Functionality of fluorine-containing dyes

Article abstract of DOI:10.1016/S0022-1139(98)00323-6

The introduction of a perfluoroalkyl moiety into dye molecules changes the properties of the compounds. The 4-perfluoroalkyl disazo dyes were more soluble in hexane and showed a better dichroism than the alkyl analogs. A novel methacrylate copolymer with

Full text of DOI:10.1016/S0022-1139(98)00323-6

Journal of Fluorine Chemistry 96 (1999) 65±69
Functionality of ¯uorine-containing dyes
Masaki Matsui*
Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan
Received 20 October 1997; accepted 7 April 1998
Abstract
The introduction of a per¯uoroalkyl moiety into dye molecules changes the properties of the compounds. The 4-per¯uoroalkyl disazo
dyes were more soluble in hexane and showed a better dichroism than the alkyl analogs. A novel methacrylate copolymer with a pendant
naphthylene disazo dye containing a per¯uorobutylsulfonyl group showed a slow relaxation behavior after corona poling. 7-Diethylamino-
4-methyl-3-(per¯uoroalkyl)coumarins were more stable than the non-per¯uoroalkylated derivatives to UV irradiation. # 1999 Elsevier
Science S.A. All rights reserved.
Keywords: Per¯uoroalkyl dyes; Per¯uorobutylsulfonyl dyes; Azo dyes; Coumarins; Functional dyes
1. Perfluoroalkyl derivatives of soluble and rigid
dichroic dyes for guest±host liquid crystal displays
calculated to be 0.76. For the practical use as dichroic
dyes, the S value is required to be larger than 0.70. The S
values of selected disazo dyes are indicated in Table 1. The
dichroism increased with the substituent: per¯uorooctyl>
per¯uorohexyl>per¯uorobutyl>butyl, showing that the long
and rigid per¯uoroalkyl group could be successfully used to
increase dichroism. All the derivatives showed a good
dichroism (S>0.70), and could be used as practical dichroic
dyes.
Linear polyazo and anthraquinone dyes bearing long alkyl
chain(s) have been used as dichroic dyes [1]. It is anticipated
that the introduction of per¯uoroalkyl groups into disazo
dyes will induce a high solubility in organic solvents and
host liquid crystals due to the weak intermolecular interac-
tions and a high dichroism because of the rigidity of the
per¯uoroalkyl moiety. The synthesis and application of
disazo dyes containing a per¯uoroalkyl moiety to guest±
host liquid crystal displays have been examined.
The synthesis of per¯uoroalkyl-containing disazo dyes is
indicated in Scheme 1. The condensation reaction of anilines
with 4-nitrosonitrobenzene afforded the 4-nitroazoben-
zenes, which were reduced by sodium sul®de to give the
4-(arylazo)anilines, followed by diazotization-coupling
reaction to form the desired disazo dyes.
The solubility of the disazo dyes in hexane is indicated in
Table 1. The per¯uoroalkyl derivatives were more soluble
than the unsubstituted, the alkyl, the alkylthio, and the
per¯uoroalkylthio analogs. The highest solubility was
obtained for the per¯uorobutyl and the per¯uorohexyl deri-
vatives. The poor solubility of the per¯uorooctyl derivative
was attributed to the low lipophilicity of the long-chain
per¯uoroalkyl substituent.
2. Perfluorobutylsulfonyl-containing disazo dyes as
enhanced and improved second-order nonlinear
optical chromophores (NLOphores)
A large second-order optical nonlinearity is observed with
NLOphores bearing terminal-strong electron-withdrawing
and donating groups at both the ends of the molecule
separated by a ꢀ-electron conjugated system [2]. The strong
electron-withdrawing nature of the per¯uoroalkylsulfonyl
group (ꢁp (CF3SO2)ˆ0.93, ꢁp (NO2)ˆ0.78) can enhance
the nonlinearity. The improvement of the relaxation beha-
vior of the NLOphore after corona poling is also important.
These facts led us to examine the second-order optical
nonlinearity of a novel methacrylate polymer with a pendant
per¯uorobutylsulfonyl-substituted naphthylene disazo
NLOphore.
A typical dichroic spectrum of the disazo dye is shown in
Fig. 1. The order parameter (S), de®ned by equation 1, was
The synthesis of copolymer P1 is shown in Scheme 2.
The diazotization-coupling reaction of 4-(per¯uorobutyl-
sulfonyl)aniline with 1-naphthylamine gave the monoazo
*Fax: +81-58-230-1893; e-mail: matsui@apchem.gifu-u.ac.jp
0022-1139/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ( 9 8 ) 0 0 3 2 3 - 6

66
M. Matsui / Journal of Fluorine Chemistry 96 (1999) 65±69
Scheme 1.
intermediate in moderate yield. By using an acetone±
ethanol±water system as the reaction medium, the NLO-
phore 1 was obtained in 30% yield. The copolymer P1 was
prepared by radical polymerization reaction using azobisi-
sobutyronitrile (AIBN) as a radical initiator. The copolymer
P2 was also prepared by the same procedure.
The physical and NLO properties of the copolymers P1
and P2 are summarized in Table 2. The glass transition
temperatures (Tg's) for both the copolymers were similar.
The copolymer P1 was more bathochromic than P2, due
to the per¯uorobutylsulfonyl and naphthylene moieties in
the NLOphore 1.
The second harmonic generation (SHG) of the poled
polymer ®lms was measured using a rotational Maker fringe
method at a fundamental wavelength of 1064 nm using an
Nd:YAG laser. The second-order nonlinear optical coef®-
cient (d33) of the samples were compared with the d11 value
(0.33 pm V 1) of y-cut quartz and obtained by the curve-
®tting method as described in our previous report [3].
The copolymers P1 and P2 showed the d33 values of 20
and 15 pm V 1, respectively. As the absorption coef®cients
of both the copolymers P1 and P2 at 532 nm were similar,
the contribution of the resonance effect on the d33 values
seems to be similar. This suggests that the d33 values are
comparable.
Fig. 2 shows the changes in the absorption spectra of P1
®lm before and after corona poling (0 and 900 h) at 808C.
The absorbance at 544 nm decreased after corona poling
(0 h). After 900 h, the absorbance became similar to that
before corona poling. No change in the absorption max-
imum was observed. The decomposition temperature (Td) of
the NLOphore 1 was measured to be 2858C. These results
suggest that the NLOphore 1 is oriented by corona poling
and relaxed without decomposition.
The relaxation behavior of the oriented NLOphore is
indicated in Fig. 3. The ®lms were stored at 808C through-
out the measurements. The copolymers P1 and P2 showed a
slower relaxation than the poly(methyl methacrylate)
(PMMA) doped with the NLOphore 1 because of lower
mobility of the NLOphore in the chemically bonded co-
Table 1
Physical properties of disazo dyes
a
RfX
ꢂmax
(nm)
Solubilityb
(mmol dm
S a
3
)
H
491
491
507
504
510
499
509
511
507
0.48
1.84
3.86
3.67
1.70
0.54
0.92
0.88
0.27
0.71
0.75
0.76
0.78
0.79
0.76
0.76
0.78
0.76
C4H9
C4F9
C6F13
C8F17
C4H9S
C4F9S
C6F13
S
C8F17
S
a Measured in ZLI-4792.
b Measured in hexane at 258C.
Fig. 1. Order parameters (S) of disazo dyes.

M. Matsui / Journal of Fluorine Chemistry 96 (1999) 65±69
67
Scheme 2.
polymers. The copolymer P1 was more stable than P2. This
3. Photostable 3-(perfluoroalkyl)coumarins
can be attributed to the longer conjugated aromatic skeleton
and to the rigidity of the per¯uorobutylsulfonyl moiety of
the NLOphore 1.
Fluorescent coumarins, where emission maxima range
from 400 to 600 nm, were used as laser dyes. Bis(per¯uoro-
Table 2
Physical and NLO properties of the copolymers P1 and P2
a
b
1
)
Copolymer
Mw
Tg (8C)
ꢂmax (nm)
Film thickness (mm)
Refractive index
d33 (pm V
532 nm
1064 nm
P1
P2
171 000
259 000
130
126
544
490
0.3
0.5
1.52
1.53
1.49
1.49
20
15
a Determined by gel permeation chromatography.
b DSC analysis (108C min 1, under an air atmosphere).

68
M. Matsui / Journal of Fluorine Chemistry 96 (1999) 65±69
Scheme 3.
Fig. 2. Change in the absorption spectra of P1 films before and after
corona poling.
alkanoyl) peroxides have been reported to act as ef®cient
per¯uoroalkylation reagents for electron-rich substrates [4].
The reaction of coumarins and quinolinone with the
bis(per¯uoroalkanoyl) peroxides afforded the 3-(per¯uor-
oalkyl) derivatives as shown in Scheme 3 and Table 3. The
yields were low with quinolinone (XˆNH), due to the low
solubility of the substrate. A single electron-transfer
mechanism from the substrates to the peroxides was pro-
posed for the per¯uoroalkylation reactions [4].
Fig. 4. Photostability of 7-diethylamino-4-methylcoumarins. An ethanol
solution (30 ml) of a coumarin (0.05 mol dm 3) in a borosilicate glass
tube was irradiated with a 200 W high pressure mercury lamp using a
merry-go-round apparatus in the presence of air at room temperature.
Both the absorption and the emission maxima of 3-
(per¯uoroalkyl) derivatives were more bathochromic than
those of the unsubstituted ones. This could be attributed to
the stronger electron-withdrawing nature of the lactone or
lactam moiety in the 3-(per¯uoroalkyl) derivatives. The
relative ¯uorescence intensity (RFI) decreased with the
introduction of the per¯uoroalkyl group.
3-(per¯uoroalkyl) substituent could inhibit the dimerization
and depress the photooxidation reactions of the 4-methyl
and 7-diethylamino moieties.
The photostability of 7-diethylamino-4-methylcoumarins
is shown in Fig. 4. It is clear that the 3-(per¯uoroalkyl)
derivatives are more stable than the unsubstituted one. The
4. Conclusion
Per¯uoroalkyl-substituted disazo dyes showed higher
solubility and better dichroism than alkyl derivatives. These
dyes could be used as practical dichroic dyes in guest±host
liquid crystal displays. Methacrylate copolymers with a
pendant disazo NLOphore containing a per¯uorobutylsul-
Table 3
Reaction of coumarins and quinolinone with bis(perfluoroalkanoyl)per-
oxides
a
a
X
R1
R2
Rf
Yield
(%)
ꢂex
(nm)
ꢂem
(nm)
RFIb
O
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
N(C2H5)2
N(C2H5)2
N(C2H5)2
N(C2H5)2
N(C2H5)2
N(C2H5)2
N(CH3)2
N(CH3)2
N(CH3)2
H
±
21
36
29
±
378
402
403
405
405
473
361
381
381
445
460
460
460
505
555
420
440
440
1.00
0.26
0.17
0.30
0.11
0.05
1.11
0.88
0.90
O
CF3
C3F7
C7F15
H
O
O
O
O
C3F7
H
24
±
NH
NH
NH
C3F7
C6F13
5
6
a Measured in ethanol.
b Measured in ethanol at 258C (substrate: 1Â10 6 mol dm 3).
Fig. 3. Relaxation behavior of the oriented NLOphore. The curve
represents the % retention (d33 (t)/d33) at 808C.

M. Matsui / Journal of Fluorine Chemistry 96 (1999) 65±69
69
fonyl group showed the d33 value of 20 pm V 1 and a slow
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The photostabilities of 7-diethylamino-4-methyl-3-(per-
¯uoroalkyl)coumarins were better than that of the unsub-
stituted one.
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