A new class of ZnII and CrIII porphyrins incorporated into porous polymer matrices via an atmospheric pressure plasma enhanced CVD to form gas sensing layers

Article abstract of DOI:10.1039/c3ta13488a

Designed Zn^II and Cr^III porphyrins (Zn^IIP, Cr^IIIP(Cl)(H₂O)) and conventional Zn^IITPP and Cr^IIITPP(Cl)(H₂O) are immobilized into porous polysiloxane films via chemical vapor deposition enhanced by an atmospheric pressure dielectric barrier discharge. UV/vis spectroscopy and mass spectrometry prove the integrity of the chromophores after the plasma treatment. The optical amine sensing capabilities of the films are investigated spectroscopically on exposure to triethylamine vapors. A series of coatings with different porphyrin loadings indicate influences of the deposition conditions on the growth of the sensing films and hence the device performance. Additionally, the synthesis and characterization of the novel porphyrin complex Cr^IIIP(Cl)(H ₂O) is reported.

Full text of DOI:10.1039/c3ta13488a

Journal of
Materials Chemistry A
View Article Online
View Journal | View Issue
PAPER
A new class of ZnII and CrIII porphyrins incorporated
into porous polymer matrices via an atmospheric
pressure plasma enhanced CVD to form gas sensing
layers†
Cite this: J. Mater. Chem. A, 2014, 2,
1560
a
c
b
Philip Heier,ab Nicolas D. Boscher, Torsten Bohn, Katja Heinze
*
*
and Patrick Choqueta
Designed ZnII and CrIII porphyrins (ZnIIP, CrIIIP(Cl)(H2O)) and conventional ZnIITPP and CrIIITPP(Cl)(H2O) are
immobilized into porous polysiloxane films via chemical vapor deposition enhanced by an atmospheric
pressure dielectric barrier discharge. UV/vis spectroscopy and mass spectrometry prove the integrity of
the chromophores after the plasma treatment. The optical amine sensing capabilities of the films are
investigated spectroscopically on exposure to triethylamine vapors. A series of coatings with different
porphyrin loadings indicate influences of the deposition conditions on the growth of the sensing films
and hence the device performance. Additionally, the synthesis and characterization of the novel
porphyrin complex CrIIIP(Cl)(H2O) is reported.
Received 2nd September 2013
Accepted 24th November 2013
DOI: 10.1039/c3ta13488a
www.rsc.org/MaterialsA
freshness indicators for several food categories.29–31 Therefore
their detection by smart food packages using colorimetric
A. Introduction
sensor surfaces may lead to simple yet powerful devices for food
quality control used by customers and manufacturers.32
Preparation of porphyrin based sensing layers has been
achieved by different techniques including spin-coating,22,13
vacuum evaporation,13,22 glow-discharge induced sublima-
tion21,13 and Langmuir–Blodgett33,34 as well as Langmuir–
Schaefer35 techniques. An important approach to improve the
overall performance of gas sensing devices is to incorporate the
sensing molecules into a suitable stable and adherent matrix.
The sensing molecules should be well dispersed within the
matrix to prevent agglomeration and tightly trapped to enhance
the mechanical stability of the device. On the other hand, the
matrix needs to be porous to allow diffusion of analytes towards
the sensing sites. Porphyrins have been incorporated into
different matrices to form composite sensing layers typically by
immobilization in polymers and plasticizers25,27,36 or sol-gel
deposited silica lms.12,20,24
Porphyrin based and porphyrin containing coatings are widely
investigated for dye-sensitized solar cells,1–5 photonic and
electronic devices6–10 and sensing applications.11–28 Porphyrins
are of special interest for the design of colorimetric sensors as
they exhibit intense absorptions within the visible part of the
electromagnetic spectrum. Their absorption characteristics can
be changed by interaction of different analytes with the
porphyrin macrocycle and especially with the metal center of
metalloporphyrins.
Applications of porphyrin based colorimetric sensing
13–15
surfaces range from the detection of explosives11,12 and NO2
over volatile organic compounds (VOC) in general16–20 to alcohol
vapors21–23 and volatile amines in particular.24–28 The detection
of volatile amines is of special interest as they can be used as
aScience and Analysis of Materials Department, Centre de Recherche Public – Gabriel
Lippmann, 41 rue du Brill, Belvaux L-4422, Luxembourg. E-mail: nboscher@
lippmann.lu
A new arising technology for the preparation of smart
composite coatings is chemical vapor deposition (CVD)
enhanced by an atmospheric pressure dielectric barrier
discharge (AP-DBD). It is a versatile method to deposit thin
lms from a broad range of precursors and on several
substrates.37,38 Even heat sensitive polymers can be treated as
AP-DBD creates cold plasmas.39 During the process only minor
amounts of waste or by-products are produced and inexpensive
process gases such as nitrogen40 or even air41 can be used. In
contrast to the limitations of industrial implementations of low-
pressure plasmas and sol-gel methods, AP-DBD based processes
bInstitute of Inorganic and Analytical Chemistry, Johannes Gutenberg-University
Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany. E-mail: katja.heinze@
uni-mainz.de
cEnvironment and Agro-Biotechnologies Department, Centre de Recherche Public –
Gabriel Lippmann, 41 rue du Brill, Belvaux L-4422, Luxembourg
† Electronic supplementary information (ESI) available: Molecular structures of
aa- and ab-H2P (Fig. S1), UV/vis spectra of CrIIIP(Cl)(H2O) in CH2Cl2 pure and
with NEt3 (Fig. S2), IR spectra of Cr-1, Cr-2 and Cr-3 (Fig. S3), UV/vis spectra of
Zn-1 under dry and humid conditions with and without NEt3 (Fig. S4), UV/vis
spectra of Cr-3 under dry and humid conditions with and without NEt3
(Fig. S5), and SEM pictures of Cr-1, Cr-2 and Cr-3 (Fig. S6). See DOI:
10.1039/c3ta13488a
1560 | J. Mater. Chem. A, 2014, 2, 1560–1570
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
Synthesis of CrIIIP(Cl)(H2O)
can be easily integrated into roll-to-roll production lines and are
indeed already used in industry for thin lm deposition, surface
cleaning, sterilizing as well as wettability and adhesion
enhancement.42
Deposition of lanthanide-containing polymer particles along
with siloxane precursors by an AP-DBD method lead to lumi-
nescent composite coatings43 while the incorporation of AlCeO3
nanoparticles in a similar matrix gave rise to anti-corrosive
layers.44 Bio-active coatings could be achieved by immobilizing
enzymes in AP-DBD polymerized acetylene and pyrrole
matrices.45 The enzymes are reported to be protected from
plasma alteration by a surrounding water shell, yet helium has
to be used as a process gas.
Recently, the successful incorporation of metallo meso-
tetraphenylporphyrins (M ¼ ZnII, CrIII) into plasma polymer-
ized siloxane matrices has been achieved.46,47 The porosity of
the matrices could be controlled by tuning the deposition
parameters and rst demonstrations of amine sensing prop-
erties of these composite coatings have been shown.46,48 In
this context, novel porphyrins have been developed to
improve the optical response upon interaction with amines
and to enhance their solubility in the matrix precursor in
order to achieve highly colored coatings.49 Based on these
developments, we herein report the co-deposition of these
sophisticated metalloporphyrins ZnIIP and CrIIIP(Cl)(H2O)
along with siloxane precursors in an AP-DBD enhanced
chemical vapor deposition onto aluminum and polyethylene
terephthalate (PET) substrates. The integrity of the porphyrin
based sensor molecules in the siloxane matrix is investigated
by UV/vis spectroscopy as well as by mass spectrometry, while
A mixture of aa/ab-H2P metal-free porphyrins (see Fig. S1†) has
been synthesized according to literature procedures.49 Under an
inert atmosphere a 1 : 1 mixture of aa/ab-H2P isomers (300 mg,
0.33 mmol, 1.0 eq.) and Cr(CO)6 (1.47 g, 6.67 mmol, 20 eq.) have
been dissolved in dry and degassed toluene (175 mL) and the
mixture was heated to reux for 24 h. The Cr(CO)6, which has
sublimated on the top of the ask during this time, was trans-
ferred back into the solution several times. The reaction mixture
was cooled to room temperature (RT) and 0.5 mL of concen-
trated aqueous HCl was added. Aer stirring at RT under air for
2 h, the solvents have been removed via distillation and residual
Cr(CO)6 via sublimation. The obtained dark solid was dissolved
in CHCl3 (75 mL) and ltered. The ltrate was puried via
column chromatography on Al2O3 (Brockmann activity IV,
CHCl3). The rst fraction containing metal free aa/ab-H2P has
been discarded while the second collected fraction contained
the puried product. Aer removing the solvent under reduced
pressure, 231 mg (0.23 mmol, 70%) of CrIIIP(Cl)(H2O) was iso-
lated as a purple solid.
UV/vis (CH2Cl2): lmax (3) ¼ 282 (7.2 ꢀ 104), 290 (6.7 ꢀ 104),
300 (6.6 ꢀ 104), 322 (3.6 ꢀ 104), 337 (3.2 ꢀ 104), 363 (2.8 ꢀ 104),
398 (4.17 ꢀ 104), 452 (26.4 ꢀ 104), 565 (1.16 ꢀ 104), 602 (0.63 ꢀ
104 Mꢁ1 cmꢁ1) nm. MS (ESI+): m/z ¼ 948.33 [M ꢁ Cl ꢁ H2O]+,
966.34 [M ꢁ Cl]+, 989.33 [M ꢁ Cl + Na]+, 1005.30 [M ꢁ Cl + K]+.
HR-MS (ESI+): m/z ¼ 948.3282 (calcd for C66H48CrN4: 948.3284).
Plasma deposition
the chemical composition of the hybrid coatings is analyzed The general procedure employed to create the composite coat-
by IR and XPS spectroscopy. The gas sensing capabilities of ings via an AP-DBD enhanced CVD has been described before,
the novel layers are spectroscopically investigated by exposing including the schematic setup of the prototype.43,47 The coatings
them to NEt3 vapors. To rationalize the performances of these described here vary in the type of the porphyrin and the
coatings, comparable layers containing the meso-tetraphe- porphyrin concentration within the precursor solutions, while
nylporphyrins ZnIITPP and CrIIITPP(Cl)(H2O) were deposited all other deposition parameters were kept constant.
under similar conditions. The amine sensing performance of
With help of an ultrasonic atomizing nozzle (Sono-Tek
the devices is correlated with the porphyrin loading of Corporation, Milton, NY) operating at 48 kHz and fed by a
the foils.
syringe driver delivering 0.25 mL minꢁ1 the precursor solution
was sprayed onto the respective substrate (PET foil, 50 mm thick;
aluminum foil, 200 mm thick), which was placed on the
aluminum moving stage of the AP-DBD reactor. The moving
stage speed, set up to 6 m minꢁ1, allowed prompt exposition of
the formed liquid layer to the plasma discharge in order to
B. Experimental section
General materials
The porphyrins ZnIIP49 and CrIIITPP(Cl)(H2O)50 have been polymerize the siloxane precursor. The delay time between the
synthesized according to literature procedures and their phys- liquid layer deposition and the plasma treatment was one
ical properties agree with reported data. Zinc 5,10,15,20-tetra- second. The AP-DBD reactor consisted of two at parallel high
phenylporphyrin (ZnIITPP), hexamethyldisiloxane (HMDSO, voltage electrodes (0.7 ꢀ 13 cm2) covered with alumina and the
98.5%), vinyltrimethoxysilane (VTMOS, 98%), dichloromethane moving stage as the grounded electrode. The discharge gap
(DCM, 99.8%) and triethylamine (NEt3, 99%) have been between the high voltage electrode and the substrate placed on
obtained from Sigma-Aldrich (St. Louis, MO) and were used the grounded electrode was maintained at 1 mm. The AP-DBD
without further purication. Nitrogen (99.999%, Air Liquide, reactor was fed by a 20 L minꢁ1 nitrogen ow containing
´
Petange, Luxembourg) was moisturized by bubbling through 200 ppm HMDSO vapor. The plasma discharge was ignited by
18 MU water (Millipore, Billerica, MA). Polyethylene tere- means of a 10 kHz sinusoidal signal, chopped by a 1667 Hz
phthalate foil (50 mm thick) has been received from Goodfellow rectangular signal. The operating discharge power density was
(Huntington, UK) and cold-rolled aluminum foil (200 mm thick, maintained at 0.5 W cmꢁ2. 100 passes were performed, corre-
8011 series) from Eurofoil (Belvaux, Luxembourg).
sponding to 14 s effective deposition time.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 1560–1570 | 1561

View Article Online
Journal of Materials Chemistry A
Paper
Coatings on PET foils were used for UV/vis studies, amine
sensing experiments, XPS analysis and top view SEM. Coatings
on aluminum foils were used for IR measurements.
Characterization of deposited layers
Scanning electron microscopy (SEM) was performed on a
Hitachi SU-70 FE-SEM. Prior to SEM observations the non-
conductive samples were sputter coated with a thin layer of
platinum to prevent charging. FT-IR analysis was performed on
a Bruker Hyperion 2000 spectrometer equipped with a Ge-ATR-
crystal. XPS analyses were realized with a Kratos Axis-Ultra DLD
instrument using a monochromatic Al Ka X-ray source (hn ¼
1486.6 eV) at a pass energy of 20 eV. Extracts of the deposited
layers were obtained by rinsing the foils repetitively with 10 mL
of ethanol. The collected extracts were concentrated prior to
analysis. The HPLC-MS analysis of the Zn-1 extracts were per-
formed on a Dionex Ultimate 3000 HPLC system coupled with
an AB/Sciex API 3200 triple-quadrupole tandem MS. The
analytical column was an Agilent Zorbay Bonus-RP (150 mm ꢀ
4.6 mm ꢀ 5 mm). The eluents were H2O and acetonitrile, both
containing 0.1% formic acid. The gradient prole started with
50% acetonitrile during 2 min, then the acetonitrile fraction
Fig. 1 (a) Molecular structures of the deposited porphyrin complexes
ZnIIP and CrIIIP(Cl)(H2O) and (b) molecular structures of the deposited
reference compounds ZnIITPP and CrIIITPP(Cl)(H2O).
C. Plasma deposition of sensor
was increased to 100% over 3 min and then kept at 100% for coatings
7 min. The ow rate was kept constant at 1 mL minꢁ1 and the
Four different metalloporphyrins were incorporated into porous
column temperature was 40 ꢂC. The mass spectrometer was
operated in positive electrospray ionization mode and detection
was done in full-scan mode. The high-resolution mass spectra
of the Cr-1 extracts were collected using a LTQ-Orbitrap Elite
hybrid mass spectrometer (ThermoFisher Scientic) equipped
with an electrospray ionization source (ESI). The liquid samples
were injected by loop injection in a constant ow of methanol.
No separation step by liquid chromatography was performed
before analysis. The averaged mass spectra were collected in full
scan mode at high resolution, allowing a relative error of the
measured m/z ratio below 2 ppm.
siloxane matrices via AP-DBD enhanced CVD to form colored,
transparent and adherent sensing lms. The porphyrin
complexes ZnIIP and CrIIIP(Cl)(H2O) shown in Fig. 1a have been
tailored for colorimetric amine sensing by introduction of two
phenylalkynyl arms shielding the coordination site.49 Both
metalloporphyrins were used as a 1 : 1 mixture of aa- and
ab-isomers. For comparison, the corresponding 5,10,15,20-tet-
raphenylporphyrins ZnIITPP and CrIIITPP(Cl)(H2O) (Fig. 1b)
were deposited by the same technique and similar process
parameters. Table 1 summarizes the compositions of the
precursor solutions, which differ in the type and concentration
of the porphyrins. All solutions were based on 20 vol.%
dichloromethane (DCM) and 80 vol.% vinyltrimethoxysilane
(VTMOS), as a siloxane precursor, and contained 0.08 to 3.0 g
Lꢁ1 of the respective porphyrin. The plasma process gas was
enriched with hexamethyldisiloxane (HMDSO) vapors, which
also contribute to the growth of the porous siloxane matrix in
Amine sensing experiments
The gas sensing properties of the deposited coatings were tested
at 20 ꢂC by a DU800 Beckman Coulter UV/vis spectrometer with
a home-build gas ow setup, which has been described in detail
elsewhere.48 The foils were placed in 3 mL septum capped
quartz cuvettes through which a constant gas ow of 250 mL
minꢁ1 was passed. Prior to amine exposure, the cuvette was
purged with the carrier gas, nitrogen with 50% RH, to monitor
the baseline response of the sensing foils and aer 10 min the
carrier gas was enriched with 1 vol.% NEt3. The change of the
absorption was monitored over 120 min in intervals of 10 s at
the specic wavelength at which the foils show the largest
change before and aer exposure to the amine. These moni-
toring wavelengths are 434 nm for Zn-1, 428 nm for ZnTPP-1,
446 nm for Cr-1, Cr-2, Cr-3 and 441 nm for CrTPP-1, CrTPP-2
and CrTPP-3. Baseline absorbance was monitored at 500 nm for
every data point. Additionally, absorption spectra of the Soret
region have been measured before and aer exposure to NEt3.
Table 1 Compositions of the precursor solutions
Porphyrin
Concentrationa [g Lꢁ1
]
Foil sample
ZnIIP
0.75
0.75
0.75
1.50
3.00
0.75
0.32
0.08
Zn-1
ZnTPP-1
Cr-1
ZnIITPP
CrIIIP(Cl)(H2O)
Cr-2
Cr-3
CrIIITPP(Cl)(H2O)
CrTPP-1b
CrTPP-2
CrTPP-3
a
In 80 vol.% VTMOS and 20 vol.% DCM. b Has been described in ref. 48.
1562 | J. Mater. Chem. A, 2014, 2, 1560–1570
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
which the porphyrins are incorporated. The general deposition gas.40 No distinct vibrations from the incorporated porphyrin
parameters were adapted from the successful process condi- macrocycles can be observed, as they are hidden by the intense
tions that allowed the deposition of the reference foil CrTPP-1, matrix vibrations. XPS analysis shows an elemental composi-
which has been proven to show the best amine sensing prop- tion as expected for carbon rich plasma-polymerized organo-
erties within a series of CrIIITPP(Cl)(H2O) containing layers siloxanes due to high methyl group retention. Zn-1 is composed
prepared by the same method (for details see Experimental of 16 at.% silicon, 25 at.% oxygen, 55 at.% carbon and 4 at.%
section).48
nitrogen, while for ZnTPP-1 16 at.% silicon, 26 at.% oxygen,
54 at.% carbon and 4 at.% nitrogen are observed. This is in good
agreement with literature values.46,47 As the zinc content of the
incorporated porphyrins is rather low (0.84 at.% in ZnIIP and
1.3 at.% in ZnIITPP) only traces of zinc could be detected by XPS
in the foil. The deposited matrix Zn-1 contains (0.2 ꢃ 0.1) at.%
zinc and ZnTPP-1 (0.3 ꢃ 0.1) at.%, which represents a relatively
high porphyrin loading of the matrix of about (22 ꢃ 8)% in
both cases.
Deposition of ZnII porphyrin containing coatings
For the ZnIIP based coating Zn-1 a solution of 0.75 g Lꢁ1 of the
respective porphyrin in VTMOS/DCM has been used as the
precursor solution (Table 1). The solution was sprayed onto
the PET substrate by an ultrasonic atomizing nozzle and the
sample was subsequently exposed to the AP-DBD. To form the
nal layer, the substrate was passed 100 times through
the precursor mist and the atmospheric plasma (see Experimental
section for details). The ZnIITPP containing reference ZnTPP-1
has been prepared using 0.75 g Lꢁ1 ZnIITPP in the precursor
solution employing the same general deposition process.
Both coatings are adherent to the PET substrate foils and are
stable towards water. Neither visually noticeable cracks nor
particles were observed on the surface by eye. They show similar
FT-IR spectra with the characteristic absorptions of plasma-
polymerized organosiloxanes (see Fig. 2). The strong and broad
band observed at 1087 cmꢁ1 is assigned to a Si–O–Si network
vibration while the absorptions at 806 cmꢁ1 (n(Si–CH3)), 847
cmꢁ1 (n(Si–C) and r(CH3)), 1261 cmꢁ1 (dS(Si–CH3)), 1409 cmꢁ1
(na(CH3)), 2915 and 2960 cmꢁ1 (n(CH3)) prove the high retention
of the methyl groups from the siloxane monomer.51 The peak
observed at 1675 cmꢁ1 is commonly observed for nitrogen
plasma-polymerized organosiloxanes and is attributed to C]N
vibrations, as nitrogen is partially incorporated from the plasma
Both foils show uniform transparent pale orange-green
coloration and exhibit the characteristic UV/vis absorption
spectra of the incorporated intact metalloporphyrin macrocycle.
The foils show Soret band absorptions at 433 nm for Zn-1
(Fig. 3a) and at 428 nm for ZnTPP-1 (Fig. 4a). These absorptions
are shied bathochromically by 14 nm as compared to the
spectra observed for ZnIIP and ZnIITPP in n-hexane solutions.
Q-band absorptions are found at 565 and 603 nm and at 560 and
600 nm for Zn-1 and ZnTPP-1, respectively. UV/vis spectra of
porphyrins are known to be affected by their environment as
emphasized by the solvatochromic series. In solution their
absorption is known to be red-shied in polar solvents.49
A
similar effect may be responsible for the bathochromic shi
within the polysiloxane matrix, as it contains several polar
groups. The rigidity of the matrix can additionally lead to a
slight distortion of the entrapped porphyrin macrocycles which
is also known to induce bathochromic shis. The red-shi of
the porphyrins' absorption within the matrix may therefore be
attributed to a general solvatochromic effect. The UV/vis spectra
Fig. 3 (a) Normalized UV/vis absorption spectrum of Zn-1 with the
Soret band absorption at 433 nm and Q-band absorptions at 565 and
Fig. 2 FT-IR absorption spectra of Zn-1 on aluminum (bottom, black) 603 nm and (b) magnification of the Soret band region before (black,
and ZnTPP-1 on aluminum (top, grey).
solid) and after (grey, dotted) 2 h exposure to 1% NEt3 vapor.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 1560–1570 | 1563

View Article Online
Journal of Materials Chemistry A
Paper
Fig. 4 (a) Normalized UV/vis absorption spectrum of ZnTPP-1 with the
Soret band absorption at 428 nm and Q-band absorptions at 560 and
600 nm and (b) magnification of the Soret band region before (black,
solid) and after (grey, dotted) 2 h exposure to 1% NEt3 vapor.
Fig. 5 Top: chromatogram of the HPLC-MS analysis of extracts from
Zn-1; bottom: ESI-MS analysis of the respective peaks at 8.1 min (front)
and 11.9 min (back).
complexes,49 CrIIIP(Cl)(H2O) does not outclass its simple tetra-
phenylporphyrin equivalent CrIIITPP(Cl)(H2O) with respect to
spectral shis upon interaction with NEt3 in solution. In DCM,
both CrIII porphyrin complexes show a large hypsochromic shi
upon NEt3 exposure of about 17 nm of the Soret band. For
CrIIIP(Cl)(H2O) a shi from 452 to 435 nm is observed in DCM
(see Fig. S2†), while CrIIITPP(Cl)(H2O) shows a shi from 448 to
431 nm. The benet of the CrIIIP(Cl)(H2O) complexes is their
strikingly higher solubility in the precursor solution as
compared to CrIIITPP(Cl)(H2O). The solubility of CrIIITPP
(Cl)(H2O) in VTMOS : DCM 80 : 20 is 7.8 mmol Lꢁ1 while
39.3 mmol Lꢁ1 of CrIIIP(Cl)(H2O) can be dissolved in the
precursor solution. The increased solubility of the
CrIIIP(Cl)(H2O) complexes is attributed to their molecular
structures with the two arms above one or both sites of the
porphyrin macrocycle, which suppresses p–p stacking of the
porphyrins.49 Therefore, signicantly higher complex concen-
trations in the precursor solutions can be used during the
deposition process leading to sensing foils with a more intense
coloration as compared to the intensities achievable with
CrIIITPP(Cl)(H2O). This is a crucial step towards simple devices
for the inspection of food freshness whose response should be
visible by the human eye instead of spectrometers.
strongly indicate that the macrocycle is unaltered by the plasma
deposition process. As FWHM values of the Soret band are
similar to values observed in solution, stacking and aggregation
of the porphyrins is obviously suppressed by their thorough and
stable dispersion within the matrix.
The integrity of the relatively simple ZnIITPP sensor mole-
cule aer the described plasma treatment has already been
successfully proven by mass spectrometry of ethanol extracts
from the layer.47 To prove the preservation of the more complex
ZnIIP structure aer the plasma deposition, ethanol extracts of
Zn-1 have been analyzed by HPLC-MS. The only prominent
peaks seen in the HPLC chromatogram in Fig. 5 can be clearly
assigned to the ab-isomer of ZnIIP at 8.1 min and to the
aa-isomer at 11.9 min based on the mass spectral analysis as
well as by comparison with literature retention data.49 Hence,
the entire molecular structure of the sensor molecules,
including the shielding phenylalkynyl arms and the labile
bound ZnII, is preserved. Moreover, the initial isomeric ratio of
1 : 1 (aa : ab) is unaltered, showing that both isomers are
incorporated in the matrix.
Deposition of CrIII porphyrin containing coatings
CrIII porphyrin complexes are known to have high affinity
As indicated in Table 1, CrIIIP(Cl)(H2O) based coatings were
towards nitrogen containing axial ligands (e.g. amines) and they deposited from three different precursor solutions containing
show large spectral changes upon interaction with amines in 0.75 g Lꢁ1 (Cr-1), 1.50 g Lꢁ1 (Cr-2) and 3.00 g Lꢁ1 (Cr-3). The
solution. Therefore, they are good candidates for the prepara- deposition parameters in all cases were equivalent to the ones
tion of amine sensing devices. We have recently reported the used for the reference foil CrTPP-1 (see Experimental section
formation of CrIIITPP(Cl)(H2O) containing layers by AP-DBD for details).48 All three CrIII porphyrin containing coatings are
which are capable of colorimetric amine sensing.48 In this adherent to the PET substrate foils and are stable towards
context, we have developed the novel porphyrin complex water. Neither visually noticeably cracks nor particles were
CrIIIP(Cl)(H2O). Its synthesis is described in the Experimental observed on the surface by eye. As the FT-IR spectra are
section. In contrast to the trends observed for zinc porphyrin dominated by the absorptions of the plasma-polymerized
1564 | J. Mater. Chem. A, 2014, 2, 1560–1570
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
organosiloxane matrix rather than by the different incorpo-
rated porphyrins, the FT-IR spectra of all foils are similar
among each other and also to the one shown in Fig. 2 for Zn-1.
Therefore, no signs of the incorporated CrIII porphyrins are
detected in the FT-IR spectra of Cr-1, Cr-2 and Cr-3 (Fig. S3†).
The chromium percentage of Cr-1 is expected to be around the
0.2 at.% as that observed for zinc in Zn-1, as deposition
parameters and solution concentrations are equal for ZnII and
CrIII containing coatings. But in contrast to zinc, chromium
contents could not be quantied in foils Cr-1, Cr-2 and Cr-3
reliably down to this range by XPS, as the signals are hardly
above the noise level. This is probably because the Relative
Sensitivity Factor (RSF) of the Cr 2p is smaller compared to Zn
2p (RSFCr2p ¼ 2.4; RSFZn2p ¼ 5.59). The elemental composition
estimated by XPS regarding silicon, oxygen, carbon and
nitrogen is similar to the one measured for the zinc porphyrins
containing coating Zn-1 and ZnTPP-1.
The coloration of the three CrIIIP(Cl)(H2O) containing foils
varies from slightly green for Cr-1 to intense green for Cr-3 (see
insets in Fig. 6). Their UV/vis absorption spectra show the char-
acteristic absorptions of intact CrIII porphyrin complexes at the
same energy for each foil. The absorptions of Cr-1 to Cr-3 only
grow in intensity (Fig. 6). Hence even though the different
porphyrin loadings within the coatings could not be estimated by
XPS, the absorption spectra corroborate that the porphyrin
content is proportional to their concentration within the initial
precursor solutions. The intense Soret band absorption is seen at
458 nm and the weaker Q-band absorptions at 572 and 612 nm.
The weak absorption at 400 nm is characteristic for CrIII porphyrin
complexes with anionic axial ligands and is attributed to a p(a2u,
a1u) / d(eg) charge transfer absorption from the porphyrin to the
metal center.52 The presence of these UV/vis absorptions is a
strong indicator that neither the molecular structure of the
porphyrin macrocycle nor the oxidation state of the chromium
central metal is changed during the plasma deposition process.
Fig. 7 (a) ESI mass spectrum of extracts from Cr-1 (black, front) and
the reference ESI mass spectrum of CrIIIP(Cl)(H2O) before plasma
deposition (grey, back); each spectrum is normalized to the most
intense peak; (b) and (d) magnification of the most intense peak of the
reference spectrum and the layer extract analysis, respectively; (c) and
(e) calculated isotopic pattern for [(M) ꢁ Cl]+ and [(M) ꢁ Cl + K]+,
respectively.
To further substantiate the integrity of the molecular struc-
ture during the deposition, ethanol extracts of the coatings were
studied by mass spectrometry (for details see Experimental
section). As no method could be developed to separate the
CrIIIP(Cl)(H2O) isomers via HPLC, as was successful for ZnIIP,49
the samples were analyzed via high resolution ESI mass spec-
trometry. Fig. 7a shows a representative mass spectrum of the
Cr-1 extracts in the front (black) and the reference mass spec-
trum of molecular CrIIIP(Cl)(H2O) before plasma deposition in
the back (grey). The spectra clearly demonstrate the integrity of
the porphyrin macrocycle, the retention of the shielding phe-
nylalkynyl arms and the presence of the metal in the porphyrin.
Experimental isotopic patterns shown in Fig. 7b and d match
with calculated patterns (Fig. 7c and e, respectively) revealing
the correct assignments of the fragmentation peaks.
D. Amine sensing experiments
Fig. 6 UV/vis absorption spectra of Cr-1 (dotted), Cr-2 (dashed) and
Cr-3 (straight) with a charge transfer absorption at 400 nm, the Soret
band absorption at 458 nm and Q-band absorptions at 572 and 612
nm; insets show photographs of the respective foils.
To probe the colorimetric amine sensing ability of the deposited
coatings, foil samples were placed in a 3 mL ow cuvette and
exposed to a constant ow of 1 vol.% NEt3 vapor in the carrier
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 1560–1570 | 1565

View Article Online
Journal of Materials Chemistry A
Paper
gas (N2 with 50% relative humidity) over 2 h (for details see
Experimental section). The initial absorption of the ZnII and
CrIII containing foils does not change under humid conditions
as compared to the inert atmosphere. The amine sensing
performance of zinc porphyrin containing foils is also not
affected by change of the relative humidity (RH) in the carrier
gas (see Fig. S4†). In contrast, the performance of the chromium
porphyrin based matrices is greatly enhanced under humid
conditions (see Fig. S5†). For real-life applications like e.g. food
packaging the compatibility under humid conditions is rather
benecial than detrimental, as the ubiquitous humidity gives
no false response with the sensor system but enhances its
performance. The detailed mechanism of the interaction of CrIII
porphyrins with NEt3 either in solution or in polymer matrices
under different humid conditions is currently under investiga-
tion in our laboratories and mechanistic results will be pub-
lished in due course.
Fig. 8 Soret band UV/vis absorption before (solid lines) and after
(dashed lines) 2 h exposure to a constant nitrogen flow containing
1 vol.% NEt3 for Cr-1, Cr-2 and Cr-3; hypsochromic shifts upon
interaction with NEt3 are indicated above the respective curves.
Amine sensing with ZnII porphyrins
The Soret band absorptions of Zn-1 and ZnTPP-1 before (solid
line) and aer (dotted line) 2 h of exposure to 1 vol.% NEt3 in the
carrier gas are shown in Fig. 3b and 4b, respectively. Zn-1 shows
a small 1 nm bathochromic shi of the Soret band from 433 to
434 nm upon interaction with NEt3 and a slight increase in
intensity along with a decrease of the FWHM of the signal.
Similar minor changes are observed for ZnTPP-1 with a Soret
band shi from 428 to 429 nm. The colorimetric responses of
the sensing foils are not as large as the ones reported for the
respective porphyrin complexes exposed to NEt3 in n-hexane
solutions. Under homogenous conditions, the Soret band of
ZnIITPP in n-hexane is shied by 11 nm from 414 to 425 nm and
the one of ZnIIP by even 13 nm from 419 to 432 nm upon amine
coordination.49 As intact molecular sensors are embedded
within the matrix (see previous section), the observed discrep-
ancy between the sensor's performance in n-hexane solution
and in the matrix must be attributed to other reasons. One
possibility may be a poor accessibility of the chromophores
within the matrix. Another issue could be an environmental
matrix effect. It has been shown in serial trials with different
solvents that the absorption shis upon NEt3 coordination
decrease as the initial Soret absorption is shied bath-
ochromically.49 For instance in chloroform solutions the bath-
ochromic shi upon interaction with NEt3 also amounts only to
1 nm from 428 to 429 nm. Therefore, we propose that the
diminished absorbance shis of the sensor molecules entrap-
ped in the matrix is rather ascribed to sensor–matrix interac-
tions, comparable to the solvatochromic effect observed in
solution, than indicating a low porosity of the matrix.
line) two hours exposure to a nitrogen ow containing NEt3. The
absorptions are shied hypsochromically between 2 and 3 nm
along with a slight increase in intensity and a broadening of the
band (see Table 2). The changes are similar to that of the
reference foil CrTPP-1 under identical conditions. The differ-
ence spectra of Cr-1, Cr-2 and Cr-3, calculated by subtraction of
the spectra before interaction with NEt3 from the spectra aer
NEt3 treatment, are shown in Fig. 9. As already indicated by the
different absorptions shown in Fig. 8, the foil with the highest
porphyrin loading, Cr-3, gives the largest absolute response
upon amine exposure. For all foils the maximum change in
absorption is observed at 446 nm.
To measure the dynamic responses of the foils towards
amine exposure the changes of the absorptions at 446 nm were
monitored referenced to the absorption at 500 nm (baseline)
every ten seconds while exposed to a constant ow of 1 vol.%
NEt3 in the carrier gas (N2 with 50% RH). As the foils have
different initial absorption intensities, the recorded responses
were normalized to their respective initial Soret band absorp-
tion intensity. These normalized absorption changes are
depicted in Fig. 10a. During the rst 10 min, the foils were
exposed to a constant ow of nitrogen with 50% RH without any
amine to record the baseline response. The evanescent signals
for all foils show that there is no interaction with humidity.
Aer 110 min exposure to a 1 vol.% NEt3 ow, Cr-1 shows a
Table 2 Compiled UV/vis data for Cr-1, Cr-2 and Cr-3 before and
after exposure to NEt3
As deposited
Aer NEt3 exposurea
Amine sensing with CrIII porphyrins
Foil
sample [nm]
Position Height FWHMb Position Height FWHMb
The foils Cr-1, Cr-2 and Cr-3 were placed in ow cuvettes and
exposed to a constant ow of nitrogen (50% RH) enriched with
1 vol.% of NEt3. The responses of the foils were monitored by
changes of the Soret band absorption by UV/vis spectroscopy
(see Experimental section for details). Fig. 8 shows the Soret
band absorptions of the foils before (solid line) and aer (dotted
[a.u.]
[nm]
[nm]
[a.u.]
[nm]
Cr-1
Cr-2
Cr-3
458
458
458
0.03
0.07
0.15
23.8
27.5
28.1
456
455
455
0.04
0.09
0.19
27.8
29.2
30.6
110 min exposure to 1% NEt3. b Full width at half maximum.
a
1566 | J. Mater. Chem. A, 2014, 2, 1560–1570
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
normalized response of about 0.25 a.u. This is about one third
smaller than that observed with the reference CrTPP-1, which is
prepared from the corresponding CrIIITPP(Cl)(H2O) containing
precursor solution under the same deposition conditions. As
the responses are normalized to the initial absorption intensi-
ties, this is a sign of less sensor molecules interacting with the
analyte in Cr-1 than within CrTPP-1. This difference is also
expressed by the absolute responses of the foils and depicted in
Fig. 10b. Even though the initial Soret band intensity of the two
foils is similar, a signicantly smaller signal change is observed
for Cr-1 as compared to CrTPP-1.
When the amount of CrIIIP(Cl)(H2O) is doubled within the
sensing layers, the absolute response of the foils towards amine
exposure proportionally increases, as can be seen from a
comparison of the responses of Cr-1 (0.009 a.u.) and Cr-2
(0.018 a.u.) in Fig. 10b. The normalized responses of Cr-1 and
Cr-2, however, are superimposable. The identical normalized
responses of Cr-1 and Cr-2 show that the same fraction of sensor
molecules interacts with the amines. The similar time prole of
the two foils additionally proves that diffusion of the analyte
through the matrix is similar. We ascribe this to a similar
porosity and similar incorporation of the chromophores
accomplished during the deposition process. This indicates
that the growth of the matrix and thereby the matrix properties
are not signicantly affected by doubling the porphyrin
concentration within the precursor solution from 0.75 g Lꢁ1 (Cr-
1) to 1.50 g Lꢁ1 (Cr-2).
Fig. 9 Difference spectra of Cr-1 (dotted), Cr-2 (dashed) and Cr-3
(solid) calculated by subtraction of the UV/vis spectra before exposure
to NEt3 from the respective spectra after 2 h exposure.
This behavior obviously changes when the initial porphyrin
concentration is increased to 3.00 g Lꢁ1 (Cr-3). The normalized
response of this foil (see Fig. 10a) is increased as compared to
Cr-1 and Cr-2 and is rather similar to that observed for the
reference compound CrTPP-1. And even though the initial Soret
band intensity is doubled compared to Cr-2 (see Table 2), the
absolute response as shown in Fig. 10b is increased by a factor
of three. Both illustrations suggest that in Cr-3 a higher fraction
of porphyrin molecules interacts with the amines compared to
Cr-1 and Cr-2 with lower porphyrin concentrations. This
observation indicates that above
a certain threshold of
porphyrin concentration within the precursor solution, the
mechanism of the matrix growth is changed which enables
more chromophores to interact with the amine. As can be seen
from the normalized response, the fraction of porphyrin sites
interacting with the analyte in Cr-1 is comparable to that in
CrTPP-1. On the other hand the absolute number of porphyrins
within the matrix is higher, which leads to a stronger absolute
response of Cr-1. Aer 110 min exposure to NEt3 an absolute
response of 0.049 a.u. is observed for Cr-1, which represents a
1.6 fold increase as compared to the 0.030 a.u. of CrTPP-1.
To compare the sensors' performance with results from
other sensing systems, the foils' responses towards NEt3 expo-
sure were converted into the respective signal-to-noise ratio
(SNR) parameter (see Fig. 10b). This dimensionless value is
dened by the observed signal change divided by the signal
noise of the chosen analytical method. For a positive detection
event, a SNR $ 3 has been dened.12,28 The superior perfor-
mance of Cr-3 compared to the reference compound CrTPP-1 is
also expressed by their SNR values of 117.6 and 70.6,
Fig. 10 Time traces of the absorption change at 446 nm relative to the
absorption at 500 nm upon exposure to a constant flow of 1 vol.%
NEt3; data points measured every 10 s; exposure starts at 10 min; (a)
values normalized to the initial Soret band intensity; (b) absolute values
as measured by the spectrometer (left scale) and converted to the
respective signal-to-noise ratio (SNR, right scale).
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 1560–1570 | 1567

View Article Online
Journal of Materials Chemistry A
Paper
respectively. This has been achieved by the increased solubility
of the novel porphyrin chromophores and hence the higher
loading of the foil.
E. Influence of CrIII porphyrin
concentration on the sensor properties
As shown in the previous part for Cr-1, Cr-2 and Cr-3, the
performance of the deposited layers with respect to colorimetric
amine sensing is associated with the porphyrin concentration
within the precursor solutions. The normalized responses of the
foils as depicted in Fig. 10a show a disproportional dependence
on the solution concentrations, with a sudden increase upon a
certain threshold. The solubility of the porphyrins in the
precursor solution seems to be decisive for this behavior. If the
solutions are nearly saturated before deposition, like for Cr-3,
small aggregates may be formed upon solvent evaporation
during the spray process which may inuence the later sensor
performance in two ways.
Fig. 11 Time traces for CrTPP-1, CrTPP-2 and CrTPP-3 of the
absorption change at 441 nm relative to the absorption at 500 nm
upon exposure to a constant gas flow of 1 vol.% NEt3; data points
measured every 10 s; exposure starts at 10 min and response
normalized to the initial Soret band intensity.
On the one hand, the formed aggregates may act as seeds for
the matrix growth leading to a more porous material and
therefore enable more chromophores to interact with the
amine. Unfortunately, no direct experimental evidence could so
far be obtained for this assumption as SEM analyses of the three
foils show a similar surface morphology (see Fig. S6†). Cr-1, Cr-2
and Cr-3 do all show smooth surfaces with potential small
porosities covered by the platinum layer which has been sput-
tered onto the samples to avoid charging effects. Attempts to
obtain SEM pictures with less or no platinum coating were
unsuccessful due to the insulating properties of both the
substrate and the layer. On the other hand formation of
aggregates during the deposition from nearly saturated solu-
tions may more oen lead to spatially close incorporation of the
chromophores within a matrix pore. If more than one chro-
mophore is involved in the actual sensing event with NEt3, this
could explain the remarkably higher response of Cr-3.
Even though there is no direct experimental proof for these
assumptions, the general dependence of the sensor foils'
performances on the initial chromophore concentration in
solution becomes obvious by further comparison of the
CrIIIP(Cl)(H2O) and CrIIITPP(Cl)(H2O) systems. As Cr-3 and
CrTPP-1 show a similar normalized response towards NEt3
vapors (Fig. 10a), which reects a similar fraction of porphyrin
molecules interacting with NEt3, a similar constitution of both
matrices can be assumed. To achieve these properties, an initial
deposited from diluted CrIIITPP(Cl)(H2O) precursor solutions
containing 0.32 g Lꢁ1 and 0.08 g Lꢁ1 porphyrin to form CrTPP-2
and CrTPP-3, respectively. As shown in Fig. 11, their optical
response towards NEt3 exposure is also signicantly lowered by
52% as compared to CrTPP-1 and is comparable to that
observed for Cr-2 and Cr-3. This shows that also in
CrIIITPP(Cl)(H2O) based coatings only a smaller fraction of
chromophores interact with the analyte if they are deposited
from diluted solutions.
The similar dependence of the sensor responses on the
respective initial concentration of CrIIIP(Cl)(H2O) or
CrIIITPP(Cl)(H2O) in the precursor solutions reveals a common
inuence on the matrix growth mechanism. If the precursor
solution's concentration is increased above a certain threshold
value, approaching the saturation limit, a matrix/chromophore
constitution is achieved which facilitates the interaction of a
higher fraction of chromophores with the analyte leading to a
remarkably better sensor performance. The detailed mecha-
nism, however, is so far unclear and is under current investi-
gation in our laboratories.
F. Conclusions
porphyrin concentration of 3.00 g Lꢁ1 within the precursor Four different metalloporphyrins, ZnIIP, CrIIIP(Cl)(H2O),
solution was necessary for Cr-3, while for CrTPP-1 0.75 g Lꢁ1 ZnIITPP and CrIIITPP(Cl)(H2O) were successfully incorporated
CrIIITPP(Cl)(H2O) has been used. Both concentrations represent into porous polysiloxane matrices via an atmospheric pressure
almost saturated solutions for the respective porphyrin, as the plasma enhanced chemical vapor deposition. The structure of
solubility of CrIIIP(Cl)(H2O) in the precursor solution is the metalloporphyrin complexes was entirely stable during the
approximately
5
times higher than the solubility of plasma treatment, even the complex molecular structures of
CrIIITPP(Cl)(H2O). From diluted solutions as used for the ZnIIP and CrIIIP(Cl)(H2O) with two phenylalkynyl substituents
preparation of Cr-1 (0.75 g Lꢁ1) and Cr-2 (1.50 g Lꢁ1), sensors are fully retained.
with lower performance have been obtained. This is seen by
Due to the porous nature of the matrix and the amine
their superimposable, but lower, normalized response towards sensing properties of the incorporated porphyrins, the depos-
NEt3 as depicted in Fig. 10a. Accordingly, layers have been ited layers can be used for the colorimetric detection of volatile
1568 | J. Mater. Chem. A, 2014, 2, 1560–1570
This journal is © The Royal Society of Chemistry 2014

View Article Online
Paper
Journal of Materials Chemistry A
amines as exemplied by exposure to NEt3. The layers based on
zinc porphyrins show a 1 nm bathochromic shi of the Soret
band absorption along with a slight increase of intensity upon
interaction with NEt3. The remarkable color changes observed
in n-hexane solutions, especially of ZnIIP, could not completely
be transferred to the deposited thin coatings. This behavior is
attributed to a solvatochromic effect of the matrix on the
porphyrins' absorption properties, as a similar effect is also
observed e.g. in chloroform solutions.
2 A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran,
M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh,
¨
S. M. Zakeeruddin and M. Gratzel, Science, 2011, 334, 629.
3 H. Imahori, S. Kang, H. Hayashi, M. Haruta, H. Kurata,
S. Isoda, S. E. Canton, Y. Infahsaeng, A. Kathiravan,
´
¨
T. Pascher, P. Chabera, A. P. Yartsev and V. Sundstrom,
J. Phys. Chem. A, 2011, 115, 3679.
4 A. Huijser, T. J. Savenije, A. Kotlewski, S. J. Picken and
L. D. A. Siebbeles, Adv. Mater., 2006, 18, 2234.
5 C.-L. Wang, W.-B. Zhang, R. M. Van Horn, Y. Tu, X. Gong,
S. Z. D. Cheng, Y. Sun, M. Tong, J. Seo, B. B. Y. Hsu and
A. J. Heeger, Adv. Mater., 2011, 23, 2951.
6 Z. Liu, A. a. Yasseri, J. S. Lindsey and D. F. Bocian, Science,
2003, 302, 1543.
7 M. O. Senge, M. Fazekas, E. G. A. Notaras, W. J. Blau,
M. Zawadzka, O. B. Locos and E. M. N. Mhuircheartaigh,
Adv. Mater., 2007, 19, 2737.
8 M. H. Hoang, Y. Kim, M. Kim, K. H. Kim, T. W. Lee,
D. N. Nguyen, S.-J. Kim, K. Lee, S. J. Lee and D. H. Choi,
Adv. Mater., 2012, 24, 5363.
9 S.-J. Choi, Y.-C. Lee, M.-L. Seol, J.-H. Ahn, S. Kim, D.-I. Moon,
J.-W. Han, S. Mann, J.-W. Yang and Y.-K. Choi, Adv. Mater.,
2011, 23, 3979.
The CrIII porphyrin containing layers show a larger spectral
shi and exhibit a stronger sensor response signal upon inter-
action with NEt3. Layers based on the novel metalloporphyrin
CrIIIP(Cl)(H2O) show a 3 nm hypsochromic shi when exposed
to NEt3, which is comparable to responses observed for coatings
containing CrIIITPP(Cl)(H2O). Due to the signicantly higher
solubility of CrIIIP(Cl)(H2O) as compared to CrIIITPP(Cl)(H2O),
coatings with higher chromophore loading could be produced.
This leads to a visible intense coloration of the foils and a
stronger response upon NEt3 exposure. The 3 nm shi of the
Soret band may only be seen by a trained eye without any
support. Nevertheless, the absorbance change can easily be
monitored spectroscopically fully similar to existing amine
sensors. The signal-to-noise ratio is greatly enhanced up to
117.6 which is benecial for the production of amine sensing 10 A. Huijser, B. M. J. M. Suijkerbuijk, R. J. M. Klein Gebbink,
devices.
Higher porphyrin loadings not only proportionally increase
T. J. Savenije and L. D. A. Siebbeles, J. Am. Chem. Soc.,
2008, 130, 2485.
the coloration and the sensitivity of the sensor, but also a 11 B. Johnson-White, M. Zeinali, K. M. Shaffer, C. H. Patterson
certain non-linear effect is noted. Above a certain threshold
concentration the constitution of the deposited matrices is
Jr, P. T. Charles and M. A. Markowitz, Biosens. Bioelectron.,
2007, 22, 1154.
changed in such a way that a higher fraction of chromophores 12 S. Tao, G. Li and H. Zhu, J. Mater. Chem., 2006, 16, 4521.
interacts with the analyte. This leads to an improvement of the 13 M. Tonezzer, G. Maggioni and E. Dalcanale, J. Mater. Chem.,
normalized sensor response of 140% for CrIIIP(Cl)(H2O) based
coatings and 200% for CrIIITPP(Cl)(H2O) based ones.
2012, 22, 5647.
14 T. H. Richardson, R. A. Brook, F. Davis and C. A. Hunter,
Colloids Surf., A, 2006, 284–285, 320.
As functionalized porphyrins have been deposited unaltered
via an atmospheric pressure plasma enhanced CVD for the rst 15 O. Worsfold, C. M. Dooling, T. H. Richardson,
time, new possibilities to improve the sensing layer properties
open up. The possibility to use further optimized porphyrins or
M. O. Vysotsky, R. Tregonning, C. A. Hunter and
C. Malins, Colloids Surf., A, 2002, 200, 859.
other chromophore classes may nally lead to colorimetric 16 N. A. Rakow and K. S. Suslick, Nature, 2000, 406, 710.
sensing foils which (i) show a visible color change and (ii) have 17 A. D. F. Dunbar, S. Brittle, T. H. Richardson, J. Hutchinson,
been produced by this environmentally friendly and easy to
scale up process. The potential demonstrated here may be
C. A. Hunter, D. Building, B. Hill and S. Sheffield, J. Phys.
Chem. B, 2010, 11697.
inspiring for researchers working in the elds of hybrid func- 18 S. a. Brittle, T. H. Richardson, A. D. F. Dunbar, S. M. Turega
tional materials and immobilization of organic compounds in
general.
and C. a. Hunter, J. Mater. Chem., 2011, 21, 4882.
19 C. Di Natale, D. Salimbeni, R. Paolesse, A. Macagnano and
A. D'Amico, Sens. Actuators, B, 2000, 65, 220.
20 S. H. Lim, L. Feng, J. W. Kemling, C. J. Musto and
K. S. Suslick, Nat. Chem., 2009, 1, 562.
Acknowledgements
21 M. Tonezzer, G. Maggioni, A. Quaranta, S. Carturan and
G. Della Mea, Sens. Actuators, B, 2009, 136, 290.
22 M. Tonezzer, A. Quaranta, G. Maggioni, S. Carturan and
G. Della Mea, Sens. Actuators, B, 2007, 122, 620.
23 S. Kladsomboon and T. Kerdcharoen, Anal. Chim. Acta, 2012,
757, 75.
The authors thank the Luxembourgish “Fonds National de la
Recherche” (FNR) for nancial support through the SurfAmine
CORE project. Skillful characterizations of and valuable
discussions with Dr C. Guignard, Dr G. Frache and J. Didierjean
from the CRP-Gabriel Lippmann are gratefully acknowledged.
24 D. Delmarre and C. Bied-Charreton, Sens. Actuators, B, 2000,
62, 136.
25 W. Qin, P. Parzuchowski, W. Zhang and M. E. Meyerhoff,
Anal. Chem., 2003, 75, 332.
References
1 L.-L. Li and E. W.-G. Diau, Chem. Soc. Rev., 2013, 42, 291.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 1560–1570 | 1569

View Article Online
Journal of Materials Chemistry A
Paper
26 J. Spadavecchia, R. Rella, P. Siciliano, M. G. Manera and 40 N. D. Boscher, P. Choquet, D. Duday and S. Verdier, Plasma
A. Alimelli, Sens. Actuators, B, 2006, 115, 12. Processes Polym., 2010, 7, 163.
27 F. A. Nwachukwu and M. G. Baron, Sens. Actuators, B, 2003, 41 N. D. Boscher, P. Choquet, D. Duday and S. Verdier, Surf.
90, 276. Coat. Technol., 2011, 205, 5350.
28 N. A. Rakow, A. Sen, M. C. Janzen, J. B. Ponder and 42 U. Kogelschatz, Plasma Chem. Plasma Process., 2003,
K. S. Suslick, Angew. Chem., Int. Ed., 2005, 44, 4528. 23, 1.
29 M. T. Veciana-Nogues, A. Marine-Font and M. C. Vidal- 43 N. D. Boscher, P. Choquet, D. Duday, N. Kerbellec,
´
´
Carou, J. Agric. Food Chem., 1997, 45, 2036.
30 C. Balamatsia, A. Patsias, M. Kontominas and I. Savvaidis,
Food Chem., 2007, 104, 1622.
31 Y. Xu, W. Xia and J. M. Kim, Int. J. Food Sci. Technol., 2009,
44, 1547.
J.-C. Lambrechts and R. R. Maurau, J. Mater. Chem., 2011,
21, 18959.
44 J. Bardon, J. Bour, D. Del Frari, C. Arnoult and D. Ruch,
Plasma Processes Polym., 2009, 6, S655.
45 P. Heyse, A. Van Hoeck, M. B. J. Roeffaers, J.-P. Raffin,
¨
¨
32 J. P. Kerry, M. N. O'Grady and S. A. Hogan, Meat Sci., 2006,
74, 113.
33 T. H. Richardson, C. M. Dooling, L. T. Jones and R. A. Brook,
Adv. Colloid Interface Sci., 2005, 116, 81.
A. Steinbuchel, T. Stoveken, J. Lammertyn, P. Verboven,
P. A. Jacobs, J. Hoens, S. Paulussen and B. F. Sels,
Plasma Processes Polym., 2011, 8, 965.
46 N. D. Boscher, D. Duday, P. Heier, K. Heinze, F. Hilt and
P. Choquet, Surf. Coat. Technol., 2013, 234, 48.
34 C. M. Dooling, O. Worsfold, T. H. Richardson,
R. Tregonning, M. O. Vysotsky, C. A. Hunter, K. Kato, 47 N. D. Boscher, D. Duday, P. Heier, K. Heinze, F. Hilt and
K. Shinbo and F. Kaneko, J. Mater. Chem., 2001, 11, 392. P. Choquet, Plasma Processes Polym., 2013, 10, 336.
35 A. D. F. Dunbar, T. H. Richardson, J. Hutchinson and 48 N. D. Boscher, T. Bohn, P. Heier, F. Moisy, B. Untereiner,
C. A. Hunter, Sens. Actuators, B, 2008, 128, 468.
36 A. A. Vaughan, M. G. Baronb and R. Narayanaswamya, Anal.
Commun., 1996, 33, 393.
K. Heinze and P. Choquet, Sens. Actuators, B, 2014, 191,
553.
¨
49 P. Heier, C. Forster, D. Schollmeyer, N. Boscher, P. Choquet
37 P. Heyse, R. Dams, S. Paulussen, K. Houthoofd, K. Janssen,
and K. Heinze, Dalton Trans., 2013, 42, 906.
P. a. Jacobs and B. F. Sels, Plasma Processes Polym., 2007, 4, 50 D. A. Summerville, R. D. Jones, B. M. Hoffmann and
145. F. Basolo, J. Am. Chem. Soc., 1977, 99, 8195.
38 C. Tendero, C. Tixier, P. Tristant, J. Desmaison and 51 N. D. Boscher, P. Choquet, D. Duday and S. Verdier, Surf.
P. Leprince, Spectrochim. Acta, Part B, 2006, 61, 2. Coat. Technol., 2010, 205, 2438.
39 R. Prat, Y. Koh, Y. Babukutty, M. Kogoma, S. Okazaki and 52 M. Gouterman, L. K. Hanson, G.-E. Khalil, W. R. Leenstra
M. Kodama, Polymer, 2000, 41, 7355.
and J. W. Buchler, J. Chem. Phys., 1975, 62, 2343.
1570 | J. Mater. Chem. A, 2014, 2, 1560–1570
This journal is © The Royal Society of Chemistry 2014