ¼ 0.499 g Lꢁ1) (c) in CHCl3 at 25 ꢀC.
PdTPP-PENDANT PSP, OBATA ET AL.
665

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of PdTPP-
pendant PSP.
Photonics; 1000 ꢂ 1018 pixels and 16-bit intensity resolu-
which are identical to those of PdTPP. Hence, the 2-methacry-
loxyethoxycarbonyl group has no influence on the electronic
structure of PdTPP dye. Radical copolymerization of isobutyl
methacrylate (IBM), 2,2,2-trifluoroethyl methacrylate (TFEM),
and monomer 1a was carried out at 60 ꢀC in toluene in the
dark, using AIBN as an initiator (Scheme 1). The molar ratio
of TFEM to IBM was 1 and the feed ratio of monomer 1a was
1 wt % to the total monomer. After reprecipitation with chlo-
roform-methanol, no unreacted monomer 1a was found by
SEC. The resulting copolymer 2a was an orange powder solu-
ble in common organic solvent, such as chloroform and tetra-
hydrofuran. The number-average molecular weight (Mn) and
the polydispersity index (Mw/Mn) of the copolymer 2a were
estimated to be 2.59 ꢂ 104 and 1.46, respectively, by SEC
tion) with a bandpass filter of 590–710 nm.
Luminescence Lifetime Measurement
The luminescence lifetime of PSP-coated samples was deter-
mined in a temperature-controlled pressure chamber. Excita-
tion was provided with UV-LED (ETG, ETG-5UV395-30)
equipped with a bandpass filter of 400 6 50 nm. The emis-
sion from the sample was detected with a multigate CCD
camera (Hamamatsu Photonics; 1344 ꢂ 1024 pixels and
14 bit intensity resolution, 0.1 ls gate time) with a bandpass
filter of 650 6 20 nm.
RESULTS AND DISCUSSION
1
Synthesis of PdTPP-Bearing Copolymer 2a
using polystyrene standards. The H NMR spectrum of the co-
5-[4-(2-Methacryloyloxyethoxycarbonyl)phenyl]-10,15,20-tri-
phenylporphinato palladium(II) (1a) was prepared by a sim-
ilar method to that used previously by us for 5-[4-(2-metha-
cryloyloxyethoxycarbonyl)phenyl]-10,15,20-triphenylporphinato
platinum(II) (1b).14 The structure of monomer 1a was con-
polymer 2a indicated that the molar ratio of IBM and TFEM
units was 1:1. The UV–vis spectrum of the copolymer 2a
showed essentially identical absorption bands to those of
monomer 1a, namely the Soret band at 417 nm and two Q
bands at 524 and 555 nm [Fig. 2(c)], indicating that there
is no significant interaction between PdTPP units of the
copolymer 2a in chloroform. The amount of PdTPP dye in the
copolymer 2a was estimated to be 0.89 wt % calculated on
the basis of the absorption at 417 nm (Soret band) in the UV–
vis spectrum, with PdTPP (e ¼ 320 ꢂ 103 Mꢁ1 cmꢁ1) as a
standard. The steady-state luminescence spectrum of the co-
polymer 2a was also almost identical to that of PdTPP in
degassed chloroform at room temperature (Fig. 3). To examine
1
firmed by H NMR and 13C NMR spectroscopies (Fig. 1), ESI-
TOF high-resolution mass spectrometry, and elemental analy-
sis. Figure 2(a,b) shows UV–vis spectra of monomer 1a and
5,10,15,20-tetraphenylporphyrinato palladium(II) (PdTPP) in
chloroform. Monomer 1a showed a strong absorption band
(Soret band) at 417 nm (e ¼ 385 ꢂ 103 Mꢁ1 cmꢁ1) with
relatively weak absorption bands (Q bands) at 523 and 555
nm (e ¼ 33.6 ꢂ 103 and 3.6 ꢂ 103 Mꢁ1 cmꢁ1, respectively),
FIGURE 3 Steady-state luminescence spectra of monomer 1a (a), PdTPP (b), and copolymer 2a (c) in degassed CHCl3 at 25 ꢀC.
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ARTICLE
TABLE 1 Structural Parameters Derived from EXAFS Analysis
for Copolymer 2a
˚
˚
Shell
N
r (A)
dE (eV)
r (A)
R (%)
Pd-N
Pd-C
3.7
5.6
2.01
3.04
2.19
1.53
0.054
0.033
1.3
N, coordination number; r, interatomic distance; dE, energy shift; r,
Debye–Waller factor; R, R-factor defined as R[k3v(k)obs
ꢁ
k3v(k)calc]2/
2
R[k3v(k)obs
]
ꢂ 100. The estimated errors in the N and r values are
˚
616% and 60.05 A. The back-scattering functions FN(k) and FC(k) and
phase shifts UN(k) and UC(k) were derived from the EXAFS spectrum of
a boron nitrate pellet incorporating PdTPP.
Pressure-Sensing Properties of Copolymer 2a
To examine the effect of the dye-conjugation in copolymer
2a on the pressure-sensing properties, two types of sensing
films were prepared, that is, a film consisting of a simple
mixture of PdTPP and poly(IBM-co-TFEM) (IBM:TFEM ¼ 1:1,
Mn ¼ 2.20 ꢂ 104, Mw/Mn ¼ 1.76) and a film of the copoly-
mer 2a. The polymer films were formed on an aluminum
plate with a conventional air-brush filled with a toluene so-
lution of the paint (polymer concentration was 25 g Lꢁ1), as
described in our previous article.14 Figure 5 shows a repre-
sentative SEM image of an aluminum plate which was
painted with the copolymer 2a on half of the surface (left
side of the plate in the picture). The picture clearly shows
that the thickness of the film was about 10 lm. The lumines-
cence intensity from these films was collected in the air
pressure range from 5 to 100 kPa and in the temperature
FIGURE 4 Fourier transform of EXAFS oscillation (k3v(k)) of co-
polymer 2a at the Pd K edge. The inserted plots show the
observed (o) and calculated (ꢁ) k3v(k) for both the Pd-N and
Pd-C regions.
the coordination structure at the palladium(II) atom in the co-
polymer 2a, the EXAFS of 2a was measured at the Pd K edge.
Figure 4 shows the Fourier transform of the k3-weighted
EXAFS oscillation (k3v(k)). Two peaks were found at 1.6 and
2.7 Å (before phase correction), and were assigned to the
back-scattering contribution of nitrogen atoms and carbon
atoms of the porphyrin ring (Scheme 2). The k3v(k) obtained
was fitted with a sum of these contributions k3vN(k) and
k3vC(k) using the back-scattering amplitudes Fi(k) and the
phase shifts Ui(k) derived from the k3v(k) and X-ray crystallo-
graphic data17 of PdTPP. The inset of Figure 4 shows the
k3v(k) and the best-fitted function k3vcalc(k) to confirm
the reliability of the fitting. The structural parameters, i.e., the
interatomic distance ri, the coordination number Ni and the
Debye–Waller factor ri are listed in Table 1. The ri values are
quite close to those of PdTPP determined by X-ray crystallog-
raphy. This clearly indicates that the radical polymerization
proceeds without significantly affecting the structure of the
PdTPP dye.
ꢀ
range from 0 to 60 C. Figure 6 shows the Stern–Volmer plot
for the two films, made from the copolymer 2a and the mix-
ture of PdTPP and poly(IBM-co-TFEM). The Stern–Volmer
plots for both films showed downward curvature, which is
likely to be due to the microheterogeneity of the films. How-
ever, the plot for the film made from copolymer 2a is quite
different from that for the film made from the mixture of
PdTPP and poly(IBM-co-TFEM). To explore the details, these
plots were fitted with a two-site model,8
f1
1 ꢁ f1
þ
I0
I
1 þ KSV1P0 1 þ KSV2P0
¼
(2)
f1
1 ꢁ f1
þ
1 þ KSV1
P
1 þ KSV2
P
where KSV1 and KSV2 are the Stern–Volmer constants for dis-
tinct domains 1 and 2, and f1 is the fractional contribution
of the domain 1 to the total luminescence intensity in the
absence of oxygen. The best fits are shown as solid lines in
Figure 6, and the parameters KSV1, KSV2, and f1 are listed in
Tables 2 and 3. The minor domain (domain 2) showed sub-
stantially no response (KSV2 < 0.01 kPaꢁ1) to oxygen in ei-
ther the film made from the copolymer 2a or that made
from the mixture of PdTPP and poly(IBM-co-TFEM). The KSV1
values increased with increase of the temperature, and the
KSV1 values of the copolymer 2a are greater than those of
the mixture of PdTPP and poly(IBM-co-TFEM). A noteworthy
feature of these films is the temperature dependence of the
SCHEME 2 Single scattering paths for EXAFS analysis.
PdTPP-PENDANT PSP, OBATA ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 5 SEM image of a film made from copolymer 2a.
Figure 8 shows the luminescence decay curves of films
consisting of a mixture of PdTPP and poly(IBM-co-TFEM), a
mixture of PtTPP and poly(IBM-co-TFEM), copolymer 2a and
copolymer 2b under vacuum at 10 and 60 ꢀC. The lumines-
cence decay curves for the copolymer 2a and the mixture of
PdTPP and poly(IBM-co-TFEM) were fitted with three expo-
nential functions as follows:
f1 values (Fig. 7). While the f1 values of the copolymer 2a
are almost constant at ꢃ0.98 in the range from 0 to 60 C,
ꢀ
the f1 value of the mixture of PdTPP and poly(IBM-co-
TFEM) increases from 0.889 to 0.967 with increase of tem-
perature. This indicates that the origin of the microhetero-
geneity of the film made from the copolymer 2a is
different from that of the film made from the mixture of
PdTPP and poly(IBM-co-TFEM). In addition, the f1 values
of the mixture of PdTPP and poly(IBM-co-TFEM) seem to
be asymptotic to those of the copolymer 2a with increase
of the temperature. This suggests that there are two types
of microheterogeneity, namely temperature-dependent and
temperature-independent types, in the mixture of PdTPP
and poly(IBM-co-TFEM). If this is so, the conjugation of
dye with polymer main chain in copolymer 2a effectively
reduced the temperature-dependent microheterogeneity
effectively, but not the temperature-independent microhe-
terogeneity. This hypothesis is supported by the results for
copolymer 2b and the mixture of PtTPP in poly(IBM-co-
TFEM) in our previous article.14 While copolymer 2b gave
a linear Stern–Volmer plot, indicating f1 ¼ 1, the f1 value
of the mixture of PtTPP in poly(IBM-co-TFEM) increased
from 0.891 to 0.954 with increase of temperature from 0
IðtÞ ¼ A1 expðꢁt=s1Þ þ A2 expðꢁt=s2Þ þ A3 expðꢁt=s3Þ (3)
The pre-exponential factors (Ai) and the lifetimes (si) are
listed in Table 4. The decay curves for the copolymer 2a
were different from those for the mixture of PdTPP and poly
(IBM-co-TFEM). On the other hand, the decay curves for the
copolymer 2b were substantially identical to those for the
mixture of PtTPP and poly(IBM-co-TFEM) at 10 and 60 ꢀC.
Hence, the photophysical properties of the copolymer 2b
and the mixture of PtTPP and poly(IBM-co-TFEM) are identi-
cal with each other in the absence of oxygen. These results
suggest that the origin of the temperature-dependent micro-
heterogeneity involves an oxygen-diffusion process. In addi-
tion, dye-conjugation efficiently eliminated the temperature-
dependent microheterogeneity for both the PtTPP and PdTPP
systems. However, the PdTPP system includes a substantial
ꢀ
to 60 C.
FIGURE 6 Stern–Volmer plots for
copolymer 2a (a) and a mixture
of PdTPP and poly(IBM-co-TFEM)
(b). Solid lines represent best-fit
with a two-site model.
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ARTICLE
TABLE 2 Fitting Parameters for the Stern–Volmer Plot of a Film
made from Copolymer 2a
T (ꢀC)
KSV1 (kPaꢁ1
)
KSV2 (kPaꢁ1
)
f1
0
0.63
0.66
0.75
0.80
0.87
0.93
0.99
0.00034
0.00004
0.00016
0.00016
0.00012
0.00006
0.00012
0.981
0.982
0.982
0.981
0.981
0.981
0.980
10
20
30
40
50
60
temperature-independent microheterogeneity, resulting in a
distorted Stern–Volmer plot.
FIGURE 7 The f1 value as a function of temperature.
CONCLUSIONS
A luminescent methacrylate monomer having 5,10,15,20-tet-
raphenylporphinato palladium(II) (PdTPP) moiety, that is, 5-
[4-(2-methacryloyloxyethoxycarbonyl)phenyl]-10,15,20-triphe-
nylporphinato palladium(II) (1a), was synthesized in moder-
ate yield. Copolymerization of isobutyl methacrylate (IBM),
2,2,2-trifluoroethyl methacrylate (TFEM) and monomer 1a
was carried out by conventional radical polymerization to
yield poly(IBM-co-TFEM) bearing PdTPP moieties (copolymer
2a). The composition of copolymer 2a was essentially identi-
cal to the feed ratio. The coordination structure around the
palladium(II) atom was examined by means of EXAFS analy-
sis, and the results indicated that the copolymerization pro-
ceeded without damage to the PdTPP dye. The oxygen-sens-
ing properties of a simple mixture of PdTPP and poly(IBM-
co-TFEM) and copolymer 2a were evaluated in the air
pressure range of 5–100 kPa and in the temperature range of
the film made from mixture of PdTPP and poly(IBM-co-
TFEM) increased from 0.89 to 0.97 with increase of the tem-
perature. The results suggest that there are two distinct
ꢀ
0–60 C. Unlike the PtTPP-bearing poly(IBM-co-TFEM) (copol-
ymer 2b), films made from the copolymer 2a and from a
mixture of PdTPP and poly(IBM-co-TFEM) both showed sig-
nificant deviation from a single Stern–Volmer relation. The lu-
minescence quenching behavior was analyzed by applying a
two-site model consisting of an oxygen-responsive major do-
main and an almost nonresponsive minor domain. The
fraction of the major domain (f1) in the film made from
the copolymer 2a was constant at 0.98 in the range from
0 to 60 ꢀC. On the other hand, interestingly, the f1 value for
TABLE 3 Fitting Parameters for the Stern–Volmer Plot of a Film
Consisting of a Mixture of PdTPP and Poly(IBM-co-TFEM)
T (ꢀC)
KSV1 (kPaꢁ1
)
KSV2 (kPaꢁ1
)
f1
0
0.29
0.28
0.29
0.30
0.38
0.49
0.61
0.0046
0.0045
0.0037
0.0020
0.0012
0.0006
0.0003
0.889
0.908
0.926
0.945
0.956
0.964
0.967
10
20
30
40
50
60
FIGURE 8 Luminescence decay curves for copolymer 2a and
the mixture of PdTPP and poly(IBM-co-TFEM) (a) and copoly-
mer 2b and the mixture of PtTPP and poly(IBM-co-TFEM) (b) at
10 and 60 ꢀC under vacuum.
PdTPP-PENDANT PSP, OBATA ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 4 Fitting Parameters for Luminescence Decay Curves
T (ꢀC)
s1 (ls) (A1)
s2 (ls) (A2)
s3 (ls) (A3)
2a
10
60
10
60
10
60
10
60
602 (0.62)
459 (0.58)
834 (0.34)
573 (0.37)
87.6 (1)
84.4 (0.16)
77.7 (0.20)
359 (0.46)
234 (0.43)
1.7 (0.22)
1.7 (0.22)
1.4 (0.20)
1.5 (0.20)
PdTPP in poly(IBM-co-TFEM)
2b
70.3 (1)
PtTPP in poly(IBM-co-TFEM)
87.1 (1)
71.7 (1)
6 DeRosa, M. C.; Mosher, P. J.; Yap, G. P. A.; Focsaneanu,
K.-S.; Crutchley, R. J.; Evans, C. E. B. Inorg Chem 2003, 42,
4864–4872.
microheterogeneities in the sensing film using PdTPP dye,
one being temperature-dependent, and the other is tempera-
ture-independent. The dye-conjugation approach efficiently
reduced the temperature-dependent microheterogeneity for
both PdTPP and PtTPP dyes, but was not effective to reduce
the temperature-independent microheterogeneity, which app-
ears to be inherent in PdTPP.
7 Sacksteder, L.; Demas, J. N.; DeGraff, B. A. Anal Chem 1993,
65, 3480–3483.
8 Carraway, E. R.; Demas, J. N.; DeGraff, B. A. Anal Chem
1991, 63, 332–336.
The EXAFS experiments were performed with the approval of
the Photon Factory Program Advisory Committee (proposal no.
2002G104). This work was supported by a Grants-in-Aid for
Scientific Research on Priority Areas (417), and a Grant-in-Aid
for Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology of the Japanese Government.
9 Bacon, J. R.; Demas, J. N. Anal Chem 1987, 59, 2780–2785.
10 Ishiji, T.; Kaneko, M. Analyst 1995, 120, 1633–1638.
11 Amao, Y.; Ishikawa, Y.; Okura, I. Anal Chim Acta 2001, 445,
177–182.
12 Amao, Y.; Okura, I.; Miyashita, T. Bull Chem Soc Jpn 2000,
73, 2663–2668.
13 Hah, H.; Sakai, T.; Asai, K.; Nishide, H. Macromol Symp
REFERENCES AND NOTES
2003, 204, 27–35.
1 Liu, T.; Sullivan, J. P.; Pressure and Temperature Sensitive
14 Obata, M.; Tanaka, Y.; Araki, N.; Hirohara, S.; Yano, S.; Mit-
suo, K.; Asai, K.; Harada, M.; Kakuchi, T.; Ohtsuki, C. J Polym
Sci Part A: Polym Chem 2005, 43, 2997–3006.
Paints; Springer: Berlin, 2005.
2 Takeuchi, Y.; Amao, Y. In Frontiers in Chemical Sensors;
Orellana, G.; Moreno-Bondi, M. C., Eds.; Springer-Verlag:
Berlin, Heidelberg, 2005; pp 303–322.
15 Buchler J. W. In The Porphyrins; Dolphine, D., Ed.;
Academic Press, New York, 1978; Vol. 1, Chapter 10, pp 471–
474.
3 Liu, T.; Campbell, B. T.; Burns, S. P.; Sullivan, J. P. Appl
Mech Rev 1997, 50, 227–246.
16 Araki, N.; Obata, M.; Ichimura, A.; Mikata, Y.; Yano, S. Chem
Lett 2004, 450–451.
4 Bell, H. J.; Schairer, T. E.; Hand, A. L.; Mehta, R. D. Annu Rev
Fluid Mech 2001, 33, 155–206.
17 Fleischer, E. B.; Miller, C. K.; Webb, L. E. J Am Chem Soc
1964, 86, 2342–2347.
5 Asai, K. J Visualization 2001, 21, 203–208.
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