Synthesis of Novel Porphyrin Derivatives with Mesogenic Properties

Article abstract of DOI:10.1080/00397911.2015.1103873

Two novel porphyrin derivatives, 5,10,15,20-tetra(4-(N-octane-carboxamide)phenyl)porphyrin (4NC₈-TPP) and 5,10,15,20-tetra(4-(N-stearyl-carboxamide)phenyl)porphyrin (4NC1₈-TPP), were synthesized. Their molecular structures were characterized by means of time-of-flight mass spectrometer (TOF-MS), nuclear magnetic resonance (NMR), and infrared spectra (IR). The thermal behavior and morphologies of 4NC₈-TPP and 4NC1₈-TPP were examined by thermal gravity (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarizing optical microscope (POM). It was found that both 4NC₈-TPP and 4NC1₈-TPP had mesogenic properties.

Full text of DOI:10.1080/00397911.2015.1103873

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Synthesis of Novel Porphyrin Derivatives with
Mesogenic Properties
Xiaoyuan Zhang, Biaobiao Zhu, Li Zhou, Ping Liu & Wenji Deng
To cite this article: Xiaoyuan Zhang, Biaobiao Zhu, Li Zhou, Ping Liu & Wenji Deng
(2015) Synthesis of Novel Porphyrin Derivatives with Mesogenic Properties, Synthetic
Communications, 45:23, 2730-2739
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Date: 12 December 2015, At: 09:50

Synthetic Communications1, 45: 2730–2739, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397911.2015.1103873
SYNTHESIS OF NOVEL PORPHYRIN DERIVATIVES
WITH MESOGENIC PROPERTIES
Xiaoyuan Zhang,1 Biaobiao Zhu,1 Li Zhou,1 Ping Liu,1 and
Wenji Deng2
1State Key Laboratory of Luminescent Materials and Devices, Research
Institute of Materials Science, South China University of Technology,
Guangzhou, China
2Department of Applied Physics, South China University of Technology,
Guangzhou, China
GRAPHICAL ABSTRACT
Abstract Two novel porphyrin derivatives, 5,10,15,20-tetra(4-(N-octane-carboxamide)
phenyl)porphyrin (4NC8-TPP) and 5,10,15,20-tetra(4-(N-stearyl-carboxamide)phenyl)
porphyrin (4NC18-TPP), were synthesized. Their molecular structures were
characterized by means of time-of-flight mass spectrometer (TOF-MS), nuclear
magnetic resonance (NMR), and infrared spectra (IR). The thermal behavior and
morphologies of 4NC8-TPP and 4NC18-TPP were examined by thermal gravity (TG),
differential scanning calorimetry (DSC), x-ray diffraction (XRD), and polarizing
Received June 27, 2015.
Address correspondence to Ping Liu, State Key Laboratory of Luminescent Materials and Devices,
Research Institute of Materials Science, South China University of Technology, Guangzhou, China.
E-mail: mcpliu@scut.edu.cn
Color versions of one or more of the figures in the article can be found online at www.tandfonline.
com/lsyc.
2730

PORPHYRIN DERIVATIVES WITH MESOGENIC PROPERTIES
2731
optical microscope (POM). It was found that both 4NC8-TPP and 4NC18-TPP had
mesogenic properties.
Keywords Mesogenic property; morphology; porphyrin derivative; thermal behavior
INTRODUCTION
Because porphyrin and their derivatives play important roles in nature, such as
chlorophyll in photosynthesis and hemoglobin in human blood, they have received
extensive attention and study in many years. They have been expected to be applied
in many areas, for example, photodynamic therapy,[1] photoelectronic transition,[2]
organic light-emitting diodes,[3] biosensors,[4] and optical information storage[5] because
of their favorable optoelectronic properties and chemical and thermal stabilities.
Since porphyrin derivatives with liquid-crystalline properties were reported,[6]
many mesogenic porphyrins have been synthesized.[7] Researchers have synthesized
2,3,7,8,12,13,17,18-octakis(3-hydroxyethyl) porphyrin and its octaalkyl ether deriva-
tives, which exhibited
2,3,7,8,12,13,17,18-octakis(octylthio)tetraazaporphyrin copper(II) complex, which
showed
mesophase ranging from 67.6 to 151.7 °C.[9] These mesogenic
a
discotic liquid crystalline character,[8] and
a
compounds have a well-organized intermolecular arrangement, which benefits the
transition of charge carrier. They can be used as semiconductor materials in photo-
voltaic devices. So far, the substituent groups of porphyrin derivatives with
mesogenic properties are usually alkyl, alkoxy, or acyloxy, and there have been
few reports regarding the alkylamide group as substituent groups of porphyrin
derivatives with mesogenic properties.
In this article, we synthesized two novel porphyrin derivatives, 5,10,15,20-
tetra(4-(N-ste-aryl-carboxamide)phenyl)porphyrin(4NC18-TPP) and 5,10,15,20-tetra
(4-(N-octane-carboxam-ide)phenyl)porphyrin (4NC8-TPP) (Scheme 1), and their
thermal behaviors and morphologies were investigated.
Scheme 1. Molecular structures of 4NC8-TPP and 4NC18-TPP.

2732
X. ZHANG ET AL.
Figure 1. TG curves of 4NC8-TPP and 4NC18-TPP.
RESULTS AND DISCUSSION
Thermal gravity (TG) and differential scanning calorimetry (DSC) were
measured to examine the thermal properties. The initial decomposition temperature
of 4NC8-TPP and 4NC18-TPP are 187 and 385 °C according to the TG (Fig. 1).
Figure 2 shows the DSC curves of 4NC8-TPP and 4NC18-TPP under the first cooling
and second heating. The DSC measurement of 4NC8-TPP from room temperature to
350 °C showed that 4NC8-TPP did not exhibit liquid-crystalline behavior either on
heating or cooling, but showed only melting and crystallization transitions at 312
and 264 °C, respectively. In the cooling process, there was a small peak at 119 °C,
which was the glass transition temperature. By contrast, when 4NC18-TPP was
heated from room temperature, it showed a small wide peak at 45 °C, which was
the glass transition. On further heating, an endothermic peak was observed at
120 °C and the mesophase was obtained. The onset of the transition from the meso-
phase into isotropic liquid was observed at 271 °C and the peak at 283 °C. In the
cooling process, the onset of the isotropic liquid transition into the mesophase was
Figure 2. DSC curves of 4NC8-TPP and 4NC18-TPP for heating and cooling rates at 10 °C=min.

PORPHYRIN DERIVATIVES WITH MESOGENIC PROPERTIES
2733
Table 1. Calorimetric data for 4NC8-TPP and 4NC18-TPP
Compound
4NC8-TPP
Temp. [°C] (DH=kJ · molꢀ1
)
DTemp [°C]
Heating
Cooling
Heating
Cooling
C 312 (ꢀ56.00), I
I 264 (52.30), Cr 118, g
4NC18-TPP
g 45, Cr 120 (ꢀ46.72), Col 271 (ꢀ45.46), I
151
150
I 272 (38.37), Col 122 (31.65), Cr 61, g
Notes. Heating rate 10 °C=min; cooling rate 10 °C=min. Cr, crystal; Col, columnar phase; I, isotropic
liquid; g, glass.
observed at 272 °C and the peak at 268 °C. The mesophase crystallized at 122 °C.
There was a wide mesomorphic state from crystal to liquid crystal lasting about
150 °C. The small peak at 61 °C was glass transition temperature like 4NC8-TPP.
From the DSC curves of 4NC8-TPP and 4NC18-TPP, we conclude that the increase
of the length of the side chain benefits the formation of liquid-crystalline phase. The
phase transition temperatures and enthalpy changes are listed in Table 1.
The morphology of 4NC8-TPP and 4NC18-TPP was observed on the polarizing
optical microscope (POM). Figure 3 shows the optical texture of 4NC8-TPP and
4NC18-TPP by slow cooling from isotropic liquid. Judging from the DSC of
4NC8-TPP, it should have a crystalline phase below melting temperature. However,
in the POM image, a liquid-crystal-like texture was observed and some areas
presented crystal morphology. This showed that there were both crystalline and
liquid-crystalline phase in 4NC8-TPP below 264 °C on the cooling process but the
liquid-crystalline phase was metastable. 4NC8-TPP tended to crystallize in the alumi-
num pan used in the DSC measurement but formed a liquid-crystalline phase on the
glass substrate used for the POM.[10] For 4NC18-TPP, a birefringent fan-shaped tex-
ture was observed in the POM image, which was the evidence of columnar phase.[11]
X-ray diffraction was performed from 3° to 50° and the profile is shown in
Fig. 4. 4NC8-TPP and 4NC18-TPP were vacuum deposited on the glass, and the
thicknesses of the 4NC8-TPP and 4NC18-TPP film were about 100 nm and 100 nm
respectively. The results showed that both of the 4NC8-TPP and 4NC18-TPP were
amorphous on the glass at room temperature. These results conformed with the
DSC rusults.
Figure 3. POM texture of 4NC8-TPP and 4NC18-TPP cooling from the isotropic state, ×200.

2734
X. ZHANG ET AL.
Figure 4. XRD of 4NC8-TPP and 4NC18-TPP films on glass substrate.
For many of the conjugated compounds, the absorbance in the visible region is
undoubtedly an important parameter.[12] Figure 5 showed the UV-visible absorption
spectra of 4NC8-TPP and 4NC18-TPP using CH2Cl2 as solvent, and the two curves
were similar due to their similar conjugated structure. It was found that there were
two major absorbances, the Soret band and the Q band. The Soret band of 4NC8-
TPP and 4NC18-TPP were 422 and 421 nm, respectively. The Q band values of
4NC8-TPP (or 4NC18-TPP) were 517 (or 516), 552 (or 551), 592 (or 592), and 647
(or 647). According to the molecular orbital theory of porphyrin put forth by
Gouterman,[13] the Soret band was due to the electronic transition from the ground
state (S0) to the second singlet excited state S2, and the Q band was from the S0 to the
first singlet excited state S1. We also measured the UV-visible absorption of the two
compounds’ films. The absorption edges of 4NC8-TPP and 4NC18-TPP were 673 and
Figure 5. UV-vis spectra of 4NC8-TPP and 4NC18-TPP in CH2Cl2.

PORPHYRIN DERIVATIVES WITH MESOGENIC PROPERTIES
2735
Figure 6. Fluorescence spectra of 4NC8-TPP and 4NC18-TPP in CH2Cl2.
677 nm, respectively. According on the formula DE ¼ 1240=kedge, the optical band
gaps (DE) of 4NC8-TPP and 4NC18-TPP were 1.84 and 1.83 eV.
Figure 6 is the flourescence emission spectra of 4NC8-TPP and 4NC18-TPP. It
showed that they both had two emission bands at the same wavelength. These rusults
illustrated that the electron emission occured on the porphyrin rings and the length
of the side chain had little influence on the emission spectra.
Electrochemical cyclic voltammetric was carried out to evaluate the oxidation
and reduction property. The cyclic voltammograms of 4NC8-TPP and 4NC18-TPP
were obtained in a solution of tetra-n-butylammonium perchlorate (0.1 mol=L) in
CH2Cl2, and an Ag=AgCl electrode was used as reference electrode as shown in
Fig. 7. Both 4NC8-TPP and 4NC18-TPP exhibited two anodic oxidation and two
cathodic reduction waves. The first oxidation potential was 0.79 V vs. Ag=AgCl
while the second was 1.53 V vs. Ag=AgCl for 4NC8-TPP. The reduction values were
ꢀ0.98 V and ꢀ1.33 V vs. Ag=AgCl, respectively. For 4NC18-TPP, the first oxidation
Figure 7. Cyclic voltammograms curves of 4NC8-TPP and 4NC18-TPP.

2736
X. ZHANG ET AL.
potential was 0.78 V vs. Ag=AgCl and the second was 1.53 V vs. Ag=AgCl while the
reduction values were ꢀ0.96 V vs. Ag=AgCl and ꢀ1.32 V vs. Ag=AgCl. It was found
that the difference between 4NC8-TPP and 4NC18-TPP was small because the por-
phyrin cores occurring from oxidation and reduction were the same. The highest
occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) energy levels of porphyrin derivatives were calculated according to the fol-
lowing equations[14]
:
À
Á
onset
ox
HOMO ¼ ꢀe E
þ 4:71 ðevÞ
À
Á
onset
red
LUMO ¼ ꢀe E
þ 4:71 ðevÞ
The HOMO levels of 4NC8-TPP and 4NC18-TPP were ꢀ5.50 and ꢀ5.49 eV
while the LUMO levels of 4NC8-TPP and 4NC18-TPP were ꢀ3.73 and ꢀ3.75 eV,
respectively. The HOMO-LUMO gap can be expressed as DE. The DE values of
4NC8-TPP and 4NC18-TPP were 1.77 and 1.74 eV. Both the oxidation and reduction
took place on the porphyrin ring.
CONCLUSIONS
Two novel porphyrin derivatives, 4NC8-TPP and 4NC18-TPP, were prepared
and characterized. Both of the two compounds had high thermostability from TG
analysis. 4NC8-TPP did not exhibit mesophase from the DSC curves but the POM
image was typical liquid-crystalline texture. However, 4NC18-TPP had a broad
column mesogenic phase about 150 °C. It indicated that the length of side chains
influenced the liquid-crystalline property of the compounds. X-ray diffraction results
showed that 4NC8-TPP and 4NC18-TPP were amorphous on the glass at room tem-
perature. UV-vis spectra, fluorescence, and CV properties were similar in 4NC8-TPP
and 4NC18-TPP. These liquid-crystalline materials may be useful for the practical
applications in photovoltaic devices.
EXPERIMENTAL
Pyrrole was newly distilled before use because of its self-polymerization.
Methyl 4-formylbenzoate and propionic acid were purchased and used without
further purification. The MS were recorded on a Bruker Agilent 1100=Esquire
HCT Plus (Bruker Autoflex III smartbean for TOF-MS). The 1H NMR was
recorded on a Bruker Avance 400(MHz) NMR spectrometer in CDCl3 or dimethyl-
sulfoxide (DMSO) using tetramethylsilane (TMS) as the internal standard. IR
spectra were taken on a Nicolet 6700 Fourier transform (FT) IR spectrometer with
KBr pellets. UV-vis spectra was obtained from Thermo Helios-c spectrometer. The
fluorescence spectra were recorded on a WGY-10 spectrofluorometer using CH2Cl2
as solvent. TG was examined on Netzsch TGA209F3. DSC was performed with
Netzsch 204-F1 thermal analysis system (scanning rate 10 °C=min). Optical texture
was investigated on Olympus BX51-P LINKAMTHMS600 polarizing optical micro-
scope (POM). The x-ray diffraction patterns were measured on a Bruker D8 Avance

PORPHYRIN DERIVATIVES WITH MESOGENIC PROPERTIES
2737
instrument. The cyclic voltammetry curves were obtained from CHI750A electro-
chemical workstation (Zhenhua Apparatus Co., Ltd, Shanghai) using CH2Cl2 as sol-
vent and Ag=AgCl as reference electrode.
General Synthetic Procedure
The primary material meso-tetra(4-methoxycarbonylphenyl)porphyrin (TCMPP)
was synthesized through the ring formation of pyrrole and methyl 4-formylbenzoate
according to the method reported in the literature by Alder-Longgo.[15] The second
material meso-tetra(4-carboxylphenyl)porphyrin (TCPP) was obtained through the
saponification of TCMPP and the acylchloriration and then amidation of TCPP
obtained the target products 4NC8-TPP and 4NC18-TPP under a nitrogen atmos-
1
phere. All of the intermediate products were charaterized by MS, H NMR, and
IR spectra. The synthesis routes are illustrated in Scheme 2.
Typical Procedure for the Synthesis of 4NC8-TPP
A mixture of TCPP (0.1 g, 0.126 mmol), SOCl2(5 ml), and CH2ClCH2Cl
(30 ml) were refluxed for 8 h under a nitrogen atmosphere in a 100-ml, three-
necked flask. The excess SOCl2 and solvent were removed under reduced pressure
after the reaction was finished. The remanent solid was dissolved in CH2Cl2
(40 ml) and trimethylamine (2 ml) and then n-octylamine was added into the flask.
The mixture was stirred in ice water for 3 h and then at room temperature for 12 h
under the nitrogen protection. The solvent was removed, and the residue was
purified by silica-gel column chromatography using CHCl3 as eluent. The first
band was collected and condensed to obtain the target products 4NC8-TPP
(43.75 mg, 28%).
Scheme 2. Synthesis route for porphyrin derivitives.

2738
X. ZHANG ET AL.
4NC8-TPP
TOF-MS: 1235.640, calcd. for C80H98N8O4: 1235.685; H NMR (400 MHz,
1
CDCl3, TMS), d (ppm) ¼ ꢀ2.78 (s, 2H, pyrrloe NH), 0.88–0.90 (t, 12H, -CH3),
1.27–1.59 (m, 48H, alkyl CH2), 3.64–3.66 (t, 8H, -NH-CHꢁ2ꢀ), 6.45–6.49 (t, 4H,
-CO-NH-), 8.16–8.56 (d, 16H, -C6H4), 8.85 (s, 8H, pyrrole ring); IR(KBr), t (cmꢀ1
)
¼ 3315 (n amide N-H and pyrrole N-H), 2924, 2852 (n C-H), 1634 (n C=O), 1554 (b,
amide N-H), 966 (b, pyrrole N-H).
FUNDING
This work was supported by the NSFC (Nos. 20674022, 20774031, and
21074039). The authors also thank the Natural Science Foundation of Guangdong
(Nos. 2006A10702003, 2009B090300025, 2010A090100001, 2014A030313241, and
2014B090901068) and the Ministry of Education of the People's Republic of China
(No. 20090172110011) for financial support.
SUPPLEMENTAL MATERIAL
1
Experimental details, characterization data of all compounds, and H NMR,
FT-IR, and mass spectra for this work can be accessed on the publisher’s website.
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