Synthesis and photoluminescence properties of some novel fluorenophanes

Article abstract of DOI:10.1016/j.tetlet.2007.02.051

Fluorenophanes derived from 2,7-bis-(bromomethyl)-9,9′-diheptyl-9H-fluorene and various diols exhibit excellent photoluminescence properties.

Full text of DOI:10.1016/j.tetlet.2007.02.051

Tetrahedron Letters 48 (2007) 2761–2764
Synthesis and photoluminescence properties of some
novel fluorenophanes
Perumal Rajakumar* and Rajagopal Kanagalatha
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
Received 28 November 2006; revised 26 January 2007; accepted 7 February 2007
Available online 15 February 2007
Abstract—Fluorenophanes derived from 2,7-bis-(bromomethyl)-9,90-diheptyl-9H-fluorene and various diols exhibit excellent photo-
luminescence properties.
Ó 2007 Elsevier Ltd. All rights reserved.
One of the most characteristic features of supramolecu-
lar chemistry is that it provides information about inter-
molecular and intramolecular interactions.1 During the
course of our studies on the synthesis of cyclophanes,2,3
the fluorene unit was selected as the component of such
cyclic compounds because of its remarkable fluorescent
nature. Fluorene-based derivatives were extensively
investigated for electronic and photonic applications,
such as light emitting diodes,4 charge-transfer agents,5
field effect transistors,6 sensors,7 and more recently,
two-photon absorbing materials.8 The synthesis of
2,7-bridged fluorenophanes and their conformational
studies were reported by Tsuge et al.9 indicating the
importance of the orientation between the fluorene
component with reference to the other aromatic
components.
We describe here the synthesis of 2,7-bridged fluoreno-
phanes 1a–5a and 1b–5b consisting of o-, m-, and
p-benzene diols and S-(ꢀ)-Binol units and their confor-
mational, absorption and photoluminescence behavior.
The synthetic pathway leading to precyclophane 8b is
outlined as an example (Scheme 1). The reaction of
1.0 equiv of 2,7-bis-(bromomethyl)-9,90-diheptyl-9H-flu-
orene 7b with 2.5 equiv of catechol in dry acetone at rt
gave precyclophane 8b as a pale yellow solid in 62%
1
yield. The H NMR spectrum of 8b showed a triplet
R
R
R
R
R
R
O
O
O
O
O
O
O
O
O
O
O
O
R R
R R
1a R = C2H5
1b R = C7H15
2a R = C2H5
ortho
4a R = C2H5
4b R = C7H15
meta
para
R R
2b R = C7H15
5a R = C2H5
3a R = C2H5
5b R = C7H15
3b R = C7H15
Keywords: Fluorenophanes; Photoluminescence; Bathochromic.
*
Corresponding author. Tel.: +91 44 22351269x213; fax: +91 44 22300488; e-mail: perumalrajakumar@hotmail.com
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.02.051

2762
P. Rajakumar, R. Kanagalatha / Tetrahedron Letters 48 (2007) 2761–2764
R
R
R
R
OH
ii
i
1a-3a R = C2H5
1b-3b R = C7H15
+
O
O
Br
Br
OH
OH
HO
7a R = C2H5
7b R = C7H15
8a-
8b-
9a-
o
o
R = C2H5
R = C7H15
m
R = C2H5
9b-m
R = C7H15
10a-
10b-
p
R = C2H5
p R = C7H15
Scheme 1. Reagents and conditions: (i) K2CO3, dry acetone, rt, 48 h, 8a (68%), 8b (62%); 9a (62%), 9b (59%); 10a (50%), 10b (58%); (ii) 7a/7b,
K2CO3, dry acetone, rt, 120 h, 1a (31%), 2a (28%), 3a (19%), 1b (21%), 2b (27%), 3b (16%).
at d 0.79 (J = 7.34 Hz) for the CH3 protons of the ali-
phatic unit, a multiplet at d 1.02–1.25 integrating for
twenty aliphatic methylene protons, and a triplet at d
1.94 (J = 7.96 Hz) integrating for four methylene pro-
tons attached to C-9 of the fluorene moiety. The O-
methylene protons appeared as a singlet at d 5.18 in
addition to the aromatic protons. In the 13C NMR
spectrum, the aliphatic carbons of 8b appeared at d
14.3–40.4, the methylene carbon attached to C-9 of the
fluorene moiety and the O-methylene carbons appeared
at d 55.1 and d 66.9 in addition to the aromatic carbons.
chol, resorcinol and hydroquinone in 68%, 62%, 59%,
50%, and 58% yields, respectively. The structures of pre-
cyclophanes 8a, 9a–b, and 10a–b were confirmed from
spectroscopic and analytical data.10,11 Precyclophanes
8a, 9a–b, and 10a–b were next coupled with 1.0 equiv
of 7a or 7b under high dilution conditions to give fluo-
renophanes 1a–3a and 2b–3b in 31%, 28%, 19%, 27%,
and 16% yields, respectively (Scheme 1). The structures
of fluorenophanes 1a–3a and 2b–3b were characterized
by spectral and analytical data.12,13
Using similar methodology, chiral precyclophanes 11a–
b were treated with 7a–b to give chiral fluorenophanes
4a and 4b in 21% and 18% yields, respectively (Scheme
2). The structures of chiral fluorenophanes 4a and 4b14
were confirmed from spectroscopic and analytical data.
The synthesis of fluorenophane 1b could be achieved un-
der high dilution conditions. The reaction of 1.0 equiv of
precyclophane 8b with 1.0 equiv of 7b in dry acetone at
rt for 120 h afforded fluorenophane 1b as a yellow solid
1
in 21% yield. The H NMR spectrum of compound 1b
showed a triplet at d 0.80 (J = 7.34 Hz) for the 12 pro-
tons of the methyl groups of the aliphatic unit, a multi-
plet at d 1.04–1.28 for the methylene protons of the alkyl
unit, and a triplet (J = 7.84 Hz) at d 1.95 for the CH2
protons attached to C-9 of the fluorene moiety. The
O-methylene protons appeared as a singlet at d 5.30 in
addition to the aromatic protons. In the 13C NMR spec-
trum, the aliphatic carbons appeared at d 14.3–40.5 and
the methylene carbon attached at C-9 of the fluorene
moiety and O-methylene carbons appeared at d 54.8
and at d 71.6, respectively, in addition to the aromatic
carbons.
The synthesis of a fluorenophane with a large cavity
would be of interest. The treatment of 1.0 equiv of dibro-
mide 7a–b with 2.1 equiv of ethyl 4-hydroxybenzoate 6
in dry DMF in the presence of K2CO3 at 60 °C for
48 h afforded diesters 12a–b in 82% and 87% yields.
Reduction of diesters 12a–b with LAH in THF gave
diols 13a–b in 68% and 71% yields. Dibromide 7a–b
was slowly added to a suspension of diol 13a–b in excess
NaH in dry THF over a period of 6 h to give fluoreno-
phanes 5a–b in 32% and 27% yields (Scheme 3). The
structures of fluorenophanes 5a–b were characterized
by spectral and analytical data.15
In order to test the utility of this synthetic process, pre-
cyclophanes 8a, 9a, 9b, 10a, and 10b were synthesized by
the reaction of 1.0 equiv of 7a–b with 2.5 equiv of cate-
Semi empirical energy minimization calculations using
the MOPAC (AM1) method were carried out for the
syn and anti isomers of fluorenophane 1a. The heat of
R
R
R
R
i
O
ii
O
4a R = C2H5
4b R = C7H15
Br
Br
HO
OH
7a R = C2H5
7b R = C7H15
11a R = C2H5
11b R = C7H15
Scheme 2. Reagents and conditions: (i) S-Binol, K2CO3, dry acetone, rt, 48 h, 11a (58%), 11b (62%); (ii) 7a/7b K2CO3, dry acetone, high dilution
condition, rt, 120 h, 4a (21%), 4b (18%).

P. Rajakumar, R. Kanagalatha / Tetrahedron Letters 48 (2007) 2761–2764
2763
R
R
R
R
5a R = C2H5
5b R = C7H15
iii
i
O
E
O
E
Br
Br
7a R = C2H5
7b R = C7H15
12a R = C2H5
12b R = C7H15
E = CO2Et
ii
13a R = C2H5
13b R = C7H15
E = CH2OH
Scheme 3. Reagents and conditions: (i) 6, K2CO3, dry DMF, 60 °C, 48 h, 12a (82%), 12b (87%); (ii) LAH, THF, 60 °C, 12 h, 13a (68%), 13b (71%);
(iii) 7a/7b NaH, THF, 60 °C, 12 h, 5a (32%), 5b (27%).
formation of the syn isomer of 1a is 8.165 kcal molꢀ1
,
while that of the anti isomer is 8.901 kcal molꢀ1 (Figs.
1 and 2). Thus the syn isomer is more stable than the anti
isomer and hence formation of the syn isomer is more
1
favored than the anti isomer. The H NMR spectrum
of the syn isomer of 1a shows a sharp singlet at d 5.30
for the O-methylene protons. If the anti isomer of 1a
had been obtained there would have been two singlets
and the chemical shifts of the O-methylene protons
would also have been different.
All the fluorenophanes showed UV–vis absorption max-
ima at 301–310 nm. The photoluminescence emission
spectra of the fluorenophanes show typical vibronically
structured bands comprising a maximum, a shoulder
and a tail at 400, 425, and 460 nm, 410, 420, and
450 nm, and 380, 430, and 460 nm, for 1a, 1b, and 4a,
respectively.
Figure 2. The heat of formation of the anti isomer of fluorenophane 1a
is 8.901 kcal molꢀ1
.
The results obtained in the present study reveal that the
conformational properties of the 2,7-bridged fluoreno-
phanes depend on the molecular structure, especially
that of the polynuclear aromatic components as well
as the length of the alkyl chain. The bathochromic shift
of the fluorenophanes originated from transannular
interactions between the two aromatic components.
The fluorenophanes described herein exhibited a charac-
teristic behavior that might be due to efficient energy
Dibromide 7a shows weaker fluorescence when com-
pared to 7b. Because of the increasing alkyl chain length
a slight increase in the emission was observed at 352 nm.
The photoluminescence emission of fluorenophanes 1a,
1b, and 4a exhibited red shifts (bathochromic shift) of
about 68, 68, and 78 nm, respectively (Fig. 3).
Figure 1. The heat of formation of the syn isomer of fluorenophane 1a
Figure 3. Photoluminescence spectrum of fluorenophanes 1a, 1b, and
4a.
is 8.165 kcal molꢀ1
.

2764
P. Rajakumar, R. Kanagalatha / Tetrahedron Letters 48 (2007) 2761–2764
J = 7.32 Hz, 4H); 4.75 (s, 4H); 6.43 (d, J = 8.8 Hz, 4H);
6.56 (d, J = 8.8 Hz, 4H); 7.01–7.38 (m, 6H); 8.36 (s, 2H,
exchangeable with D2O): 13C NMR (100 MHz, CDCl3): d
56.0, 71.4, 116.3, 119.6, 122.2, 122.8, 126.4, 126.7, 127.0,
135.9, 141.1, 152.9; Mass 466 (M+ 466). Elemental Anal.
Calcd for C31H30O4: C, 79.83; H, 6.44. Found: C, 79.68;
H, 6.37.
transfer from the fluorene moiety to the aromatic
component.
Acknowledgements
The authors thank CSIR, New Delhi, for financial assis-
tance and RSIC, IIT Madras, for recording NMR spec-
tra. R.K. thanks CSIR, New Delhi, for the award of
SRF.
1
11. Precyclophane 10b: Yield 58%; mp 111–118 °C; H NMR
(400 MHz, CDCl3): d 0.71 (t, J = 7.1 Hz, 6H); 1.06–1.18
(m, 20H); 1.84–1.88 (m, 4H); 5.00 (s, 4H); 6.67 (d,
J = 8.8 Hz, 4H); 6.80 (d, J = 8.8 Hz, 4H); 7.23–7.61 (m,
6H); 8.24 (s, 2H, exchangeable with D2O): 13C NMR
(100 MHz, CDCl3): d 14.0, 22.5, 23.7, 28.6, 29.9, 31.7,
40.2, 54.9, 71.4, 119.6, 119.6, 122.8, 124.0, 126.2, 126.6,
127.0, 135.9, 140.9, 151.0; (QIP-MS) 606 (M+ 606).
Elemental Anal. Calcd for C41H50O4: C, 81.18; H, 8.25.
Found: C, 81.01; H, 8.18.
References and notes
1. (a) Vogtle, F. Supramolecular Chemistry; Wiley: Chiches-
ter, 1989; (b) Diederich, F. Cyclophanes; The Royal
Society of Chemistry: Cambridge, 1991; (c) Vogtle, F.
Cyclophane Chemistry; Wiley: Chichester, 1899.
2. Tsuge, A.; Ueda, Y.; Araki, T.; Moriguchi, T.; Sakata, K.;
Koya, K.; Mataka, S.; Tashiro, M. J. Chem. Res. (S)
1997, 168.
12. Cyclophane 3a: Yield 19%; mp 132–137 °C; 1H NMR
(500 MHz, CDCl3): d 0.31 (t, J = 6.8 Hz, 12H); 2.02 (q,
J = 6.1 Hz, 8H); 5.07 (s, 8H); 6.93–7.32 (m, 12H); 7.69 (d,
J = 7.6 Hz, 8H): 13C NMR (100 MHz, CDCl3): 8.6, 32.7,
52.0, 72.3, 101.4, 116.2, 119.9, 122.1, 123.4, 126.3, 126.9,
133.6, 139.2, 157.6; (QIP-MS) 712 (M+ 712). Elemental
Anal. Calcd for C50H48O4: C, 84.26; H, 6.74. Found: C,
84.12; H, 6.60.
3. Tsuge, A.; Araki, T.; Noguchi, Y.; Yasutake, M.; Mori-
guchi, T.; Sakata, K. Chem. Lett. 1998, 603.
4. (a) Belfield, K. D.; Bondar, M. V.; Morales, A. R.; Yavuz,
O.; Przhonska, O. V. J. Phys. Org. Chem. 2003, 16, 194–
201; (b) Geng, Y.; Chen, A. C. A.; Ou, J. J.; Chen, S. H.
Chem. Mater. 2003, 15, 4352–4360; (c) Son, S. W.; Jung, S.
H.; Cho, H. N. Synth. Met. 2003, 137, 1065–1066.
5. (a) Perepichka, D. F.; Bryce, M. R.; Perepichka, I. F.;
Lyubchik, S. B.; Christensen, C. A.; Godbert, N.; Batsa-
nov, A. S.; Levillain, E.; McInnes, E. J. L.; Zhao, J. P. J.
Am. Chem. Soc. 2002, 124, 14227–14238; (b) Omereq, B.;
Grasso, C.; Maldonado, J. L.; Halik, M.; Barlow, S.;
Marder, S. R.; Kippelen, B. J. Phys. Chem. B 2004, 108,
8647–8651.
13. Cyclophane 3b: Yield 16%; mp 102–107 °C; 1H NMR
(400 MHz, CDCl3): d 0.78 (t, J = 11.2 Hz, 12H); 1.04–1.26
(m, 40H); 1.96 (t, J = 8.4 Hz, 8H); 5.08 (s, 8H); 6.93–7.37
(m, 12H); 7.68 (d, J = 7.6 Hz, 8H); (QIP-MS) 992 (M+
992). Elemental Anal. Calcd for C70H88O4: C, 84.67; H,
8.87. Found: C, 84.56; H, 8.97.
25
14. Chiral cyclophane 4b: Yield 18%; mp 169–172 °C; ½aꢁD
1
ꢀ118 (c, 0.2, CHCl3); H NMR (400 MHz, CDCl3): d 0.8
(t, J = 7.32 Hz, 12H); 0.92–1.24 (m, 40H); 1.84 (m, 8H);
5.15 (s, 8H); 6.92–8.09 (m, 36H): 13C NMR (100 MHz,
CDCl3): d 14.2, 22.7, 23.7, 29.0, 30.9, 40.3, 54.9, 71.6,
116.0, 119.2, 119.6, 121.2, 122.8, 123.9, 126.5, 126.9, 127.0,
128.1, 129.4, 129.6, 134.3, 136.3, 140.9, 151.0; (QIP-MS)
1344 (M+ 1344). Elemental Anal. Calcd for C98H104O4: C,
86.43; H, 7.73. Found: C, 86.22; H, 7.51.
6. Burgi, L.; Richards, T. J.; Friend, R. H.; Sirringhaus, H. J.
Appl. Phys. 2003, 94, 6129–6137.
7. Gaylor, B. S.; Heeger, G. C. J. Am. Chem. Soc. 2003, 125,
896–900.
8. Belfield, K. D.; Hagan, D. J.; Van Stryland, E. W.;
Schafer, K. J.; Negres, R. A. Org. Lett. 1999, 1575–1578.
9. Tsuge, A.; Yamasaki, T.; Moriguchi, T.; Matsuda, T.;
Nagano, Y.; Nago, H.; Mataka, S.; Kajigaeshi, S.;
Tashiro, M. Synthesis 1993, 205.
15. Cyclophane 5a: Yield 32%; mp 152–158 °C; 1H NMR
(400 MHz, CDCl3): d 0.02 (t, J = 7.2 Hz, 12H); 1.70–1.74
(m, 8H); 4.19 (s, 8H); 4.46 (s, 4H); 6.94–7.43 (m, 20H):
(QIP-MS) 740 (M+ 740). Elemental Anal. Calcd
for C52H52O4: C, 84.32; H, 7.03. Found: C, 84.11; H,
6.93.
1
10. Precyclophane 10a: Yield 50%; mp 148–150 °C; H NMR
(400 MHz, CDCl3): d 0.32 (t, J = 7.34 Hz, 6H); 1.70 (q,