Synthesis, photophysical, electrochemical and photoluminescent oxygen sensing studies of trans-Pt(II)-porphyrins

Article abstract of DOI:10.1016/j.dyepig.2019.02.016

A series of fluorinated trans-porphyrins (1a-6a) bearing thienyl/biphenyl/naphthyl/fluorenyl/pyrenyl moieties were synthesized and characterized by various spectroscopic methods and electrochemical analysis. The scrambled products such as tetrakis(pentafl

Full text of DOI:10.1016/j.dyepig.2019.02.016

Accepted Manuscript
Synthesis, photophysical, electrochemical and photoluminescent oxygen sensing
studies of trans-Pt(II)-porphyrins
Monisha Manathanath, Maichong Xie, Chellaiah Arunkumar, Zhonggang Wang,
Jianzhang Zhao, Subramaniam Sujatha
PII:
S0143-7208(18)31745-5
https://doi.org/10.1016/j.dyepig.2019.02.016
DYPI 7350
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 6 August 2018
Revised Date: 29 December 2018
Accepted Date: 10 February 2019
Please cite this article as: Manathanath M, Xie M, Arunkumar C, Wang Z, Zhao J, Sujatha S, Synthesis,
photophysical, electrochemical and photoluminescent oxygen sensing studies of trans-Pt(II)-porphyrins,
Dyes and Pigments (2019), doi: https://doi.org/10.1016/j.dyepig.2019.02.016.
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ACCEPTED MANUSCRIPT
Synthesis, Photophysical, Electrochemical and Photoluminescent
Oxygen Sensing Studies of trans-Pt(II)-porphyrins
a†
b†
a
c
Monisha Manathanath , Maichong Xie , Chellaiah Arunkumar , Zhonggang Wang , Jianzhang
b
a
Zhao * and Subramaniam Sujatha *
trans-Pt(II)-porphyrins were examined for its oxygen sensing abilities on polymer
matrices and EC-porphyrin films showed better sensitivity with good photostability than
IMPEK-C and PMMA; the KSV value exhibited for EC-Pt-3a is higher compared to
reference compound Pt(II)-(pentafluorophenyl)porphyrin.

ACCEPTED MANUSCRIPT
Synthesis, Photophysical, Electrochemical and Photoluminescent Oxygen
Sensing Studies of trans-Pt(II)-porphyrins
a†
b†
a
c
Monisha Manathanath , Maichong Xie , Chellaiah Arunkumar , Zhonggang Wang ,
b
a
Jianzhang Zhao * and Subramaniam Sujatha *
a
Bioinorganic Materials Research Laboratory, Department of Chemistry, National Institute of Technology Calicut,
NIT Campus P.O., Calicut, India-673 601.
b
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, E 208
Western Campus, 2 Ling-Gong Road, Dalian 116012, P.R. China.
c
School of Chemical Engineering, Dalian University of Technology, Western Campus, 2 Ling-Gong Road, Dalian
1
16012, P.R. China.
Abstract:
A series of fluorinated trans-porphyrins (1a-6a) bearing thienyl / biphenyl / naphthyl /
fluorenyl / pyrenyl moieties were synthesized and characterized by various spectroscopic
methods and electrochemical analysis. The scrambled products such as
tetrakis(pentafluorophenyl)porphyrin, H T(PFP)P and tris(pentafluorophenyl)-mono-(aryl)
2
porphyrins (1b-6b), obtained during the synthesis of these trans-porphyrins were also
characterized. Four of the porphyrins were structurally characterized by single crystal XRD
analysis. The luminescent oxygen sensing properties of the trans-Pt(II)-porphyrins were
investigated in solution. Besides, the sensing properties of the complexes were compared in three
different polymer films such as IMPEK-C, ethyl cellulose (EC) and poly(methylmethacrylate)
(PMMA). The results revealed that the EC-porphyrin films show better sensitivity and good
photostability than the other two films. The highest Stern-Volmer quenching constant of 0.096
−1
Torr was obtained for EC-Pt-3a which is 1.4 fold higher than the commonly used Pt(II)-
pentafluorophenyl)porphyrin.
(
Keywords:
Electrochemistry, Phosphorescent Oxygen Sensing.
_______________________________________________________________________
Scrambling,
trans-Pt(II)-porphyrins,
Structure,
Photophysical,
_
†Equally contributed to this work.
E-mail: zhaojzh@dlut.edu.cn (J. Zhao); sujatha@nitc.ac.in (S. Sujatha)
1

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Introduction
Probing and sensing of molecular oxygen at ambient condition has been paid great
attention due to the fact that lack of maintaining adequate oxygen levels will pose profound
consequences and threatens sustainable ecosystem. Systematic monitoring of oxygen level is
essential in diverse areas like biological, automobile, medicinal and industrial. Among the
various established techniques, Clarke electrode is considered as the conventional model
employs the quantitative measurement of oxygen being reduced on the surface of electrode on
applying a voltage [1]. Due to the intrinsic drawbacks such as expensive nature, difficulty in
maintenance and consumption of oxygen that results in uncertain data etc., made the device less
analytical demand. This resulted in the need of development of low-cost alternatives with good
efficiency and quality performance. Despite of the amperometric sensors, potentiometric, optical,
ceramic based are also being used [2]. One of the good alternatives is optical sensor, offering fast
response, ease to use and immunity to environmental effects. Indeed, the reports [3] on the
−1
development of sensors which can be used to monitor low (< 1 µgL ) as well as high oxygen
−1
concentration (> 400 µgL ), those used for gaseous and dissolved oxygen etc. deserve
appreciation. An ideal sensor constitutes a luminophore whose spectral properties are reversibly
affected by molecular oxygen, usually embedded in a polymer matrix. Several factors that
influence the sensitivity of the sensor include the lifetime of the luminophore, and the choice of
encapsulating medium with good oxygen permeability [2]. The principle of an optical sensor is
that, the populated photo excited state of the dye employed gets depleted via collisional
quenching of O resulting decrease in luminescent intensity when exposed to varying oxygen
2
levels. The change in intensity serves as the tool for the quantitative measurement of oxygen
being analyzed [4]. The relation between the intensity of luminescence and concentration (partial
pressure, pO ) of oxygen can be well explained by Stern-Volmer equation and sensor molecules
2
with increased lifetime render better sensitivity towards oxygen. Generally, the polymer based
sensors exhibit non-linear kinetics and displays downward curvature in Stern-Volmer intensity
plots. Demas et al [5] suggested a fitting model to resolve the non-linearity exhibited by the
molecules arise from the level of heterogeneity of the matrix used. The downward curvature of
the ideal Stern-Volmer plot predicting complex decay kinetics can be fitted using two-site model
[6]. It assumes the existence of the sensor molecule in two distinct sites, one being quenched and
the other not being quenched, both with independent quenching constants [5]. This model
2

ACCEPTED MANUSCRIPT
provides some insight for the accurate prediction of sensor response and made it of considerable
interest nowadays.
Luminescent transition metal complexes are widely accepted as oxygen sensitive probes
owing to their long lived metal to ligand excited state, good photostability and visible absorption.
A variety of Ru(II)-diamine based complexes [7] incorporated in various polymer matrices have
also been the area of thorough research. Moreover, porphyrin and metalloporphyrins, particularly
Pt(II) and Pd(II) porphyrins with tunable photophysical properties, high quantum yield and
specific response to molecular oxygen became promising candidates over Ru(II)-complexes [8].
Halogenated porphyrins generally show better photostability towards continuous irradiation
compared to classical tetraphenylporphyrins. Lee and Okura [9] introduced platinum
tetrakis(pentafluorophenyl) porphyrin (PTFPP) dispersed in polystyrene as reliable and
photostable oxygen sensor over Pt(II)-(octaethyl)porphyrin. Furthermore, Xiang and coworkers
[10] designed a meso-di(pentafluorophenyl) Pt(II)-fluorene copolymer and well demonstrated it
as a ratiometric dual emissive oxygen sensor. Recently, we have reported the oxygen sensing
properties of a series of fluorinated Pt(II)-porphyrins with reasonably high sensitivity and
photostability [11]. In continuation with this, here we report the synthesis, photophysical and
electrochemical properties of six different fluorinated trans-Pt(II)-porphyrins bearing thienyl /
biphenyl / naphthyl / fluorenyl / pyrenyl moieties. The particular aryl groups are selected to
affect the emission properties, owing to the fact that extended pi-conjugation leads to more red
shifted spectra [12,13]. The oxygen sensitivities of the emission of these porphyrins were
investigated in solution. To evaluate the influence of matrix effect, we have chosen porphyrins-
IMPEK-C / EC / PMMA films and the luminescence oxygen sensing properties were explored
by monitoring the response of the films to the saturation switch between the oxygen and nitrogen
as well as against the variation of oxygen partial pressure.
3

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F
F
Ar
F
F
N
F
N
Pt
F
N
N
F
F
Ar
F
F
S
Ar =
S
Pt-1a
Pt-2a
Pt-3a
Pt-4a
Pt-5a
Pt-6a
Fig. 1. Molecular structures of trans-Pt(II)-porphyrins.
Experimental
Materials and methods
All reagents and chemicals of analytical grade were purchased, used as such without any
further purification. Solvents employed for the reaction and separation methods were purified as
per the standard procedures before its use. Potassium tetrachloroplatinate(II), K [PtCl ] was
2
4
purchased from Aldrich. The solvent benzonitrile was obtained from Alfa Aeser and used after
dried over molecular sieves. UV-Visible spectra were recorded at room temperature in CH Cl
2
2
using a JASCO V-750 UV-Visible spectrophotometer and NMR spectra were obtained on a
Bruker Avance III 400 MHz spectrometer with CDCl as the solvent. The HRMS spectra were
3
recorded with Bruker maxis impact 282001.00081 / Thermo Scientific Exactive instrument by
electron spray ionization method. The emission spectra were measured by exciting at Soret band
on a PerkinElmer LS 55 spectrophotometer at room temperature over the range of 550-700 nm.
Electrochemical studies were performed on a CH-instruments equipped with a potentiostat /
galvanostat with Fourier transform AC Voltammeter and the cell assembly consists of three-
electrode system containing glassy carbon as working electrode, a standard calomel electrode
(
SCE) as the reference electrode, and a platinum wire as the auxiliary electrode. The
concentration of the samples employed was 0.5 mM and the measurements were done in CH Cl
at 25 °C under N atmosphere using 0.1 M tetrabutylammonium hexafluorophosphate
2
2
2
(
TBAHFP) as the supporting electrolyte. Single crystal X-ray structure data collections were
performed on a Bruker AXS Kappa Apex II CCD diffractometer with graphite monochromated
Mo K radiation (λ = 0.71073 Å) at 298 K.
α
4

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Synthesis of trans-porphyrins using BF ⋅OEt as catalyst
3
2
The precursor, 5-(pentafluorophenyl)dipyrromethane was prepared using reported literature
method [14]. All the free base porphyrins were synthesized according to Lindsey method using
BF ⋅OEt as the catalyst [15]. 5-(Pentafluorophenyl)dipyrromethane (0.64 mmol) and appropriate
3
2
2 2
aryl aldehyde (0.64 mmol) were added to 300 mL of CH Cl in a round bottomed flask and purged
with N for few minutes. To that, BF ⋅OEt (0.25 mL, 2.5 M) was added and stirred for 40 minutes.
2
3
2
The oxidizing agent DDQ (1.28 mmol) was then added and again stirred for 1 hr. The solvent was
evaporated and subjected to silica column chromatography in hexane / chloroform mixture. All the
reactions resulted in the formation of three products, among them first fraction was found to be
5
,10,15,50-tetrakis(pentafluorophenyl)porphyrin, H T(PFP)P (Scheme 1). The yields of trans
2
porphyrins (1a-6a) were found to be 11-19 % whereas for the tris(pentafluorophenyl)-mono-
aryl) porphyrins (1b-6b) it is of 6-14 %.
UV-Visible data of porphyrins in DMF, λmax (log ε / M cm ): 1a - 419 (5.39), 514 (4.22), 548
(
−1
−1
(
(
(
-
(
(
-
3.75), 655 (3.80); 1b - 415 (5.92), 541 (4.24), 585 (3.82), 657 (3.67); 2a - 417 (5.36), 511
4.39), 546 (4.01), 644 (2.80); 2b - 414 (5.55), 538 (4.43), 584 (4.03), 638 (3.72); 3a - 418
5.44), 513 (4.78), 545 (3.90), 588 (3.71); 3b - 415 (5.01), 508 (4.46), 582 (3.93), 638 (3.77); 4a
418 (5.04), 511 (3.82), 585 (3.47), 642 (3.29); 4b - 414 (5.33), 507 (4.18), 582 (3.76), 638
3.36); 5a - 420 (5.24), 513 (3.98), 550 (3.48), 587 (3.59), 643 (3.38); 5b - 416 (5.35), 509
4.18), 543 (3.45), 584 (3.80), 639 (3.53); 6a - 418 (5.66), 513 (4.90), 586 (3.57), 642 (3.01); 6b
413 (5.47), 509 (4.63), 582(3.52), 637 (3.01). Emission data in DMF, λ : 1a - 657, 716; 1b -
em
6
5
1
5
57, 707; 2a - 650,712; 2b - 643, 706; 3a - 644,708; 3b - 642,704; 4a - 644, 708; 4b - 640, 703;
1
a - 646, 708; 5b - 643,705; 6a - 646,709; 6b - 643,705. H NMR (300 MHz, CDCl ), δ (ppm):
3
a - 9.19-9.07 (m, 4H), 8.83 (d, J = 17.7 Hz, 4H), 7.95 (dd, J = 3.4, 1.2 Hz, 2H), 7.90 (dd, J =
.2, 1.1 Hz, 2H), 7.53 (dd, J = 5.2, 3.4 Hz, 2H), -2.77 (s, 2H); 1b - 9.20 (d, J = 4.3 Hz, 2H), 8.87
(
d, J = 16.2 Hz, 6H), 7.97 (d, J = 3.3 Hz, 1H), 7.92 (d, J = 4.2 Hz, 1H), 7.58-7.52 (m, 1H), -2.84
s, 2H); 2a - 9.07 (d, J = 4.8 Hz, 4H), 8.80 (d, J = 4.7 Hz, 4H), 8.05 (dd, J = 3.0, 1.1 Hz, 2H),
(
8
.01 (dd, J = 4.8, 1.1 Hz, 2H), 7.77 (dd, J = 4.8, 3.0 Hz, 2H), -2.80 (s, 2H); 2b - 9.10 (d, J = 4.7
Hz, 2H), 8.93 – 8.81 (m, 6H), 8.07 (dd, J = 2.9, 1.1 Hz, 1H), 8.01 (dd, J = 4.8, 1.1 Hz, 1H), 7.78
dd, J = 4.8, 3.0 Hz, 1H), -2.83 (s, 2H); 3a - 9.05 (d, J = 4.7 Hz, 2H), 8.97 (s, 2H), 8.87 (s, 2H),
(
8
7
.80 (d, J = 4.6 Hz, 2H), 8.29 (d, J = 8.2 Hz, 4H), 8.02 (d, J = 8.2 Hz, 4H), 7.97-7.92 (m, 4H),
.61 (t, J = 7.6 Hz, 4H), 7.49 (t, J = 7.4 Hz, 2H), -2.72 (s, 2H); 3b - 9.06 (d, J = 4.7 Hz, 2H),
5

ACCEPTED MANUSCRIPT
8
2
.90 (d, J = 2.0 Hz, 4H), 8.83 (d, J = 4.5 Hz, 2H), 8.29 (d, J = 8.1 Hz, 2H), 8.03 (d, J = 8.1 Hz,
H), 7.96-7.92 (m, 2H), 7.61 (t, J = 7.6 Hz, 2H), 7.49 (t, J = 7.4 Hz, 1H), -2.81 (s, 2H); 4a - 8.88
(s, 2H), 8.68 (d, J = 3.4 Hz, 4H), 8.49 (d, J = 3.4 Hz, 2H), 8.32-8.22 (m, 2H), 8.16-8.10 (m, 2H),
7
2
.89-7.82 (m, 2H), 7.52-7.46 (m, 2H), 7.15-7.10 (m, 2H), 7.08 (dd, J = 7.8, 4.5 Hz, 2H), -2.54 (s,
H); 4b - 8.90 (s, 4H), 8.70 (s, 4H), 8.34 (d, J = 8.3 Hz, 1H), 8.26 (d, J = 6.9 Hz, 1H), 8.17 (d, J
=
8.3 Hz, 1H), 7.89 (dd, J = 8.2, 7.1 Hz, 1H), 7.52 (t, J = 7.5 Hz, 1H), 7.19-7.10 (m, 1H), 7.06
(
d, J = 8.4 Hz, 1H), -2.73 (s, 2H); 5a - 9.02 (d, J = 4.8 Hz, 2H), 8.93 (s, 2H), 8.86 (s, 2H), 8.78
d, J = 4.6 Hz, 2H), 8.37 (s, 2H), 8.24 (d, J = 7.7 Hz, 2H), 8.17 (d, J = 7.7 Hz, 2H), 8.06 (d, J =
(
7
4
8
.5 Hz, 2H), 7.71 (d, J = 7.4 Hz, 2H), 7.54 (t, J = 7.4 Hz, 2H), 7.45 (dd, J = 10.8, 4.2 Hz, 2H),
.21 (s, 4H), -2.68 (s, 2H); 5b - 9.04 (d, J = 4.6 Hz, 2H), 8.90 (s, 4H), 8.82 (d, J = 4.4 Hz, 2H),
.37 (s, 1H), 8.24 (d, J = 7.7 Hz, 1H), 8.18 (d, J = 7.7 Hz, 1H), 8.07 (d, J = 7.5 Hz, 1H), 7.71 (d,
J = 7.4 Hz, 1H), 7.54 (t, J = 7.5 Hz, 1H), 7.46 (t, J = 7.4 Hz, 1H), 4.21 (s, 2H), -2.79 (s, 2H); 6a -
8
8
.94-8.62 (m, 8H), 8.56 (d, J = 7.7 Hz, 1H), 8.50 (d, J = 7.8 Hz, 1H), 8.46-8.29 (m, 8H), 8.16-
.01 (m, 4H), 7.79-7.70 (m, 2H), 7.48-7.36 (m, 2H), -2.40 (s, 2H); 6b - 8.93-8.67 (m, 8H), 8.63
(d, J = 4.7 Hz, 1H), 8.55 (d, J = 7.8 Hz, 1H), 8.46-8.32 (m, 3H), 8.15-8.07 (m, 2H), 7.74 (d, J =
1
3
9
1
1
1
1
1
1
1
1
1
1
1
1
8
9
3
.3 Hz, 1H), 7.36 (d, J = 9.3 Hz, 1H), -2.65 (s, 2H). C NMR (101 MHz, CDCl ) δ: 1b - 141.45,
35.40, 134.62, 132.0, 128.58, 127.10, 126.33, 114.44, 111.8, 107.70; 2b - 134.47, 128.98,
27.32, 126.10, 125.10, 122.90, 119.9, 107.71, 103.2; 3a -140.91, 140.61, 140.41, 135.08,
29.10, 127.81, 127.40, 125.54, 122.54; 3b - 147.83, 145.37, 141.13, 140.49, 139.92, 135.12,
29.13, 127.40, 125.65, 123.05, 103.04, 101.86; 4a - 138.38, 136.77, 136.73, 133.05, 132.97,
32.93, 129.13, 128.56, 127.95, 126.59, 125.91, 124.27, 119.17, 102.23 4b - 138.17, 136.07,
36.3, 133.05, 129.30, 127.92, 126.59, 124.24, 119.13, 107.77; 5a - 143.77, 141.83, 141.68,
41.34, 139.88, 133.56, 131.43, 127.30, 127.15, 125.33, 123.28, 120.39, 118.08, 37.12; 5b -
43.78, 141.95, 141.90, 141.23, 139.34, 133.62, 131.50, 127.42, 127.20, 125.37, 123.80, 118.20,
03.01, 37.12; 6a - 135.80, 133.50, 132.62, 131.71, 130.71, 128.31, 128.04, 127.60, 126.89,
26.43, 125.80, 125.49, 124.49, 124.12, 122.81, 120.76, 101.64; 6b - 135.39, 133.58, 132.67,
31.87, 131.73, 130.71, 128.48, 128.25, 127.59, 126.74, 126.53, 125.93, 125.60, 124.48, 124.17,
+
22.88, 121.26, 103.17; Mass data [MH] : 1a - 807.0741 (calc: 807.0734); 1b - 891.0708 (calc:
91.0699); 2a - 807.0754 (calc: 807.0734); 2b - 891.0706 (calc: 891.0699); 3a - 947.2239 (calc:
47.2232); 3b - 961.1458 (calc: 961.1448); 4a - 895.1931 (calc: 895.1919); 4b - 935.1302 (calc:
6

ACCEPTED MANUSCRIPT
9
35.1292); 5a - 971.2244 (calc: 971.2232); 5b - 973.1455 (calc: 973.1448); 6a – 1043.2247
(calc: 1043.2232); 6b - 1009.1463 ( calc: 1009.1448).
Synthesis of trans-Pt(II)-porphyrins
Further, the porphyrin ligands were metallated using platinum salt by the available literature
method [16]. The general procedure is as follows: 1a and 2a (0.04 mmol), 3a - 6a (0.03 mmol) were
added to 8 ml of pre-heated benzonitrile containing 0.04 mmol of K [PtCl ] under N at 140 °C for
2
4
2
2
18 hrs. The reaction mixture was refluxed under N for 18 hrs. Then, the reaction mixture was
cooled; solvent was removed under vacuum and subjected to column chromatography in CHCl3 /
Hexane mixture. This afforded orange colored product with yield in the range 60-70 %. UV-visible
−1
−1
data of porphyrins in CH Cl at room temperature, λ (log ε / M cm ): Pt-1a, 399 (5.59), 510
2
2
max
(4.44), 542 (4.25); Pt-2a, 399 (5.59), 510 (4.52), 542 (4.37); Pt-3a, 401 (5.21), 510 (4.01), 541
(3.70); Pt-4a, 400 (5.60), 510 (4.52), 543 (4.52); Pt-5a, 397 (5.20), 509 (4.26), 541 (4.21); Pt-6a,
1
3
5
97 (5.29), 512 (4.36), 544 (3.64). H NMR data in CDCl (400 MHz), δ (ppm): Pt-1a, 9.06 (d, J =
3
.1 Hz, 4H), 8.70 (d, J = 5.0 Hz, 4H), 7.90 (d, J = 2.3 Hz, 2H), 7.86 (d, J = 5.2 Hz, 2H), 7.50 (dd,
J = 5.2, 3.5 Hz, 2H); Pt-2a, 8.92 (d, J = 5.1 Hz, 4H), 8.64 (d, J = 5.1 Hz, 4H), 7.95 (d, J = 1.7
Hz, 2H), 7.88 (d, J = 4.8 Hz, 2H), 7.70-7.66 (m, 2H); Pt-3a, 8.96 (d, J = 5.1 Hz, 2H), 8.89 (s,
2
7
H), 8.79 (s, 2H), 8.72 (d, J = 4.9 Hz, 2H), 8.23 (d, J = 8.0 Hz, 4H), 8.00 (d, J = 7.9 Hz, 4H),
.96 – 7.89 (m, 4H), 7.60 (t, J = 7.7 Hz, 4H), 7.49 (t, J = 7.4 Hz, 2H); Pt-4a, 9.05 (s, 1H), 8.85
(
s, 6H), 8.65 (d, J = 6.2 Hz, 1H), 8.36-8.25 (m, 4H), 8.13-8.06 (m, 2H), 7.90-7.82 (m, 2H), 7.45
s, 2H), 6.93-6.73 (m, 4H); Pt-5a, 8.95 (d, J = 5.1 Hz, 4H), 8.72 (d, J = 4.9 Hz, 4H), 8.31 (s, 2H),
(
8
.18 (s, 4H), 8.07 (d, J = 7.5 Hz, 2H), 7.72 (d, J = 7.4 Hz, 2H), 7.58 – 7.52 (m, 2H), 7.50 – 7.44
m, 2H); Pt-6a 8.80-8.74 (m, 2H), 8.62 (d, J = 5.1 Hz, 2H), 8.59-8.53 (m, 8H), 8.45-8.34 (m,
H), 8.16 (d, J = 7.4 Hz, 2H), 8.10 (t, J = 7.6 Hz, 2H), 7.82-7.76 (m, 2H), 7.49-7.38 (m, 2H).
Mass data (HRMS-ESI): Pt-1a, calcd (C40 PtS .K) m/z =1038.979, found m/z =
038.9787; Pt-2a, calcd (C H F N PtS .K) m/z =1038.9790, found m/z = 1038.9787; Pt-3a,
(
6
H F
14 10
N
4
2
1
4
0
14 10
4
2
+
calcd (C H F N Pt) (MH) m/z =1140.1728, found m/z = 1140.1725; Pt-4a, calcd
5
6
26 10
4
(C
52
H
22
F
10
N
4
Pt.K) m/z =1126.097, found m/z = 1126.0969; Pt-5a, calcd (C58
26 10 4
H F N Pt.H)
+
(
MH) m/z =1164.1723, found m/z = 1164.1702; Pt-6a, calcd (CH F N Pt.K) m/z =1275.1282,
2
6
10
4
found m/z = 1275.1292.
7

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Single crystal X-ray structure determination
X-Ray diffraction quality of single crystals of ligands and trans-Pt(II) porphyrin (1a, 2a,
Pt-2a and 6a) were mounted on a glass capillary and the data collections were achieved on a
Bruker AXS Kappa Apex II CCD diffractometer. The reflections with I > 2σ(I) were employed
for structure solution and refinement. The structure was solved using SIR92 [17] (WINGX32)
program by direct methods. And, structure refinement was done using the SHELXL97 [18]
2
software by successive Fourier synthesis on |F| using the full-matrix least squares refinement.
Hirshfeld surface analysis
Non-covalent interactions present in the crystal structures were quantified using Crystal
Explorer 3.1 [19] and presented in the form of Hirshfeld surfaces (HSs) and 2D fingerprint plots
(
FPs) based on results of single crystal X-ray diffraction analysis.
Oxygen sensing studies
The polymers used for the fabrication of the O sensing film are cardo poly(aryl ether
2
ketone) (IMPEK-C), ethyl cellulose (EC) and poly(methylmethacrylate) (PMMA) (Figure S38).
Typical film preparation procedures: About 9.95 mg of IMPEK-C polymer was dissolved in 1
−3
mL acetone, then 0.70 mL of the porphyrin solution in dichloromethane (1 × 10 M) was added
into the solution. After thorough mixing, about 0.1 mL of the solution was dropped on a silica
glass disk of diameter 1.6 cm by micro syringe. The solvent was evaporated at room temperature
and a transparent film was obtained. The thickness of the films was estimated averagely as 44
−
3
µm, by the average weight of the films (20.8 mg) and the density of the polymer (2.35 g cm ).
To make the EC-porphyrin film, about 9.95 mg of EC was dissolved in 1 mL dichloromethane.
About 0.1 mL of porphyrin solution (0.5mg/mL mother liquors of Pt(II) complex) was added to
the solution. About 80 µL of the mixture was dropped on a silica glass disk and the film was
obtained thorough mixing and the average thickness of the films was estimated by the average
−3
weight of the film (14.7 mg) and the density of the polymer (2.47 g cm ) as 27 µm. To prepare
the PMMA-porphyrin film, about 19.9 mg of PMMA was dissolved in 720 µL of
dichloromethane. To that, about 0.3 mL of porphyrin solution (0.5 mg/mL mother liquors of
Pt(II) complex) was added to the solution. About 100 µL of the mixture was dropped on a silica
glass disk and the film was obtained thorough mixing and the thickness of the films was
−3
averagely estimated as 22 µm, by the density of the polymer (3.17 g cm ) and the average
8

ACCEPTED MANUSCRIPT
weight of the film (13.5 mg). A home-assembled fused silica fiber optical system and a flow cell
were coupled to a fluorospectrometer, used for the spectra and intensity measurement of the
sensing film [20]. The sensing film was put in a home-assembled flow cell for real-time intensity
2 2 2
monitoring. High purity O and N was used. Different O percentages were obtained by using
gas flow meters (rotometers).
The T → S phosphorescence quantum yield (Φ ) of the porphyrins, were measured in
1
0
f
acetonitrile using Ru(bpy)
3
(PF
6
)
2
f
as reference [21] (Φ = 0.06). The triplet state lifetime is
approximated with the phosphorescence lifetimes, which were measured with OB920
luminescence lifetime spectrometer (Edinburg Instruments, U.K). The intermolecular energy
transfer between the complexes and the electron donor, DMT (N,N-dimethyl-p-toluidine) are
analyzed by studying the quenching of the phosphorescent lifetimes of the complexes in
increasing concentration of DMT (22). The lifetime of deaerated 3 ml solution of each
-5
compound (1.0×10 mol/L) in acetonitrile was obtained by OB920 fluorescent/ phosphorescent
-3
lifetime determinator. Then 0.5 µL DMT in acetonitrile [1 X 10 M] was added to the cuvette
and tested the lifetime. For each complex four such additions were made. The interaction was
0
quantified with the Stern-Volmer constants KSV, according to the equation of τ /τ = 1 + KSV[Q],
where, τ and τ are the excited state lifetime in the absence and presence of quencher
0
respectively, KSV is the Stern–Volmer quenching constant, k is the bimolecular quenching rate
q
constant, and [Q] is the quencher (DMT) concentration. KSV is obtained by the linear plots of τ0 /
τ vs. [DMT].
Results and discussion
Synthesis of trans-fluorinated porphyrins with thienyl / biphenyl / naphthyl / fluorenyl /
pyrenyl substituents at its meso-position have been carried out by MacDonald type 2 + 2
condensation reactions of 5-(pentafluorophenyl)dipyrromethane and appropriate aryl aldehyde in
presence of BF ⋅OEt as acid catalyst (Scheme 1). All the reactions end up with the expected
3
2
trans-A
2
B
2
porphyrins, 1a-6a along with the scrambled porphyrins such as
tetrakis(pentafluorophenyl)porphyrin, H T(PFP)P and the tris(pentafluorophenyl)-mono-(aryl)
2
porphyrins
pentafluorophenyl)dipyrromethane with the starting material or other oligomers are the major
cause of scrambling [23, 24]. Using, K [PtCl ] the free ligands were metallated and the yields
(1b-6b).
Reports
reveal
that
recombination
of
acidolysed
5-
(
2
4
9

ACCEPTED MANUSCRIPT
obtained are 60-70 % (Scheme 2). The most downfielded β-pyrrolic protons appeared in the
region of 8-9 ppm in all cases. The peak correspond to shielded imino (-NH) protons was
observed around -3 ppm, whose disappearance indicated the insertion of platinum metal in the
porphyrinic core. The signals of aromatic thienyl protons of Pt-1a and Pt-2a were in accordance
with the number of hydrogens. A singlet at 4.20 ppm consistent with the four –CH protons in
2
Pt-5a confirmed the presence of fluorene moiety at the meso-position. As expected, in Pt-3a the
resonance of five different aromatic protons were according to their respective spin multiplicity.
The naphthyl and pyrenyl protons of Pt-4a and Pt-6a were observed in usual aromatic region as
multiplets due to extended conjugation. Although change in spectra upon the insertion of
platinum metal is negligible, but an upfield shift in the resonance of β-pyrrolic hydrogen is
observed in most of the cases, which can be due to the metal to porphyrin-π-back bonding [25].
The observed mass spectral data of the Pt(II) complexes are in concordance with the calculated
values.
F
BF
3
⋅OEt
2
, DCM, N
2
, DDQ
F
F
F
F
S
F
F
F
F
F
F
F
F
CHO
NH
N
N
F
F
BF
3
⋅OEt
2
2
, DCM, N , DDQ
HN
S
F
F
F
F
CHO
F
F
BF ⋅OEt , DCM, N , DDQ
3
2
2
H
2
T(PFP)P
F
F
F
F
CHO
F
OHC
F
Ar
F
F
F
F
i) TFA, N
2
atm
+
F
F
N
F
N
H
ii) NaOH
HN
NH
HN
F
NH
N
F
BF ⋅OEt , DCM, N , DDQ
F
F
3
2
2
CHO
Ar
Ar = 2-thienyl / 3-thienyl /
biphenyl / naphthyl /
fluorenyl / pyrenyl
F
F
trans-porphyrin
F
F
F
F
3 2 2
BF ⋅OEt , DCM, N , DDQ
F
OHC
F
F
NH
N
N
F
Ar
BF
3
⋅OEt
2
, DCM, N
2
, DDQ
HN
F
F
F
F
F
F
F
CHO
Tris(pentafluorophenyl)-mono-(aryl) porphyrin
Scheme 1. Synthetic scheme of various porphyrin ligands.
1
0

ACCEPTED MANUSCRIPT
The UV-Vis absorption and emission spectra of the Pt(II) complexes were studied in
1
1
CH
transition in the range of 397 - 401 nm as well as two weak absorptions around 509-537 nm and
39-598 nm corresponds to S → S and S → S respectively. The biphenyl derivative of
3 u
CN. All the complexes exhibited a high intense Soret (B) band due to an allowed A1g → E
5
0
1
0
2
fluorinated trans-Pt(II) porphyrin show ~ 10 nm red shifted absorption spectrum compared to
PtT(PFP)P. On excitation at the Soret band, the porphyrin complexes exhibit two well-defined
emission bands in the range of 701 - 724 nm and 645 - 658 nm (Table 1). The T → S
1
0
phosphorescence quantum yield (Φ ) values are high compared to our previously reported
f
fluorinated porphyrins except for Pt-6a [11].
F
F
F
Ar
HN
F
Ar
F
F
F
F
2
K PtCl4
N
Pt
F
N
F
N
F
NH
Ar
N
N
C H CN
6 5
F
N
F
F
F
F
Ar
F
F
F
F
Pt-1a, Ar = 2-thienyl; trans-Pt-B(TF )D(2-Thien)P
5
Pt-2a, Ar = 3-thienyl; trans-Pt-B(TF )D(3-Thien)P
5
Pt-3a, Ar = biphenyl; trans-Pt-B(TF )D(BiPh)P
5
Pt-4a, Ar = naphthyl; trans-Pt-B(TF )D(Naph)P
5
Pt-5a, Ar = fluorenyl; trans-Pt-B(TF )D(Fluo)P
5
Pt-6a, Ar = pyrenyl; trans-Pt-B(TF )D(Pyre)P
5
Scheme 2. Synthetic scheme of trans-Pt-porphyrins.
Table 1. Photophysical data of trans-Pt-porphyrins in CH
2
Cl
2
at 298 K.
Compound
λabs (nm)
log ε /
−1
λem (nm)
Quantum yield (Φ)
Luminescence
life time τ (µs)
43.86
−
1
M cm
a
b
b
PtT(PFP)P
Pt-1a
391, 509,539 5.69, 4.53, 4.66
399, 510, 542 5.59, 4.44, 2.45
399, 510, 542 5.59, 4.52, 4.37
401, 510, 541 5.21, 4.01, 3.70
400, 510, 543 5.60, 4.52, 4.52
397, 509, 541 5.20, 4.26, 4.21
651, 706
0.088
652, 722
658, 724
645, 701
648, 708
647, 708
654, 713
0.134
0.140
0.144
0.164
0.113
0.005
50.8
66.4
84.7
82.7
78.6
59.1
Pt-2a
Pt-3a
Pt-4a
Pt-5a
Pt-6a
397, 512, 544 5.29, 4.36, 3.64
a
a
Values taken from ref 11; Measured in CH CN
3
In order to check the photostability, absorption spectral changes of the Pt(II) complexes were
recorded after exposing the compounds with xenon lamp (150 W) over a period of 50 min (Fig.
S37). Except Pt-1a, other porphyrins are more photostable (> 90 %) with minimal absorption
changes and the values are comparable with the commonly used oxygen indicater, PtOEP [26].
1
1

ACCEPTED MANUSCRIPT
Thus all the complexes are much photo stable under xenon light except the thienyl derivative, Pt-
1
a.
The quenching effect of the electron donor, DMT on the phosphorescence emission of the
Pt(II) complexes was analyzed and the efficiency of intermolecular energy transfer by triplet-
triplet annihilation process (TTA) of DMT was observed quantitatively using the Stern-Volmer
equation, τ / τ = 1 + K [Q], KSV = K τ . Where, τ and τ are the excited state lifetime in the
0
SV
q
0
0
absence and presence of quencher respectively, KSV is the Stern–Volmer quenching constant, k
q
is the bimolecular quenching rate constant, and [Q] is the quencher (DMT) concentration. Linear
plots of τ / τ vs. [DMT] indicates the dynamic quenching process and yield K as shown in
0
SV
5
−1
figure 2; highest value of 1.05 x 10 M is obtained for the fluorinated porphyrin Pt-2a with 3-
thienyl moieties. And, this value is comparable with the bimolecular quenching of the triplet
excited state phosphorescence of platinum(II) tetraphenyl- tetrabenzoporphyrin and perylene
reported earlier [22]. The reasonably high value of quenching constant is attributed to the long-
lived triplet excited state of Pt-2a and the order is as follows: Pt-2a > Pt-3a > Pt-4a > Pt-1a >
Pt-6a > Pt-5a.
2
1
1
0
0
.0
.5
.0
.5
.0
Pt-1a
Pt-2a
Pt-3a
Pt-4a
Pt-5a
Pt-6a
0
1
2
3
c x 10−
5
Fig. 2. Stern-Volmer plots for phosphorescence quenching of Pt-1a – Pt-6a. Pt-1a: λex = 399 nm; Pt-2a: λex = 399
nm; Pt-3a: ex = 413 nm; Pt-4a: ex = 399 nm; Pt-5a: ex = 397 nm; Pt-6a: ex = 397 nm. Phosphorescence was
λ
λ
λ
λ
-5
measured as a function of DMT concentration in CH CN (1.0 × 10 M; 25 ℃).
3
Electrochemical studies of fluorinated Pt(II)-porphyrins
To examine the effect of aryl groups such as thienyl / biphenyl / naphthyl / fluorenyl /
pyrenyl in trans-porphyrins, the redox potentials were measured in dichloromethane (Table 2).
1
2

ACCEPTED MANUSCRIPT
They exhibited one / two successive pseudo-reversible oxidation and two reversible reduction
potentials as similar to our previous report [11] and the representative cyclic voltammograms of
Pt-2a and Pt-5a are shown in figure 3. From the first oxidation potentials of the synthesized
trans-Pt(II)-porphyrins shown in table 2, it is evident that the stability of the thienyl porphyrins
(Pt-1a and Pt-2a) are comparable to that of reference compound PtTPFPP whereas the other
complexes bearing aryl groups (Pt-3a − Pt-6a) are less stable owing to their more electron
richness which is reflected as greater extent of cathodic shift (0.13-0.24 V).
Table 2.Comparison of half-wave potentials (in V) for trans-Pt-porphyrins in CH Cl using 0.1 M TBAHFP at 25
2
2
°C.
Porphyrin
Oxidation
Reduction
EHOMO (eV) ELUMO (eV) HOMO-LUMO
c
I
II
I
II
gap (eV)
a
PtTPP
1.19
1.57
1.51
1.51b
1.33
1.39
1.44
1.42
1.55
1.80
-0.98
-0.88
-0.99
-1.02
-1.24
-1.08
-1.07
-1.11
-1.37
-1.38
-1.48
-1.53b
-1.70
-1.59
-1.57
-1.65
-5.59
-5.97
-5.91
-5.91
-5.73
-5.79
-5.84
-5.82
-3.42
-3.52
-3.41
-3.38
-3.16
-3.32
-3.33
-3.29
2.17
2.45
2.50
2.53
2.57
2.47
2.51
2.53
a
PtTPFPP
Pt-1a
Pt-2a
Pt-3a
Pt-4a
Pt-5a
Pt-6a
-
-
-
-
-
-
b
a
b
Taken from reference Arunkumar et al., New. J. Chem. 2017, 41, 4908-4917; From differential pulse voltammetry;
c
EHOMO = -(EIOxdn + 4.4) eV and ELUMO = -(EIRedn + 4.4) eV taken from Chem. Commun., 2012, 48, 8377-8379.
-1.07
-1.02
2
.0 x 10-5
1.51
1.44
0.0
-
-
-
-
2.0 x 10-5
4.0 x 10-5
6.0 x 10-5
8.0 x 10-5
Pt-2a
Pt-5a
2
1
0
-1
-2
Potential / V
2 2
Fig. 3. Overlaid cyclic voltammograms of Pt-2a and Pt-5a in CH Cl with a scan rate of 0.1 V/s.
Crystal structure determination of trans-porphyrins
Single crystals of diffraction quality of 1a, 2a, Pt-2a and 6a were achieved by slow
evaporation technique using appropriate solvents and the data are presented in table 3. The
1
3

ACCEPTED MANUSCRIPT
ORTEP and molecular crystal packing diagrams of all compounds were shown in figure 4 and 5
respectively. In Pt-2a, the platinum(II) atom is tetra-coordinated and forms nearly a square
planar geometry with inner core nitrogens. The metal ion is nearly coplanar with the porphyrin
plane with a minimal displacement of 0.0363 Å which is comparable to the reported values. The
average Pt-N distance in Pt-2a is 2.011(5) Å which is comparable to the reported platinum(II)
porphyrins [11].
Table 3. Crystallographic data of porphyrins, 1a, 2a, Pt-2a and 6a.
1
a
2a
Pt-2a
6a
Empirical formula
fw
C H F N S
806.69
C H F N S
806.69
C H F N S Pt C H F N
4
0
16 10
4
2
40 16 10
4
2
40 14 10 4 2 64 28 10 4
999.76
1042.90
CCDC
1811222
1811675
1811676
1811161
Solvent
Colour
CHCl /hexane
violet
CHCl /methanol CHCl /hexane
CHCl /hexane
purple
3
3
3
3
red
red
Crystal system
Space Group
a (Å)
b (Å)
c (Å)
monoclinic
triclinic
P-1
monoclinic
triclinic
P-1
P 2 /c
P 2 /c
1
1
14.3597(12)
10.4594(10)
12.1474(12)
90
107.073(3)
90
1744.1(3)
2
1.536
7.11750(10)
9.1271(2)
14.1391(2)
75.176(7)
89.766(6)
74.055(6)
851.60(4)
1
14.5429(2)
10.5830(2)
11.8563(3)
90
108.960(2)
90
1725.77(6)
2
1.924
13.0873(10)
15.5150(11)
15.9776(11)
116.632(4)
95.511(4)
94.410(5)
2860.3(4)
2
α (deg)
β (deg)
γ (deg)
Volume (A )
3
Z
3
Dcalcd (mg/m )
1.573
1.211
Wavelength (λ) Å
Temperature (K)
0.71073
296(2)
0.71073
296(2)
0.71073
296(2)
0.71073
293(2)
Data / restraints / 3024 / 10 / 294
parameters
3602 / 5 / 269
3031 / 5 / 266
10069 / 2 / 711
F(000)
GOF on F
812
0.979
0.0421, 0.1038
406
1.026
0.0503, 0.1200
964
1.293
1060
0.917
0.0893, 0.2235
2
a
b
R
1
, wR
2
0.0234, 0.0510
a
b
2
o
2 2
c
2 2 1/2
o
R = Σ||F |–|Fc||/Σ|F |; I > 2σ (I ). wR = [Σ w(F –F ) /Σw(F ) ] .
1
o
o
o
o
2
The dihedral angles between pentafluorophenyl ring and porphyrin core in various
structures are as follows the order: 68.26° (1a) < 71.24° (Pt-2a) ≈ 71.40° (6a) ≈ 71.56° (2a).
Similarly, the dihedral angles between thienyl ring and porphyrin core are as follows: 64.11°
(2a) < 77.04° (1a) < 81.38° (Pt-2a). Interestingly, upon metallation of 2a into Pt-2a, it is
observed that there is an enhancement in the dihedral angle between thienyl ring and porphyrin
core indicating that the former is more orthogonal than later.
1
4

ACCEPTED MANUSCRIPT
Fig. 4. ORTEP diagrams of 1a, 2a, Pt-2a and 6a. (Thermal ellipsoids are shown at 35 % probability level; Solvent
molecules were not shown for clarity). Atom colors: Gray-Carbon; Blue-Nitrogen; Green-Fluorine; Pink-Platinum;
White-Hydrogen; Brown-Sulphur.
It is observed that 1a and Pt-2a exhibit similar kind of packing through various
intermolecular interactions namely, (pyrrole)C−H···C(pyrrole), (thienyl)C−H···C(pyrrole), (ph)C‒F···C(pyrrole)
,
(
pyrrole)C···C(pyrrole), and (thienyl)S···S(thienyl) (Figure 4a, c) indicating the presence of isostructural
behavior in them. While the crystal packing of 2a exhibited to show an one dimensional array of
molecules in a slip-stack fashion through (pyrrole)C−H···F(ph) and (thienyl)C−H···N(pyrrole) interactions
(
Figure 4b). Interestingly, the packing of 6a forms zigzag 3D structural arrangements (Figure 4d)
between porphyrin core and pyrenyl moiety through numerous close contacts as listed in table 4.
Table 4. Distances (in Å) for different types of interactions in 1a, 2a, Pt-2a and 6a.
i
ii
ii
ii
ii
Interaction
1a
2a
-
-
Pt-2a
6a
-
2
.571-2.874 (12)
2.848 (4)
(
(
pyrrole)C−H···C(pyrrole)
pyrrole)C−H···C(ph)
-
-
2.852-2.899 (6)
(ph)C−H···C(pyrrole)
(thienyl)C−H···C(pyrrole)
(pyrrole)C−H···F(ph)
(pyrrole)C−H···S(thienyl)
-
-
-
-
-
-
-
2.793-2.883 (10)
2.877-2.898 (8)
-
2.542-2.561 (8)
-
-
2.595-2.639 (6)
2.893 (4)
-
(
ph)C−H···N(pyrrole)
-
-
-
2.686-2.725 (6)
(
thienyl)C−H···N(pyrrole)
-
2.670 (4)
-
-
(ph)C‒F···C(pyrrole)
(pyrrole)C···C(pyrrole)
3.097 (4)
3.320 (4)
-
-
-
-
-
-
-
-
-
-
3.160 (2)
-
(
pyrrole)C···F(ph)
-
-
-
(thienyl)S···S(thienyl)
(ph)H···H(pyrrole)
3.247 (4)
-
2.357-2.382 (6)
i
ii
Different types. Value in parenthesis gives the number of interactions present in the molecule.
The intermolecular interactions of 1a, 2a, Pt-2a and 6a were also analyzed quantitatively
using Crystal Explorer 3.1 as Hirshfeld surfaces (HSs) and 2D fingerprint plots (FPs). The red
spots on the Hirschfield surfaces (HSs) designate the close-contact interactions, which are
mainly accountable for the molecular packing in the crystals. The breakdown of fingerprint plots
1
5

ACCEPTED MANUSCRIPT
(
FPs) of the HSs is shown in figure S39. The division of contributions is possible for different
interactions such as C···H, F···H/C/F, H···H and N···H and C···C from the FP plots through
interactive computer graphics. From FPs, it is observed that the crystal packing is mainly
stabilized due to the close contacts involving organic fluorine viz., F···H, F···C and F···F [52 %
for 1a and Pt-2a; 54 % for 2a; 39 % for 6a]. Besides, the close contact involving C···H [13-24
%] and the H···H contacts [10-15 % for 1a, 2a and Pt-2a; 21 % for 6a] also be a significant role
in the formation of supramolecular network.
Fig. 5. Molecular crystal packing diagrams of (a) 1a viewed down ‘a’ axis; (b) 2a viewed down ‘b’ axis; (c) Pt-2a
viewed down ‘a’ axis and (d) 6a viewed down ‘b’ axis through various intermolecular interactions.
Oxygen sensing studies
Initially, the oxygen sensitivities of the Pt(II) complexes were studied in solution (CHCl
3
/
CH CN). All the porphyrins are strongly phosphorescent and emission peaks are observed
3
around 647-658 nm in acetonitrile and 651-659 nm in chloroform medium (Figure 6). The
1
6

ACCEPTED MANUSCRIPT
phosphorescence emission of the complexes are sensitive to oxygen and its intensities decreases
with increasing concentration of oxygen due to energy transfer between the triplet state
porphyrins and molecular oxygen by dynamic quenching [4]. Also, we observed that the lifetime
of the porphyrins are longer compared to our earlier report on fluorinated Pt(II) porphyrins; the
most long lived luminescence of 85 µs is observed in acetonitrile solution of Pt-3a which is
significantly quenched in oxygen atmosphere (Figure S40). Thus, incorporation of various aryl
substituents (thienyl / biphenyl / naphthyl / fluorenyl / pyreneyl) at the meso position enhances
the sensitivity towards oxygen which can be represented by the ratio I / I , where I and I are
0
100
o
100
the emission intensity under 100 % nitrogen and oxygen atmosphere respectively. Interestingly,
the porphyrins in acetonitrile shows better sensitivity compared to chloroform; the sensitivity of
Pt-6a in acetonitrile is 2.25 fold greater than in chloroform. Among the porphyrins, higher
sensitivity in solution is observed for Pt-4a with naphthyl / pentafluorophenyl substituents
whereas Pt-1a with 2-thienyl / pentafluorophenyl moieties exhibit low sensitivity.
250
200
150
100
(
a)
(b)
200
150
100
N2
air
O2
N2
air
O2
50
50
0
0
600
650
700
750
800
600
650
700
750
800
Wavelength / nm
Wavelength / nm
Fig. 6. Phosphorescent emission intensity response of Pt-1a (a) in CHCl
3 3
and (b) in CH CN under nitrogen, air and
oxygen atmosphere (λex = 399 nm). The solution is purged with O or N for about 10 min before measurements.
2
2
The volume of the solution was kept constantly by adding solvent to compensate the evaporation. A = 0.045.
To study the influence of polymer matrices towards oxygen sensing, three polymers were
selected namely, IMPEK-C, poly(methylmethacrylate) (PMMA) and ethyl cellulose (EC).
Several reports revealed that IMPEK-C is an ideal matrix for oxygen sensing that shows high
oxygen permeability, fast response and offers significant quenching effect [11, 27]. PMMA
matrix is not expensive, exhibit larger surface area as well as possess inherent robustness
compared with standard silica fibers [28, 29]. Also, film of EC [30] is easily permeable to
1
7

ACCEPTED MANUSCRIPT
1
3
2
-1
oxygen with permeability coefficient of 11 x 10 cm (s Pa) . The response of the various
porphyrin-polymer matrices to the saturation switch between the nitrogen to oxygen was
analyzed (Figure 7). The luminescence intensities of the porphyrins quench reversibly in
saturated oxygen and shows reasonable recovering properties under nitrogen concentration. The
response time (t 95) and recovery time (t 95) of various porphyrin-polymer matrices were
↓
↑
analyzed in order to assess the sensing properties of various polymer films embedded in
porphyrins. The response time represents the time taken for 95 % luminescent intensity changes
from 100 % nitrogen to 100 % oxygen whereas the recovery time denotes the intensity variation
from 100 % oxygen to 100 % nitrogen. Fast response time is witnessed for EC-porphyrin
matrices compared to the previously reported [31] naphthyl appended Pt(II) complexes and the
values are found to be in the range of 0.9-1.9 s. Note that the 2-thienyl derivative show better
response time of 1.1 s in EC film and a recovery time of 6.67 s in IMPEK-C films. Besides, both
the response as well as recovery time is too high in PMMA film for all the Pt(II)-porphyrins of
1
a-6a. The percentage of quenching is high and almost comparable for all the porphyrin-polymer
films at the first two cycles and for the consequent cycles the order follows as: PMMA <
IMPEK-C < EC.
(
a)
(b)
(c)
N
2
N
2
N
2
N
2
N
2
N
2
N
2
280
240
200
160
120
150
2
00
50
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
1
1
00
50
0
100
50
0
10.6 % O2 V/V
9
2
% O V/V
9
2
% O V/V
2
10.2 % O V/V
10.6 % O
2
V/V
9
% O
2
V/V
O
2
O
O
2
2
0
200
400
600
800
1000
0
200
400
600
800
0
200
400
600
800 1000 1200
Time / s
Time / s
Time / s
2 2
Fig. 7. Phosphorescent emission intensity response of Pt-1a in (a) IMPEK-C, (b) EC and (c) PMMA to O /N
saturation switch at 20 °C (λ = 399 nm).
ex
It is found that the photostability of the porphyrin-polymer films are very much depends
on the nature of the matrices chosen for the study. Among the porphyrin-polymer films, one with
EC shows better stability even after six cycles of N to O switch with irradiation of 800-1000 s.
2
2
In the case of IMPEK-C films, 2-thienyl derivative shows higher stability and biphenyl
derivative shows lower stability whereas in the case of PMMA films 2-thienyl and pyrenyl
1
8

ACCEPTED MANUSCRIPT
derivatives show poor photostability compared to other porphyrins. The poor stability is likely
attributed to the decomposition of the porphyrin-polymer films upon irradiation [11].
1
50
20
N
2
(b)
(a)
270
N2
(c)
N
2
N
2
200
1
N2
N
2
2
40
9
.0%
9
.0%
150
90
60
30
0
9.0%
2.2%
4.3%
9.0%
12.2%
14.3%
12.8%
1
2.8%
9
.0%
12.8%
15.1%
9.4%
210
1
15.1%
15.1%
9
.0%
2.8%
5.1%
9.4%
1
1
100 10.6%
20.0%
2
9.4%
1
2
9.4% 29.4%
45.5%
29.4%
10.6%
20.0%
1
80 10.2%
0.0%
10.2%
20.0%
2
45.5%
62.5%
2
45.5%
2.5%
2
62.5%
6
50
1
0.6%
10.6%
20.0%
3.8%
150
20.0%
5
53.8% 71.4% 53.8%
5
3.8%
53.8%
5
3.8% 71.4%
71.4%
0
200
400
600
800
0
200 400 600 800 1000
Time / s
0
400
800
1200
Time / s
Time / s
Fig. 8. Dynamic response of Pt-1a films vs. small steps of variation of O partial pressure in IMPEK-C, EC and
2
PMMA respectively. λ = 399 nm, λ = 650 nm.
ex
em
To quantitatively evaluate the oxygen sensing properties, experiments were carried out by
varying the oxygen partial pressure from 0 to 71.4 % (v/v) (Figure 8). Among the three polymer
films studied, the EC sensing film gives a good response to oxygen variation and hence ideal for
practical applications. The highest quenching of ~ 83 % emission intensity was observed in EC
polymer films of biphenyl / naphthyl derivative and the lowest quenching of 64 % is observed
for EC film of pyrenyl derivative. The 2-thienyl derivative shows a quenching of ~ 37 % in
IMPEK-C and PMMA polymer films. As expected, the oxygen sensing ability of polymer films
shows the same order as mentioned earlier (EC > IMPEK-C > PMMA). The quenching constants
of the porphyrin-polymer films were determined using Stern–Volmer equation (Figure 9) or
modified Stern–Volmer equation (two-site model). A modified Stern–Volmer or two-site model is
employed for porphyrin-IMPEK-C films except Pt-4a by fitting the quenching data in which the
O -sensitive dyes are considered as two different portions such as f and f and the fitting results
2
1
2
are summarized in table 5. Fitting of the oxygen sensing property of the IMPEK-C films of
complexes based on the two site model given in the below equation [5, 6]
I0
I
1
=
;
f + f =1
1 2
f1
f2
+
1
+ Ksv pO2 1+ Ksv pO2
1
2
But, when it comes to EC and PMMA films, we found most porphyrin films exhibit a
good linearity of the Stern-Volmer dependence except Pt-6a PMMA film. And, between
1
9

ACCEPTED MANUSCRIPT
IMPEK-C and EC, the former is much more unsymmetrical in each repeat unit than EC. Besides,
between IMPEK-C and PMMA, the group atoms of the latter one would be much smaller than
the phenyl in IMPEK-C. So, there is more possibility for IMPEK-C film to generate
heterogeneous system. And the complexes can distribute more even in EC and PMMA to have a
homogeneous system. The linear Stern-Volmer equation in which the oxygen partial pressure at
which initial emission intensity of film is quenched by 50 % can be calculated as 1/Ksv is given
as I / I = C + K · pO , where I , and I are the emission intensities in the absence and presence
0
sv
2
0
of oxygen, respectively.
Thus among the three porphyrin films, EC shows the highest quenching constant (EC-Pt-
−1
−1
3
a: 0.096 Torr , EC-Pt-4a / Pt-2a: 0.060 Torr for) due to its high oxygen permeability [30].
The former value is high compared to the previously reported fluorinated porphyrins [11] and
comparable with the naphthyl / pyrenyl appended Pt(II)-porphyrins [31]. It is observed that upon
installation of two biphenyl moieties at the trans-positions of Pt(II)-TPFPP enhances the oxygen
sensitivity by 1.4 fold; and hence it is expected to be a promising candidate for oxygen sensing
applications.
Pt-1a
6
Pt-2a
Pt-3a
Pt-4a
Pt-5a
Pt-6a
4
2
0
0
200
400
600
Time / s
Fig. 9. Oxygen sensitivity of the emission of Pt(II)-complexes in PMMA films. All the fittings are based on Stern-
Volmer equation.
2
Table 5. Parameters of O sensing films with IMPEK-C / EC / PMMA as a supporting matrices (fitting result with
Stern-Volmer equation / two-site model. The respond florescent intensity to pure oxygen and pure nitrogen of Pt-6a
are too close to calculate the dynamic response. So there is no valuable data to obtain the KSV for Pt-6a.
a
−1
−1
2
a
−1
b
Compound
f
1
Ksv1 / Torr
0.01147
0.00505
0.00429
f2
Ksv2 / Torr
0.00000
0.00032
0.00000
r
Ksv / Torr
pO / Torr
2
IMPEK-C Pt-1a 0.52542
IMPEK-C Pt-2a 0.76572
IMPEK-C Pt-3a 0.59047
0.47458
0.23428
0.40953
0.99781
0.99901
0.99793
0.00603
0.00394
0.00253
217.816
207.566
405.846
2
0

ACCEPTED MANUSCRIPT
IMPEK-C Pt-4a 0.57900
0.00577
0.42100
0.00035
0.99812
0.99652
-
0.00349
0.0067
-
248.732
68.824
-
IMPEK-C Pt-5a
IMPEK-C Pt-6a
-
-
-
-
-
-
-
-
EC Pt-1a
EC Pt-2a
EC Pt-3a
EC Pt-4a
EC Pt-5a
EC Pt-6a
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0.99744
0.99581
0.99215
0.99544
0.99643
0.95051
0.043
0.058
0.096
0.062
0.050
0.0386
23.256
17.241
10.417
16.129
20.000
25.907
-
-
-
-
0.83963
0.04602
0.16037
-0.00008
PMMA Pt-1a
PMMA Pt-2a
PMMA Pt-3a
PMMA Pt-4a
PMMA Pt-5a
PMMA Pt-6a
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
0.99145
0.99695
0.96089
0.99514
0.9712
0.00858
0.00683
0.00385
0.01068
0.00445
0.00276
116.55
146.41
259.74
93.63
224.72
362.32
0.97833
ɑ
Weighted quenching constant by the equation, ꢀꢁꢂ
The oxygen partial pressure at which the initial emission intensity of film is quenched by 62.5 % (I
ꢃ
=ꢄ ꢅ ꢀ + ꢅ ꢀ
ꢆ
ꢁꢂ
ꢇ
ꢈ ꢁꢂ
ꢉ
b
0
/ I = 1.6) and
can be calculated as 1/ꢀ . In Torr.
ꢁꢂ
Conclusions
In conclusion, we synthesized and characterized a series of trans-porphyrins bearing
thienyl / biphenyl / naphthyl / fluorenyl / pyrenyl moieties along with the scrambled products.
The corresponding Pt(II) porphyrins were also prepared and the single crystals of 1a, 2a, Pt-2a
and 6a were structurally characterized and their crystal packing is mainly stabilized by C···H and
H···F close contacts. The luminescent oxygen sensing properties of the trans-Pt(II)-porphyrins
were investigated in solution as well as in polymer films of IMPEK-C / EC / PMMA. Higher
sensitivity in solution is observed for Pt-4a with naphthyl / pentafluorophenyl substituents. The
quenching effect of the electron donor, DMT on the phosphorescence emission of the Pt(II)
5
−1
complexes was analyzed; highest value of 1.05 x 10 M is obtained for Pt-2a and is attributed
to its long-lived triplet excited state. The results disclose that the incorporation of various aryl
substituents at the meso-position enhances the sensitivity towards oxygen. Among the three
polymer films used, EC-porphyrin films show fast response, excellent sensitivity with good
photostability. We found that introduction of two biphenyl moieties at the trans-positions of
Pt(II)-TFPP enhances the long lived excited state and also improves the oxygen sensitivity by 1.4
fold. We believe that our findings will be of great interest for the development of porphyrin
based optical oxygen sensors.
2
1

ACCEPTED MANUSCRIPT
Supplementary Data
Crystallographic data of the porphyrins, 1a, 2a, Pt-2a and 6a have been deposited with
the Cambridge Crystallographic Data Centre, CCDC reference numbers are 1811222, 1811675,
1
811676 and 1811161. Copies of this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: + 44 1233336 033; e-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgements
Department of Science and Technology (DST), New Delhi through SR/WOS-A/CS-
8
2
2/2016 project is acknowledged for funding to SS. JZ thanks the NSFC (21273028, 21473020,
1673031, 21761142005) and Dalian University of Technology for financial support
(DUT2016TB12). We also thank Dr. P. K. Sudhadevi Antharjanam, SAIF, IIT Madras for the
single crystal data collection, structure solution and refinement.
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Highlights
•
•
•
•
Series of fluorinated trans-porphyrins bearing thienyl / biphenyl / naphthyl / fluorenyl
pyrenyl moieties were synthesized and four of them were structurally characterized.
/
The oxygen sensing properties of the Pt(II)complexes were compared in three different
polymer films
EC-porphyrin films show fast response, excellent sensitivity with good photostability
than the other two films.
Introduction of two biphenyl moieties at the trans-positions of Pt(II)-TFPP enhances
the long lived excited state and also improves the oxygen sensitivity by 1.4 fold higher
than the commonly used Pt(II)-(pentafluorophenyl)porphyrin.