Synthesis and characterization of triphenylamine appended porphyrins and their intramolecular energy transfer

Article abstract of DOI:10.14233/ajchem.2014.15648

A series of 5,10,15-triphenyl-20-(triphenylamino)porphyrinato zinc(II) (ZnTPP(TPA)1 (1), 5-phenyl-10,15,20-tris(triphenylamino)- porphyrinato zinc(II) (ZnTPP(TPA)3 (2) and 5,10,15,20-tris(triphenylamino)porphyrinato zinc(II) (ZnTPP(TPA)4 (3) were synthesized using 4-(N,N-diphenylamino)benzaldehyde, benzaldehyde and pyrrole as starting materials. All porphyrins were characterized with various spectroscopic methods, MALDI-TOF mass, UV-vis, 1H NMR and 2D COSY spectroscopy. The structure of 5,10,15-triphenyl- 20-(triphenylamino)porphyrin [H2TPP(TPA)] was also established by X-ray diffraction analyses. The absorption and emission spectra indicate that there are strong interactions between zinc porphyrin core and triarylamine at ground states. Excited energy transfer from triphenylamine to porphyrin was proved by the fluorescence spectra.

Full text of DOI:10.14233/ajchem.2014.15648

Asian Journal of Chemistry; Vol. 26, No. 7 (2014), 2053-2056
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.15648
Synthesis and Characterization of Triphenylamine Appended
Porphyrins and their Intramolecular Energy Transfer
*
M. BAI , Q. MA, R. SONG and F. MENG
Marine College, Shandong University, Weihai 264209, P.R. China
*Corresponding author: Tel./Fax: + 86 631 5688303; E-mail: ming_bai@sdu.edu.cn
Received: 17 April 2013; Accepted: 13 June 2013; Published online: 22 March 2014;
AJC-14959
A series of 5,10,15-triphenyl-20-(triphenylamino)porphyrinato zinc(II) (ZnTPP(TPA)1 (1), 5-phenyl-10,15,20-tris(triphenylamino)-
porphyrinato zinc(II) (ZnTPP(TPA)3 (2) and 5,10,15,20-tris(triphenylamino)porphyrinato zinc(II) (ZnTPP(TPA)4 (3) were synthesized
using 4-(N,N-diphenylamino)benzaldehyde, benzaldehyde and pyrrole as starting materials. All porphyrins were characterized with
various spectroscopic methods, MALDI-TOF mass, UV-vis, 1H NMR and 2D COSY spectroscopy. The structure of 5,10,15-triphenyl-
20-(triphenylamino)porphyrin [H2TPP(TPA)] was also established by X-ray diffraction analyses. The absorption and emission spectra
indicate that there are strong interactions between zinc porphyrin core and triarylamine at ground states. Excited energy transfer from
triphenylamine to porphyrin was proved by the fluorescence spectra.
Keywords: Triphenylamine, Porphyrin, Energy transfer.
evolution13. Thin polymer films of 5-(2-phenoxyacetamide)-
INTRODUCTION
or 5-(2,5-phenylenebis(oxy)diacetamide)-10,15,20-tris-
Porphyrins are versatile functional molecules for their
(triphenylamino)porphyrinato zinc(II), which deposited by
unique photophysical and electrochemical properties which
multicyclic potentiodynamic electropolymerization, could be
also can be expediently controlled by modified with proper
used as sensor to determine alkaloids, such as, nicotine, cotinine
functional groups at the meso and/or β positions on the macro-
and myosmine at the concentration level of 0.1 mM with high
cycle1,2. Triphenylamine (TPA)-originated derivatives are
sensitivity and selectivity14.
widely investigated as optoelectronic materials in different
Due to these magnificent properties of porphyrin-triphenyl-
applications, such as organic light-emitting diode3-5, dye-sensi-
amine compounds as mentioned above, the interaction of
tized solar cells (DSSC)3,6-9 and electrochromic polymer3,10
.
triphenylamine group with porphyrinato zinc attracted much
attention. Spectral and electrochemical investigation of
porphyrin-triphenylamine dendrimers has been reported.
Because of the presence of antenna effect of the triphenylamine
dendrons in these dendrimers, the fluorescence quantum yields
of prphyrin were strongly enhanced when more triphenylamine
moieties were selectively excited15. The electronic interaction
between porphyrin and triphenylamine was also investigated
through a series of Por-triphenylamine conjugate16. In this
work, we synthesized a mono-, tri- and tetra-triphenylamine
substituted porphyrinato zinc complexes. The photoinduced
intramolecular energy transfer from triphenylamine to the zinc
porphyrin core was investigated by absorption and emission
spectra. The difference on the properties between these comp-
ounds, which caused by the different number of triphenylamine
groups, are discussed.
Recently, hybridizations of porphyrin and triphenylamine have
attracted much attention. Porphyrins that have a π-conjugated
triphenylamine at the meso-position opposite the anchoring
group have been synthesized and its application as sensitizer
in dye-sensitized solar cells resulted in extremely high power
conversion efficiencies11. The compound with hexyl chains
on the diarylamino-substituent, giving an overall power conver-
sion efficiency of 6.6 %. The compound zinc(II) 5,15-bis(4-
(diphenyl-amino)phenyl)-10-(3,4,5-trimethoxyphenyl)-20-(4-
carboxylphenylethynyl)porphyrin is synthesized and its overall
power conversion efficiency of the dye-sensitized solar cells
is as high as 5.45 %12. Donor-bridge-acceptor conjugates,
5,10,15,20-tetrakis[4-(N,N-diphenylaminostyryl)phenyl]
porphyrin and (5,10,15,20-tetrakis[4-(N,N-diphenylamino-
benzoate)phenyl]porphyrin, were used for synthesizing
platinum nanocomposite for photocatalyzing hydrogen

2054 Bai et al.
Asian J. Chem.
5-Phenyl-10,15,20-tris(triphenylamino)porphyrinato
zinc(II) [ZnTPP(TPA)3] (2): Yield: 283.37 mg (4.8 %). δ H
(400 MHz, CDCl3): 9.13 (s, 4H, ArH), 9.10 (d, 2H, J = 4.8
Hz, ArH), 8.98 (d, 2H, J = 4.4 Hz, ArH), 8.24 (d, 2H, J = 6.4
Hz, ArH), 8.09 (d, 6H, J = 8.0 Hz, ArH), 7.76-7.80 (m, 3H,
ArH), 7.47 (d, 6H, J = 8.4 Hz,ArH), 7.42-7.43 (m, 24H, ArH),
7.15 (br s, 6H, ArH). MS (MALDI-TOF) m/z: 1010.31 [M]+
1010.34.
5,10,15,20-Tris(triphenylamino)porphyrinato zinc(II)
[ZnTPP(TPA)4] (3): Yield: 107.85 mg (1.6 %). δ H (400 MHz,
CDCl3): 9.12 (s, 2H, ArH), 8.09 (d, 2H, J = 8.0 Hz, ArH), 7.47
(d, 2H, J = 8.0Hz, ArH), 7.42-7.43 (m, 8H, ArH), 7.15 (t, 2H,
J = 4.0 Hz, ArH). MS (MALDI-TOF) m/z: 1344.46 [M]+
1345.00.
EXPERIMENTAL
All of the other chemicals and solvents such as 4-(N,N-
diphenylamino)benzaldehyde, benzaldehyde and Zn(OAc)2·2H2O
were bought from commercial source and used as received.
Column chromatography was carried out on a silica gel column
(Qingdao Haiyang, 200-300 mesh) with the indicated eluents.
Detection method: 1H NMR spectra were recorded on a
Bruker DPX 400 spectrometer (1H: 400 MHz) in CDCl3 solutions
unless otherwise stated. Spectra were referenced internally
using the residual solvent resonances (δ = 7.26 for 1H NMR)
relative to SiMe4 (δ = 0 ppm). Electronic absorption spectra
were recorded on a Hitachi U-4100 spectrophotometer. The
fluorescence spectra were recorded on Perkin Elmer LS-45.
MALDI-TOF mass spectra were taken on a Bruker BIFLEX
III ultrahigh resolution Fourier transformation cyclotron
resonance (FT-ICR) mass spectrometer with R-cyano-4-
hydroxycinnamic acid as a matrix. Single crystals of all the
complexes for X-ray diffraction analysis with suitable
dimensions were mounted on the glass rod and the crystal
data were collected on an Oxford Diffraction Gemini E diffrac-
tometer.
Synthesis of triphenyl-substituted porphyrinato zinc(II)
complexes (1-3): Added in succession 4-(N,N-diphenyl-
amino)benzaldehyde 2.73 g (10 mmol), benzaldehyde 1.06 g
(10 nmol) and pyrrole 1.32 g (20 mmol) to 30 mL of refluxing
propionic acid. Reflux the mixture for 3 h and then cool it to
room temperature. Then the reaction mixture was poured into
100 mL methanol. After filtration, the solid product was
purified by silica-gel column chromatography using CH2Cl2/
hexane (from 1/10 to 5/10) as eluent. The metal free porphyrins
and Zn(OAc)2·2H2O were dissolved in 50 mL DMF and refluxed
for 1 h. After the solvent was removed in vacuo, the product
was purified by silica-gel column chromatography using
CH2Cl2 as eluent.
RESULTS AND DISCUSSION
The synthetic procedures of these compounds are shown
in Scheme-I. The metal free porphyrins were synthesized using
4-(N,N-diphenylamino)benzaldehyde, benzaldehyde and pyrrole
as starting materials. After metalized with Zn(OAc)2·2H2O in
CH2Cl2 and CH3OH, the porphyrinato zinc compolexes,
ZnTPP(TPA) (1), ZnTPP(TPA)3 (2) and ZnTPP(TPA)4 (3) were
prepared and separated successfully.
These compounds were characterized by MALDI-TOF
mass, 1H NMR, UV-vis spectroscopy. The MALDI-TOF mass
spectra of these compounds clearly showed intense signals
1
for the molecular ion (M+). H NMR spectra of compound
ZnTPP(TPA), ZnTPP(TPA)3 and ZnTPP(TPA)4 were recorded
in CDCl3.
Single crystals of H2TPP(TPA) suitable for X-ray diffrac-
tion analysis were obtained by slow diffusion of MeOH into
the corresponding CHCl3 solution17. Compound H2TPP(TPA)
crystallizes in the monoclinic system with P2/c space group.
As shown in Fig.1, the four indole rings form the planar core
with the average dihedral angel of 2.16° between the pyrrole
and porphin core. The average dihedral angle between the three
benzene groups on the meso-position and porphin core is
80.07° due to the steric effect. Strong electronic interaction
requires efficient π-orbital overlap and this can be examined
by the dihedral angles between the aromatic rings. The dihedral
angle between the meso-position benzene ring of triphenyl-
amine and porphin core is 53.35°, which is much smaller than
5,10,15-Triphenyl-20-(triphenylamino)porphyrinato
1
zinc(II) [ZnTPP(TPA)] (1): Yield: 219.78 mg (5.2 %). H
NMR (400 MHz, CDCl3): δ 9.10 (d, 2H, J = 4.4 Hz, ArH),
8.98 (d, 2H, J = 4.8 Hz, ArH), 8.95 (s, 4H, ArH), 8.23 (br s,
6H, ArH), 8.08 (d, 2H, J = 8.4 Hz, ArH), 7.77(br s, 9H, ArH),
7.45 (d, 2H, J = 8.4 Hz, ArH), 7.41-7.42 (m, 8H, ArH), 7.14
(br s, 2H,ArH). MS (MALDI-TOF) m/z: 843.23 [M]+ 843.99.
R1 = R2 = R3 = Phenyl,
R4 = Triphenylamine
ZnTPP(TPA) (1)
ZnTPP(TPA)3 (2)
R1 = R2 = R3 = Triphenylamine,
R4 = Phenyl
ZnTPP(TPA)4 (3) R1 = R2 = R3 = R4 = Triphenylamine
Scheme-I: Synthesis of porphyrins ZnTPP(TPA) (1), ZnTPP(TPA)3 (2) and ZnTPP(TPA)4 (3)

Vol. 26, No. 7 (2014)
Synthesis and Characterization of Triphenylamine Appended Porphyrins 2055
TABLE-1
ELECTRONIC ABSORPTION DATA FOR ZnTPP AND COMPOUNDS 1-3 IN TOLUENE
λmax (nm) (log ε/dm3 mol-1 cm-1)
422 (5.81) 549 (4.46)
425 (5.55) 550 (4.39)
Φf (%)a
3.3
3.6
5.8
Compound
ZnTPP
ZnTPP(TPA) (1)
ZnTPP(TPA)3 (2)
ZnTPP(TPA)4 (3)
588 (3.65)
591 (3.85)
597 (4.02)
598 (4.18)
302 (4.69)
306 (4.84)
306 (5.02)
436 (5.43)
440 (5.49)
554 (4.32)
556 (4.38)
6.2
Quantum yield of ZnTPP in toluene (Φf = 3.3 %) as standard; TPA = Triphenylamine.
that between the benzene rings and porphin ring. The dihedral
angles of neighboring benzene rings of triphenylamine are
69.78, 69.78 and 74.72°. It is noteworthy that the neighboring
molecules are connected by the intermolecular π-π interaction
between the triphenylamine and the porphyrin core (Fig. 2).
Absorption spectra of all compounds were recorded in
toluene and the data are given in Table-1. The spectra shown
in Fig. 3 indicate that large change on the shape has been
induced by the introduction of triphenylamine groups on the
porphyrin ring. For comparison purpose, the absorption spectra
of triphenylamine in the same solvent are also shown in Fig. 4.
Along with the increase on the number of triphenylamine
groups connected, the Soret band of porphyrin red shifted
gradually from about 420 for ZnTPP to 440 nm for
ZnTPP(TPA)4. Similar red shifts are also observed for the
Q bands in the range of 550-600 nm. This indicates that
presence of strong ground state interactions between the
triphenylamine groups and porphyrin. The broad absorption
of triphenylamine groups of these compounds in the range of
280-340 nm does not shown distinctive change in comparison
with that of pure triphenylamine.
Fig. 1. ORTEP drawing of compound H2TPP(TPA) (30 % probability
thermal ellipsoids). Hydrogen atoms and the pyridine molecule are
omitted for clarity
Fig. 3. UV-visible spectra of compounds ZnTPP, 1-3 in toluene. The
concentrations were fixed at 2 × 10-6
M
The fluorescence spectra of triphenylamine in toluene
show a broad emission band in the range of 340-440 nm with
the maximum peak at about 380 nm (Fig. 4). But this emission
is missing in the fluorescence spectra of ZnTPP(TPA),
ZnTPP(TPA)3 and ZnTPP(TPA)4 when triphenylamine was
selectively excited at 300 nm (Fig. 5). This means that the
emission of triphenylamine was efficiently quenched by
porphyrin ring. Meanwhile, the emission of porphyrin at about
620 nm was observed with a large intensity. Because the
absorption of porphyrin at the excitation wavelength (300 nm)
is extremely small, the direct excitation of ZnTPP at 300 nm
did not induce strong emission at 620 nm as shown in Fig 5.
The strong emission of ZnTPP(TPA), ZnTPP(TPA)3 and
ZnTPP(TPA)4 at 620 nm when triphenylamine were excited
are therefore can be attributed to the efficient intramolecular
Fig. 2. Crystal-packing diagrams for compound H2TPP(TPA) (A) and (B).
Hydrogen atoms are omitted for clarity

2056 Bai et al.
Asian J. Chem.
energy transfer from triphenylamine to porphyrin. Because
the triphenylamine’s emissions at 380 nm were completely
quenched, the energy transfer efficiencies are therefore
estimated to be 100 %. The increased fluorescence quantum
yields of ZnTPP(TPA), ZnTPP(TPA)3 and ZnTPP(TPA)4 in
Table-1 suggest again the efficient antenna effects of the
triphenylamine groups in these compounds.
were enhanced when more triphenylamine moieties were
linked. The results of this research revealed that triphenylamine
and porphyrin hybrid compounds are ideal models for the
mimic of light harvesting arrays in natural photosynthesis
systems. Further studies on this kind of compounds will be
helpful for us on deeper understanding the natural light
harvesting process and developing new artificial photosynthetic
systems.
ACKNOWLEDGEMENTS
Financial support from the Natural Science Foundation
of China (Grant No. 21001069) and the Independent Innova-
tion Foundation of Shandong University, IIFSDU.
REFERENCES
1. K.M. Kadish, in eds.: K.M. Kadish, K.M. Smith and R. Guilard, The
Porphyrin Handbook, Academic Press, San Diego, CA, vol. 1, pp. 1-44
(2000).
2. K.M. Kadish, E.V. Caemelbecke and G. Royal, in eds.: K.M. Kadish,
K.M. Smith and R. Guilard, The Porphyrin Handbook, Academic Press,
San Diego, CA, vol. 8, pp. 3-114 (2000).
3. A. Iwana and D. Sek, Prog. Polym. Sci., 36, 1277 (2011).
4. Y. Tao, C. Yang and J. Qin, Chem. Soc. Rev., 40, 2943 (2011).
5. A. Chaskar , H.F. Chen and K.T. Wong, Adv. Mater., 23, 3876 (2011).
6. J. He, F. Guo, X. Li, W. Wu, J. Yang and J. Hua, Chem. Eur. J., 18,
7903 (2012).
Fig. 4. UV-Vis (full) and the fluorescence (dotted) spectra of compound
triphenylamine in toluene
7. K. Pei, Y. Wu, W. Wu, Q. Zhang, B. Chen, H. Tian and W. Zhu, Chem.
Eur. J., 18, 8190 (2012).
8. D.W. Chang, H.J. Lee, J.H. Kim, S.Y. Park, S.-M. Park, L. Dai and J.-B.
Baek, Org. Lett., 13, 3880 (2011).
9. Y. Ooyama and Y. Harima, Eur. J. Org. Chem., 2903 (2009).
10. H.-J. Yen and G.-S. Liou, Polym. Chem., 3, 255 (2012).
11. C.-P. Hsieh, H.-P. Lu, C.-L. Chiu, C.-W. Lee, S.-H. Chuang, C.-L. Mai,
W.-N. Yen, S.-J. Hsu, E.W.-G. Diau and C.-Y. Yeh, J. Mater. Chem.,
20, 1127 (2010).
12. B. Liu, W. Zhu, Y. Wang, W. Wu, X. Li, B. Chen, Y.-T. Long and Y.
Xie, J. Mater. Chem., 22, 7434 (2012).
13. M. Zhu, Y. Dong, Y. Du, Z. Mou, J. Liu, P. Yang and X. Wang, Chem.
Eur. J., 18, 4367 (2012).
14. K. Noworyta, W. Kutner, C.A. Wijesinghe, S.G. Srour and F. D'Souza,
Anal. Chem., 84, 2154 (2012).
15. C.-Y. Huang and Y.O. Su, Dalton Trans., 39, 8306 (2010).
16. C.-Y. Huang, C.-Y. Hsu, L.-Y. Yang, C.-J. Lee, T.-F. Yang, C.-C. Hsu,
C.-H. Ke and Y.O. Su, Eur. J. Inorg. Chem., 1038 (2012).
17. Crystal data C57H40Cl3N5, M = 901.29, monoclinic, P2/c, Z = 4, a =
10.3366(3) Å, b = 22.2075(6) Å, c = 20.2667(5) Å, α = 90°, β =
91.983(2)°, γ = 90°, U = 4649.4(2) Å3, Dcalc = 1.288 g cm-3, 15,870
independent data were collected with graphite monochromatic CuKα
radiation (λ = 1.54178 Å) using the SMART and SAINT programs at
293(2) K using Oxford Diffraction Gemini E diffractometer. The struc-
tures were solved by the direct method (SHELXS-97).Anisotropic ther-
mal parameters were used for the non-hydrogen atoms and isotropic
parameters for the hydrogen atoms. Hydrogen atoms were added geo-
metrically and refined using a riding model. The structure was refined
by full-matrix least-squares (SHELXS-97) on F2 to R1 = 0.0537, wR2
= 0.1582 for 7880 reflections with I > 2σ(I) respectively. CCDC 723302
contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam. ac.uk/data_request/cif.
Fig. 5. Fluorescence spectra of compounds ZnTPP, 1-3 were excited at
310 nm in toluene. The concentrations of porphyrins were fixed at
2 × 10-6
M
Conclusion
A series of triphenylamine substituted porphyrinato
zinc(II) complexes have been prepared. All porphyrins were
characterized with spectroscopic methods. In the emission
spectroscopy study, the efficient intramolecular energy transfer
from triphenylamine to porphyrin is found in 1-3. Triphenyl-
amine absorb the UV light and then transfer the energy to the
porphyrin core. Fluorescence in the visible region subsequently
is emitted from porphyrin. The fluorescence quantum yields