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Sensors and ActuatorsB 190 (2014) 93–100

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical

 journa l homepage: www.elsevier .com/ locate /snb

Synthesis, characterization, and oxygen sensing properties of functionalized mesoporous silica SBA-15 and MCM-41 with aPt(II)–porphyrin complex

Binbin Wang a,b, Liming Zhang c, Bin Li c, Yao Li b, Yuhua Shi a, Tongshun Shi a,∗

a College of Chemistry, Jilin University, Changchun 130021, PR Chinab College of Chemistry, ChangchunNormal University, Changchun 130032, PR Chinac Key Laboratory of Excited State Processes, Changchun Institute of OpticsFineMechanicsand Physics, Changchun130033, PR China

a r t i c l e i n f o

 Article history:

Received 27 December 2012

Received in revised form 16 July 2013

Accepted 7 August 2013

Available online 30 August 2013

Keywords:

Platinum(II) complex

Oxygen sensing

Mesoporous silica

High response

a b s t r a c t

A novel luminescent platinum(II) complex platinum 5,10,15,20-tetra{4-[(N -

carbazyl)butyloxyphenyl]}porphyrin (PtTCBPyP) has been synthesized and characterized by   1H

NMR, elemental analysis, IR  and UV–vis. The platinum porphyrin is assembled with mesoporous silica

SBA-15 and MCM-41 resulting in the assembly materials PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41.

The luminescence of  platinum porphyrin complex/silicate assemble materials can be quenched

by molecular oxygen with very high response (I 0/I 100 > 8700 for PtTCBPyP/SBA-15(20 mg/g) and

I 0/I 100 > 3800 for PtTCBPyP/MCM-41(20 mg/g)), indicating that platinum porphyrin complex/silicate

systems can be employed to develop high performance oxygen sensors. Among this assembly system,

PtTCBPyP/SBA-15(20 mg/g) exhibits the highest response of platinum porphyrin complex/silica.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Over the past decades, luminescence-based optical oxygen sen-

sors have been largely developed because the determination of 

molecular oxygen both in the gas and in the liquid phase is very

important in many different fields such as analytical chemistry,

medical chemistry, environmental monitoring andindustrial appli-

cations [1–4]. These sensors are based upon the principle that

oxygen is a powerful quencher of the luminescent intensity and

lifetime of luminescent complexes. The optical oxygen sensing sys-

tems consists of various complexes such as polypyridyl transition

metal complexes [5,6] and metalloporphyrins [7,8] owing to their

highquantumyields, large Stokes shifts, longluminescent lifetimes

and short response times, and they canbe used for measuring oxy-

gen concentration in gas, aqueous, and organic phase [5,6,8–10].

The host materials used to encapsulate the luminescent complexesare sol–gel and polymer films. Some interesting systems based on

sol–gel or polymer immobilized transition metal complexes have

been reported [11–15].

After the discovery of mesoporous silicas prepared by the coop-

erative organization of surfactant and inorganic species in 1992

[16,17], the synthesis, characterization, and applications of the

supramolecular-templated mesostructured materials have been

∗ Corresponding author. Fax: +86 431 85168898.

E-mail address: tsshi163@163.com (T. Shi).

of widespread interest in materials science. Ordered mesoporous

materials continue to be widely and extensively used as excel-lent host materials due to their unique properties such as high

surface area, ordered pore structure of varying morphologies,

and controllable pore size over wide ranges [18–22]. Mesoporous

materials are able to physically encapsulate and immobilize the

functional molecules into the pores, while the solvent and other

small molecules or ions are allowed into the interior of the meso-

porous silicas through channels.In orderto obtain excellent optical

oxygen sensors, high response is necessary for some transition

metal complex based oxygen sensing materials [23–27]. However,

few of these oxygen sensors display high response. The design and

assembly of high performance oxygen sensors based on lumines-

centtransitionmetal complexesremaina challenge for chemists.To

obtain moreefficient oxygen sensing materials, in thiscontribution,

we report the synthesis of a novel luminescent platinum(II) com-plex (PtTCBPyP) and the assembly of PtTCBPyP with mesoporous

silica SBA-15 andMCM-41.The optical oxygen sensingproperties of 

assembly materials PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41 also

will be presented.

2. Experimental

 2.1. Materials

Analytical grade solvents and compounds were used for prepa-

rations. Pyrrole, 1, 4-dibromobutane and platium(II) chloride were

0925-4005/$ – seefrontmatter © 2013 Elsevier B.V. All rights reserved.

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Scheme 1. Synthesisprocedure of theporphyrin ligand and its complex.

purchased form Aldrich. 4-hydroxybenzaldehyde and carbazole

were obtained from Acros. All the other chemicals were obtained

from Tianjin Tiantai Pure Chemicals Co., Ltd. 5, 10, 15, 20-tetra(4-

hydroxyphenyl)porphyrin [28] and N -(8-bromooctyl)carbazole

[29] were synthesized according to the literature procedures.

Mesoporous silica (SBA-15 and MCM-41) [30,31] was hydrother-mally prepared following literature procedures. Then the template

was removed from the mesoporous silicate by calcinations at

560 ◦C for 8h. The solvent dichloromethane (CH2Cl2) was used

after desiccation with anhydrous calcium chloride. Dimethyl for-

mamide (DMF) was pre-dried over activated 4 A molecular sieves

and vacuum distilled from calcium hydride (CaH2) prior touse.Dry

benzonitrile was obtained by distillation from CaH2. Anhydrous

potassium carbonate was dried under vacuum at 80◦C for half an

hour.

 2.2. Synthetic procedures

The synthesis procedures for the porphyrin derivatives were

illustrated in Scheme 1.

 2.2.1. Synthesis of 5,10,15,20-tetra{4-[(N-

carbazyl)butyloxyphenyl]} porphyrin(TCBPyP)

Under nitrogen, 5, 10, 15, 20-tetra(4-hydroxyphenyl)porphyrin

(0.80g, 1mmol) was added to 250mL of DMF with K2CO3   (1.4 g,

10mmol). The mixture was heated to reflux for 1h, and then N -

(8-bromobutyl)carbazole (2.4g, 8 mmol) was added. Heating the

mixture to reflux for 24h was continued. After distilling off DMF,

the residue was purified by column chromatography using silica

gel with dichloromethane as eluent (yield 25%). 1HNMR (300MHz,

CDCl3, 25 ◦C,TMS): ı= 8.835 (s,8H, pyrrole ring), 8.431–8.478(t, 8H,о-C6H4), 8.142–8.168(d, 8 H, carbazole ring C1   H), 8.069–8.096(d,

8 H, m-C6H4), 7.545 (t, 16H, carbazole ring C2,3   H), 7.236–7.276

(t, 8H, carbazole ring C4   H), 4.548–4.569 (t, 8H, O CH2   ),4.221–4.261( t, 8H, N CH2   ), 2.259–2.309 (m, 8H, N C CH2   ),

2.027–2.073 (m, 8H, O C CH2   ),−2.785(s,2H,pyrroleN H). MS

m/ z (%): found [M+] 1563.8, calcd. 1563.9.

 2.2.2. Synthesis of platinum

5,10,15,20-tetra{4-[(N-carbazyl)butyloxyphenyl]} porphyrin

(PtTCBPyP)

Under nitrogen, PtCl2   (50mg, 0.2mmol) and TCBPyP (30 mg,

0.02mmol) were suspended in 100mL  of benzonitrile. The mix-

ture was then heated to reflux for 10h. The mixture was cooled

to room temperature, and the solvent was removed by vacuum

distillation. The crude product was purified by columnchromatog-

raphy using silica gel with dichloromethane as the eluent (yield

99%).1

HNMR (300 MHz,CDCl3, 25◦

C,TMS): ı = 8.764(s, 8H,pyrrole

ring), 8.317–8.336 (t, 8H, o-C6H4), 8.140–8.162(d, 8 H, carbazole

ring C1   H), 8.063–8.090(d, 8 H, m-C6H4), 7.539 (t, 16H, carbazole

ring C2,3   H),7.233–7.274 (t, 8H,carbazole ring C4   H),4.548–4.569

(t, 8H, O CH2   ), 4.212–4.257 (t, 8H, N CH2   ), 2.238–2.292 (m,

8H, N C CH2   ), 2.001–2.056 (m, 8H, O C CH2   ). Anal. Calcd.

for C108H88N8O4Pt: C, 73.83; H, 5.05; N. 6.38. Found: C, 73.79; H,5.09; N, 6.35. IR (KBr pellets): 3050, 2925, 2854, 1599, 1459, 1328,

1245, 1174, 1008, 811, 725 cm−1.

 2.2.3. Synthesis of PtTCBPyP/SBA-15

PtTCBPyP was immobilized into SBA-15 by the following pro-

cedure. In a typical preparation, 1mg PtTCBPyP was added into

10ml dichloromethane andthe mixture was stirred for5 min. Then

SBA-15 (0.1g) was added into the dichloromethane solution of 

PtTCBPyP.The resultingmixturewas stirred for1 h atroomtemper-

ature, andfiltrated. The obtainedwhite powder waswashed several

times with the solvent until no PtTCBPyP existed in the filtrate. The

powder was dried in air, and the target sample PtTCBPyP/SBA-15

wasobtained. Thesamples with differentloading levels (10, 20 and

40mg/g SBA-15) were prepared by altering the concentrations of initial solution of PtTCBPyP.

 2.2.4. Synthesis of PtTCBPyP/MCM-41

The samples with different loading levels (10, 20 and 40mg/g

MCM-41) were prepared with procedure similar to that described

above.

 2.3. Apparatus and measurements

1H NMR  spectra were acquired on a Varian Clnity 300MHz

spectrometer by using standard pulse sequences. Spectra were

recorded at 25◦C inCDCl3 unless otherwise stated. Chemical shifts

were reported on the ı scale relative to tetramethylsilane (TMS).

Elemental analyses were measured by a Perkin–Elmer 240C autoelementary analyzer. The excited state lifetime was detected by

a systemequipped with a TDS 3052 digital phosphor oscilloscope

pulsed Nd:YAG laser with a THG 355nm output and a computer-

controlled digitizing oscilloscope. UV–vis spectra werecollected on

a Shimadzu UV-365 spectrometer. Infrared spectra were recorded

on a Nicolet 5PC-FT-IR spectrometer in the region 4000–400cm−1.

Massspectrawere obtainedusinga VG-Quattro massspectrometer.

Thin layer chromatography was performed on glass micro-plates

coated with silica gel G. The photoluminescence (PL) spectrawere

obtained by a Hitachi F-4500 fluorescence spectrophotometer

equipped with a monochromator (resolution: 0.2nm) and a 150W

Xe lamp as the excitation source. The photoluminescence quan-

tum yield was defined as the number of photons emitted per

photon absorbed by the system and was measured with an

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Fig.1. UV–vis absorptionspectraof TCBPyP and PtTCBPyPin dichloromethane solu-

tion.

integrating sphere by literature method. The powder X-ray

diffraction (XRD) data were collected on a Bruker D2 PHASER diffractometer equipped with CuK1  target (= 0.15405 nm). The

scanning range is 0.2–10◦ with 0.02◦ step and scanning speed is

1 s/step.

The oxygen-sensing properties of our samples were discussed

based on the fluorescence intensity quenching. The excitation

wavelength of all samples was 421 nm. In the measurement of 

Stern–Volmer plots, oxygen and nitrogen were mixed at differ-

ent concentrations via gas flow controllers and passed directly

into the sealed gas chamber at 25◦C, 45% relative humidity (Oxy-

gen response properties almost remain unchanged on the different

relative humidity, see supplementary file). We typically allowed

1min between changes in the N2/O2  concentration to ensure that

a new equilibrium point had been established. Equilibrium was

evident when the luminescence intensity remained constant. Thesensor response curves were obtained using the similar method.

Theexperiments were carried outin thedark at room temperature.

3. Result and discussion

 3.1. UV–vis absorption spectra

UV–vis absorption bands of the porphyrins are due to elec-

tronic transitions from the ground state (S 0) to the two lowest

singlet excited states S 1   (Q  state) and S 2   (Soret state) [28]. The

S 0 → S 1 transition gives the weakQ bands in the visible region while

S 0 → S 2 transition produces the strong Soret band in the near UV

region [32,33]. The absorption spectra of TCBPyP and PtTCBPyP in

dichloromethane solution are shown in Fig.1. The UV–vis spectrumof TCBPyP showed a maximum peak at 421nm which is typical

for Soret band, and four Q -bands were appeared at 518, 554, 593,

650nm. The Q band consists of four absorptions typical of Q  x(0,0),

Q  x(0,1), Q  y(0,0), Q  y(0,1) transitions. The relative intensities of these

bands are: 421 >>518> 554 >593> 650nm. These intensities are

similar to those observed for TPP [34]. The absorption peaks and

relative intensities of porphyrin ligand is almost identical, indicat-

ing that covalent linking of carbazole side groups to TPP has little

effect on the -electron system of the porphyrin. The absorption

bands of PtTCBPyP are almost identical too, which appear at 429,

523, 560nm. Compared with the porphyrin ligand, the number of 

the absorption bands of the metalloporphyrin complex decrease,

the most remarkable difference is the absence of some Q bands.

When the metal ions substitute the protons on the N  atoms in

Fig. 2. UV–vis absorption spectra of PtTCBPyP in dichloromethane solution (a),

PtTCBPyP/SBA-15(20mg/g) (b) and PtTCBPyP/MCM-41 (20mg/g) (c).

pyrrole rings, the symmetry of the molecule was changed fromD2h to D4h, therefore their absorption spectra are changed to some

extent.

UV–vis absorption spectra of PtTCBPyP in dichloromethane

solution, PtTCBPyP/SBA-15(20mg/g) and PtTCBPyP/MCM-

41(20mg/g) are shown in Fig. 2. UV–vis absorption spectra of 

PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41 are similar to that

of PtTCBPyP in dichloromethane solution, indicating that the

luminophors incorporated in composite systems remain intact

and keep their photochemical properties unchanged during the

process of encapsulation.

 3.2. Photoluminescence spectra

Luminescence quantum yield is defined as the ratio of the num-

ber of photons emitted to the number of photons absorbed. The

room-temperature luminescence quantum yield of TCBPyP and

PtTCBPyP in degassed dichloromethane solution have been con-

firmed by comparingwith the known luminescence quantum yield

from platinum meso-tetrakis(phenyl)porphyrin (PtTPP, ˚= 0.046)

[35]. Sample andstandardsolutions are degassed with no less than

fourfreeze–pump–thawcycles.Quantumyield is identified accord-

ing to the following Eq (1):

˚sample  =F sample

F PtTPP×

 APtTPP

 Asample˚PtTPP   (1)

where F sample   and F PtTPP   are measured photoluminescence inte-

gral areas (under the photoluminescence spectra) of the sampleand the reference PtTPP, respectively,  Asample   and  APtTPP   are the

absorbances of the sample andthe reference,˚sample and˚PtTPP are

the quantum yields of the sample and the reference PtTPP at same

excitation wavelength. The S 1 → S 0 quantum yield depends on the

relative rates of the radiativeprocess S 1 → S 0 andtwo radiationless

processes S 1 ∼→S 0 and S1 ∼→ T n. The photoluminescent quantum

yields of TCBPyP and PtTCBPyP in solution are 0.246 and 0.202at

a concentration of 1.0×10−5 mol/L, which are much more than

that of TPP and PtTPP. This indicates fairly certainly that the radia-

tive process S 1 → S 0 is predominant for S 1 →S 0 in these porphyrin

compounds and TCBPyP and PtTCBPyP possess good luminescence

properties in anaerobic surroundings. The raise of luminescence

quantum yield can be explained by the insert of the strong hole

transport carbazole group.

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Fig. 3. Solid-state emissionspectra of PtTCBPyP in air, pure nitrogen andpure oxy-

gen. ex = 420 nm, slit widthex/em  =5.0/2.5nm.

The emission spectra in solid-state have been obtained in air,pure nitrogen and oxygen, respectively, and the data indicate that

the emission intensity of PtTCBPyP is significantly influenced by

the concentration of oxygen, as shown in Fig. 3. The striking differ-

ence in emission intensity under different oxygen concentration is

noteworthy, because it indicates that PtTCBPyP probably possesses

oxygen-sensing properties.

Excited-state lifetime of PtTCBPyP, PtTCBPyP/SBA-15 and

PtTCBPyP/MCM-41 in air is measured (see Table 1). All of the data

are found to be well-fit by the double exponential. Where ˛ and

  are the pre-exponential factors and the excited-state lifetime

of the related decay profile, respectively. The subscripts 1 and 2

denote the assigned lifetime components. Longer lifetime values

can be observed from PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41

samples than PtTCBPyP. This result can be attributed to the factthat the PtTCBPyP/MCM-41 and PtTCBPyP/SBA-15 samples avoid

self-quenching efficiently compare with solid state Pt (II) complex.

Such lifetime values also can be explained on the basis of the sup-

pression of the vibrational deactivation and the restriction on the

mobility of the Pt (II) complex in an excited state due to the rigidity

of the silica matrix [36].

 3.3. Oxygen-sensing properties

Powder XRD patterns of SBA-15, PtTCBPyP/SBA-15, MCM-41

and PtTCBPyP/MCM-41 are shown in Fig. 4. It shows three Bragg

reflections in the low angle indexed to d100, d110, and d200, which

are characteristic peaksof highly ordered hexagonal mesostructure

[37,38]. Powder XRD measurement results indicate that the hexag-onal arrangement of channels in mesoporous molecular sieves

remains unchanged after the incorporation of PtTCBPyP.

The luminescence of platinum porphyrin complex could be

quenched efficiently by molecular oxygen. The mechanism of the

quenching process consists of the exchange energy transfer from

the lowest triplet excited state of metalloporphyrin to molecular

 Table 1

Excited-state lifetime of PtTCBPyP, PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41 in air.

sample ˛1    1  (s) ˛2    2 (s) < > (s) r 2

PtTCBPyP 0.08 4.23 0.02 10.00 6.37 0.9987

PtTCBPyP/SBA-15(20 mg/g) 0.35 10.00 0.60 3.72 7.55 0.9972

PtTCBPyP/MCM-41 (20 mg/g) 0.58 4.96 0.02 18.20 6.45 0.9960

Fig. 4. (A) PowderXRD patterns of SBA-15 (a)and PtTCBPyP/SBA-15

(B)Powder XRD patterns of MCM-41 (a) and PtTCBPyP/MCM-41 (b).

oxygen, which is accompanied by the formation of singlet oxy-

gen. As a result, the complex could be commonly used to develop

oxygen-sensing materials. The oxygen concentration dependent

emission spectra of PtTCBPyP/SBA-15(20mg/g) are shown in

Fig. 5. The emission maximum of PtTCBPyP/SBA-15(20mg/g) is

at 651 nm and is constant under different oxygen concentrations.

Fig. 5. Emission spectra of PtTCBPyP/SBA-15(20mg/g) under different oxygen con-

centrations:(a) 0; (b) 0.1; (c) 10; (d) 100% oxygen.

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Fig. 6. Emission spectra of PtTCBPyP/MCM-41 (20mg/g) under different oxygen

concentrations:(a) 0; (b) 0.1; (c) 10; (d) 100% oxygen.

However, the relative intensity decreases markedly upon increas-ing oxygen concentration. The variations of the emission spectra

of PtTCBPyP/SBA-15(10 or 40mg/g) display similar trends to that

of PtTCBPyP/SBA-15(20 mg/g). The relative luminescent intensi-

tiesof PtTCBPyP/SBA-15(10mg/g),PtTCBPyP/SBA-15(20 mg/g), and

PtTCBPyP/SBA-15(40mg/g)decreaseby 99.94%, 99.99% and99.98%,

respectively, upon changing from pure nitrogen to pure oxygen

conditions. PtTCBPyP/SBA-15(20mg/g) is more sensitive compared

with PtTCBPyP/SBA-15(10mg/g) and PtTCBPyP/SBA-15(40mg/g),

suggesting that the optimum loading level is 20mg/g. The oxygen

concentration dependent emission spectra of PtTCBPyP/MCM-

41 (20 m g/g) are shown in Fig. 6. The emission maximum of 

PtTCBPyP/MCM-41 (20mg/g) is at 646nm and the emission inten-

sity drops quickly. For PtTCBPyP/MCM-41 (20mg/g), similar results

are observed by comparing the emission spectra under differ-ent concentrations of oxygen. Upon changing from pure nitrogen

to pure oxygen conditions, the relative luminescent intensities

of PtTCBPyP/MCM-41 (10mg/g), PtTCBPyP/MCM-41 (20mg/g) and

PtTCBPyP/MCM-41 (40mg/g) decrease by 99.77%, 99.97% and

99.92%, respectively, andthe optimum loading level is 20mg/g. The

two opposite factors probably affect the sensing properties of the

compositesystems.When the loadinglevel is 10 mg/g, the emission

from the complex is comparatively weak which results in the low

response.When theloadinglevel is 40 mg/g, concentration quench-

ing existing among the platinum porphyrin molecules in the pores

of mesoporous silica may become stronger.

Luminescent molecule quenching in homogeneous media with

negligible matrix effects are expected to show single-exponential

excited state decay and the emission intensity or decay time with

oxygen concentration can be described by the Stern–Volmer (SV)

Eq. (2):

I 0/I =  0/ = 1+ K SV[Q ] = 1+ K q 0[Q ] (2)

where I and  are the luminescence intensity and the excited-state

lifetime of the related decay profile, respectively, the subscript 0

denotes the absence of oxygen, K SV  is the Stern–Volmer constant,

K q  is the bimolecular rate constant describing the efficiency of the

collisional encounters between the luminophore and the quencher,

and [Q ] is the O2  concentration. In the idea case, the plot of I 0/I or

 0/ versus oxygen concentration should give a straight-line rela-

tionship with slope K SV. However, non-linear Stern–Volmer plots

are often obtained when quenching takes place in a solid matrix

[39–41].

Fig. 7. Stern–Volmer plot for PtTCBPyP/SBA-15 at different concentrations of oxy-

gen. (I 0   and I  are luminescent intensities in the absence and in the presence of 

oxygen).

Figs. 7 and 8 present the Stern–Volmer plots for PtTCBPyP/SBA-

15 and PtTCBPyP/MCM-41, respectively. The plots are nonlinear

within a wide range of oxygen concentrations. The deviationfrom linearity is attributed to a distribution of slightly differ-

ent quenching environments for the luminophore molecules. It is

believed that there are two sites of platinum porphyrin complex

micro-environments within the ormosil matrix: one site is oxygen-

easy accessible and the others are oxygen-difficult accessible sites

[42–45]. Platinum porphyrin complex may exhibits characteristic

quenchingconstants within eachdistinct platinum porphyrincom-

plex site,and the overall Stern–Volmer expressionbecomes Eq. (3):

I 0I   =

1 f 01

1+K SV1[Q ] +

  f 021+K SV2[Q ]

(3)

Here,  f 01   and  f 02   denote the fractional contributions of the total

intensity from the platinum porphyrin complex located at two dif-ferent sites that exhibit two discrete Stern–Volmer constants K SV1

andK SV2, respectively. This two-site model accounts for nonlinear-

ity commonly observed for Stern–Volmer plots. The I 0/I 100  ratio

has been used as an indicator of the response of the sensing device,

and a sensor with I 0/I 100 more than 3.0 is a suitable oxygen sens-

ing device [46]. The value of I 0/I 100  of PtTCBPyP/SBA-15(20mg/g)

is 8779.8. To our knowledge, it is the highest value for optical oxy-

gensensors based on platinum porphyrins that have been achieved

Fig. 8. Stern–Volmerplot for PtTCBPyP/MCM-41at differentconcentrations of oxy-

gen. (I 0   and I  are luminescent intensities in the absence and in the presence of 

oxygen).

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Fig. 9. Response time and relative intensity change and reproducibility for

PtTCBPyP/SBA-15(20mg/g) on switching between 100% nitrogen (a) and 100% oxy-

gen(b).

until now. It can be seen from the Stern–Volmer plots that high

response is obtained at low oxygen concentrations (less than 10%,

I 0/I 10). Evenwhen the concentration is only10%, for PtTCBPyP/SBA-

15(10, 20 and 40 m g/g) the quenching of luminescence can

reach 99.81% (I 0/I 10 = 526.9), 99.96% (I 0/I 10 =2634.6) and 99.89%

(I 0/I 10 = 1881.8), for PtTCBPyP/MCM-41(10, 20 and 40mg/g) the

quenching of luminescence canreach 99.24%(I 0/I 10 = 131.7),99.80%

(I 0/I 10 = 1038.3)and 99.73% (I 0/I 10 = 376.4),respectively.Even when

the concentration is only 0.1%, for PtTCBPyP/SBA-15(20 mg/g) the

quenching of luminescence can reach 96.14% (I 0/I 0.1 =25.9), for

PtTCBPyP/MCM-41 (20mg/g) the quenching of luminescence can

reach 95.42% (I 0/I 0.1 = 21.8), respectively. It is important that the

measurement, so PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41 has a

great potential for application in oxygen sensors.

The response time and recovery time are also very impor-tant factors in evaluating an oxygen sensor. Traditionally, 95%

response time, i.e. t ↓ (95%, N2 →O2) refers to the time required

for the luminescent intensity to decrease by 95% on chang-

ing from 100% nitrogen to 100% oxygen, and 95% recovery

time, i.e. t ↑ (95%N2→O2), is defined as the time required for

the luminescent intensity to reach 95% of the initial value

recorded under 100% nitrogen on changing from100% oxygen

to 100% nitrogen. Figs. 9 and 10 show the response property

of PtTCBPyP/SBA-15(20mg/g) and PtTCBPyP/MCM-41 (20mg/g).

The emission intensity of the samples drops quickly with the

increasing of oxygen concentration, and recovers when 100%

nitrogen replacing oxygen. The samples are repeatedly exposed

to an alternating atmosphere of nitrogen and oxygen and the

emission intensity changes with the oxygen concentration are

Fig. 10. Response time and relative intensity change and reproducibility for

PtTCBPyP/MCM-41 (20mg/g) on switching between 100% nitrogen (a) and 100%

oxygen (b).

reversible. The values of response (I 0/I 100), t ↓, t ↑ and Demas model

oxygen-quenching fitting parameters are compiled in Table 2.

Oxygen sensing materials based on PtTCBPyP/SBA-15 have good

response (I 0/I 100 > 1700), especially PtTCBPyP/SBA-15(20 mg/g)

with an excellent response (I 0/I 100 > 8700). Oxygen sensing mate-

rials based on PtTCBPyP/MCM-41 (20 mg/g) have fast recovery

time (t ↑<15.0s), response time (t ↓<2.0s) and good response

(I 0/I 100 > 3800).Theoxygen sensing propertyof this kind ofmaterial

is much betterthanthatof other Pt–porphyrinbasedsensingmate-

rials reported previously [47–50]. These results provide possible

explanation as follows: Even though some PtTCBPyP molecules are

encapsulated in the pores of mesoporous silica, there is still excess

space to allow oxygen molecules to transport freely, so oxygen

moleculescan easily diffuse into/outof thepores of PtTCBPyP/silica.

The molecular dimensions of PtTCBPyP are bigger than those of other Pt–porphyrin, but the conjugacy of PtTCBPyP is weaker. At

the concentration of 20mg/g, the distribution of PtTCBPyP is bet-

ter than other Pt–porphyrin in the pores of mesoporous silica.

The long alkyl-carbazole arms of PtTCBPyP can avoid concentra-

tion quenching among the platinum porphyrin molecules, which

make the energy can transfer from excited porphyrin molecule to

the ground state oxygen more effectively but not transfer among

the platinum porphyrin molecules. Bigger molecular dimensions

and weaker conjugated structure could make the luminescence of 

PtTCBPyP/silica quenched by oxygen molecules efficiently [51,52].

The results illustrate that the recovery time is significantly longer

than the response time. Since small molecules such as oxygen are

well known to be adsorbed strongly on silica surfaces, we suggest

that the longer recovery time may be attributed to slow desorption

 Table 2

Values of response (I 0/I 100 ), t ↓, t ↑, and Demas modela oxygen-quenching fitting parameters of PtTCBPyP/SBA-15 and PtTCBPyP/MCM-41.

PtTCBPyP/SBA-15 PtTCBPyP/MCM-41

10 mg/g 20 mg/g 40 mg/g 10 mg/g 20 mg/g 40 mg/g

I 0/I 100   1756.0 8779.8 6271.3 439.0 3853.0 1254.3

t ↓(s) 4.5 3.0 3.0 2.5 1.5 1.5

t ↑(s) 15.5 17.0 19.0 16.0 14.5 17.5

K SV1(O2%−1) 0.00338 ± 0.00059 0.00339 ± 0.00059 0.00338 ± 0.00059 0.00335 ± 0.00059 0.00029 ± 0.00037 0.00338 ± 0.00059

K SV2(O2%−1) 71.7061 ± 3.05388 359.18093 ± 15.32362 256.51536 ± 10.94195 17.80357 ± 0.75323 131.50852 ± 3.44677 51.17177 ± 2.17744

 f 01b 0.00057 ± 0.00003 0.00011 ± 0.00001 0.00016 ± 0.00001 0.00226 ± 0.00012 0.00019 ± 0.00001 0.00079 ± 0.00004

r 2 0.99958 0.99958 0.99958 0.99959 0.99974 0.99958

a Terms arefrom Eq. (3).b

 f 01 + f 02 = 1.

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Biographies

BinbinWang Receivedhis BScin 2004 andMSc in 2007in inorganicchemistryfromNortheastNormal University (NNU),and then he began hisPhD student experiencein inorganic chemistry, Jilin Universityunder the supervisingof Prof. Tongshun Shi.

He has been a lecturer since 2010 at Changchun Normal University. His researchinterest is the synthesis of porphyrin metal complexes. He is also interested in theexploration of porphyrin metal complexesas gas sensors.

Liming Zhang Received his BSc degree in 2005 from NNU and PhD in 2010 in con-densed statephysics fromChangchunInstituteof OpticsFineMechanicsand Physics(CIOMP). He has been a research assistant at the CIOMP. He has been working onluminescence materials.

Bin Li Received his BSc in 1986 and MSc in 1991 in inorganic chemistry fromNNU,andPhD in1997 ininorganic chemistryfromChangchunInstitute ofApplied Chem-istryof Chinese Academy of Sciences.He hasbeenan associateprofessor since 1999at NNU and a professor since 2003 at CIOMP. Hiscurrent research interests are thestudyof applicationof transitionmetal complex as gas sensors,and theorganic lightemitting devices (OLED).

 Yao Li Received herBSc in 2005 andMSc in 2008 in inorganicchemistry from NNU,and then she began her PhD student experience in inorganic chemistry, BeijingInstitute of Technology. Her research interest is luminescent materials.

 Yuhua Shi Received her BSc in 1996 and PhD in 2001 in analytical chemistry from Jilin University, and then she became an associate professor at Jilin University. Herresearch interest is luminescent materials.

 Tongshun Shi Received his BSc degree in 1969 from Jilin University. He has beenan associate professor since 1992 and a professor since 1998 at Jilin University.His current research interests arethe synthesisand application of porphyrin metalcomplexes.