Synthesis and photophysical properties of pyrrole/polycyclic aromatic units hybrid fluorophores

Article abstract of DOI:10.1021/jo100158a

A series of pyrrole/polycyclic aromatic unit hybrid fluorophores was developed by a two-stage synthetic strategy. Their central aryl-substituted pyrrole cores were constructed by a Paal-Knorr pyrrole synthesis reaction. The reaction conditions and mechanism are also discussed in detail. End-capping triflate onto the central pyrrole core enables the core to incorporate various polycyclic aromatic units. The Buchwald-Hartwig amination reaction and the Suzuki-Miyaura cross-coupling reaction were adopted to incorporate the triflate end-capping pyrrole with N-phenylnaphthalen-1-amine and various polycyclic aromatic units to form the hybrid fluorophores. The photophysical properties and thermal properties of the fluorophores were characterized. Most of the pyrrole fluorophores emitted blue light and exhibited high quantum efficiency. The fluorescence properties of these pyrrole fluorophores were induced by manipulating the surrounding polycyclic aromatic units. When the central pyrrole core was incorporated with amino or naphthalene moieties, the fluorescence efficiency and thermal stability of fluorophores 1 and 2 were low (φ_f < 0.35, T_g <140 °C). Rigid and highly fluorescent moieties (such as pyrenyl, 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and spirofluorenyl groups) were grafted onto the pyrrole. Fluorophores 3-6 had high fluorescence efficiency (φ_f > 0.99) and stable glassy morphology (the T_g value of the fluorophore 6 was as high as 220 °C). Results of this study demonstrate that the sterically induced fluorescence of crowded pyrrole and the fluorescent polycyclic aromatic units significantly affect the emission properties of the hybrid fluorophores.

Full text of DOI:10.1021/jo100158a

pubs.acs.org/joc
Synthesis and Photophysical Properties of Pyrrole/Polycyclic Aromatic
Units Hybrid Fluorophores
Chang-Shun Li, Ya-Hsuan Tsai, Wei-Chen Lee, and Wen-Jang Kuo*
Department of Applied Chemistry, National University of Kaohsiung, Kaohsiung, Taiwan 811
wjkuo@nuk.edu.tw
Received January 31, 2010
A series of pyrrole/polycyclic aromatic unit hybrid fluorophores was developed by a two-stage
synthetic strategy. Their central aryl-substituted pyrrole cores were constructed by a Paal-Knorr
pyrrole synthesis reaction. The reaction conditions and mechanism are also discussed in detail. End-
capping triflate onto the central pyrrole core enables the core to incorporate various polycyclic
aromatic units. The Buchwald-Hartwig amination reaction and the Suzuki-Miyaura cross-coupling
reaction were adopted to incorporate the triflate end-capping pyrrole with N-phenylnaphthalen-1-amine
and various polycyclic aromatic units to form the hybrid fluorophores. The photophysical properties and
thermal properties of the fluorophores were characterized. Most of the pyrrole fluorophores emitted blue
light and exhibited high quantum efficiency. The fluorescence properties of these pyrrole fluorophores
were induced by manipulating the surrounding polycyclic aromatic units. When the central pyrrole core
was incorporated with amino or naphthalene moieties, the fluorescence efficiency and thermal stability of
fluorophores 1 and 2 were low (φf < 0.35, Tg <140 °C). Rigid and highly fluorescent moieties (such as
pyrenyl, 9,9-dimethylfluorenyl, 9,9-diphenylfluorenyl, and spirofluorenyl groups) were grafted onto the
pyrrole. Fluorophores 3-6had high fluorescence efficiency (φf>0.99) and stable glassy morphology (the
Tg value of the fluorophore 6 was as high as 220 °C). Results of this study demonstrate that the sterically
induced fluorescence of crowded pyrrole and the fluorescent polycyclic aromatic units significantly affect
the emission properties of the hybrid fluorophores.
Introduction
starburst- and dendron-type conjugated molecules.2 Such con-
gested structures prevent these compounds from their aggrega-
tion/excimer formation and render them strong emission and
amorphous characteristics in the film state.1d,2a,3 A variety of
palladium-catalyzed reactions, such as Suzuki-Miyaura cross-
coupling,1b,d,4 Stille cross-coupling,5 and Buchwald-Hartwig
amination,6 are used to construct the congested structures.
However, the Pd-catalyzed coupling reaction has some
limitations.1a,7 The first is that a large amount of palladium
Organic materials have been extensively applied in light-
emitting diodes because of their versatility and color-tunability.
Quantum efficiency, film-forming properties, and temporal
stability of the fluorophores remain challenges in science and
engineering. To improve the aforementioned fluorescence and
film-forming properties, fluorophores were introduced as steri-
cally crowded substituents on their periphery1 or made into
4004 J. Org. Chem. 2010, 75, 4004–4013
Published on Web 05/27/2010
DOI: 10.1021/jo100158a
r
2010 American Chemical Society

Li et al.
JOCArticle
catalyst and excess arylboronic acids are required to form the
multifunctionalized fluorophores. The Pd-catalyzed aryla-
tion reaction is a useful tool for mono- or difunctionalization
with little steric effect. As the amount of steric substituents
increases, the coupling reaction is inhibited. Therefore, more
palladium and arylboronic acid are required to increase the
coupling yield. Another question regarding the palladium-
catalyzed arylation reaction concerns the purification of the
multifunctionalized products. One or two substituents were
introduced to the periphery of the central core in a palla-
dium-catalyzed coupling reaction; products can be obtained
in high yield and purified easily.1a,4a,b,8 As the amount of
peripheral aryl substituents increases, the activity of the
arylation reaction decreases, and some byproducts with
fewer substituents appear. The target product is difficult to
isolate from these side products. This reaction is less effective
than the preceding one in forming asymmetric aryl substit-
uents on the periphery of the structure. To solve the afore-
mentioned problems, Paal-Knorr condensation was used in
the laboratory to generate a variety of asymmetric aryl-
substitued pyrroles.9 Not only do these fluorophores pro-
duce fluorescence in the solid state, but also their intrinsic
electrical, optical, and morphological properties can be
tuned by modifying the peripheral aryl groups. To increase
the fluorescence efficiency, some fluorescence-active poly-
cyclic aromatic units such as fluorene, pyrene, and hole-
transporting moieties, such as diarylamine, are introduced.
The trflate-capping pyrrole is the key intermediate to incor-
porate with these fluorescence-active polycyclic aromatic
units and hole-transporting moieties. Aryl triflates are a very
attractive alternative to aryl halides in the palladium-cata-
lyzed reaction.10 They can be easily synthesized from readily
available phenolic derivatives.11 Aryl triflate has been widely
adopted to extend the aromatic ring in a palladium-catalyzed
reaction. However, few works have been published on the
synthesis of fluorescent materials.
(1) (a) Huang, D. F.; Moorthy, J. M.; Natarajan, P.; Venkatakrishnan,
P.; Chow, T. J. Org. Lett. 2007, 25, 5215–5218. (b) Huang, W.; Tang, C.; Liu,
F.; Xia, Y. J.; Xie, L. H.; Wei, A.; Li, S. B.; Fan, Q. L. J. Mater. Chem. 2006,
16, 4074–4080. (c) Yu, G.; Jiao, S. B.; Liao, Y.; Xu, X. J.; Wang, L. P.; Wang,
L. M.; Su, Z. M.; Ye, S. H.; Liu, L. Q. Adv. Funct. Mater. 2008, 18, 2335–
2347. (d) Shen, W. J.; Dodda, R.; Wu, C. C.; Wu, F.; Liu, T. H.; Chen, H. H.;
Chen, Ch. H.; Shu, C. F. Chem. Mater. 2004, 16, 930–934. (e) Lee, J.; Liu,
Q. D.; Bai, D. R.; Kang, Y.; Tao, Y.; Wang, S. Organometallics 2004, 23,
6205–6213. (f) Chen, C. T.; Chiang, C. L.; Lin, Y. C.; Chan, L. H.; Huang,
C. H.; Tsai, Z. W.; Chen, C. T. Org. Lett. 2003, 5, 1261–1264.
(2) (a) Setayesh, S.; Grimsdale, A. C.; Weil, T.; Enkelmann, V.; Mu1llen,
K.; Meghdadi, F.; List, E. J. W.; Leising, G. J. Am. Chem. Soc. 2001, 123,
946–953. (b) Gronheid, R.; Hofkens, J.; Kohn, F.; Weil, T.; Reuther, E.;
€
Mullen, K.; De Schryver, F. C. J. Am. Chem. Soc. 2002, 124, 2418–2419.
(c) Freeman, A. W.; Koene, S. C.; Malenfant, P. R. L.; Thompson, M. E.;
Frechet, J. M. J. J. Am. Chem. Soc. 2000, 122, 12385–12386. (d) Justin
Thomas, K. R.; Thompson, A. L.; Sivakumar, A. V.; Bardeen, C. J.;
Thayumanavan, S. J. Am. Chem. Soc. 2005, 127, 373–383. (e) Kwon,
T. W.; Alam, M. M.; Jenekhe, S. A. Chem. Mater. 2004, 16, 4657–4666.
(f) Chen, C. H.; Lin, J. T.; Yeh, M. C. P. Org. Lett. 2006, 8, 2233–2236.
(g) Lupton, J. M.; Samuel, I. D. W.; Beavington, R.; Burn, P. L.; Bassler, H.
Adv. Mater. 2001, 13, 258–261. (h) Lo, S. C.; Male, N. A. H.; Markham,
J. P. J.; Magennis, S. W.; Burn, P. L.; Salata, O. V.; Samuel, I. D. W. Adv.
Mater. 2002, 14, 975–979. (i) Anthopoulos, T. D.; Frampton, M. J.; Namdas,
E. B.; Burn, P. L.; Samuel, I. D. W. Adv. Mater. 2004, 16, 557–560.
(3) (a) Gensch, T.; Hofkens, J.; Heirmann, A.; Tsuda, K.; Verheijen, W.;
Vosch, T.; Crist, T.; Basche, T.; Mullen, K.; De Schryver, F. C. Angew.
Chem., Int. Ed. 1999, 38, 3752–3756. (b) Pogantsch, A.; Wenl, E. G.; List,
E. J. W.; Leising, G.; Mullen, K. Adv. Mater. 2002, 14, 1061–1064. (c) Wu,
R. L.; Schumm, J. S.; Pearson, D. L.; Tour, J. M. J. Org. Chem. 1996, 61,
6906–6921. (d) Tour, J. M.; Wu, R.; Schumm, J. S. J. Am. Chem. Soc. 1990,
112, 5662–5663. (e) Wong, K. T.; Chien, Y. Y.; Chen, R. T.; Wang, C. F.; Lin,
Y. T.; Chiang, H. H.; Hsieh, P. Y.; Wu, C. C.; Chou, C. H.; Su, Y. O.; Lee,
G. H.; Peng, S. M. J. Am. Chem. Soc. 2002, 124, 11576–11577. (f) Xia, C. J.;
Advincula, R. C. Macromolecules 2001, 34, 5854–5859. (g) Steuber, F.;
Staudigel, J.; Stossel, M.; Simmerer, J.; Winnacker, A.; Spreitzer, H.;
Weissortel, F.; Salbeck, J. Adv. Mater. 2000, 12, 130–133. (h) Oldham,
W. J., Jr.; Lachicotte, R. J.; Bazan, G. C. J. Am. Chem. Soc. 1998, 120,
2987–2988.
In this work, a two-stage synthetic strategy is adopted to
generate a variety of asymmetric pyrrole/polycyclic aromatic
unit hybrid fluorophores. The factors that affect and the
optimal conditions for the Paal-Knorr condensation reac-
tion that yields the aryl-substituted pyrrole core are dis-
cussed herein. The pyrrole core was further transformed into
triflate end-capping pyrrole. Many palladium-catalyzed cou-
pling reactions were further examined by incorporating with
a series of polycyclic aromatic units into the triflate end-
capping pyrrole core.
Results and Discussion
(4) (a) Kanibolotsky, A. L.; Berridge, R.; Skabara, P. J.; Perepichka, I. F.;
Bradley, D. D. C.; Koeberg, M. J. Am. Chem. Soc. 2004, 126, 13695–13702.
(b) Sonntag, M.; Kreger, K.; Hanft, D.; Strohriegl, P. Chem. Mater. 2005, 17,
3031–3039. (c) Lyu, Y. Y.; Kwak, J.; Jeon, W. S.; Byun, Y.; Lee, H. S.; Kim,
D.; Lee, C.; Char, K. Adv. Funct. Mater. 2009, 19, 420–427. (d) Culligan,
S. W.; Chen, A. C. A.; Wallace, J. U.; Klubek, K. P.; Tang, C. W.; Chen, S. H.
Adv. Funct. Mater. 2006, 16, 1481–1487. (e) Geng, Y.; Katsis, D.; Culligan,
S. W.; Ou, J. J.; Chen, S. H.; Rothberg, L. J. Chem. Mater. 2002, 14, 463–470.
(5) (a) Sotgiu, G.; Zambianchi, M.; Barbarella, G.; Aruffo, F.; Cipriani,
F.; Ventola, A. J. Org. Chem. 2003, 68, 1512–1520. (b) Su, Y. Z.; Lin, J. T.;
Tao, Y. T.; Ko, C. W.; Lin, S. C.; Sun, S. S. Chem. Mater. 2002, 14, 1884–
1890. (c) Barbarella, G.; Favaretto, L.; Zanelli, A.; Gigli, G.; Mazzeo, M.;
Anni, M.; Bongini, A. Adv. Funct. Mater. 2005, 15, 664–670. (d) Radke,
K. R.; Ogawa, K.; Rasmussen, S. C. Org. Lett. 2005, 7, 5253–5256.
(6) (a) Lee, Y. T.; Chiang, C. L.; Chen, C. T. Chem. Commun. 2008, 217–
219. (b) Palayangoda, S. S.; Cai, X.; Adhikari, R. M.; Neckers, D. C. Org.
Lett. 2008, 10, 281–284. (c) Lai, M. Y.; Chen, C. H.; Huang, W. S.; Lin, J. T.;
Ke, T. H.; Chen, L. Y.; Tsai, M. H.; Wu, C. C. Angew. Chem., Int. Ed. 2008,
47, 581–585. (d) Huang, T. H.; Lin, J. T.; Chen, L. Y.; Lin, Y. T.; Wu, C. C.
Adv. Mater. 2006, 18, 602–606. (e) Shen, J. Y.; Yang, X. L.; Huang, T. H.;
Lin, J. T.; Ke, T. H.; Chen, L. Y.; Wu, C. C.; Yeh, M. C. P. Adv. Funct. Mater.
2007, 17, 983–995.
Synthesis. Chart 1 presents the chemical structure of the
pyrrole/polycyclic aromatic units’ hybrid fluorophores. In
this work, Paal-Knorr condensation was adopted to con-
struct a functionalized aryl-substituted pyrrole core as a key
intermediate 11b. The methoxy-capping pyrrole 11b was
hydrated and further formed triflate end-capping pyrrole
12b. Incorporating N-phenylnaphthalen-1-amine or the syn-
thesized aromatic boronic acids 13-17 into the triflate 12b
by the Buchwald-Hartwig amination reaction or the Suzuki-
Miyaura cross-coupling reaction yielded pyrrole/polycyclic
aromatic units hybrid fluorophores 1-6.
(9) Kuo, W. J.; Chen, Y. H.; Jeng, R. J.; Chan, L. H.; Lin, W. P.; Yang,
Z. M. Tetrahedron 2007, 63, 7086–7096.
(10) (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483. (b) Oh-e,
T.; Miyaura, N.; Suzuki, A. Synlett 1990, 221. (c) Oh-e, T.; Miyaura, N.;
Suzuki, A. J. Org. Chem. 1993, 58, 2201–2208. (d) Riggleman, S.; DeShong,
P. J. Org. Chem. 2003, 68, 8106–8109. (e) Seganish, W. M.; DeShong, P.
J. Org. Chem. 2004, 69, 1137–1143. (f) Furstner, A.; Grabowski, J.; Leh-
(7) (a) Dang, T. T.; Ahmad, R.; Dang, T. T.; Reinke, H.; Langer, P.
Tetrahedron Lett. 2008, 49, 1698–1700. (b) Sun, X.; Liu, Y.; Chen, S.; Qiu,
W.; Yu, G.; Ma, Y.; Qi, T.; Zhang, H.; Xu, X.; Zhu, D. Adv. Funct. Mater.
2006, 16, 917–925.
€
mann, C. W. J. Org. Chem. 1999, 64, 8275–8280. (g) Bringmann, G.; Gotz,
(8) (a) Tao, S.; Peng, Z.; Zhang, X.; Wang, P.; Lee, C. S.; Lee, S. T. Adv.
Funct. Mater. 2005, 15, 1716–1721. (b) Li, Y.; Ding, J.; Day, M.; Tao, Y.; Lu,
J.; D’iorio, M. Chem. Mater. 2004, 16, 2165–2173. (c) Kim, Y. H.; Shin,
D. C.; Kim, S. H.; Ko, C. H.; Yu, H. S.; Chae, Y. S.; Kwon, S. K. Adv. Mater.
2001, 13, 1690–1693. (d) Wu, Q.; Lavigne, J. A.; Tao, Y.; D’Iorio, M.; Wang,
S. Chem. Mater. 2001, 13, 71–77.
R.; Keller, P. A.; Walter, R.; Boyd, M. R.; Lang, F.; Garcia, A.; Walsh, J. J.;
Tellitu, I.; Bhaskar, K. V.; Kelly, T. R. J. Org. Chem. 1998, 63, 1090–1097.
(h) Malapel-Andrieu, B.; Merour, J.-Y. Tetrahedron 1998, 54, 11079–11094.
(11) (a) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122,
4020–4028. (b) Marion, N.; Navarro, O.; Mei, J.; Stevens, E. D.; Scott,
N. M.; Nolan, S. P. J. Am. Chem. Soc. 2006, 128, 4101–4111.
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CHART 1. Chemical Structures of the Pyrrole/Polycyclic Aromatic Unit Hybrid Fluorophores
SCHEME 1. Synthesis of the Triflate End-Capping Pyrrole 12b
Scheme 1 presents the route for synthesizing the triflate
end-capping pyrrole 12b. In the first step, anisole was in-
corporated into 2-naphthylacetic acid chloride, which was
synthesized from 2-naphthylacetic acid or purchased com-
mercially, using the Friedel-Crafts acylation to yield inter-
mediate 7. Base tBuOK and I2 were used to dimerize 7 and
thus obtain intermediate 8. Notably, the yield of the dimer-
ization depended strongly on the doses of I2 and tBuOK and
on the reaction time.
The intermediates Ia and Ib reacted with 0.5 equiv of I2 and
afforded 0.5 equiv of II. The intermediate II further reacted
with the remaining 0.5 equiv of Ib to yield 8. However, excess
base and I2 decrease the yield of intermediate 8. A large
amount of intermediate II and a few of byproducts of 10 were
obtained when 0.5 equiv of I2 and an excessive amount of
base was added. Moreover, large amounts of byproduct 9
generate when excess I2 and base were added. Scheme 3
proposes the mechanism of the formation of the side pro-
ducts. Intermediate II further reacted with excess tBuOK to
generate III. The intermediate formation inhibited the enol-
ate Ib to react with II when an excessive amount of base was
Scheme 2 shows the mechanism by which intermediate 8 is
t
formed. In the general procedure, equivalent base BuOK
abstracted the R-H of 7 to yield resonance forms Ia and Ib.
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SCHEME 2. Formation Mechanism of Intermediate 8
SCHEME 3. Mechanism of the Formation of the Side Product
added. Once an excess of I2 (I2>0.5 equiv) was added in the
reaction, a competition reaction between enolates III and Ib
to react with II led to formation of the byproduct 9.
Lengthening the reaction time also caused intermediate 8
to undergo Paar-Knorr furan cyclization to yield byproduct
10. Experimental results indicate that the optimal conditions
for the synthesis of intermediate 8 are refluxing the inter-
mediate 7 with 1 equiv of tBuOK and 0.5 equiv of I2 in THF
solution for 4 h.
Intermediate 8 further reacted with ammonium acetate
and acetic acid by the Paal-Knorr condensation reaction to
afford pyrrole intermediate 11a (See Scheme 1). The compe-
titive Paal-Knorr furan condensation reaction also pro-
ceeded, generating the byproduct 10. The concentration of
ammonium acetate in acetic acid is a key factor in the
inhibition of the side reaction. Reaction of intermediate 8
with saturated ammonium acetate solution yielded the great-
est possible amount of the pyrrole intermediate 11a. To
prevent the high activity of N-H in the following reaction
and to improve the fluorescent characteristics, pyrrole 11a
was ethylated under strong base NaH and bromoethane to
yield intermediate 11b. To transform the methoxy end-
capping pyrrole 11b into a hydroxyl form, attempts were
made to apply various demethylation methods. Simple
methods based on Lewis acid AlCl3 in toluene12 or HBr in
HOAc13 gave a low yield of demethylated product, despite
many trials. Demethylation of 11b with BBr3 in CH2Cl2 at
-78 °C gave the corresponding phenolic intermediate 12a in
an excellent yield (∼99%).14 The crude phenolic intermediate
12a was directly esterified with triflic anhydride in CH2Cl2 at
0 °C to give triflate end-capping pyrrole 12b in 70% isolated
yield (two steps). Palladium-catalyzed Suzuki cross-coupling
was adopted to incorporate the triflate end-capping pyrrole 12b
with the aromatic boronic acids 13-17 to yield the hybrid fluo-
rophores 2-6.
Aromatic boronic acids, pyreneboronic acid 14, and
9,90-spirobifluorenylboronic acid 17 were purchased commer-
cially. 2-Naphthylboronic acid 13, 9,90-dimethylfluorenylboro-
nic acid 15, and 9,90-diphenylfluorenylboronic acid 16 were
synthesized as described in the literature.8b,15 The detailed
synthetic route and experiment are depicted in the Supporting
Information (see Scheme S1).
To establish an efficient protocol for Suzuki-Miyaura
cross-coupling, several ligands and reaction conditions were
adopted in the reaction between bistriflate 12b and naphthyl-
boronic acid 13. Table 1 lists the reaction conditions of the
Suzuki-Miyaura cross coupling under argon atmosphere.
Phosphine ligands PCy310c,11a and SPhos16 were applied under
various conditions in the reaction between 1-naphthylboronic
acid and bistriflate 12b, but the coupling yield was low.
€
(12) (a) Mensonides-Harsema, M. M.; Liao, Y.; Bottcher, H.; Bartos-
(14) Kawaguchi, K.; Nakano, K.; Nozaki, K. Org. Lett. 2008, 10, 11991–
202.
€
€
zyk, G. D.; Greiner, H. E.; Jurgen Harting, P.; de Boer; Wikstrom, H. V.
J. Med. Chem. 2000, 43, 432–439. (b) Lednicer, D.; Grostic, M. F. J. Org.
Chem. 1967, 32, 3251–3253.
(13) (a) Reichwagen, J.; Hopf, H.; Guerzo, A.; Belin, C.; Bouas-Laurent,
H.; Desvergne, J. P. Org. Lett. 2005, 7, 971–974. (b) Sittisombut, C.;
Boutefnouchet, S.; Trinhvan-Dufat, H.; Tian, W.; Michel, S.; Koch, M.;
Tillequin, F.; Pfeiefer, B.; Pierre, A. Chem. Pharm. Bull. 2006, 54, 1113–1118.
(c) Grethe, G.; Toome, V.; Lee, H. L.; Uskokovic, M.; Brossi, A. J. Org.
Chem. 1968, 33, 504–508.
(15) (a) Katsis, D.; Geng, Y. H.; Ou, J. J.; Culligan, S. W.; Trajkovska, A.;
Chen, S. H.; Rothberg, L. J. Chem. Mater. 2002, 14, 1332–1339. (b) Li, Z. H.;
Wong, M. S.; Fukutani, H.; Tao, Y. Chem. Mater. 2005, 17, 5032–5040.
(c) Rehahn, M.; Schluter, A. D.; Wegner, G.; Feast, W. J. Polymer 1989, 30,
1060–1062. (d) Vahlenkamp, T.; Wegner, G. Macromol. Chem. Phys. 1994,
195, 1933–1952. (e) Ding, J.; Day, M.; Robertson, G.; Roovers, J. Macro-
molecules 2002, 35, 3474–3483. (f) Li, Z. H.; Wong, M. S.; Tao, Y.; Lu, J.
Chem.;Eur. J. 2005, 11, 3285–3293.
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TABLE 1. Screen of Ligands and Bases for Suzuki-Miyaura Cross-Coupling Reactions of Naphthalen-1-yl-1-boronic Acid with Triflate 12ba
entry
Pd
ligand
base (6 equiv)
temp (°C)
solvent
yieldb (%)
1
2
3
4
5
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PCy3
PCy3
PCy3
SPhos
PPh3
KF
KF
KF
K3PO4
K2CO3
rt
40
reflux
rt
reflux
THF
THF
THF
THF
benzene
trace
trace
trace
trace
74
aReaction conditions: 1 equiv of aryl trflate 12b, 2.5 equiv of boronic acid, 6 equiv of base, 2 mol % of Pd(OAc)2, and 9 mol % of ligand. bIsolated yield
based upon an average of two runs.
TABLE 2. Suzuki-Miyaura Cross-Coupling Reactions of Arylboronic
TABLE 3. Screen of Ligands and Bases for Buchwald-Hartwig Ami-
Acid with Triflate 12ba
nation Reactions of Triflate 12ba
entry
Pd(0)
ligand
base
solvent
yieldb (%)
1
2
3
4
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
Pd2(dba)3
P(tBu)3
DPPF
BINAP
BPCy2
tBuONa
tBuONa
tBuONa
tBuONa
toluene
toluene
toluene
toluene
trace
trace
10
70
aReaction conditions: 1 equiv of aryl trflate 12b, 2.05 equiv of amine,
2 equiv of base, 3 mol % of Pd2dba3, and 6 mol % of ligand. bIsolated
yield based upon an average of two runs.
Table 2 presents the synthesis of target fluorophores via
a Suzuki-Miyaura cross-coupling reaction. All of the
fluorophores dissolved in common organic solvents such as
n-hexane, toluene, CH2Cl2, and acetonitrile. Therefore, they
were purified by silica gel column chromatography and char-
1
acterized using H and 13C NMR spectroscopy as well as
HRMS.
To establish another efficient method for the production
of fluorophores 1 by Buchwald-Hartwig amination, vari-
ous ligands were used in the coupling of bistriflate 12b with
N-naphthyl-N-phenylamine.14,16a,18 Table 3 presents the
Buchwald-Hartwig amination of the bistriflate 12b with
N-naphthyl-N-phenylamine examined in the presence of
3 mol % of Pd2(dba)3, 9 mol % of ligand, and 2 equiv of
tBuONa in toluene solution. The amination with ligands
P(tBu)3,6c-e,19 DPPF,20 and BINAP21 is inefficient. The
aReaction conditions: 1 equiv of aryl trflate 12b, 2.5 equiv of boronic
acid, 6 equiv of base, 2 mol % of Pd(OAc)2, and 9 mol % of ligand.
bIsolated yield based upon an average of two runs.
The highest yield of 70% was obtained when 2 mol % of
Pd(OAc)2, 9 mol % of triphenylphosphine, and 6 equiv of
K2CO3 (2 M) were used as the base in a heterogeneous
solution of benzene and degassed water.17
(18) (a) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L.
J. Org. Chem. 2000, 65, 1158–1174. (b) Anderson, K. W.; Mendez-Perez, M.;
Priego, J.; Buchwald, S. L. J. Org. Chem. 2003, 68, 9563–9573. (c) Tundel,
R. E.; Anderson, K. W.; Buchwald, S. L. J. Org. Chem. 2006, 71, 430–433.
(d) Rostovtsev, V. V.; Bryman, L. M.; Junk, C. P.; Harmer, M. A.; Carcani,
L. G. J. Org. Chem. 2008, 73, 711–714.
(16) (a) Martin, R.; Buchwald, S. L. Acc. Chem. Res. 2008, 41, 1461–1473.
(b) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S. L. J. Am.
Chem. Soc. 2005, 127, 4685–4696. (c) Barder, T. E.; Buchwald, S. L. Org.
Lett. 2007, 9, 137–139. (e) Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc.
2007, 129, 3358–3366.
(19) (a) Thomas, K. R. J.; Lin, J. T.; Tao, Y. T.; Ko, C. W. J. Am. Chem.
Soc. 2001, 123, 9404–9411. (b) Yamamoto, T.; Nishiyama, M.; Koie, Y.
Tetrahedron Lett. 1998, 39, 2367–2370. (c) Hartwig, J. F. Angew. Chem., Int.
Ed. 1998, 37, 2046–2067.
(20) (a) Louie, J.; Driver, M. S.; Hamann, B. C.; Hartwig, J. F. J. Org.
Chem. 1997, 62, 1268–1273. (b) Li, J.; Ma, C.; Tang, J.; Lee, C. S.; Lee, S.
Chem. Mater. 2005, 17, 615–619.
(17) Bouchard, J.; Wakim, S.; Leclerc, M. J. Org. Chem. 2004, 69, 5705–
5711.
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FIGURE 1. Absorption spectra of the hybrid fluorophores 1 (A), 2 (B), 3 (C), 4 (D), 5 (E), and 6 (F) in ethyl acetate. The concentrations were
controlled in 1 ꢀ 10-5 M.
steric effect of the secondary amine and bulky triflate restrict
the formation of fluorophore 1.20a,21a The more active
catalyst BPCy2 gives a high yield.22 The fluorophore 1 was
also dissolved in common organic solvents, purified by silica
gel column chromatography, and then characterized using
1H and 13C NMR spectroscopy as well as HRMS.
Photophysical Properties. Figure 1 shows the absorption
spectra of the hybrid fluorophores 1-6 in ethyl acetate. The
absorption around 286 nm was caused by the π-π* excita-
tion of the pyrrole cores,9 and the longest absorption around
290-350 nm was caused by the π-π* excitation of the
hybrid fluorophores. As shown in Figure 1, the maximum
absorption wavelength of the hybrid fluorophores was
greatly shifted by the terminal polycyclic aromatic units.
Introducing arylamino or naphthylenyl groups to the termi-
nus gave the shortest maximum absorption wavelength of
fluorophores 1 and 2, of 292-296 nm. As the terminal poly-
cyclic aromatic unit such as pyrene, or fluorene, was intro-
duced, the maximum absorption wavelength of the fluoro-
phores 4-6 was red-shifted to 320-340 nm.
determined by linear regression of the data using Beer’s
law (see the Supporting Information, Figure S1). When
excited with the maximum absorption wavelength, these
hybrid fluorophores emitted blue light.
Figure 2 presents the fluorescence spectra of the fluoro-
phores in ethyl acetate solution and solid films. The inset
photographs display the photoluminescence of the fluoro-
phores in dichloromethane solution and solid film. Table 4 also
summarizes the fluorescence data. The fluorescence data de-
monstrate that the terminal polycyclic aromatic units strongly
affected the quantum efficiency of the fluorophores. Pyrroles
bearing naphthylphenylamino and naphthyl groups had quan-
tum efficiency of 30 and 35%. The fluorescent characteristic
may have resulted from the sterically inhibiting π-stacking of
the crowded pyrrole core.1a,9 Naphthylphenylamino and
naphthyl groups slightly increase the quantum efficiency.
However, the quantum efficiency of the hybrid fluorophores
3-6 is markedly increased to 99%, when the fluorophores bear
polycyclic aromatic units such as pyrene and fluorene deri-
vative moieties. The combination of the sterically inhibit-
ing π-stacking of the crowded pyrrole and the highly
fluorescent polycyclic units gives the hybrid fluorophores
3-6 possessing high quantum efficiency. Bright blue emis-
sion in the solid film makes fluorophores 3-6 highly
promising as blue emitters or phosphorescence hosts.
Electrochemical Properties and Energy Levels. To examine
the electrochemical behavior of the hybrid fluorophores,
Table 4 summarizes the absorption wavelength and the
corresponding molar extinction coefficient, which was
(21) (a) Wolfe, J. P.; Buchwald, S. L. J. Org. Chem. 1997, 62, 1264–1267.
(b) Ahman, J.; Buchwald, S. L. Tetrahedron Lett. 1997, 38, 6363–6366.
(c) Zhang, W.; Nagashima, T. J. Fluorine Chem. 2006, 127, 588–591.
(22) Old, D. W.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1998,
120, 9722–9723.
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Li et al.
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TABLE 4. Thermal and Photophysical Characteristics of the Hybrid Fluorophores 1-6
11b
NPANPy9
1
2
3
4
5
6
λambasx/nm
259 (3.85)
309 (4.73)
256 (4.75)
296 (4.65)
434 (3660)
263 (4.71)
292 (4.61)
429 (3580)
276 (5.07)
344 (4.91)
460 (3470)
284 (4.79)
320 (4.77)
442 (3530)
301 (4.78)
325 (4.76)
441 (3240)
307 (4.87)
326 (4.80)
441 (3220)
(log ε)a,b
λemmax,solution/nma,d
404 (5920)
13860
453 (3420)
10290
(fwhm/cm-1
Stokes shift
)
11460
11080
7310
8600
8090
8000
(cm-1
)
Φfc
0.04
416 (4200)
0.40
461 (4340)
0.30
462 (2710)
0.35
428 (3400)
>0.99
463 (2970)
>0.99
445 (2920)
>0.99
446 (2780)
>0.99
445 (2890)
λemmax,film/nma,d
(fwhm/cm-1
E01/2/eV e
)
0.93
3.47
5.26
1.79
89
0.79, 1.04
2.61
5.05
2.44
118
0.71, 0.85
3.13
5.04
1.91
137
1.05
3.41
5.38
1.97
122
1.05
3.16
5.38
2.22
162
1.01
3.25
5.34
2.09
158
1.01
3.20
5.34
2.14
191
1.03
3.23
5.36
2.09
220
Egap/eVf
HOMO/eV f
LUMO/eVe
Tg/°Cg
Tm/°Cg
234
325
277
525
269
512
303
522
Tdec/°Cg
419
515
530
540
aPhotophysical properties of the molecules were examined by UV-vis and fluorescence in ethyl acetate solution. The concentrations of the
fluorophores were controlled in 1 ꢀ 10-5 M and 5 ꢀ 10-8 M in ethyl acetate for UV-vis and fluorescence, respectively. bThe molar extinction coefficient;
ε was determined by means of a linear regression fit of the data to Beer’s law. cQuantum yield; Φf was determined with reference to EA solution of
coumarin 1. dFull width at half-maximum of PL spectra given in parentheses. eMeasured in CH2Cl2. All of the potentials (Eox) are reported relative to
ferrocene (EFc). The concentrations of the compounds were 1 ꢀ 10-3 M, and the scan rates were 100 mV/s. fHOMO calculated from CV potentials
[HOMO = 4.8 þ (Eox - EFc)]. LUMO = HOMO )- Egap. Energy gap (Egap) estimated from absorption on-set energy. gGlass transition temperatures;
Tgs, and melting temperatures; Tm’s were measured from DSC at heating rate of 10 °C/min under N2, Tdec’s were defined as weight loss at 5 wt % which
was measured by TGA at heating rate of 10 °C/min under N2.
FIGURE 2. Emission spectra of the hybrid fluorophores 1-6 in ethyl acetate and solid films. The concentrations were controlled in 5 ꢀ 10-8
M. Inset: photo of the hybrid fluorophores luminescence in solutions and solid films.
cyclic voltammetry (CV) experiments were carried out in a
three-electrode cell setup with 0.10 M of tetrabutylammonium
perchlorate (TBAP) in anhydrous CH2Cl2 solution. The oxida-
tion potentials were determined to be 0.71-1.05 V. All of the
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Li et al.
JOCArticle
hybrid fluorophores undergo a reversible oxidation process
around 1.03 V, except for fluorophore 1. These oxidation
potentials exhibited insignificant variations by modifying the
peripheral aryl substituents. The results exhibit the oxidation
process corresponding to the removal of electrons from the
pyrrole core to form radical cations. On the other hand, the
hybrid fluorophore 1 shows two reversible oxidation processes
at 0.71 and 0.85 V. In contrast to other hybrid fluorophores, the
two lower oxidation processes correspond to the sequential
removal of electrons from the two arylamine segments.9 The
absence of central pyrrole oxidation in the fluorophore 1 is
attributed to the destabilization of the two cation radicals
formed from the peripheral arylamine segments.19a,23 Based
on the oxidation potential and the band gap which was
determined from the optical absorption threshold, the HOMO
and LUMO energy levels of the fluorophores were estimated
with regard to the energy level of the ferrocene reference (4.8 eV
below the vacuum level).24 The results are tabulated in Table 1.
The peripheral substituents also affected the energy levels of the
hybrid fluorophores. Upon the incorporation of diarylamino
end-caps, the HOMO level of fluorophore 1 is raised to 5.04 eV.
Such a high HOMO level makes it a candidate for hole-
transporting/injection material.
Thermal Properties. To enhance morphological stability
and prevent aggregation/excimer formation for the pyrrole-
based fluorophores, a variety of polycyclic aromatic units
were attached onto the phenyl group at the C2- and C5-
positions in the pyrrole core. Table 1 summarized the
thermal properties of the hybrid fluorophores by using dif-
ferential scanning calorimetry (DSC) and thermogravimetric
analyzer (TGA). The DSC traces of the second heating run
are shown in the Supporting Information (Figure S2). All of
the hybrid fluorophores exhibit stable amorphous morphol-
ogies. They have distinct glass transition temperatures (Tg),
some even (fluorophores 1-3) have melting points in the first
heating run. It is important to note that the hybrid fluor-
ophores bearing rigid and bulky flurenyl substituents exhibit
high Tg values of 191 and 220 °C for fluorophores 5 and 6,
respectively. Furthermore, all of the hybrid fluorophores
show improved thermal stabilities, with decomposition tem-
peratures, Tdec’s, in the range 512-540 °C. These results
suggest that the incorporation of rigid and bulky fluorenyl
moieties at the ends of pyrroles may be used as a tool to induce
morphologically stable amorphous thin-film formation.
can be minimized by controlling the stoichiometric dos-
age, the addition sequence, and the reaction time. This study
also confirmed that bulky triflate can undergo a palladium-
catalyzed reaction. After the terminal methoxy group in the
crowded pyrrole core was transferred into triflate moieties, a
palladium-active intermediate 12b was obtained. A Buchwald-
-Hartwig amination reaction and a Suzuki-Miyaura cross-
coupling reaction were performed using the triflate end-capping
intermediate 12b as the key intermediate to yield the fluoro-
phores 1-6. The aforementioned studies of the optical proper-
ties and thermal properties revealed that the fluorescence effici-
ency and morphological stability of these fluorophores 3-6 can
be markedly enhanced by incorporating the sterically induced
fluorescence of crowded pyrrole into the fluorescent polycyclic
aromatic units. These hybrid fluorophores have great potential
as blue fluorescence emitters or phosphorescence hosts.
Experimental Section
Preparation of Pyrrole Precursors. 1-(4-Methoxyphenyl)-2-
(naphthalen-6-yl)ethanone (7). 2-Naphthylacetic acid (10 g,
53.7 mmol) was dissolved in 200 mL of anhydrous dichloro-
methane in a 250 mL two-neck round-bottom flask that was
equipped with a condenser, a magnetic stirrer, and a hot plate.
After 30 mL of thionyl chloride was added, the mixture was
refluxed for 6 h. Excess thionyl chloride and dichloromethane
were evaporated, and the residue viscous liquid was dried under
a vacuum. Fresh anhydrous dichloromethane (250 mL) and
anisole (8.8 mL, 81.3 mmol) were added. The mixture solution
was cooled in an ice bath. Aluminum chloride (9 g, 68.3 mmol)
was added in small portions for a period of 30 min. The solution
changed from brown to dark red after all of the aluminum chlo-
ride was added. The solution was stirred for another 24 h after
the temperature recovered to room temperature. Adding 100 mL
of1 M aqueous HCltoterminatethisreactioncaused the dark red
solution to recover its brown color. The mixed solution was
extracted with ethyl acetate three times (100 mL ꢀ 3). The
combined organic solution was then washed with water and dried
over anhydrousMgSO4. After the MgSO4 powder was filtered off
and the filtrate was condensed, a dark crude solid was left.
Further purification by column chromatography on silica gel
gave 13.7 g of product 7 in the form of white powder in a yield of
89%: 1H NMR(300 MHz, CDCl3, δ) 3.85 (s, 3H), 4.40 (s, 2H),
6.93 (d, J = 9.0 Hz, 2H), 7.39-7.49 (m, 3H), 7.73 (s, 1H),
7.77-7.82 (m, 3H), 8.04 (d, J = 9.0 Hz, 2H); 13C NMR(75
MHz, CDCl3, δ) 45.4, 55.4, 113.8, 125.6, 126.0, 127.5, 127.6,
127.6, 127.9, 128.2, 129.6, 131.0, 132.3, 132.5, 133.5, 163.5, 196.2;
HRMS (FAB) m/z calcd for C19H17O2 277.1229 ([M þ H] þ),
found 277.1227 ([M þ H] þ).
Conclusion
1,4-Bis(4-methoxyphenyl)-2,3-di(naphthalen-2-yl)butane-1,4-
dione (8). Compound 7 (5 g, 18.1 mmol) was dissolved in 100 mL
of anhydrous THF in an ice bath in a 250 mL two-neck round-
bottom flask that was equipped with a magnetic stirrer. Potas-
sium tert-butoxide (4.061 g, 36.2 mmol) was added in small
portions over a period of 20 min. The transparent solution bec-
ame orange when the potassium tert-butoxide was added. After
10 min of stirring, a solution of iodine (2.2965 g, 9.05 mmol) in
50 mL of anhydrous THF was added dropwise. During the
addition process, the red solution turned to brown. The solution
continued to be stirred in an ice bath for another 4 h. Aqueous
sodium bisulfite was added to remove excess iodine. The mixed
solution was extracted with ethyl acetate (100 mL ꢀ 3). The
combined organic solution was then dried over anhydrous
MgSO4. After the MgSO4 powder was filtered off and the filtrate
was condensed, a dark crude solid was left. Further purificat-
ion by column chromatography on silica gel gave 4.7 g of the
In this study, a series of highly bright luminescent fluor-
ophores 1-6 were constructed using two-stage synthetic
methods. In the first stage, the central aryl-substituted pyr-
role core was formed in a Paal-Knorr condensation reac-
tion. Studies of the reaction mechanism and experimental
testing revealed that the amounts of some side products, such
as furan derivatives 10 and but-2-ene1,4-dione derivatives 9,
(23) (a) Justin Thomas, K. R.; Lin, J. T.; Tao, Y.-T.; Ko, C.-W. Adv.
Mater. 2000, 12, 1949–1951. (b) Ko, C.-W.; Tao, Y.-T.; Lin, J. T.; Thomas,
K. R. J. Chem. Mater. 2002, 14, 357–361. (c) Justin Thomas, K. R.; Lin, J. T.;
Tao, Y.-T.; Ko, C.-W. Chem. Mater. 2002, 14, 1354–1361.
(24) Anderson, J. D.; McDonald, E. M.; Lee, P. A.; Anderson, M. L.;
Ritchie, E. L.; Hall, H. K.; Hopkins, T.; Mash, E. A.; Wang, J.; Padias, A.;
Thayumanavan, S.; Barlow, S.; Marder, S. R.; Jabbour, G. E.; Shaheen, S.;
Kippelen, B.; Peyghambarian, N.; Wightman, R. M.; Armstrong, N. R.
J. Am. Chem. Soc. 1998, 120, 9646–9655.
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Li et al.
JOCArticle
product 8 as a white powder in a yield of 95%: 1H NMR (300 MHz,
CDCl3, δ) 3.76 (s, 3H), 5.66 (s, 2H), 6.83 (d, J=9.3 Hz, 2H), 7.12
(dd, J=8.4, 1.8 Hz, 2H), 7.34-7.38 (m, 2H), 7.52 (d, J=8.4 Hz,
1H), 7.59-7.67 (m, 3H), 8.05 (d, J = 9.0 Hz, 2H); 13C NMR
(75 MHz, CDCl3, δ) 55.3, 58.1, 113.6, 125.7, 125.9, 126.8, 127.5,
127.6, 127.7, 128.3, 129.4, 131.2, 132.3, 133.3, 134.4, 163.3, 197.9;
HRMS (FAB) m/z calcd for C38H31O4 551.2222 ([M þ H] þ),
found 551.2234 ([M þ H] þ).
was dissolved in 50 mL of anhydrous dichloromethane in a 250 mL
two-neck round-bottom flask that was equipped with a magnetic
stirrer. Five milliliters of 1 M tribromoborane in dichloromethane
was added dropwise in an ice bath. As the triboromoborane solu-
tion was added, the transparent solution became dark brown. The
solution was stirred at the same temperature for another 11 h.
Deionized water was added to terminate the reaction at 0 °C. After
50 mL of ethyl acetate was added, the solution was washed three
times with 50 mL of deionic water. The combined organic layer was
dried over anhydrous magnesium sulfate and condensed under
vacuum conditions. The crude product was recrystallized from
dichloromethane and n-hexane solution. Product 12a (1.8 g) was
obtained as a white solid in a yield of 99%: 1H NMR (300 MHz,
DMSO-d6, δ) 0.91(t, J=6.9 Hz, 3H), 3.79 (q, J=6.9 Hz, 2H), 6.75
(d, J=8.1 Hz, 4H), 7.04 (d, J=8.4 Hz, 2H), 7.20 (d, J=8.4 Hz,
4H), 7.27-7.35 (m, 4H), 7.44-7.52 (m, 6H), 7.69 (d, J=7.5 Hz,
2H); 13C NMR (75 MHz, DMSO-d6, δ)16.0, 114.8, 120.6, 122.6,
124.7, 125.3, 126.1, 126.9, 127.0, 128.0, 129.0, 130.5, 132.1, 132.4,
133.3, 156.5; HRMS (FAB) m/z calcd for C38H29NO2 531.2198,
found 531.2199 (Mþ).
1-Ethyl-2,5-bis(4-trifluoromethanesulfonylphenyl)-3-(naphth-
alen-2-yl)-4-(naphthalen-3-yl)-1H-pyrrole (12b). Compound 12a
(2.6 g, 4.9 mmol) and 5 mL of triethylamine were dissolved in
50 mL of anhydrous dichloromethane in a round-bottom flask.
The solution was cooled in an ice bath, and 3.92 g of triflic anhy-
dride was added dropwise. During the addition, the solution
became dark brown. The solution was stirred for another 7 h. Aqu-
eous ammonium chloride (1 M, 10 mL) was added to terminate the
reaction. After 50 mL of deionic water was added, the reaction
mixture was transferred to a separatory funnel, and the dichlor-
omethane layer was separated. The aqueous phase was extracted
threetimes(50mLꢀ3). The combined organic layer was dried over
anhydrous magnesium sulfate and condensed under vacuum con-
ditions. It was further purified by column chromatography on
silica gel using ethyl acetate and n-hexane as a diluent. Compound
12b (2.0 g) was obtained as a white powder in a yield of 70%: 1H
NMR (300 MHz, CDCl3, δ) 1.073 (t, J=6.9 Hz, 3H), 3.98 (q, J=
6.9 Hz, 2H), 7.03 (dd, J=8.4, 1.8 Hz, 2H), 7.27 (d, J=8.7 Hz, 4H),
7.32-7.37 (m, 6H) 7.45-7.50 (m, 8H), 7.68 (d, J = 7.2 Hz, 2H);
13C NMR (75 MHz, CDCl3, δ) 16.6, 39.7 (112.3, 116.6, 120.8,
125.1) (q, J = 128 Hz, OTf C), 121.4, 123.4, 125.3, 125.6, 127.1,
127.4, 127.7, 129.2, 129.2, 130.0, 131.6, 132.2, 133.1, 133.2, 133.4,
148.9; 19F NMR (470 MHz, CDCl3, CFCl3, δ) -73.182; HRMS
(FAB) m/z calcd for C40H27F6NO6S2 795.1184, found 795.1177
(Mþ).
Synthesis of Hybrid Fluorophores. 1-Ethyl-2,5-bis(4-(N-
naphthylanilino)phenyl)-3,4-bis(naphthalen-2-yl)-1H-pyrrole (1).
A 100 mL two-necked round-bottom flask that had been
dried in a vacuum was charged with compound 12b (0.5 g,
0.63 mmol), N-phenylnaphthalen-1-amine (0.285 g, 1.30 mmol),
tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3, 0.028 g,
0.03 mmol), sodium tert-butoxide (0.151 g, 1.57 mmol), and
dry toluene (2 mL). When a solution of BPCy2 (2-dicyclohexyl-
phosphino-20-(N,N-dimethylamino)biphenyl) (0.1 M 0.628 mL)
was added, the solution became dark red. The solution was
warmed and refluxed for 24 h. It was then cooled to room temper-
ature, and 50 mL of deionized water was added. The reaction
mixture was transferred to a separatory funnel, and 50 mL of
ethylacetate was added. After the organiclayer was separated, the
aqueous phase was extracted twice with ethyl acetate (50 mLꢀ2).
The combined organic solution was dried over anhydrous mag-
nesium sulfate, filtered, and then condensed under vacuum
conditions. It was further purified by column chromatography
on silica gel (EA/hexane=10:1). Product 1 (0.32 g) was obtained
asa slightlyyellow powderina yieldof70%:1H NMR (500 MHz,
CDCl3, δ) 1.12 (t, J = 7.0 Hz, 3H), 4.00 (q, J = 7.0 Hz, 2H),
6.94-6.98 (m, 6H), 7.05-7.12 (m, 6H), 7.20 (t, J=7.0 Hz, 8H),
7.35-7.38 (m, 8H), 7.45-7.53 (m, 10H), 7.71 (q, J=3.0 Hz, 2H),
1,4-Bis(4-methoxyphenyl)-2,3-di(naphthalen-2-yl)-2-butene-1,4-
dione (9). Compound 9 (3-12%) was obtained as a byproduct in
the synthesis of compound 8 according to the reaction conditions:
1H NMR (300 MHz, CDCl3, δ) 3.76 (s, 6H), 6.80 (d, J=9.0 Hz,
4H), 7.23 (dd, J=8.4, 1.8 Hz 2H), 7.36-7.44 (m, 4H), 7.56 (d, J=
8.4 Hz, 2H), 7.60-7.72 (m, 4H), 7.78 (s, 2H), 7.91 (d, J=9.0 Hz,
4H); 13C NMR (75 MHz, CDCl3, δ) 55.3, 113.6, 126.2, 126.7, 127.2,
127.6, 128.2, 128.3, 129.2, 129.3, 132.6, 132.7, 132.8, 133.1, 143.4,
163.4, 195.4; HRMS (FAB) m/z calcd for C38H29O4 549.2066
([M þ H]þ), found 549.2079 ([M þ H]þ).
2,5-Bis(4-methoxyphenyl)-3,4-di(naphthalen-2-yl)furan (10).
Compound 10 (10-20%) was obtained as a byproduct in the
synthesis of compound 11a (acid-catalyzed Parr-Knorr furan
condensation) and 1-10% in the synthesis of compound 8
(base-catalyzed Paal-Knorr furan condensation) according to
the reaction conditions: 1H NMR (300 MHz, CDCl3, δ) 3.78 (s,
6H), 6.80 (d, J=8.4 Hz, 4H), 7.29 (d, J=8.4 Hz, 2H), 7.36-7.44
(m, 4H), 7.48 (d, J=8.7 Hz, 4H), 7.60-7.72 (m, 6H), 7.78 (d, J=
7.8 Hz, 2H); 13C NMR (75 MHz, CDCl3, δ) 55.1, 113.8, 123.3,
123.8, 125.8, 125.8, 127.3, 127.6, 127.9, 127.9, 128.6, 129.2,
131.0, 132.3, 133.4, 147.7, 158.8; HRMS (FAB) m/z calcd for
C38H28O3 532.2038, found 532.2044 (Mþ).
1-Ethyl-2,5-bis(4-methoxyphenyl)-3,4-di(naphthalen-2-yl)-1H-
pyrrole (11b). Compound 8 (2.5 g, 4.5 mmol) and ammonium
acetate (7 g, 90.8 mmol) were dissolved in 14 mL of acetic acid in
a 250 mL two-neck round-bottom flask that was equipped with
a reflux condenser, a magnetic stirrer, and a hot plate. The mixed
solution was refluxed for 36 h. After the reaction had run to
completion, the solution was poured into icy deionic water, and
white powder precipitated out. The crude powder product
was filtered and washed with deionized water. It was dissolved
in ethyl acetate and washed with 1 M sodium bicarbonate
(100 mL ꢀ 2) and deionic water (100 mL ꢀ 2). The solution
was dried over anhydrous magnesium sulfate. The magnesium
sulfate was filtered off, and the filtrate was condensed and dried
under a vacuum. The crude solid was dissolved in 50 mL of
anhydrous DMF. The DMF solution was cooled to 0 °C, and
sodium hydride (0.54 g, 60 wt % in mineral oil; 13.5 mmol) was
added in small portions. After the solution was stirred for
10 min, 1.0 mL of ethyl bromide (13.5 mmol) was added. The
solution recovered to room temperature and was stirred for
another 12 h. During this process, the milky solution became
brown. The solution was terminated by addition of ethanol until
the bubbles disappeared. Excess ethyl bromide and solvent
DMF were removed under a vacuum. The residue was dissolved
in 100 mL of ethyl acetate and washed twice using deionized
water (100 mL ꢀ 2). The organic solution was condensed after
drying over anhydrous magnesium sulfate and filtered off. It
was further purified by column chromatography on silica gel
using dichloromethane and n-hexane as diluent. White powder
(2.0 g) was afforded in 70% yield: 1H NMR (300 MHz, CDCl3,
δ) 1.06 (t, J=6.9 Hz, 3H), 3.81 (s, 6H), 3.93 (q, J=6.9 Hz, 2H),
6.88 (d, J = 8.7 Hz, 4H), 7.12 (dd, J = 8.7, 1.5 Hz, 2H),
7.27-7.34 (m, 8H), 7.46-7.49 (m, 6H), 7.68 (d, J = 7.2 Hz,
2H); 13C NMR (75 MHz, CDCl3, δ) 16.7, 39.3, 55.1, 113.7,
121.6, 124.8, 125.1, 125.3, 126.6, 127.3, 127.8, 129.0, 129.7,
131.0, 131.3, 132.6, 133.3, 133.5, 158.8; HRMS (FAB) m/z calcd
for C40H33NO2 559.2511, found 559.2497 (Mþ).
1-Ethyl-2,5-bis(4-hydroxyphenyl)-3-(naphthalen-2-yl)-4-(naph-
thalen-3-yl)-1H-pyrrole (12a). Compound 11b (1.9 g, 3.40 mmol)
4012 J. Org. Chem. Vol. 75, No. 12, 2010

Li et al.
JOCArticle
7.78 (d, J = 8.0 Hz, 2H), 7.90 (d, J = 8.0 Hz, 2H), 7.95 (d, J =
8.5 Hz, 2H); 13C NMR (125 MHz, CDCl3, δ) 16.8, 39.4, 121.1,
121.5, 122.0, 122.2, 124.2, 124.8, 125.2, 126.0, 126.1, 126.3, 126.5,
127.2, 127.4, 127.7, 128.4, 129.0, 129.1, 129.8, 131.1, 131.2, 131.3,
132.2, 133.4, 133.4, 135.3, 143.3, 147.7, 148.1; HRMS (FAB)
m/z calcd for C70H52N3 934.4161 ([M þ H] þ), found 934.4160
([M þ H] þ).
purified by column chromatography (ethyl acetate/n-hexane
=1:10) on silica gel to afford the fluorophores 4 (0.44 g) as a
slightly yellow powder in a yield of 79%: 1H NMR (500 MHz,
CDCl3, δ) 1.16 (t, J = 7.0 Hz, 3H), 1.56 (s, 12H), 4.13 (q, J =
7.0 Hz, 2H), 7.20 (dd, J=8.5, 1.5 Hz, 2H), 7.30-7.40 (m, 8H),
7.47-7.56 (m, 12H), 7.64 (dd, J = 8.0, 1.5 Hz, 2H), 7.69-7.72
(m, 8H), 7.77 (d, J=6.5 Hz, 2H), 7.81 (d, J=8.0 Hz, 2H); 13
C
NMR (125 MHz, CDCl3, δ) 16.8, 27.2, 39.7, 46.9, 120.1, 120.3,
121.1, 122.4, 122.6, 124.9, 125.2, 126.0, 126.8, 126.9, 127.0,
127.3, 127.4, 127.8, 129.2, 129.7, 131.4, 131.5, 131.8, 131.9,
133.3, 133.3, 138.6, 138.8, 139.6, 140.2, 153.9, 154.3; HRMS
(FAB) m/z calcd for C68H54N 884.4256 ([M þ H] þ), found
884.4268 ([M þ H] þ).
General Procedure for Suzuki-Miyaura Cross-Coupling Re-
action. In an atmosphere of argon, 1 equiv of bistriflate 12b (0.5
g, 0.6 mmol), 2.5 equiv of arylboronic acid 13-17, 2 mol % of
palladium acetate (0.006 g, 0.027 mmol), and 9 mol % of
triphenylphosphine (0.026 g, 0.099 mmol) were dissolved in 6
mL of benzene and 6 equiv of 2 M aqueous potassium carbonate
in a 100 mL two-necked round-bottom flask. The reaction
solution was warmed and refluxed for 3 days. Thirty milliliters
of deionized water was added, and the solution was extracted
with ethyl acetate (30 mL ꢀ 3). The combined organic solution
was dried over anhydrous magnesium sulfate, filtered, and
condensed under vacuum conditions. It was further purified
by column chromatography using ethyl acetate and n-hexane as
a diluent to give products 2-6.
1-Ethyl-3,4-bis(naphthalen-2-yl)-2,5-bis(4-(9,9-diphenyl-9H-
fluoren-2-yl)phenyl)-1H-pyrrole (5). According to the general
Suzuki-Miyaura cross-coupling procedure which was descri-
bed above, triflate 12b (0.75 g, 0.94 mmol) and boronic acid 16
(0.85 g, 2.35 mmol) were used. The crude product was further
purified by column chromatography (ethyl acetate/n-hexane =
1:10) on silica gel to give fluorophore 5(0.70g) asawhitepowderin
a yield of 74%: 1H NMR (500 MHz, CDCl3, δ) 1.09 (t, J=7.0 Hz,
3H), 4.04 (q, J = 7.0 Hz, 2H), 7.15 (dd, J = 8.0, 1.5 Hz, 2H),
7.23-7.33 (m, 26H), 7.40 (t, J=7.0 Hz, 2H), 7.44-7.50 (m, 12H),
7.56 (d, J= 8.0 Hz, 4H), 7.64 (dd, J= 8.0, 1.5 Hz, 2H), 7.69 (m,
4H), 7.81 (d, J=7.5 Hz, 2H), 7.84 (d, J=8.0 Hz, 2H); 13C NMR
(125 MHz, CDCl3, δ) 16.8, 39.6, 65.6, 120.2, 120.5, 122.4, 124.6,
124.9, 125.2, 126.2, 126.5, 126.6, 126.8, 126.8, 127.3, 127.5, 127.8,
127.8, 128.2, 128.2, 129.2, 129.7, 131.3, 131.4, 131.7, 132.0, 133.2,
133.3, 139.5, 139.8, 139.9, 140.0, 145.8, 151.5, 151.9; HRMS (FAB)
m/z calcd for C88H62N 1132.4882 ([M þ H] þ), found 1132.4883
([M þ H] þ).
1-Ethyl-2,5-bis(4-(naphthalen-1-yl)phenyl)-3,4-(naphthalen-2-yl)-
1H-pyrrole (2). Following the general Suzuki-Miyaura cross-
coupling procedure which was described above, triflate 12b (1 g,
1.26 mmol) and boronic acid 13 (0.54 g, 3.15 mmol) were used. The
crude product was further purified using column chromatography
(ethyl acetate/n-hexane =1:10) on silica gel to give fluorophores 2
(0.70 g) as a white powder in a yield of 74%: 1H NMR (500 MHz,
CDCl3, δ) 1.27 (t, J= 7.0 Hz, 3H), 4.22 (q, J= 7.0 Hz, 2H), 7.22
(dd, J=8.5, 1.5 Hz, 2H), 7.34-7.39 (m, 4H), 7.42-7.57 (m, 22H),
7.73 (d, J=7.0 Hz, 2H), 7.88 (d, J=8.5 Hz, 4H), 7.93 (d, J=8.0
Hz, 2H); 13C NMR (125 MHz, CDCl3, δ) 17.0, 39.8, 122.3, 125.0,
125.3, 125.8, 125.9, 126.1, 126.8, 126.8, 127.4, 127.7, 127.8, 128.3,
129.3, 129.8, 130.0, 131.4, 131.5, 131.5, 131.6, 132.1, 133.3, 133.4,
133.8, 139.8, 139.9; HRMS (FAB) m/z calcd for C58H42N 752.3317
([M þ H] þ), found 752.3328 ([M þ H] þ).
1-Ethyl-3,4-bis(naphthalen-2-yl)-2,5-bis(4-(9,9-diphenyl-9H-
fluoren-2-yl)phenyl)-1H-pyrrole (6). According to the general
Suzuki-Miyaura cross-coupling procedure which was de-
scribed above, triflate 12b (0.75 g, 0.94 mmol) and boronic
acid 17 (0.85 g, 2.35 mmol) were used. The crude product was
further purified by column chromatography (ethyl acetate/n-
hexane=1:10) on silica gel to give the fluorophore 6 (0.87 g) as
a white powder in a yield of 82%: 1H NMR (500 MHz, CDCl3,
δ) 0.96 (t, J=7.0 Hz, 3H), 3.91 (q, J=7.0 Hz, 2H), 6.76 (d, J=
7.5 Hz, 2H), 6.80 (d, J=7.5 Hz, 4H), 7.01 (s, 2H), 7.08-7.15 (m,
8H), 7.24-7.34 (m, 8H), 7.38-7.45 (m, 16H), 7.64-7.66 (m, 4H),
7.88-7.93 (m, 8H); 13C NMR (125 MHz, CDCl3, δ) 16.6, 39.5,
66.0, 120.0, 120.3, 122.3, 122.3, 124.0, 124.1, 124.8, 125.2, 126.7,
126.7, 126.7, 127.3, 127.7, 127.8, 127.8, 129.1, 129.6, 131.2, 131.4,
131.5, 131.8, 133.1, 133.2, 139.5, 140.1, 141.1, 141.3, 141.8, 148.7,
149.2, 149.4; HRMS (FAB) m/z calcd for C88H58N 1128.4569
([M þ H] þ), found 1128.4576 ([M þ H]þ).
1-Ethyl-3,4-bis(naphthalen-2-yl)-2,5-bis(4-(pyren-1-yl)phenyl)-
1H-pyrrole (3). According to the general Suzuki-Miyaura cross-
coupling procedure described above, triflate 12b (0.5 g, 0.63
mmol) and boronic acid 14 (0.386 g, 1.57 mmol) were used. The
crude product was further purified using column chromatogra-
phy (ethyl acetate/n-hexane = 1:10) on silica gel to give the
fluorophore 3 (0.4 g) as a slightly yellow powder in a yield of
70%: 1H NMR (500 MHz, CDCl3, δ) 1.35 (t, J = 7.0 Hz, 3H),
4.32 (q, J=7.0 Hz, 2H), 7.30 (dd, J=8.5, 1.0 Hz, 2H), 7.39-7.43
(m, 4H), 7.60-7.66 (m, 14H), 7.77-7.79 (m, 2H), 8.03-8.06 (m,
6H), 8.12 (s, 4H), 8.18-8.26 (m, 8H); 13C NMR (125 MHz,
CDCl3, δ) 17.1, 39.9, 122.5, 124.6, 124.9, 124.9, 125.0, 125.0,
125.1, 125.4, 126.0, 126.8, 127.4, 127.4, 127.5, 127.5, 127.5, 127.8,
128.5, 129.3, 129.8, 130.6, 130.6, 131.0, 131.5, 131.5, 131.6, 132.1,
133.3, 133.4, 137.3, 140.3; HRMS (FAB) m/z calcd for C70H46N
900.3630 ([M þ H] þ), found 900.3634 ([M þ H] þ).
Acknowledgment. We thank the National Science Council
of the Republic of China, Taiwan, for financially supporting
this research under Contract No. NSC 97-2113-M-390-001.
1-Ethyl-2,5-bis(4-(9,9-dimethyl-9H-fluoren-2-yl)phenyl)-3,4-
bis(naphthalen-2-yl)-1H-pyrrole (4). According to the general
Suzuki-Miyaura cross-coupling procedure which was descri-
bed above, triflate 12b (0.5 g, 0.63 mmol) and boronic acid 15
(0.375 g, 1.57 mmol) were used. The crude product was further
Supporting Information Available: Experimental details,
copies of 1H and 13C NMR spectra of all new compounds, and
linear regression analysis of the absorption data. This material is
available free of charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 12, 2010 4013