Near-infrared solid-state fluorescent naphthooxazine dyes attached with bulky dibutylamino and perfluoroalkenyloxy groups at 6- and 9-positions

Article abstract of DOI:10.1016/j.tetlet.2008.12.081

No solid-state fluorescence is observed for 9-(diethylamino)benzo[a]phenoxazin-5-one (Nile Red). However, 9-dibutylamino-6-{perfluoro[4-methyl-3-(1-methylethyl)-2-penten]-2-oxy}benzo[a]phenoxazin-5-one showed fluorescence maximum at 717 nm in solid state

Full text of DOI:10.1016/j.tetlet.2008.12.081

Tetrahedron Letters 50 (2009) 1131–1135
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Near-infrared solid-state fluorescent naphthooxazine dyes attached with bulky
dibutylamino and perfluoroalkenyloxy groups at 6- and 9-positions
So-Yeon Park a, Yasuhiro Kubota a, Kazumasa Funabiki a, Motoo Shiro b, Masaki Matsui a,
*
a Department of Materials Science and Technology, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan
b X-ray Research Laboratory, Rigaku Corporation, 3-9-12 Matubara-cho, Akishima, Tokyo 196-8666, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
No solid-state fluorescence is observed for 9-(diethylamino)benzo[a]phenoxazin-5-one (Nile Red). How-
ever, 9-dibutylamino-6-{perfluoro[4-methyl-3-(1-methylethyl)-2-penten]-2-oxy}benzo[a]phenoxazin-
5-one showed fluorescence maximum at 717 nm in solid state with fluorescence quantum yield 0.024.
Received 18 November 2008
Revised 11 December 2008
Accepted 17 December 2008
Available online 24 December 2008
X-ray crystallographic analysis suggests that prevention of network
rine-containing and dibutylamino groups is essential to show solid-state fluorescence.
Ó 2009 Elsevier Ltd. All rights reserved.
p
Àp interactions by the bulky fluo-
Keywords:
Solid-state fluorescence
Naphthooxazine dye
X-ray crystallography
Perfluoropropylene trimer
Perfluoropropylene dimer
Survey of solid-state fluorescence of organic compounds is one
of the most exciting subjects in connection with emitters in organ-
ic electroluminescence (EL) devices1 and—solid-state organic dye
laser.2 7-(Diarylamino)-4-methylcoumarins,3 ter(9,9-diarylfluo-
rine-containing substituents are much more bulky than the corre-
sponding fluorine-free ones, introduction of fluorine-containing
group(s) into fluorophores is very effective to depress intermolec-
ular interactions between the molecules. It is clear that perflu-
oro[4-methyl-3-(1-methylethyl)-2-penten-2-oxy] group derived
from perfluoropropylene trimer, in which two perfluoro(isopropyl)
and one trifluoromethyl groups are contained in a molecule, is
much more bulky than well-known and usually-used tert-butyl
group. No application of bulky perfluoroalkenyloxy-containing
compounds for advanced materials has been reported so far. We
thought that introduction of this bulky fluorine-containing group
into naphthooxazine dye might be effective to prevent its intermo-
lecular interactions. We report herein NIR solid-state fluorescent
naphthooxazine dyes.
9-(Dialkylamino)benzo[a]phenoxazin-5-ones 14–20 were pre-
pared as shown in Scheme 1. 5-Dialkylamino-2-nitrosophenol
hydrochloric acid salts 1 and 2 were allowed to react with naph-
thalenediols 3–5 to give the corresponding hydroxy-substituted
naphthooxazine intermediates 6–9. Then, compounds 6–9 were al-
lowed to react with perfluoropropylene trimer 10, a 1:2 mixture of
[(F3C)2FC]2C@CF(CF3) and [(F3C)2FC](F3CF2C)C@C(CF3)2, in the
presence of sodium hydride to give 14–17. The former isomer more
smoothly reacts with phenoxide ions than the latter one to give a
perfluoro(vinylether) product.18 Compound 9 was allowed to react
with perfluoropropylene dimer 11 to give 18 in a 37% yield. Com-
pound 9 also reacted with butyl iodide (12) and 3,5-(di-tert-butyl)-
benzyl bromide (13) in the presence of potassium carbonate and
16-crown-6-ether to give 19 and 20, respectively. Compounds 21
renes)s,4 diphenylanthrazolines,5 ,b-dicyanostilbenes,6 diketopyr-
a
rolopyrroles,7 9,10-disubstituted anthracenes,8 bisazomethine
dye,9 heterocyclic quinol-type compounds,10 perylenediimides,11
and dipyroroboradiazaindacenes12 have been reported to show so-
lid-state fluorescence. A few reddish solid-state fluorescent com-
pounds
such
as
4,7-di(2-thienyl)benzothiadiazoles,13
fumaronitriles,14 3,6-dicyanopyrazines,15 and 2,3-dicyano-6H-1,4-
diazepins16 have been reported. However, no near-infrared solid-
state fluorescent compounds have been reported so far. To our
knowledge, the most bathochromic solid-state fluorescent com-
pound is 4-(dicyanomethylene)-4H-pyran derivative, there being
the fluorescence maximum (Fmax) 695 nm.17 Near-infrared (NIR)
solid-state fluorescent compounds have potential application in
the field of security technology.
Nile Red is a traditional neutral naphthooxazine dye showing
medium fluorescence in solution (fluorescence quantum yield
(Uf) = 0.59 in ethanol). However, Nile Red does not show fluores-
cence in solid state. The excited state in condensed and crystalline
states is deactivated by strong intermolecular interactions. There-
fore, introduction of bulky substituent(s) into fluorophores is good
methodology to improve solid-state fluorescence intensity. As fluo-
* Corresponding author. Tel.: +81 59 293 2601; fax: +81 58 293 2794.
E-mail address: matsui@apchem.gifu-u.ac.jp (M. Matsui).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.12.081

1132
S.-Y. Park et al. / Tetrahedron Letters 50 (2009) 1131–1135
OH
7
1
2000
1000
0
6
OH
3
0.8
0.6
0.4
0.2
0
16
15
22
2
15
16
21
17
14
18
22
19
21
OH
3-5
N
O
NO
OH
2
HCl
R12N
14
i
17
R12N
O
9
18
6
20
6: R1 = Et, 6-OH
7: R1 = Bu, 2-OH
8: R1 = Bu, 3-OH
9: R1 = Bu, 6-OH
1: R1 = Et
2: R1 = Bu
3: 2-OH
4: 6-OH
5: 7-OH
20
19
400
500
600
700
800
Wavelength / nm
OR2
3
2
Figure 1. UV–vis absorption and fluorescence spectra of 14–22 in dichloromethane
measured at the concentration of 1.0 Â 10À5 mol dmÀ3 at 25 °C. Solid and dotted
lines represent UV–vis absorption and fluorescence spectra, respectively.
N
R2X
ii or iii
R12N
O
O
9
6
14: R1 = Et, R2 = 6-(F3C)C=C[CF(CF3)2]2
15: R1 = Bu, R2 = 2-(F3C)C=C[CF(CF3)2]2
16: R1 = Bu, R2 = 3-(F3C)C=C[CF(CF3)2]2
17: R1 = Bu, R2 = 6-(F3C)C=C[CF(CF3)2]2
18: R1 = Bu, R2 = 6-(F5C2)C=C(CF3)2
19: R1 = Bu, R2 = 6-Bu
10: R2X = (F3C)FC=C[CF(CF3)2]2
11: R2X = (F5C2)FC=C(CF3)2
12: R2X = BuI
cients (
e
) of 14–22 were observed in the range of 54,800–
there being no significant difference
61,900 dm3 molÀ1 cmÀ1
,
among them. The Fmax was more bathochromic in the order of
compound: 17 (632 nm), 18 (631), 20 (630), 19 (627), 14
(625) > 16 (614), 15 (613) > 22 (608), 21 (604). This result is attrib-
uted to slightly large Stokes shift of 19 and 20. The Uf was larger in
the order of compound: 21 (0.87), 22 (0.87) > 16 (0.76), 15 (0.74),
17 (0.69), 18 (0.66), 14 (0.56) > 20 (0.12), 19 (0.11). Thus, 6-unsub-
stituted derivatives showed the most intense fluorescence fol-
lowed by perfluoro(alkenyloxy) and alkoxy derivatives in
solution. Low Uf of 19 and 20 may come from free rotation of
the flexible alkoxy linkage in solution.
13: R2X = BrCH2(3,5-di-t-BuC6H3)
20: R1 = Bu, R2 = 6-CH2(3,5-di-t-BuC6H3)
N
R12N
O
O
21: R1 = Et
22: R1 = Bu
Scheme 1. Reagents and conditions: (i)
1 (1.0 equiv) or 2 (1.0 equiv), 3–5
(1.0 equiv), reflux, 4 h, DMF, (ii) 6–9 (1.0 equiv), 10 (2.5 equiv) or 11 (2.5 equiv),
NaH (1.0 equiv) or TEA (1.0 equiv), rt, DMF, 2–18 h, iii) 9 (1.0 equiv), 12 (2.5 equiv)
or 13 (2.5 equiv), K2CO3 (1.0 equiv), 18-crown-6-ether, rt, 10 h.
2000
(Nile Red) and 22 were also prepared as described in the litera-
ture.19 The detailed procedure for the synthesis of 14–22 is shown
in Supplementary data.
17
The UV–vis absorption and fluorescence spectra of naphthoox-
azine dyes in dichloromethane are shown in Figure 1. The results
are also listed in Table 1. The absorption maximum (kmax) of napht-
hooxazine dyes was more bathochromic in the following order of
compound: 17 (574 nm), 18 (573), 14 (569) > 20 (551), 19
(547) > 22 (543), 21 (538). Thus, introduction of perfluoro(alkenyl-
oxy) and alkoxy group caused bathochromic shift due to less stable
HOMO energy level. 6-Perfluoro(alkenyloxy) derivative 17 (574)
was more bathochromic than the 2- and 3-perfluoro(alkenyloxy)
derivatives 15 (558) and 16 (557). The molar absorption coeffi-
1000
stray light
18
19
0
500
600
700
800
900
Wavelength / nm
Figure 2. Fluorescence spectra of 14–22 in solid state. kex was obtained by
measuring diffusion reflection spectra given in Kubelka–Munk Units.
Table 1
Optical properties of naphthooxazine dyes
Run
Compd
Dichloromethanea
Solid stated
b
b
kmax
(
e) (nm)
Fmax (nm)
Uf
SSc (nm)
Fmax (nm)
Uf
e
e
1
2
3
4
5
6
7
8
9
14
15
16
17
18
19
20
21
22
569 (58,600)
558 (61,400)
557 (61,900)
574 (58,000)
573 (54,800)
547 (60,800)
551 (58,900)
538 (61,000)
543 (60,700)
625
613
614
632
631
627
630
604
608
0.54
0.74
0.76
0.69
0.66
0.11
0.12
0.87
0.87
56
55
57
60
58
80
79
66
65
—
—
734
729
717
727
666
0.008
0.007
0.024
0.015
0.010
e
e
—
—
—
—
e
e
—
e
e
—
Measured at the concentration of 1.0 Â 10À5 mol dmÀ3 at 25 °C.
a
b
c
Determined by a Hamamatsu Photonics Absolute PL Quantum Yield Measurement System C9920-02.
Stokes shift.
d
e
Excitation wavelength (kex) was obtained by measuring diffuse reflectance spectra given in Kubelka–Munk units.
Too weak (Uf < 0.003).

S.-Y. Park et al. / Tetrahedron Letters 50 (2009) 1131–1135
1133
Figure 3. X-ray crystallographic analysis of 22.
The fluorescence spectra of 14–22 in solid state are shown in
Figure 2. The results are also listed in Table 1. No clear solid-
state fluorescence was observed for 14, 15, 16, 20, 21, and 22.
Interestingly, compounds 17 and 18, in which a bulky perflu-
oro(alkenyloxy) group is attached at the 6-position, showed Fmax
at around 717 and 727 nm with Uf 0.024 and 0.015, respectively.
The Fmax of 17 in solid state and in dichloromethane were ob-
served at 717 and 632 nm with half-wavelength of 90 and
Figure 4. X-ray crystallographic analysis of 14.

1134
S.-Y. Park et al. / Tetrahedron Letters 50 (2009) 1131–1135
Figure 5. X-ray crystallographic analysis of 17.
54 nm, respectively. Thus, the solid-state fluorescence spectra
were more bathochromic and broad compared with those in
dichloromethane due to the intermolecular interactions.
To examine the difference of fluorescence intensity of napht-
hooxazine dyes 14–22 in solid state, the X-ray crystallographic
analysis of 14, 17, and 22 was performed.20
Figure 3 shows the X-ray crystallography of 22. In this case,
compound is arranged as a herring-bone fashion. Figure 3b
shows that molecules A and B are located almost in the same
plane. Molecules C and D are packed almost in perpendicular
Compound 17 is arranged as slipped parallel. A pair of
head-to-tail dimers is formed in the crystalline, being similar
to molecular packing of 14. Molecule A is surrounded by B, C,
D, E, and F as shown in Figure 5b. Molecule B is arranged in
parallel to A. There are two
p–p and two CH/p interactions be-
tween A and B, there being the interplanar distance 3.395 Å.
Molecules C and D are also located in parallel for A. The inter-
planar distance between A and D is 5.702 Å, being too long to
have
between A and B as shown in Figure 5c. Figure 5d shows
that no overlapping is observed between A and C. One of
butyl groups of dibutylamino group at the 9-position in
can act as steric moiety for adjacent naphthooxiazine
molecule.
p–p interactions. Strong p-p overlapping is observed
for A. There are six CH/O and four CH/
p
interactions between
p–p
A and B. CH/N interactions are observed between A and C and
A and D. Figure 3c indicates that molecules A, E, and F are ar-
ranged toward the same direction. The interplanar distance
A
a
among A, E, and F is 3.344 Å. Strong
among A, E, and F as shown in Figure 3d. Thus, compound 22
has strong network stacking.
p
–
p
overlapping is observed
9-Dibutylamino-6-{perfluoro[4-methyl-3-(1-methylethy-l)-2-
penten]-2-oxy}benzo[a]phenoxazin-5-one showed solid-state
fluorescence at near-infrared region (717 nm) with Uf 0.024,
whereas well-known naphthooxazine dye, Nile Red, does not
show fluorescence in the solid state. X-ray crystallographic anal-
p–p
In the case of compound 14, a pair of head-to-tail dimer is
formed and is arranged as slipped parallel. 6-{Perfluoro[4-
methyl-3-(1-methylethyl)-2-penten]-2-oxy} group at the 6-posi-
tion inhibits CH/O intermolecular interactions between adjacent
naphthooxazine rings. Figure 4b shows that molecule A is sur-
rounded by B, C, D, E, F, and G. Molecules A, D, and G are located
almost in the same plane. CH/F interactions are observed among
A, D, and G. Molecules A, B, and C are arranged in parallel. CH/F
ysis suggests that absence of network
p–p stacking that comes
from both bulky dibutylamino group at the 9-position and per-
fluoro(alkenyloxy) group at the 6-position is essential to show
solid-state fluorescence. This is the first report of NIR solid-state
fluorescent organic dyes.
interactions are observed between A and B. CH/p interactions are
observed between A and C. The interplanar distance between A
Supplementary data
and B and A and C are 3.540 and 3.418 Å, respectively. Figure
Supplementary data (detailed synthetic procedure of 14–22)
associated with this article can be found, in the online version, at
doi:10.1016/j.tetlet.2008.12.081.
4c depicts that molecule A has strong
Figure 4d also shows that molecule A has
C. Thus, compound 14 has network packing.
p
–p
overlapping with B.
interactions for
p–p

S.-Y. Park et al. / Tetrahedron Letters 50 (2009) 1131–1135
1135
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20. Single crystals were obtained by recrystallization from ethanol. The
diffraction data were collected by using graphite monochromated Mo
K
a
radiation (k = 0.71069 Å). The structure was solved by direct methods SIR97,
and refined by fill-matrix least-squares calculations. Crystal data for 14:
ꢀ
C29H17F17N2O3, Mw = 764.45, triclinic, P1, Z = 2, a = 8.099(6), b = 12.090(11),
c = 15.545(19) Å,
a
= 90.88(10)°,
b = 94.02(8)°,
c
= 93.35(7)°,
Dcalcd = 1.675 g cmÀ3
,
T = 296(2) K, F(000) = 764,
l
= 1.629 mmÀ1
,
11,989
reflections were corrected, 4811 unique (Rint = 0.0669). 4811 observed
(I > 2 (I)), 536 parameters, R1 = 0.0849, wR2 = 0.2257. Crystal data for 17:
C33H25F17N2O3, Mw = 820.55, triclinic, P1, Z = 2, a = 820.55, b = 11.169(6),
c = 17.207(9) Å, 90.407(9), b= 96.418(8), = 92.857(8)°, Dcalcd = 1.633 g
cm-3 0.169 mm-1
T = 123(2) K, F(000) = 828, 13667 reflections were
corrected, 7583 unique (Rint = 0.0359). 7583 observed (I (I)), 513
parameters, R1 = 0.0732, wR2 = 0.1254. Crystal data for 22: C24H26N2O2,
Mw = 374.48, monoclinic, P21/n, Z = 2, a = 8.747(5), b = 11.169(6),
= 90.407(9)°, b = 96.418(8)°, = 92.857(8)°,
T = 123(2) K, F(000) = 828, 13,667
= 0.169 mmÀ1
r
ꢀ
a=
c
,
l=
,
>
2r
c = 17.207(9) Å,
a
c
Dcalcd = 1.633 g cmÀ3
,
l
,
reflections were corrected, 7583 unique (Rint = 0.0359). 7583 observed
(I > 2 (I)), 513 parameters, R1 = 0.0732, wR2 = 0.1254. Crystallographic data
r
14 (CCDC 704025), 17 (CCDC 704026), and 22 (CCDC 705404)) have been
deposited at the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK.
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