Synthesis of phenothiazine-functionalized porphyrins with high fluorescent quantum yields

Article abstract of DOI:10.1016/j.tetlet.2008.10.081

Two porphyrins with oligo-phenothiazine arms have been synthesized by a combination of Heck and Adler reaction, and their photophysical properties have been investigated by absorption and steady-state fluorescence spectroscopy. It is found that the excitation energy transfer occurs from the phenothiazine units to the porphyrin core, and that the porphyrins can emit intense red light with high fluorescent quantum yields.

Full text of DOI:10.1016/j.tetlet.2008.10.081

Tetrahedron Letters 49 (2008) 7446–7449
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Tetrahedron Letters
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Synthesis of phenothiazine-functionalized porphyrins with
high fluorescent quantum yields
*
Xianping Qiu, Ran Lu , Huipeng Zhou, Xiaofei Zhang, Tinghua Xu, Xingliang Liu, Yingying Zhao
State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two porphyrins with oligo-phenothiazine arms have been synthesized by a combination of Heck and
Adler reaction, and their photophysical properties have been investigated by absorption and steady-state
fluorescence spectroscopy. It is found that the excitation energy transfer occurs from the phenothiazine
units to the porphyrin core, and that the porphyrins can emit intense red light with high fluorescent
quantum yields.
Received 9 September 2008
Revised 15 October 2008
Accepted 17 October 2008
Available online 22 October 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Porphyrin
Phenothiazine
Energy transfer
Fluorescent quantum yield
There has been continuous interest in the synthesis of porphy-
rins because of their wide potential applications in catalysis, med-
icine, photochemical energy conversion, switches, and molecular
electronics.1 It is well known that the peripheral substituents on
the porphyrin core not only can modulate the physical properties,
but also can impart the desired chemical characteristics to the
emit intense red light in solution as well as in the film with the
fluorescent quantum yields of 0.35–0.40, which are higher than
most porphyrins reported.2a,h,3b
The synthetic routes for the phenothiazine-functionalized por-
phyrins are shown in Scheme 1. Firstly, we synthesized the alde-
hyde precursors, compounds 4 and 5 via Heck reaction from
compounds 1 and 3, respectively. The Heck coupling reaction be-
tween compound 1 and p-iodobenzaldehyde was carried out at
110 °C for 15 h in DMF using Pd(OAc)2 and tetrabutylammonium
bromide as the catalysts, affording compound 4 in a yield of 85%.
Compound 5 could be gained in a yield of 70% under similar Heck
coupling condition. In addition, compounds 1–3 were synthesized
according to the methods reported previously.5d The porphyrins
OPTZP1 and OPTZP2 with phenothiazine arms were synthesized
via Alder reaction in the mixed solvents of propionic acid, acetic
acid, and nitrobenzene6 because we found that only traces of OPT-
ZP1 and OPTZP2 were obtained when the reaction was taken place
in propionic acid alone or in xylene using p-nitrobenzoic acid as
the catalyst.7,2h Finally, the porphyrins OPTZP1 and OPTZP2 in
the yields of 18% and 15%, respectively, were gained in the mixed
solvents at 135 °C for 2 h, and they had good solubility in common
solvents, such as tetrahydrofuran, toluene, and dichloromethane.
All the intermediates and the final products were purified by col-
umn chromatography. The molecular structures were character-
ized with FT-IR, 1H NMR, elemental analysis, and MALDI/TOF
mass spectroscopy.8 The porphyrins and the corresponding alde-
hyde precursors exhibited an IR absorption band around
960 cmÀ1 arising from the wagging vibration of the trans-double
bond. 1H NMR spectra confirmed that all the vinylene groups were
in trans-conformation because no peak appeared at 6.56 ppm
macrocycle. Recently, a series of linear
p-conjugated oligomers,
such as oligofluorenes, oligo-p-phenylenevinylenes, oligothioph-
enes, and oligocarbazoles, have been introduced into the porphyrin
core to build star-shaped porphyrins,2 which are good candidates
for photoinduced energy transfer systems and fluorescence emit-
ting materials.3,2a,f On the other hand, phenothiazine is a recog-
nized pharmaceutical compound bearing electron-rich sulfur and
nitrogen heteroatoms, and the phenothiazine ring is nonplanar
with a butterfly conformation in the ground state, which can im-
pede the molecular aggregation and the formation of intermolecu-
lar excimer. Thus, phenothiazine maybe a potential p-type (hole
transport) semiconductor in organic devices, presenting unique
electronic and optical properties.4 Therefore, if oligophenothiazine
is introduced into the porphyrin, its excitation energy may transfer
to the porphyrin ring, showing interesting photophysical proper-
ties. To the best of our knowledge, there is no report on the synthe-
sis of the phenothiazine-functionalized porphyrin. In this Letter,
we designed and prepared two new porphyrins using phenothia-
zine or diphenothiazine units as the arms in the meso-positions.
It is found that the excitation energy transfer occurs from the phe-
nothiazine arms to the porphyrin core, and both compounds can
* Corresponding author. Fax: + 86 431 88923907.
E-mail address: luran@mail.jlu.edu.cn (R. Lu).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.10.081

X. Qiu et al. / Tetrahedron Letters 49 (2008) 7446–7449
7447
Scheme 1. Synthesis of the phenothiazine-functionalized porphyrins OPTZP1 and OPTZP2. Reagents and conditions: (a) 3-formyl-7-bromo-10-octylphenothiazine, Pd(OAc)2,
K2CO3, DMF, Bu4NBr, 110 °C, 12 h; (b) p-iodobenzaldehyde, Pd(OAc)2, K2CO3, DMF, Bu4NBr, 110 °C, 15 h; (c) Ph3PCH3I, t-BuOK, THF, rt, 12 h; (d) pyrrole, propionic acid, acetic
acid and nitrobenzene, 135 °C, 2 h.
assigned to the proton in cis-double bond,5 and the expected sig-
1.0
OPTZP1
OPTZP2
TPP
nals for the inner protons of the porphyrin moiety were located
at À2.70 ppm. The MALDI/TOF-MS spectra also confirmed that
the target porphyrins were generated, and some fragmentation
peaks were due to the cleavage of N-octyl bonds.5d,9
0.8
0.6
0.4
0.2
0.0
Figure 1 shows the absorption spectra of OPTZP1 and OPTZP2,
several absorption bands in the visible region could be found,
including four Q-bands in the 500–700 nm region (consistent with
a free-base porphyrin) and Soret bands, other absorption bands be-
tween 300 nm and 400 nm were due to the peripheral phenothia-
zine–vinylene arms. We found that the Soret bands of OPTZP1 and
OPTZP2 (ca. 435 nm, Table S1) were red-shifted compared to that
of TPP (418 nm), this phenomenon can be attributed to the pres-
ence of an intramolecular donor-acceptor molecular framework
as well as conjugation between the electron-withdrawing porphy-
rin unit and electron-rich oligophenothiazine–vinylene arms,
which might decrease the energy gap.10 As shown in Figure 2,
the absorption spectra of OPTZP1 and OPTZP2 in the film were
identical to those in the dilute solution except for slight red-shift,
300
400
500
600
700
800
Wavelengh (nm)
Figure 1. Absorption spectra of OPTZP1, OPTZP2, and TPP in toluene
(2 Â 10À6 mol/L).

7448
X. Qiu et al. / Tetrahedron Letters 49 (2008) 7446–7449
1.0
0.8
0.6
0.4
0.2
0.0
600
3
OPTZP1
OPTZP2
OPTZP1
OPTZP2
500
400
300
200
100
0
500
600
700
800
900
300
400
500
600
700
Wavelength nm
Wavelengh (nm)
Figure 4. Emission spectra of compound 3, OPTZP1, and OPTZP2 in toluene
(2 Â 10À6 mol/L) excited at 295 nm.
Figure 2. Normalized absorption spectra of OPTZP1 and OPTZP2 in the films.
which implied that intermolecular aggregation was suppressed in
the films owing to the nonplanar conformation of phenothiazines.4
Figure 3 gives the fluorescence spectra of OPTZP1 and OPTZP2
in toluene excited at 435 nm, and the characteristic luminescence
of the porphyrin cores at 662 nm appeared (Table S1). However,
when the excitation wavelength of 295 nm, which could excite
the phenothiazine–vinylene units instead of the porphyrin core,
was selected, the emission at 662 nm due to the porphyrin cores
could also be detected, while the feature emission from the pheno-
thiazine–vinylene (the reference compound 3 could emit intense
green light located at 500 nm under excitation at 295 nm as shown
in Figure 4) was quenched. It suggested that the excitation energy
of the phenothiazine–vinylene units might transfer to the porphy-
rin core. It was also found that the fluorescence intensity of OPT-
ZP2 was much higher than that of OPTZP1, illustrating that the
light-harvesting ability of OPTZP2 was improved compared with
OPTZP1 because of the multiplying of the number of phenothia-
zine units.11 Figure S1 shows the fluorescence emission spectra
of OPTZP1 and OPTZP2 in the films (excited at 440 nm), the por-
phyrins exhibited strong fluorescence emission and the emission
bands were also slightly red-shifted from 662 nm to 666 nm (Table
S1), indicating the phenothiazine ring was an excellent building
block for impeding the aggregation and intermolecular excimer
formation. The fluorescent quantum yields (UF) were measured
against TPP as the standard.2c,11 The UF values of OPTZP1 and OPT-
ZP2 in toluene were 0.39 and 0.40, and in thin films were 0.35 and
0.37, respectively, which were much higher than most porphyrins
reported, so they could be a good candidate for red-emitting
materials.
In conclusion, we have synthesized two new porphyrins func-
tionalized with monophenothiazine and diphenothiazine arms.
The investigation of their photophysical properties revealed that
the excitation energy of phenothiazine units could transfer to the
porphyrin core and the obtained porphyrins could emit intense
red light with higher fluorescence quantum yields than most por-
phyrins reported. They may possess potential applications in pho-
tonic devices.
Acknowledgments
This work is financially supported by the National Natural
Science Foundation of China (NNSFC, Nos. 20574027 and
20874034), 973 Program (2009CB939701), and the Program for
New Century Excellent Talents in University (NCET).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2008.10.081.
References and notes
1. (a) The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: Amsterdam, 2003; (b) Ali, H.; van Lier, J. E. Chem. Rev. 1999, 99,
2379–2450; (c) Satoh, N.; Nakashima, T.; Yamamoto, K. J. Am. Chem. Soc. 2005,
127, 13030–13038; (d) Barker, C. A.; Zeng, X. S.; Bettington, S.; Batsanov, A. S.;
Bryce, M. R.; Beeby, A. Chem. Eur. J. 2007, 13, 6710–6717; (e) Virgili, T.; Lidzey,
D. G.; Bradley, D. C . C. Adv. Mater. 2000, 12, 58–62.
2. (a) Li, B. S.; Li, J.; Fu, Y. Q.; Bo, Z. S. J. Am. Chem. Soc. 2004, 126, 3430–3431; (b) Li,
B. S.; Xu, X. J.; Sun, M. H.; Fu, Y. Q.; Yu, G.; Liu, Y. Q.; Bo, Z. S. Macromolecules
2006, 39, 456–461; (c) Paul-Roth, C. O.; Simonneaux, G. Tetrahedron Lett. 2006,
47, 3275–3278; (d) Montes, V. A.; Pérez-Bolívar, C.; Agarwal, N.; Shinar, J.;
Anzenbacher, P., Jr. J. Am. Chem. Soc. 2006, 128, 12436–12438; (e) Jiang, B.;
Yang, S.; Jones, W. E., Jr. Chem. Mater. 1997, 9, 2031–2034; (f) Wolffs, M.;
Hoeben, F. J. M.; Beckers, E. H. A.; Schenning, A. P. H. J.; Meijer, E. W. J. Am.
Chem. Soc. 2005, 127, 13484–13485; (g) Vollmer, M. S.; Würthner, F.;
Effenberger, F.; Emele, P.; Meyer, D. U.; Stü-mpfig, T.; Port, H.; Wolf, H. C.
Chem. Eur. J. 1998, 4, 260–269; (h) Xu, T. H.; Lu, R.; Liu, X. L.; Chen, P.; Qiu, X. P.;
Zhao, Y. Y. J. Org. Chem. 2008, 73, 1809–1817.
3. (a) Speiser, S. Chem. Rev. 1996, 96, 1953–1976; (b) Duan, X. F.; Wang, J. L.; Pei, J.
Org. Lett. 2005, 7, 4071–4074; (c) Pillow, J. N. G.; Halim, M.; Lupton, J. M.; Burn,
P. L.; Samuel, I. D. W. Macromolecules 1999, 32, 5985–5993.
4. (a) Kramer, C. S.; Zeitler, K.; Müller, T. J. J. Org. Lett. 2000, 2, 3723–3726; (b)
Kong, X. X.; Kulkarni, A. P.; Jenekhe, S. A. Macromolecules 2003, 36, 8992–8999;
(c) Bucci, N.; Müller, T. J. J. Tetrahedron Lett. 2006, 47, 8323–8327; (d) Lai, R. Y.;
Fabrizio, E. F.; Lu, L.; Jenekhe, S. A.; Bard, A. J. J. Am. Chem. Soc. 2001, 123, 9112–
9118; (e) Kim, G. W.; Cho, M. J.; Yu, Y. J.; Kim, Z. H.; Jin, J. I.; Kim, D. Y.; Choi, D.
1000
TPP
OPTZP1
800
OPTZP2
600
400
200
0
550
600
650
700
750
800
850
Wavelength nm
Figure 3. Emission spectra of OPTZP1, OPTZP2, and TPP in toluene (2 Â 10À6 mol/
L) excited at 435 nm.

X. Qiu et al. / Tetrahedron Letters 49 (2008) 7446–7449
7449
H. Chem. Mater. 2007, 19, 42–50; (f) Kim, S. K.; Lee, C. J.; Kang, I. N.; Lee, J. H.;
Park, J. W. Thin Solid Films 2006, 509, 132–136.
OPTZP1: 1H NMR (CDCl3, 500 MHz, ppm), d 8.92 (6H, s), 8.20 (7H, d), 7.87 (7H,
d), 7.46 (4H, s), 7.42 (4H, d), 7.30 (7H, s), 7.27 (5H, s), 7.19–7.17 (8H, m), 6.95
(4H, t), 6.91–6.89 (8H, m), 3.40 (8H, t), 1.89–1.83 (8H, m), 1.51–1.45 (8H, m),
1.38–1.29 (32H, m), 0.90 (12H, t), À2.70 (2H, s). IR (KBr, cmÀ1): 3313, 3020,
2921, 2851, 1595, 1574, 1464, 1400, 1334, 1248, 1106, 964, 881, 800, 743. mp:
231.0–232.0 °C. MALDI-TOF: calcd: 1596.8, found: 1596.5. Elemental Anal.
calcd for C132H130N8S4: C, 81.02; H, 6.70; N, 5.73; S, 6.55. Found: C, 81.06; H,
6.65; N, 5.77.
5. (a) Mizoroki, T.; Mori, K.; Ozaki, A. Bull. Chem. Soc. Jpn. 1971, 44, 581; (b)
Horner, L.; Hoffmann, H. G.; Klahre, G. Chem. Ber. 1959, 92, 2499–2505; (c)
Heck, H. F.; Nolley, J. P. J. Org. Chem. 1972, 37, 2320–2322; (d) Qiu, X. P.; Lu, R.;
Zhou, H. P.; Zhang, X. F.; Xu, T. H.; Liu, X. L.; Zhao, Y. Y. Tetrahedron Lett. 2007,
48, 7582–7585; (e) Liu, Q.; Liu, W. M.; Yao, B.; Tian, H. K.; Xie, Z. Y.; Geng, Y. H.;
Wang, F. S. Macromolecules 2007, 40, 1851–1857.
6. (a) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour, J.; Korsakoff,
L. J. Org. Chem. 1967, 32, 476; (b) Xu, T. H.; Lu, R.; Qiu, X. P.; Liu, X. L.; Xue, P. C.;
Tan, C. H.; Bao, C. Y.; Zhao, Y. Y. Eur. J. Org. Chem. 2006, 4014–4020.
7. Richardson, C.; Reed, C. A. J. Org. Chem. 2007, 72, 4750–4755.
OPTZP2: 1H NMR (CDCl3, 500 MHz, ppm), d 8.90 (6H, s), 8.16 (7H, s), 7.83 (7H,
s), 7.44 (4H, s); 7.39 (4H, d), 7.29–7.22 (28H, m), 7.14 (8H, m), 6.92–6.79 (28H,
m), 3.86–3.82 (16H, m), 1.86–1.78 (16H, m), 1.48–1.40 (16H, m),1.33–1.26
(64H, m), 0.91–0.86 (24H, m), -2.69 (2H, s). IR (KBr, cmÀ1): 3313, 3018, 2921,
2850, 1580, 1597, 1466, 1400, 1334, 1247, 1105, 958, 875, 800, 744. mp:
151.0–152.0 °C. MALDI-TOF: calcd: 3298.8, found: 3298.8; Elemental Anal.
Calcd for C220H230N12S8: C, 80.10; H, 7.03; N, 5.10; S, 7.78. Found: C, 80.15; H,
7.06; N, 5.05.
8. Compound 4: 1H NMR (CDCl3, 500 MHz, ppm), d 9.98 (1H, s), 7.85 (2H, d), 7.61
(2H, d), 7.30 (2H, t), 7.17-7.12 (3H, m), 6.98 (1H, d), 6.92 (1H, t), 6.88–6.6.83
(2H, m), 3.85 (2H, t), 1.84–1.78 (2H, m), 1.46–1.40 (2H, m), 1.33–1.25 (8H, m),
0.87 (3H, t). IR (KBr, cmÀ1): 3020, 2919, 2851, 1693, 1593, 1463, 1370, 1250,
1166, 1043, 961, 857, 742. MALDI-TOF: calcd: 441.6, found: 442.3. Elemental
Anal. calcd for C29H31NOS: C, 78.87; H, 7.08; N, 3.17; O, 3.62; S, 7.26. Found: C,
78.92; H, 7.11; N, 3.14.
9. Kramer, C. S.; Muller, T. J. J. Eur. J. Org. Chem. 2003, 18, 3534–3548.
10. (a) Ono, N.; Tomita, H.; Maruyama, K. J. Chem. Soc., Perkin Trans. 1 1992, 2453–
2456; (b) Jiu, T. G.; Li, Y. J.; Gan, H. Y.; Li, Y. L.; Liu, H. B.; Wang, S.; Zhou, W. D.;
Wang, C. R.; Li, X. F.; Liu, X. F.; Zhu, D. B. Tetrahedron 2007, 63, 232–240; (c)
Yen, W.-N.; Lo, S.-S.; Kuo, M.-C.; Mai, C.-L.; Lee, G.-H.; Peng, S.-M.; Yeh, C.-Y.
Org. Lett. 2006, 8, 4239–4242.
11. (a) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1–13; (b) Li, Y.; Cao,
L. F.; Ning, Z. J.; Huang, Z.; Cao, Y.; Tian, H. Tetrahedron Lett. 2007, 48,
975–978.
Compound 5: 1H NMR (CDCl3, 500 MHz, ppm), d 9.97 (1H, s), 7.84 (2H, d), 7.60
(2H, d), 7.31–7.21 (6H, m), 7.15–7.11 (3H, m), 6.98 (1H, d), 6.90 (1H, t), 6.86–
6.79 (6H, m), 3.83 (4H, s), 1.83–1.78 (4H, m), 1.46–1.39 (4H, m), 1.31–1.25
(16H, m), 0.88–0.85 (6H, m). IR (KBr, cmÀ1): 3019, 2922, 2851, 1694, 1595,
1467, 1362, 1248, 1164, 1037, 957, 855, 746. mp: 50.0–52.0 °C. MALDI-TOF:
calcd: 777.1, found: 778.0. Elemental Anal. calcd for C51H56N2OS2: C, 78.82; H,
7.26; N, 3.60; O, 2.06; S,8.25. Found: C, 78.88; H, 7.24; N, 3.63.