Synthesis and QCM gas-sensing properties of 3,4-dialkoxyphenyl tosylamino-substituted phthalocyanines

Article abstract of DOI:10.1142/S1088424619501906

Octa-substituted metallophthalocyanines [M = Ni(II), Zn(II), Co(II), and Cu(II)] carrying 3,4-dialkoxyphenyl tosylamino groups at the peripheral positions have been synthesized from 1,2-dicyano-4,5-bis[(3,4-dialkoxyphenyl-tosylamino)methyl]benzene in the

Full text of DOI:10.1142/S1088424619501906

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 1–10
DOI: 10.1142/S1088424619501906
Published at https://www.worldscinet.com/jpp/
Synthesis and QCM gas-sensing properties of
3,4-dialkoxyphenyl tosylamino-substituted phthalocyanines
Mika Harbeck*, Zafer S¸en, Dilek D. Erbahar, Esranur Fidan Çelik, Gülay Gümüs¸
and Emel Musluog˘lu
TÜBITAK Marmara Research Center, Materials Institute, P.O. Box 21, Gebze-Kocaeli, 41470, Turkey
Dedicated to Professor Roberto Paolesse on the occasion of his 60th birthday.
Received 14 October 2019
Accepted 2 December 2019
ABSTRACT: Octa-substituted metallophthalocyanines [M = Ni(II), Zn(II), Co(II), and Cu(II)]
carrying 3,4-dialkoxyphenyl tosylamino groups at the peripheral positions have been synthesized
from 1,2-dicyano-4,5-bis[(3,4-dialkoxyphenyl-tosylamino)methyl]benzene in the presence of the
corresponding anhydrous metal salt. Next to the metal ion center, the length of the alkyl chains in the
dialkoxyphenyl moiety (n = 4, 5, 6, and 12) was varied. In total, sixteen soluble phthalocyanines have
been characterized by elemental analysis, FT-IR and 1H-NMR spectroscopy as well as mass spectrometry.
Furthermore, the gas sensing properties of these new compounds have been studied using quartz crystal
microbalance transducers. The sensing properties are described on the basis of sensor responses to
nine different test analytes comprising volatile organic compounds, toxic gases, and chemical warfare
agent simulants. The influence of the metal ion center and substituents on sensor selectivity and
sensitivity is discussed. The compounds show good performance in the gas-sensing experiments with
diverse responses to the analytes. Phthalocyanine species with pronounced selectivity for polar analytes,
hydrocarbons or amines have been identified among the set of sensors with the help of multivariate data
exploration methods. The results reveal that quite a high diversity in terms of selectivity is introduced
through the minute variations to the phthalocyanine structure.
KEYWORDS: phthalocyanine, gas sensing, QCM, volatile organic compounds, toxic gases, CWA
simulants.
technologies for chemical sensor testing and application,
INTRODUCTION
as they are easy to use, reliable, and suitable for many
Sorption-based chemical sensors are most adequate
types of sensitive materials. The performance of these
for gas sensing applications targeting vapors of volatile
chemical sensors highly depends on the chemical and
organic compounds (VOCs) and similar compounds.
physical properties of the sensitive material. A common
Generally, for analyte detection and classification several
compound for sensitive sorption layers in chemical gas
partially selective but complementary sensing materials
sensors is phthalocyanines (Pcs). They have proven
on a suitable transducer, e.g. mechanical, optical or
their excellent sensing capabilities already in many gas
electrical, are combined to form a sensor array. Acoustic
sensing applications with acoustic transducers including
devices such as the quartz crystal microbalance (QCM)
the QCM [1].
andsurfaceacousticwavesensorsareattractivetransducer
The growing use of phthalocyanines as advanced
functional materials has encouraged research on the
synthesis of new compounds which differ from one
*Correspondence to: Mika Harbeck, TÜBITAK Marmara
another in the central metal ion or in the peripheral
substituents. Since they are usually applied as thin films,
soluble derivatives are preferred to allow easy deposition
Research Center, Materials Institute, P.O. Box 21, 41470
Gebze, Kocaeli, Turkey, tel.: +90 262 677 3123, fax: +90 262
641 2309, email: mika.harbeck@tubitak.gov.tr.
Copyright © 2019 World Scientific Publishing Company

2
M. HARBECK ET AL.
or coating from solution. This trivial but important
prerequisite has to be considered in the design of new
sensitive compounds in addition to the expected sensing
properties. This factor restricts the choice of potential
substituents, as not all possible compounds have enough
solubility in solvents suitable for the coating process.
Unsubstituted Pcs are insoluble in organic solvents,
but the solubility can be enhanced by introducing certain
functional groups to the peripheral benzene rings of the
phthalocyanine structure such as alkyl [2, 3], alkoxy
[4, 5], alkoxymethyl[6]orpoly(oxyethylene)[7, 8]groups.
Amino-substituted metallophthalocyanine derivatives are
found to be promising, since these functional groups are
known to enhance solubility and can be modified with
different moieties to alter the analyte sorption properties.
Such derivatives have been previously synthesized
mostly for the preparation of inks, dyes and pigments
[9–11]. Tosylamino-substituted phthalocyanines without
further substituents were previously studied as gas-
sensing materials with FT-IR spectroscopy and the QCM,
providing evidence of many active centers for analyte-Pc
interactions [12]. They have also been studied in the liquid
phase as sensing materials with total internal reflection
ellipsometry [13] and UV-vis spectroscopy [14, 15].
In this work, in total sixteen nickel (NiPc), zinc (ZnPc),
copper (CuPc) and cobalt (CoPc) phthalocyanines
having tosylamino substituents with 3,4-dialkoxyphenyl
moieties of different alkyl chain lengths (n = 4, 5, 6,
and 12) are presented and investigated in their gas sensing
properties using the QCM. The synthesis and chemical
characterization of the new compounds is described. For
assessment of the gas sensing performance the sensors
have been exposed to nine selected test analytes. The
influence of the metal ion center and substituents on
sensor selectivity and sensitivity is examined using
multivariate sensor data.
the Supporting information. All intermediate compounds
have been purified via column chromatography and
thoroughly characterized prior to the next reaction step.
The procedures for all other compounds including the
final phthalocyanines are given below:
Preparation of 1,2-dibromo-4,5-bis[(3,4-dialkoxy
phenyl-tosylamino)methyl]benzene (5a–5d). A solution
of N-[3,4-bis(dodecyloxy)phenyl]-4-methylbenzenesul-
fonamide (4a) (16 g, 0.026 mol) in anhydrous DMF
(200 ml) containing finely ground anhydrous K2CO3
(8.60 g, 0.062 mol) was heated under argon for 1 h at
30–40°C. A solution of 1,2-dibromo-4,5-bis(bromo-
methyl)benzene (5.49 g, 0.013 mol) in anhydrous DMF
(200 ml) was added dropwise over a period of 1 h. The
reaction mixture was stirred under argon at 50–60°C
for 5 days. It was then poured into ice water (150 g)
and extracted with dichloromethane. The extract was
dried over Na2SO4 and the solvent was evaporated.
Recrystallization from ethanol gave a pure product of
white crystals. The compound is soluble in n-hexane,
chloroform, ethanol, acetone, DMF, and THF. Yield 12 g
(62%), mp 80°C. Found: C 67.00; H 8.35; N 1.88; Anal.
calcd for C82H126Br2N2O8S2: C 66.10; H 8.38; N 1.90;
IR mmax (cm-1): 2921–2853 (CH2), 1595, 1511, 1349
(O=S=O), 1164, 1091, 813, 738, 662. 1H-NMR (CDCl3),
d (ppm): 7.48–7.47 (d, 4H, Ar-H), 7.29 (s, 2H, Ar-H),
7.23–7.21 (d, 4H, Ar-H), 6.58–6.56 (d, 2H, Ar-H), 6.31
(d, 2H, Ar-H), 6.29 (s, 2H, Ar-H), 4.61 (s, 4H, CH2),
3.84–3.83 (t, 4H, CH2-O), 3.67–3.64 (t, 4H, CH2-O),
2.36 (s, 6H, Tosyl- Ar-CH3), 1.72–1.69 (p, 4H, CH2-
CH2-O), 1.64-1.61 (p, 4H, CH2-CH2-O), 1.37–1.29 (m,
72H, CH2), 0.8 (t, 12H, CH3); MS (FAB), (m/z): 1513
[M + Na]+.
5b, 5c, and 5d were synthesized according to 5a.
5b: Yield 62%, mp 100°C. Found: C 59.57; H 6.64;
N 2.77; Anal. calcd for C58H78Br2N2O8S2: C 60.37; H
6.81; N 2.43; IR, mmax (cm-1): 2949–2868 (CH2), 1593,
1513, 1345 (O=S=O), 1165, 1090, 851, 813, 714, 658.
1H-NMR (CDCl3), d (ppm): 7.47–7.45 (d, 4H, Ar-H),
7.39 (s, 2H, Ar-H), 7.23–7.19 (d, 4H, Ar-H), 6.58–6.57
(d, 2H, Ar-H), 6.32 (d, 2H, Ar-H) 6.30 (s, 2H, Ar-H), 4.61
(s, 4H, CH2), 3.86–3.83 (t, 4H, CH2-O), 3.68–3.65 (t, 4H,
CH2-O), 2.37 (s, 6H, Tosyl-Ar-CH3), 1.74–1.68 (p, 4H,
CH2-CH2-O), 1.66–1.60 (p, 4H, CH2-CH2-O), 1.27 (m,
24H, CH2), 0.84 (t, 12H, CH3); MS (FAB), (m/z): 1177
[M + Na]+.
5c: Yield 60%, mp 113°C. Found: C 58.95; H 6.40; N
2.57; Anal. calcd for C54H70Br2N2O8S2: C 59.01; H 6.42;
N 2.55; IR, mmax (cm-1): 2953–2870 (CH2), 1592, 1511,
1339 (O=S=O), 1163, 1089, 889, 816, 708, 658. 1H-NMR
(CDCl3), d (ppm): 7.58–7.56 (d, 4H, Ar-H), 7.39 (s, 2H,
Ar-H), 7.32–7.28 (d, 4H,Ar-H), 6.68 (d, 2H,Ar-H), 6.66–
6.41 (d, 2H, Ar-H) 6.39 (s, 2H, Ar-H), 4.70 (s, 4H, CH2),
3.95–3.93 (t, 4H, CH2-O), 3.77–3.74 (t, 4H, CH2-O),
2.25 (s, 6H, Tosyl-Ar-CH3), 1.82–1.79 (p, 4H, CH2-
CH2-O), 1.78–1.74 (p, 4H, CH2-CH2-O), 1.42–1.21 (m,
16H, CH2), 0.87 (t, 12H, CH3); MS (FAB), (m/z):1099.
EXPERIMENTAL
Chemical characterization
Elemental analyses were obtained using a Thermo
Finnigan (now Thermo Fisher Scientific) Flash 1112
instrument. Infrared spectra were recorded on a Perkin
Elmer Spectrum BX FT-IR system. 1H-NMR spectra were
recorded in CDCl3 solution on a Bruker orVarian 500 MHz
spectrometer. Matrix-assisted laser desorption/ionization
time-of-flight mass spectrometry (MALDI-TOF-MS)
measurements were performed on a Bruker Daltonics
MicrOTOF. Positive ion and linear mode MALDI-
TOF MS spectra of the compounds were obtained in
2,5-dihydroxy benzoic acid (DHB) or a dithranol MALDI
matrix using a nitrogen laser accumulating 50 laser shots.
Phthalocyanine synthesis
Detailed experimental procedures and conditions and
the characterization of the compounds 1–4 can be found in
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 2–10

SYNTHESIS AND QCM GAS-SENSING PROPERTIES OF 3,4-DIALKOXYPHENYL
3
5d: Yield 60%, mp 127°C. Found: C 57.00; H 6.00;
3.51–3.49 (t, 4H, CH2-O), 2.47 (s, 6H, Tosyl-Ar-CH3),
1.83–1.80 (p, 4H, CH2-CH2-O), 1.75–1.72 (p, 4H, CH2-
CH2-O), 1.23 (m, 16H, CH2), 0.96 (t, 12H, CH3). MS
(FAB), (m/z): 1077 [M]+.
N 2.77; Anal. calcd for C50H62Br2N2O8S2: C 57.44; H
6.17; N 2.68; IR, mmax (cm-1): 2958–2867 (CH2), 1597,
1511, 1336 (O=S=O), 1166, 1090, 883, 816, 709, 658.
1H-NMR (CDCl3), d (ppm): 7.36–7.34 (d, 4H, Ar-H),
7.17 (s, 2H, Ar-H), 7.13–7.06 (d, 4H, Ar-H), 6.46 (d, 2H,
Ar-H), 6.46–6.44 (d, 2H, Ar-H) 6.19 (s, 2H, Ar-H), 4.48
(s, 4H, CH2), 3.72–3.70 (t, 4H, CH2-O), 3.56–3.53 (t, 4H,
CH2-O), 2.30 (s, 6H, Tosyl-Ar-CH3), 1.60–1.54 (p, 4H,
CH2-CH2-O), 1.51–1.45 (p, 4H, CH2-CH2-O), 1.31–1.19
(m, 8H, CH2), 0.78 (t, 12H, CH3); MS (FAB), (m/z): 1077
[M + Na + H2O ]+.
6d: Yield 62%, mp 148°C. Found: C 66.75; H 6.60;
N 5.90; Anal. calcd for C52H62N4O8S2: C 66.78; H 6.68;
N 5.99; IR, mmax (cm-1): 2959–2869 (CH2), 2236 (C≡N),
1592, 1510, 1334 (O=S=O), 1165, 1090, 857, 816, 708,
1
658. H-NMR (CDCl3), d (ppm): 7.64 (s, 2H, Ar-H),
7.58–7.47 (d, 4H, Ar-H), 7.49–7.47 (d, 4H, Ar-H), 6.60–
6.58 (d, 2H, Ar-H), 6.38–6.32 (d, 2H, Ar-H) 6.24 (s, 2H,
Ar-H), 4.89 (s, 4H, CH2), 3.96–3.94 (t, 4H, CH2-O),
3.78–3.75 (t, 4H, CH2-O), 2.47 (s, 6H, Tosyl-Ar-CH3),
1.79–1.72 (p, 4H, CH2-CH2-O), 1.71–1.70 (p, 4H, CH2-
CH2-O), 1.47 (m, 8H, CH2), 0.97 (t, 12H, CH3); MS
(FAB), (m/z): 957 [M + Na]+.
Preparation of 1,2-dicyano-4,5-bis[(3,4-dialkoxy-
phenyl-tosylamino)methyl]benzene (6a–6d). 5a (9 g,
6.04 mmol), CuCN (1.66 g, 18.5 mmol), and anhydrous
DMF (26 ml) were refluxed and stirred at 175°C for 9 h
under argon. After cooling down to room temperature,
the dark brown mixture was poured into 25% aqueous
NH4OH (132 ml) and air was passed through the
solution for 24 h. It became dark blue and a reddish
brown precipitate formed. The reddish brown precipitate
was purified by column chromatography on silica gel
with hexane-dichloromethane (5:2 v/v) to obtain a beige
product after evaporation. The compound is soluble in
n-hexane, chloroform, ethanol, acetone, DMF, and THF.
Yield3g(72%),mp89°C.Found:C73.00;H9.19;N4.05;
Anal. calcd for C84H126N4O8S2: C 72.91; H 9.11; N 4.32;
IR, mmax (cm-1): 2921–2852 (CH2), 2233 (C≡N), 1595,
Preparation of the nickel phthalocyanines (7a–7d).
6a (0.500 g, 3.6 10-4 mol) and anhydrous NiCl2 (0.116 g,
9.03 10-4 mol) were refluxed in dry quinoline (1.5 ml)
and stirred at 170°C for 5 h. After cooling to room
temperature, the reaction mixture was treated with
ethanol (60 ml) and then the crude product was washed
with water and ethanol to remove the unreacted organic
material. The green product was dried with diethyl ether
and purified by column chromatography (silica gel, 5:2
v/v; n-hexane:CH2Cl2). The compound is soluble in
n-hexane, chloroform, DMF, and acetone. Yield 0.050 g
(10%), mp > 200°C. Found: C 71.01; H 8.95; N 3.92;
Anal. calcd for C336H504N16NiO32S8: C 72.14; H 9.04;
N 4.00; IR, mmax (cm-1): 2921–2852 (CH2), 1595, 1511,
1460, 1345, 1259, 1132 (O=S=O), 1090, 941, 860, 660.
1H-NMR (CDCl3), d (ppm): 9.20 (s, 8H, Ar-H), 7.64–
7.47 (d, 16H, Ar-H), 7.35–7.19 (d, 16H, Ar-H), 6.71–6.69
(d, 8H, Ar-H), 6.59–6.55 (d, 8H, Ar-H) 6.32 (s, 8H,
Ar-H), 5.33 (s, 16H, Ar-CH2-N), 3.85–3.83 (t, 16H,
CH2-O), 3.72–3.61 (t, 16H, CH2-O), 2.42 (s, 24H, Tosyl-
Ar-CH3), 1.74–1.70 (p, 16H, CH2-CH2-O), 1.65–1.62
(p, 16H, CH2-CH2-O), 1.19 (m, 288H, CH2), 0.80 (t, 48H,
CH3); MS (FAB), (m/z): 5592 [M]+.
1
1467, 1344, 1165 (O=S=O), 1090, 942, 660. H-NMR
(CDCl3), d (ppm): 7.55 (s, 2H, Ar-H), 7.48–7.46 (d, 4H,
Ar-H), 7.25–7.23 (d, 4H, Ar-H), 6.59–6.57 (d, 2H, Ar-H),
6.32 (d, 2H, Ar-H), 6.32 (s, 2H, Ar-H), 4.81 (s, 4H, CH2),
3.85–3.83 (t, 4H, CH2-O), 3.66–3.64 (t, 4H, CH2-O), 2.38
(s, 6H, Tosyl-Ar-CH3), 1.77–1.73 (p, 4H, CH2-CH2-O),
1.67–1.63 (p, 4H, CH2-CH2-O), 1.19 (m, 72H, CH2), 0.8
(t, 12H, CH3); MS (FAB), (m/z): 1407 [M + Na]+.
6b, 6c, and 6d were synthesized according to 6a.
6b: Yield 64%, mp 120°C. Found: C 68.17; H 6.53;
N 5.57; Anal. calcd for C60H78N4O8S2: C 68.90; H 7.52;
N 5.35; IR, mmax (cm-1): 2950–2868 (CH2), 2220 (C≡N),
1593, 1513, 1345 (O=S=O), 1165, 1090, 851, 813, 714,
7b, 7c, and 7d were synthesized according to 7a.
7b: Yield 10%, mp > 200°C. Found; C 68.00; H 7.45;
N 5.27; Anal. calcd for C240H312N16NiO32S8: C 67.85; H
7.40; N 5.28; IR, mmax (cm-1): 2926–2858 (CH2), 1595,
1511, 1467, 1342, 1258, 1158 (O=S=O), 1090, 1017,
940, 810, 706, 660. 1H-NMR (CDCl3), d (ppm): 9.01 (s,
8H, Ar-H), 7.54–7.52 (d, 16H, Ar-H), 7.20–7.19 (d, 16H,
Ar-H), 6.56–6.54 (d, 8H, Ar-H), 6.46–6.44 (d, 8H, Ar-H),
6.40 (s, 8H, Ar-H), 5.21 (s, 16H, Ar-CH2-N), 3.71 (t,
16H, CH2-O), 3.53–3.51 (t, 16H, CH2-O), 2.28 (s, 24H,
Tosyl-Ar-CH3), 1.60–1.57 (p, 16H, CH2-CH2-O), 1.52–
1.49 (p, 16H, CH2-CH2-O), 1.39 (m, 96H, CH2), 0.90
(t, 48H, CH3); MS (FAB), (m/z): 4246 [M]+.
7c:Yield 12%, mp > 200°C. Found: C 66.85.; H 7.00.;
N 5.57; Anal. calcd for C224H280N16NiO32S8: C 66.87; H
7.02; N 5.57; IR, mmax (cm-1): 2930–2870 (CH2), 1595,
1509, 1467, 1343, 1259, 1160 (O=S=O), 1090, 945, 811,
706, 660. 1H-NMR (CDCl3), d (ppm): 9.23 (s, 8H, Ar-H),
1
658. H-NMR (CDCl3), d (ppm): 7.55 (s, 2H, Ar-H),
7.51–7.46 (d, 4H, Ar-H), 7.25–7.19 (d, 4H, Ar-H),
6.59–6.57 (d, 2H, Ar-H), 6.32 (d, 2H, Ar-H) 6.30 (s,
2H, Ar-H), 4.81 (s, 4H, CH2), 3.86–3.83 (t, 4H, CH2-O),
3.66–3.64 (t, 4H, CH2-O), 2.38 (s, 6H, Tosyl-Ar-CH3),
1.74–1.68 (p, 4H, CH2-CH2-O) 1.66–1.61 (p, 4H, CH2-
CH2-O), 1.25 (m, 24H, CH2), 0.8 (t, 12H, CH3). MS
(FAB), (m/z): 1046 [M]+.
6c: Yield 75%, mp 135°C. Found: C 67.75; H 7.10;
N 5.70; Anal. calcd for C56H70N4O8S2: C 67.86; H 7.12;
N 5.65; IR, mmax (cm-1): 2931–2869 (CH2), 2234 (C≡N),
1674, 1594, 1510, 1346 (O=S=O), 1231, 1160, 857,
1
812, 706, 660. H-NMR (CDCl3), d (ppm): 7.63 (s, 2H,
Ar-H), 7.57–7.54 (d, 4H, Ar-H), 7.34–7.28 (d, 4H, Ar-H),
6.68–6.67 (d, 2H, Ar-H), 6.41 (d, 2H, Ar-H), 6.40 (s, 2H,
Ar-H), 4.90 (s, 4H, CH2), 3.77–3.74 (t, 4H, CH2-O),
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 3–10

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M. HARBECK ET AL.
7.76–7.64 (d, 16H, Ar-H), 7.56–7.34 (d, 16H, Ar-H),
6.79–6.77 (d, 8H, Ar-H), 6.27–6.63 (d, 8H, Ar-H) 6.42 (s,
8H, Ar-H), 5.43 (s, 16H, Ar-CH2-N), 3.94–3.89 (t, 16H,
CH2-O), 3.76–3.70 (t, 16H, CH2-O), 2.40 (s, 24H, Tosyl-
Ar-CH3), 1.65–1.59 (p, 32H, CH2-CH2-O), 1.28 (m, 64H,
CH2), 0.94 (t, 48H, CH3); MS (FAB), (m/z):4023 [M]+.
7d:Yield 16%, mp > 200°C. Found: C 65.70.; H 6.55;
N 5.90; Anal. calcd for C208H248N16NiO32S8: C 65.75; H
6.58; N 5.90; IR, mmax (cm-1): 2930–2871 (CH2), 1595,
1508, 1465, 1342, 1258, 1162 (O=S=O), 1091, 1026,
937, 811, 706, 660. 1H-NMR (CDCl3), d (ppm): 9.19 (s,
8H, Ar-H), 7.75–7.73 (d, 16H, Ar-H), 7.42–7.40 (d, 16H,
Ar-H), 6.76–6.74 (d, 8H, Ar-H), 6.66–6.64 (d, 8H, Ar-H),
6.62 (s, 8H, Ar-H), 5.42 (s, 16H, Ar-CH2-N), 3.70–3.68
(t, 16H, CH2-O), 3.68–3.66 (t, 16H, CH2-O), 2.50 (s,
24H, Tosyl-Ar-CH3), 1.62–1.55 (p, 16H, CH2-CH2-O),
1.55–1.48 (p, 16H, CH2-CH2-O), 1.28 (m, 32H, CH2), 0.9
(t, 48H, CH3); MS (FAB), (m/z): 3799 [M]+.
(d, 16H, Ar-H), 7.32–7.15 (d, 16H, Ar-H), 7.05–6.87 (d,
8H, Ar-H), 6.52–6.45 (d, 8H, Ar-H) 6.37 (s, 8H, Ar-H),
4.03 (s, 16H, Ar-CH2-N), 3.98–3.97 (t, 16H, CH2-O),
3.67–3.62 (t, 16H, CH2-O), 1.49 (s, 24H, Tosil-Ar-CH3),
1.41–1.36 (m, 32H, CH2-CH2-O), 1.28 (m, 64H, CH2),
0.9 (t, 48H, CH3). MS (FAB), (m/z): 4029 [M]+.
8d: Yield 12%, mp > 200°C. Found: C 65.60; H 6.55;
N 5.80; Anal. calcd for C208H248N16O32S8Zn: C 65.63; H
6.57; N 5.88; IR, mmax (cm-1): 2928–2857 (CH2), 1595,
1507, 1469, 1341, 1232, 1160 (O=S=O), 1090, 811, 570,
1
660. H-NMR (CDCl3), d (ppm): 8.35 (s, 8H, Ar-H),
7.75–7.49 (d, 16H, Ar-H), 7.30–7.15 (d, 16H, Ar-H),
6.90–6.75 (d, 8H, Ar-H), 6.55–6.45 (d, 8H, Ar-H) 6.35
(s, 8H, Ar-H), 4.25 (s, 16H, Ar-CH2-N), 3.95–3.90 (t,
16H, CH2-O), 3.70–3.65 (t, 16H, CH2-O), 1.45 (s, 24H,
Tosil-Ar-CH3), 1.40–1.35 (m, 32H, CH2-CH2-O), 1.25
(m, 32H, CH2), 0.85 (t, 48H, CH3). MS (FAB), (m/z):
3963 [M + DHB (matrix)]+.
Preparation of the zinc phthalocyanines (8a–8d).
6a (1.35 g, 9.75 10-4 mol) and anhydrous Zn(OAc)2
(0.045 g, 2.46 10-4 mol) in dry quinoline (0.9 ml) were
heated and stirred at 170°C for 5 h. After cooling to
room temperature, the reaction mixture was treated with
ethanol (60 ml) and then the crude product was washed
with water and ethanol to remove the unreacted organic
material. The green product was dried with diethyl ether
and purified by column chromatography (silica gel,
1:20 v/v; MeOH:CH2Cl2). The compound is soluble in
n-hexane, chloroform, DMF, and acetone. Yield 0.070 g
(10%), mp > 200°C. Found: C 71.70; H 9.00; N 4.23;
Anal. calcd for C336H504N16O32S8Zn: C 72.05; H 9.07;
N 4.00; IR, mmax (cm-1): 2920–2851 (CH2), 1596, 1560,
1466, 1343, 1231, 1133 (O=S=O), 1090, 940, 810, 673.
1H-NMR (CDCl3), d (ppm): 9.50 (s, 8H,Ar-H), 7.55–7.50
(d, 16H, Ar-H), 7.48–7.29 (d, 16H, Ar-H), 6.59–6.57 (d,
8H, Ar-H), 6.55–6.51 (d, 8H, Ar-H) 6.36 (s, 8H, Ar-H),
5.42 (s, 16H, Ar-CH2-N), 3.85–3.80 (t, 16H, CH2-O),
3.66–3.58 (t, 16H, CH2-O), 2.38 (s, 24H, Tosyl-Ar-CH3),
1.74–1.67 (m, 32H, CH2-CH2-O), 1.19 (m, 288H, CH2),
0.8 (t, 48H, CH3); MS (FAB), (m/z): 5602 [M]+.
Preparation of the copper phthalocyanines (9a–9d).
A mixture of 5a (0.500 g, 2.62 10-4 mol), CuCN
(0.060 g, 6.81 10-4 mol) and 1-methyl-2-pyrrolidone
(0.2 ml) was heated and stirred at 177°C under argon
for 5 h. After cooling to room temperature, the reaction
mixture was treated with NaCN to precipitate the blue
product and filtered. The product was washed several
times successively with hot water, hot ethanol, hot
methanol and then with diethyl ether. The green product
was purified by column chromatography (silica gel,
1:20 v/v; MeOH:CH2Cl2). The compound is soluble in
n-hexane, chloroform, acetone, DMF, and THF. Yield
0.040 g (10%), mp > 200°C. Found: C 71.61; H 9.00;
N 3.9; Anal. calcd for C336H504CuN16O32S8: C 72.00; H
9.07; N 4.00; IR, µmax (cm-1): 2921–2852 (CH2), 1595,
1511, 1344, 1232, 1162 (O=S=O), 1017, 941, 800, 660.
MS (FAB), (m/z): 5609 [M]+.
9b, 9c, and 9d were synthesized according to 9a.
9b: Yield 12%, mp > 200°C. Found: C 67.00; H 7.20;
N 5.04; Anal. calcd for C240H312CuN16O32S8: C 67.77; H
7.39; N 5.27; IR, mmax (cm-1): 2928–2857 (CH2), 1595,
1507, 1341, 1238, 1162 (O=S=O), 1090, 920, 811, 706,
660. MS (FAB), (m/z): 4257 [M]+.
8b, 8c, and 8d were synthesized according to 8a.
8b: Yield 12%, mp > 200°C. Found: C 67.00; H 7.35;
N 5.00; Anal. calcd for C240H312N16O32S8Zn: C 67.74; H
7.39; N 5.27; IR, mmax (cm-1): 2934–2853 (CH2), 1596,
1504, 1344, 1230, 1158 (O=S=O), 1090, 811, 756,
9c: Yield 13%, mp > 200°C. Found: C 66.75; H 7.00;
N 5.50. Anal. calcd for C224H280CuN16O32S8: C 66.79; H
7.00; N 5.56; IR, mmax (cm-1): 2925–2857 (CH2), 1596,
1511, 1467, 1341, 1230, 1134 (O=S=O), 1090, 946, 812,
707, 660. MS (FAB), (m/z): 4028 [M]+.
1
660. H-NMR (CDCl3), d (ppm): 9.28 (s, 8H, Ar-H),
7.70–7.61 (d, 16H, Ar-H), 7.36–7.25 (d, 16H, Ar-H),
6.66 (d, 8H, Ar-H), 6.56–6.55 (d, 8H, Ar-H) 6.36 (s,
8H, Ar-H), 4.88 (s,16H, Ar-CH2-N), 3.83–3.80 (t, 16H,
CH2-O), 3.66–3.64 (t, 16H, CH2-O), 2.38 (s, 24H, Tosil-
Ar-CH3), 1.71–1.61 (m, 32H, CH2-CH2-O), 1.21 (m, 96H,
CH2), 0.8 (t, 48H, CH3). MS (FAB), (m/z):4252 [M]+.
8c: Yield 11%, mp > 200°C. Found: C 66.80; H 7.00;
N 5.55; Anal. calcd for C224H280N16O32S8Zn: C 66.87; H
7.02; N 5.57; IR, mmax (cm-1): 2930–2868 (CH2), 1595,
1507, 1468, 1344, 1229, 1156 (O=S=O), 1090, 811, 660.
1H-NMR (CDCl3), d (ppm): 8.47 (s, 8H,Ar-H), 7.78–7.49
9d: Yield 10%, mp > 200°C. Found: C 65.65; H 6.50;
N 5.80; Anal. calcd for C208H248CuN16O32S8: C 65.67; H
6.57; N 5.89; IR, mmax (cm-1): 2957–2870 (CH2), 1595,
1506, 1470, 1341, 1258, 1160 (O=S=O), 1090, 937, 809,
706, 660. MS (FAB), (m/z): 3804 [M]+.
Preparation of the cobalt phthalocyanines (10a–
10d). 6a (1.40 g, 1.01 mmol), anhydrous CoCl2 (0.033 g,
2.49 10-4 mol), and ethylene glycol (5.2 ml) were heated
and stirred at 175°C for 5.5 h. After cooling to room
temperature, the reaction mixture was treated with ethanol
to precipitate the blue product and filtered. The product
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SYNTHESIS AND QCM GAS-SENSING PROPERTIES OF 3,4-DIALKOXYPHENYL
5
was washed several times successively with hot water,
to produce the vapors were of high purity and used as
obtained from the manufacturer. The VOCs were selected
to represent common chemical classes and to cover a wide
range of chemical properties as expressed in their linear
solvation energy relationship (LSER) parameters [16]. The
LSER parameters of the test analytes can be found in the
Supporting information. During the measurements, the
temperature of the sensor chamber was kept at 22°C at all
times. The sensors were prepared and tested in duplicate
and the measurements were repeated at least once to assess
reproducibility and repeatability.
Hierarchical cluster analysis (HCA) and principal
component analysis (PCA) were performed with the
help of the R statistical programming language and the
FactoMineR package (V1.41) on the sensor response data
after normalization and centering. For HCA, Euclidian
distance was used as a dissimilarity measure and cluster
linkage was based on the averaging method.
hot ethanol and purified by column chromatography
(silica gel, 1:20 v/v; MeOH:CH2Cl2). The compound
is soluble in n-hexane, chloroform, acetone, and THF.
Yield: 0.140 g (10%), mp > 200°C. Found: C 71.70;
H 9.00; N 4.00; Anal. calcd for C336H504CoN16O32S8: C
72.13; H 9.08; N 4.00; IR, mmax (cm-1): 2921–2852 (CH2),
1594, 1511, 1343, 1231, 1090 (O=S=O), 1090, 940, 660.
MS (FAB), (m/z): 5619 [M + Na]+.
10b, 10c, and 10d were synthesized according to 10a.
10b:Yield 12%, mp > 200°C. Found: C 67.50; H 7.40;
N 5.20; Anal. calcd for C240H312CoN16O32S8: C 67.92; H
7.41; N 5.28; IR, mmax (cm-1): 2927–2858 (CH2), 1595,
1510, 1343, 1232, 1160 (O=S=O), 1091, 920, 811, 660.
MS (FAB), (m/z): 4248 [M]+.
10c:Yield 13%, mp > 200°C. Found: C 66.80; H 7.00;
N 5.50.; Anal. calcd for: C224H280CoN16O32S8: C 66.87; H
7.01; N 5.57; IR, mmax (cm-1): 2926–2860 (CH2), 1595,
1509, 1343, 1259, 1160 (O=S=O), 1094, 944, 809, 660.
MS (FAB), (m/z): 4023 [M]+.
10d: Yield 10%, mp > 200°C. Found: C 65.70; H
6.40; N 5.90; Anal. calcd for: C208H248CoN16O32S8:
C 65.75; H 6.58; N 5.90; IR, mmax (cm-1): 2930–2871
(CH2), 1595, 1558, 1507, 1345, 1233, 1158 (O=S=O),
1090, 937, 811, 660. MS (FAB), (m/z): 4244 [M+2
Dithranol(matrix)]+.
RESULTS AND DISCUSSION
Synthesis and characterization
The Pcs under investigation are unique in their
substituents having a 3,4-dialkoxyphenyl tosylamino
moiety which is attached to the Pc at peripheral positions
via methylene groups. To create a manifold of sensing
materials, the alkyl group has been varied from n-butyl
to n-dodecyl and the inner hydrogen atoms of the Pc core
replaced by four different metal ions. In this way, sixteen
different octa-substituted phthalocyanine derivatives
have been obtained.
The code numbers for the individual compounds
specify metal type (NiPc 7, ZnPc 8, CuPc 9, CoPc 10)
and alkyl chain type (n-dodecyl a, n-hexyl b, n-pentyl c,
n-butyl d). The full list of materials and their identification
codes are given in Fig. 1.
A common method of Pc synthesis is to start with the
substituted phthalonitrile (compounds 6a–6d) obtained
from the dibromide (5a–5d) as shown in the scheme
of Fig. 1. The phthalonitrile was prepared in several
steps as follows: First, the 1,2-dialkyloxybenzenes
(1a–1d) were prepared using a reaction of catechol in
absolute DMF in the presence of potassium carbonate
with the respective 1-bromoalkane. In the next step,
a nitro group was introduced to the aromatic system
using 65%-HNO3 and then reduced to the amine
using palladium-activated charcoal. The N-[3,4-
bis(alkyloxy)phenyl]-4-methylbenzenesulfonamide
(4a–4d) were synthesized in anhydrous pyridine
using p-toluenesulfonyl chloride. Then, 1,2-dibromo-
4,5-bis(bromomethyl)benzene was added to 4a–4d
in anhydrous DMF in the presence of anhydrous
potassium carbonate to obtain the 1,2-dibromo-4,5-
bis[(3,4-dialkoxyphenyl-tosylamino)methyl]benzenes
(5a–5d) [17]. The phthalonitriles (6a–6d) were obtained
Sensor preparation and test procedures
AT-cut QCMs with a fundamental frequency of
10 MHz (Klove B.V., NL) were used as transducers.
Solutions of the sensitive materials were prepared by
dissolving the Pcs (1 mg per 1 ml solvent) in analytical
grade chloroform or acetone. The solution was then
sprayed on the electrodes of a QCM using a jet-spray
system. During the coating process the frequency of the
QCM was monitored online and coating of the electrode
was ceased at a frequency shift of 11 kHz per side.
The gas streams containing the analyte vapors were
generated from thermostatted bubblers (at -10°C)
with synthetic air as carrier gas. The gas stream was
then diluted with pure air to achieve the desired vapor
concentration at a constant total flow rate (200 ml/min).
Flow rates of all channels are controlled by computer-
driven mass flow controllers (Sierra Instruments, NL).
Typical experiments consist of repeated exposure to
analyte vapor (1200 s) and subsequent purging with pure
air (1200 s) to reset the baseline.
The sensing materials were characterized using the
VOCs acetonitrile (ACN, 945–4720 ppm), n-heptane
(nC7, 385–1930ppm), n-propanol(nPrOH, 130–655ppm),
toluene (TLN, 245–1210 ppm), tetrachloroethylene (TCE,
145–730 ppm), triethylamine (Et3N, 70–720 ppm) as well
as the CWA simulants di(propylene glycol) methyl ether
(DPGME, 4–19 ppm) and dimethyl methylphosphonate
(DMMP, 0.3–3 ppm) and the fumigant and historical
CWA chloropicrin (CP, 20–205 ppm). All solvents used
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6
M. HARBECK ET AL.
OR
OR
OR
OR
Ts
Ts
Ts
Ts
O
N S
O
N
N
N
N
H
Br
RO
RO
Br
Br
NC
NC
Br
Br
+
2
Br
OR
OR
OR
OR
4a-4d
5a-5d
6a-6d
RO
RO
OR
OR
N
N
Ts
Ts
RO
RO
OR
OR
Ts
Ts
Ts
Ts
N
N
N
N
N
N
R
M
N
M
N
n-dodecyl
n-hexyl
n-pentyl
n-butyl
Ni 7a-d
Zn 8a-d
a:
b:
c:
d:
N
N
N
N
RO
RO
OR
OR
Cu
9a-d
Co 10a-d
Ts
Ts
N
N
RO
RO
OR
OR
Fig. 1. Scheme of the synthetic pathway for the preparation of the substituted phthalonitriles 6a–6d and the final phthalocyanines
7a–7d to 10a–10d
in a reaction with CuCN and anhydrous DMF by stirring
at an elevated temperature of 175°C. The reaction
product was poured into 25% aqueous NH4OH and air
was passed through the solution for 24 h. The Pc metal
ion complexes 7a–7d, 8a–8d, and 10a–10d of nickel,
zinc and cobalt were produced in a cyclotetramerization
reaction in a high boiling anhydrous solvent (e.g.
quinoline or ethylene glycol) from the corresponding
anhydrous metal salt. 5a–5d were converted into the
CuPcs 9a–9d directly through their reaction with CuCN
in 1-methyl-2-pyrrolidone.
the tosyl groups appear as two doublets at around 7.64
and 6.42 ppm. Methylene protons (Ar-CH2-N) appear
as singlets around at 5.33–4.03 ppm. Tosyl Ar-CH3
appears as a singlet at around 2.50–2.28 ppm. The
observed sharp peaks indicate that the bulky peripheral
substituents prevent aggregation [19]. However, peaks in
the spectra of 9a–9d and 10a–10d are very broad due to
the paramagnetic Cu(II) and Co(II) ions.
General gas sensing properties
Column chromatography with silica gel was
used to obtain the pure products from the reaction
mixtures. The intense green-blue Pcs are very soluble
in a number of solvents such as chloroform, acetone or
dichloromethane.
The QCM sensors prepared with the sixteen Pc metal
complexes were studied in their responses to vapors
of nine test analytes to evaluate the gas sorption and
sensing properties of the new materials. In Fig. 2 (top)
the transient responses of two QCMs coated with 8a
measured in parallel during exposure to vapors of TCE,
nC7, CP, and ACN in five increasing concentration steps
alternating with analyte-free carrier gas are depicted as
a typical example for the performance of the sensitive
compounds. Generally, the gas-sensing characteristics
of the compounds in terms of baseline stability,
response and recovery times, and repeatability are good.
Equilibrium responses and a full recovery of the baseline
are easily reached within the 20 min exposure window
and consecutive purging phase. The sensor responses
increase with increasing analyte concentration.
In the IR spectra, a confirmation of successful
phthalocyanine formation from the phthalonitrile is the
disappearance of the sharp and intense C≡N vibration
at 2220 cm-1. Other than that, the spectra of the Pcs are
similar to those of 4a–4d, 5a–5d, and 6a–6d including
the characteristic vibrations corresponding to the
tosyl moieties at around 1160 and 1340 cm-1 and CH2
vibrations around 2880 cm-1 [18].
1
In the H-NMR spectra of the NiPcs (7a–7d) and
ZnPcs (8a–8d), the aromatic protons of the Pc core
appear at 9.50 and 8.35 ppm as singlets and those of
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SYNTHESIS AND QCM GAS-SENSING PROPERTIES OF 3,4-DIALKOXYPHENYL
7
Fig. 2. Transient responses of two QCM sensors with 8a during exposure to vapors of TCE, nC7, ACN, and CP (top) and sensor
response curves for all test analytes (bottom). Next to the analyte label, the slope of the best fit line to the data as the sensor
sensitivity (in Hz/ppm) and r2 values are included
The graph in Fig. 2 (bottom) illustrates the obtained
response curves of the two sensors with the same
sensitive material to all test analytes. The two specimens
were repeatedly measured under the same conditions. To
better compare the responses to analytes of very different
saturation vapor pressures, relative concentrations pi/pi,0
are used, where pi is the actual analyte vapor pressure
and pi,0 is the saturation vapor pressure of the respective
analyte at measurement temperature. The responses
increase linearly with concentration and no saturation
effects can be observed in the arranged vapor pressure
ranges. The responses of the sensors vary notably in their
magnitude for the different analytes. For all compounds
Fig. 3. Heatmap of relative (indicated by colors) and absolute
and analytes the sensitivities span a range of 0.5 Hz/
partition coefficient values (grey numbers) for all sixteen Pcs
ppm for TCE and CP to around 0.006 Hz/ppm for the
grouped by substituent. Green color and red color indicate
analyte ACN. The DMMP and DPGME sensitivities are
positive and negative deviation from the respective NiPc
an order of magnitude higher and reach values between
reference (three levels for deviations larger than 50, 25, and
2 and 13 Hz/ppm and 1 and 3 Hz/ppm, respectively. All
5%, respectively)
sensitivity values are for valid for the used 10 MHz QCM
with a total of 22 kHz of coating.
The gas-phase-sensitive material partition coefficient
K is a good descriptor of the performance of a sensitive
material, as it describes the degree of enrichment of an
analyte in the sensitive material independent of transducer
sensitivity and other factors such as layer thickness. It is
defined as the ratio of the concentration of a chemical
compound in the sorbent phase and the gas phase. High
K values represent a high number of absorbed molecules
in the sensitive layer and are an indicator of high sensor
responses. From the sensor sensitivity as the slope of the
best fit line to the response data the partition coefficients
K were calculated as previously reported [20]. The full
list of partition coefficients of the compounds obtained in
the gas exposure experiments in dry air is given in Fig 3.
The values span a wide range from 220 for ACN to 6 000
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8
M. HARBECK ET AL.
for DPGME, while the values for DMMP are between
24000 and 157000. Among all tested materials, the
NiPcs 8a, 8b, and 8d show the highest overall responses
and partition coefficients.
chain length was observed. However, as for the metal
center influences, there is no general rule.
Previously, Kilinc et al. reported that sensor
response decreased with increasing the length of the
alkyl chain for a group of Pcs in conductive sensors in
some cases. However, no general relationship between
sensor response and the length of alkyl chain could be
established [22]. As the substituents used in this work
are chemically very similar to each other, other factors
than chemical properties of the substituents seem to play
a role in the sorption. Thus, not only chemical interaction
aspects [12, 23], but also sterical effects are thought to be
influential [24].
The Pcs in the K matrix of Fig. 3 are grouped by the
substituent in four blocks to illustrate the influence of
the central metal ion. The respective NiPc is chosen as
reference for each block. The colors indicate relative
deviations of the individual K values from the reference:
green color indicates a higher K, whereas red color a
lower K than the NiPc reference. The influence of the
metal ion center is different for the four substituents and
is found to depend on the analyte, as well. In the case
of Pcs with the substituent b and d, metal ion centers
other than Ni produce higher K values, whereas in the
case of Pcs with a and c substituents the opposite is true,
as in most cases the partition coefficients for the NiPcs
7a and 7c are the highest. Even though the change of the
metal ion center is known to be an effective way to alter
the sorption properties of Pcs [21], the resulting effect
is strongly dependent on the substituents, as shown by
the results. The same metal ion center can introduce a
decrease and increase in sensitivity in an unpredictable
way for a certain analyte when different substituents
are attached to the Pcs. Consequently, the sorption
preference and accordingly the sensor selectivity of a Pc
after change of central metal ion cannot be anticipated.
The chain length of the substituents is the other
influential parameter to change the sensor response
characteristics of the Pcs. Figure 4 illustrates the chain
length dependency of the partitioning for Pcs having
the same metal ion center. The plot depicts the relative
partition coefficient for all analytes for each sensing
material relative to the respective compound with the
substituent a. Mostly, a decrease in K with decreasing
Selectivity and sorption preferences
Some general observations can be obtained by
inspection of the individual data, but the sensors’ analyte
preferences and selectivities can only be evaluated
in detail using multivariable exploratory techniques,
especially as the results have shown that the effects of
metal ion centers and substituents are rather unsystematic.
Accordingly, all sensitive compounds as a whole have
been characterized with HCA and PCA. Based on the
sensor responses, these methods allow exploration
of similarities or dissimilarities among the individual
sensitive materials and show the sorption preferences of
individual sensors in comparison to the other materials.
The selected analyte molecules have miscellaneous,
very diverging physical and chemical properties, e.g.
polarity can range from very polar to non-polar, and the
molecules are capable of different chemical interactions
such as van-der-Waals forces (permanent dipole–dipole
interactions and induced dipole interactions, London
forces), p–p interactions, and hydrogen bonding. The
relevant analyte-sensitive materials interactions can be
expressed with five LSFR parameters: the hydrogen-bond
parameters a2 and b2, the dispersion parameter logL16 as
well as parameters for dipolarity and polarizability p2 and
R2. The most dominant parameters for Et3N are logL16
and b2, for DMMP p2, b2, and logL16, for ACN p2 and
b2, and for nPrOH a2 and b2. For both TLN and TCE the
dominant parameters are logL16 and R2, whereas nC7 has
only a value for logL16.
In HCA the sensitive materials are clustered or
separated according to their analyte responses, taking
into account the whole sensor space (not a projection
onto 2D as PCA), but the method does not give
information on the actual similarities/dissimilarities
between the resulting clusters. Potential preferences for
any analytes are not disclosed. On the other hand, PCA
does not directly provide a measure for the distance
between data points and clusters as HCA, but illustrates
well the relative positions in a 2D space and illustrates
the sorption preferences of the materials in the space
defined by the selected test analytes. Materials located in
PCA in the same direction from the origin might appear
Fig. 4. Heatmap of relative (indicated by colors) partition
coefficients for all sixteen Pcs grouped by metal ion center.
Green color and red color indicate positive and negative
deviation from the respective reference (Pcs with substituent
a). The data is encoded in three levels for deviations larger than
50, 25, and 5%, respectively
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SYNTHESIS AND QCM GAS-SENSING PROPERTIES OF 3,4-DIALKOXYPHENYL
9
e.g. TLN and TCE are close to each other. Similarity and
dissimilarity is related to their preferred interactions with
the sensitive materials as described above.
The preferences of the sensor materials can be
elucidated adequately in
a projection onto two
dimensions. All four compounds having the same
substituent c but different metal centers form a close
group, whereas Pcs with the substituent a (7–10a) are
located nearby, but notably separated from each other.
In the case of the Pcs with the substituents b and d,
one member of the two groups is quite different from
the others. The large cluster located near the origin
contains the compounds 7d, 9d, 10d as well as 7b,
9b, and 10b, but not the NiPcs 8b and 8d. While the
former six compounds show few specific features in
term of selectivity, the latter two are quite distinct sensor
materials having pronounced selectivity for DMMP/
Et3N and polar compounds, respectively. The results
show that a high degree of diversity can be introduced
through a simple variation in the substituent, i.e. the
alkyl chain length, and by changing the metal ion
center. A small set of Pcs selected among the sixteen
compounds shows enough variety to be allow for
classifing the various analytes in a sensor array set-up.
Only very similar analytes such as TCE and TLN cannot
be separated easily.
Fig. 5. Results of the hierarchical cluster analysis of the
normalized and centered sensor data
The biplot in Fig. 7 is produced using only
compounds identified as the most distinct in HCA and
PCA. The compounds 8a, 8b, 8d, and 9a were found to
have the highest diversity in their sorption preferences.
The PCA result is nearly identical to the one obtained
using all sensors. The possible use of other sensors,
e.g. 7a for 9a, produces similar results, while the
addition of more sensors was found to not improve the
result.
Fig. 6. PCA biplot of loadings and scores for all sensors.
Some sensor labels near the origin are omitted for clarity. The
unlabeled sensors are part of the large group near 8a and 10c
in HCA in different subclusters, but are very similar
in their sensing properties. Normalization eliminates
concentration effects, but at the same time also saturation
vapor pressure and molecular weight influences.
In Fig. 5, the result of HCA is depicted in a typical tree
diagram. The data are separated in three: one main cluster
with all but two materials which may be further divided
into several subclusters and two compounds, namely 8b
and 8d. The latter are fairly different from each other and
the other sensors. In the main cluster the sensors 8a, 9a,
9d and 10d are quite distinct from the remaining sensors.
It can be noted that the Pcs with the substituent c (8c, 9c,
7c, and 10c) have the smallest diversity.
In Fig. 6, the PCA result is presented in a biplot
of loadings and scores. The ellipses around clusters
represent a 95% confidence region around the cluster
mean (represented by open squares). The first two
principal components contain about 77% of the total
variance. In the PCA plot, dissimilar analytes are clearly
separated from each other, whereas similar compounds
Fig. 7. PCA using only selected sensors showing the best
separation of the analytes in two dimensions
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M. HARBECK ET AL.
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CONCLUSIONS
The synthesis of nickel, zinc, copper, and cobalt
3,4-dialkoxyphenyl tosylamino substituted phthalo-
cyanines having alkyl chains of different lengths (n =
4, 5, 6 and 12) for the use in chemical gas sensors as
sensitive compounds was achieved. The new compounds
are characterized in their gas sensing properties with the
QCM using selected test analyte including VOCs and
CWA simulants. In a systematic approach, a total of 16
compounds have been tested in order to allow discussion
of metal ion center and substituent effects on the gas
sorption properties.
The Pcs exhibit generally good gas-sensing properties,
as the observed responses to the analytes are high, with
short response and recovery times. The QCM results
reveal notable variations in the sensor responses and
selectivity as a consequence of the alterations made to
the substituents and Pc center. Even simple and minute
variations, such as variations in the alkyl chain length
on the substituent, are observed to have a large, but
irregular, influence on the sensing characteristics of
the compounds. The produced Pcs are diverse enough
in their sensing properties to distinguish the analytes
in a sensor array set-up. However, a general trend with
carbon chain length is not apparent, as the effects depend
much on the metal ion center, as well. Further studies
including computational and experimental methods are
needed to separate chemical and sterical factors that are
influential in the gas sorption process in order to obtain
a more systematic protocol in the search for new sensing
materials with selectivity and sensitivity required for an
envisaged application field.
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Acknowledgments
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This work was supported by the Scientific and
Technological Research Council of Turkey (TUBITAK)
project no. 115E096.
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Supporting information
Synthesis and characterization of the compounds and
LSER parameters of the test analytes are given in the
supplementary material. This material is available free of
charge via the Internet at http://www.worldscinet.com/
jpp/jpp.shtml.
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