Preparation and characterization of bridged naphthoxazinium salts

Article abstract of DOI:10.1002/(SICI)1099-0690(199904)1999:4<923::AID-EJOC923>3.0.CO;2-N

By condensation of bridged 4-arylazo-substituted 3-hydroxyanilines 18 and bridged or unbridged 4-arylazo-substituted 1-naphthylamines 19-23 with bridged 1-naphthylamines 15-17 and 3-aminophenols 14, respectively, in the presence of perchloric acid, bridge

Full text of DOI:10.1002/(SICI)1099-0690(199904)1999:4<923::AID-EJOC923>3.0.CO;2-N

FULL PAPER
Preparation and Characterization of Bridged Naphthoxazinium Salts
Andreas Kanitz[a][°] and Horst Hartmann*[a]
Dedicated to Professor Karl Heinz Drexhage on the accasion of his 65th birthday
Keywords: Bridged benzo[a]phenoxazinium salts / Diazo compounds / Cyclocondensation / Absorption / Fluorescence
By condensation of bridged 4-arylazo-substituted 3-
hydroxyanilines 18 and bridged or unbridged 4-arylazo-
substituted 1-naphthylamines 19–23 with bridged 1-
naphthylamines 15–17 and 3-aminophenols 14, respectively,
in the presence of perchloric acid, bridged naphthoxazinium
perchlorates 24–30 have been prepared. The spectral
properties of the products have been compared with those of
the bridged phenoxazinium salt 31 as well as with data for
some unbridged analogues.
Few simple routes exist for the preparation of naphthox-
azinium salts 1. The majority of these starts from ni-
trosoanilines 5 or 11 or from nitrosonaphthylamines 8,
which are condensed with appropriate 1-naphthylamines 6
(route A), 3-aminophenols 7 (route B), or 2-naphthol 12
(route C), respectively, in the presence of a strong mineral
acid such as perchloric acid.[8] In the last case, monoamino-
substituted naphthoxazinium salts 13 are the initial prod-
ucts.[9] Subsequently, these compounds may be transformed
Introduction
Benzo[a]phenoxazinium salts (naphthoxazinium salts) of
the general structure 1 possess several interesting properties.
For example, they exhibit an intense long-wavelength ab-
sorption at about 650 nm and a strong red fluorescence.[1]
Consequently, they have been utilized as dyestuffs for dye-
ing fibres and paper[2] and as laser dyes.[3] If one of their
terminal amino groups bears a free proton and is also sub-
stituted by a long fatty acid residue, they can be used as
sensor dyes in optodes for acid-base titrations.[4] This appli-
cation relies on the fact that they can be transformed by the
action of bases into naphthoxazine imines 2, which absorb
at considerably shorter wavelengths than their cationic
counterparts 1. Very recently, some naphthoxazinium dyes
have been employed as ultrasensitive indicators for biomo-
lecules.[5] Furthermore, it has also been reported that some
naphthoxazinium salts 1 are potentially useful as photosen-
sitizers in photodynamic cancer therapy[6] and as antituber-
colastatic or anticancerogenic agents.[7]
Scheme 1
[a]
Fachbereich Chemie der Fachhochschule Merseburg,
Geusaer Straße, D-06217 Merseburg, Germany
Fax: (internat.) ϩ 49(0)3461/462192
E-mail: Horst.Hartmann@cui.fh-merseburg.de
[°]
Current address: Siemens AG,
Paul-Gossen-Straße 100, D-91052 Erlangen, Germany
Scheme 2
Eur. J. Org. Chem. 1999, 923Ϫ930
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1434Ϫ193X/99/0404Ϫ0923 $ 17.50ϩ.50/0
923

A. Kanitz, H. Hartmann
FULL PAPER
into the naphthoxazinium salts 1 by reaction with amines
under the influence of an oxidizing agent. A further route D
starts from para-phenylenediamines 9, which are condensed
with 4-amino-substituted 1,2-naphthoquinones 10.[10]
The applicability of naphthoxazinium salts 1 is somewhat
restricted, however, owing to their sensitivity towards hy-
drolysis, which results in their conversion either to non-
ionic naphthoxazinones of structure 3, or, more probably,
to naphthoxazinones of structure 4.[11] Therefore, the syn-
thesis of naphthoxazinium salts that are more resistant to
hydrolysis would seem to be a worthwhile goal. In this re-
gard, anilines and 1-naphthylamines that have their amino
moieties incorporated into bridged structures should be
suitable starting compounds. The bridged amines 14Ϫ17
are examples of such compounds. However, these secondary
and tertiary amines cannot be transformed into the corre-
sponding nitroso derivatives by reaction with nitrous acid
under standard conditions. As we reported recently,[12] in
order to obtain the desired nitroso derivatives the starting
amines have to be transformed into various oxidation prod-
ucts, which cannot be used as building blocks for the syn-
thesis of naphthoxazinium salts. Hence, other routes of pre-
paring naphthoxazinium salts from the bridged anilines or
1-naphthylamines 14Ϫ17 would be desirable.
Results and Discussion
In 1890, procedures were developed at Bayer AG for pre-
paring naphthoxazinium salts 1 by heating arylazo-substi-
tuted aminophenols or naphthylamines with appropriate 1-
naphthylamines or aminophenols in high-boiling sol-
vents.[13] This reaction corresponds to routes A and B
above. Although this procedure, which starts from arylazo-
substituted precursors rather than the corresponding ni-
troso derivatives, has seemingly not been mentioned since
the 1890s, neither in the patent nor the scientific litera-
ture,[14] nor in textbooks,[15] we have found it to be well-
suited for transforming the bridged aniline and 1-naphthyl-
amine derivatives 14Ϫ17 into the corresponding bridged
naphthoxazine dyes. In order to carry out this reaction,
some modifications of the published methods[13] were, how-
ever, necessary. Thus, we used a dipolar aprotic solvent,
such as DMF, in place of the reported solvents (ethylene
glycol or glycerol); we used arylazo compounds substituted
with electron-accepting substituents on the arylazo moiety,
and added a strong mineral acid to the reaction mixture.
The desired arylazo compounds 18Ϫ23 were obtained
from the bridged aniline and 1-naphthylamine derivatives
14Ϫ17 as well as from unbridged 1-naphthylamine and 8-
Scheme 3
924
Scheme 4
Eur. J. Org. Chem. 1999, 923Ϫ930

Preparation and Characterization of Bridged Naphthoxazinium Salts
FULL PAPER
aminoquinoline by coupling these aromatic amines with an from the nitroso precursors 5, 8 and 11, the former is desig-
aryl diazonium salt in the standard manner.[16] Details of nated as route E, while the route starting from the bridged
all the azo compounds prepared in this way are presented and unbridged 4-arylazo-1-naphthylamine derivatives
in Table 1. Their structures were unambiguously confirmed 19Ϫ22 or from the 8-amino-5-arylazoquinoline 23 is desig-
on the basis of their analytical and some of their character- nated as route F.
istic spectroscopic data.
The successful use of arylazo compounds as starting ma-
Somewhat surprisingly, these azo compounds were read- terials for preparing unbridged and bridged naphthoxazin-
ily protonated in acidic solution and the absorption max- ium dyes 1 and 24؊30 can be rationalized by viewing the
ima of the resulting species proved to be strongly structure- azo moiety as an azomethine analogue of a nitroso group.
dependent. Thus, on going from neutral to acidic solutions, Hence, instead of the elimination of water that occurs dur-
hypsochromic as well as bathochromic shifts were observed, ing the condensation of nitroso compounds, a substituted
as is apparent from Table 1.
aniline group, which serves as a precursor of the azo com-
By treating the arylazo compounds 18Ϫ23 with the pound, is eliminated in the course of the naphthoxazinium
corresponding co-reagents lacking an azo group, 5, 6, 8, salt formation. This aromatic amine could be detected in
14, 15, and 17, in the presence of perchloric acid, the the reaction mixture by chromatography or isolated from it
bridged naphthoxazinium perchlorates 24Ϫ30 were pre- by adding aqueous base and extracting the resulting mix-
pared, in most cases in satisfactory yields. The sulfamido- ture with diethyl ether.
bridged naphthoxazinium salts 27 could only be isolated
as the free bases. The results achieved are presented in thoxazinium salts 24؊30 with those of their unbridged ana-
Table 2. logues 1, several such compounds were also prepared using
To allow comparison of the properties of bridged naph-
In order to differentiate the route starting from the methods A or B. Data relating to these are also collected in
bridged arylazophenol derivative 18 from those starting Table 2.
Table 1. Characterization of the diarylazo starting compounds 18Ϫ22
[a]
Compd. R
R3
R4
Yield M.p. [°C]
λmax (logε)
λ
max
(logε)[b] Emp. formula
calcd. C H
found
N
S
[%]
(ref. m.p.)
(mol. mass)
18
NO2
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
H
H
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
H
H
H
H
H
H
78
92
88
92
84
80
95
92
84
80
90
85
268Ϫ269
247Ϫ249
259Ϫ260
173Ϫ177
155Ϫ157
197Ϫ200
494 (4.74) 470 (4.71) C18H18N4O3
63.89 5.36
63.65 5.72
68.66 4.85
68.99 5.22
70.91 5.01
71.16 5.53
70.95 5.41
71.19 5.81
73.02 5.57
73.02 5.97
16.56
16.27
16.86
16.73
13.06
13.38
15.04
14.86
11.61
11.63
(338.4)
525 (4.65) 558 (4.35) C19H16N4O2
(332.4)
19a
19b
20a
20b
21b
22a
22b
22c
22d
22e
22f
22g
22h
22i
NO2
Cl
545 (4.64) 500 (4.46) C19H16N3Cl
(321.8)
NO2
Cl
544 (4.50) 577 (4.24) C22H20N4O2
(372.4)
558 (4.65) 512 (4.42) C22H20N3Cl
(361.9)
Cl
399 (4.27) 490 (4.33) C16H10N3O2SCl 55.90 2.93
12.22 9.33
12.19 9.17
19.17
(343.8)
56.11 3.41
65.75 4.14
65.53 4.42
68.21 4.29
68.56 4.51
66.66 4.61
66.52 5.05
69.04 4.77
68.98 5.08
67.49 5.03
67.29 5.40
69.79 5.21
69.76 5.73
67.49 5.03
67.86 5.50
66.08 4.38
66.04 4.78
65.01 5.46
65.02 5.83
61.87 4.06
61.54 3.96
63.37 4.16
63.52 4.50
61.43 3.78
61.57 4.27
63.72 3.92
64.05 4.41
NO2
Cl
253Ϫ255
(252)[21]
183Ϫ184
(187Ϫ188)[22]
180Ϫ182
522 (4.75) 520 (4.52) C16H12N4O2
(292.3)
18.86
539 (4.81) 458 (4.28) C16H12N3Cl
14.91
(281.7)
15.03
NO2 CH3
Cl CH3
NO2 C2H5
Cl C2H5
539 (4.63) 517 (4.34) C17H14N4O2
18.29
(306.3)
17.86
160Ϫ163
225Ϫ227
118Ϫ119
544 (4.67) 469 (4.42) C17H14N3Cl
14.21
(295.8)
13.95
531 (4.59) 530 (4.36) C18H16N4O2
17.49
(320.4)
17.20
547 (4.74) 475 (4.52) C18H16N3Cl
13.56
(309.8)
13.44
NO2 CH3
CH3 82
148Ϫ150
528 (4.61) 473 (4.24) C18H16N4O2
17.49
(156Ϫ157)[23]
213Ϫ213
(320.3)
17.46
NO2 (CH2)2CN
NO2 (CH2)5COOH
NO2 4-SO2C6H5CH3
H
H
H
H
H
H
85
80
82
78
94
80
528 (4.61) 509 (4.43) C19H15N5O2
20.28
(345.4)
20.54
204Ϫ206
208Ϫ209
191Ϫ192
198Ϫ200
180Ϫ182
532 (4.79) 536 (4.49) C22H22N4O4
13.78
(406.4)
410 (4.02) 542 ( 4.00) C23H18N4O4S
(446.5)
13.95
22j
12.55 7.81
12.73 7.41
22k
23a
23b
Cl
4-SO2C6H5CH3
393 (4.21) 477 (4.36) C23H18N3O2S
(435.9)
9.64
9.89
23.88
23.53
19.82
19.59
7.35
7.59
NO2
Cl
H
H
512 (4.61) 489 (4.37) C15H11N5O2
(293.3)
524 (4.49) 437 (4.33) C15H11N4Cl
(282.7)
[a]
[b]
Protonated species. Ϫ Unprotonated species.
Eur. J. Org. Chem. 1999, 923Ϫ930
925

A. Kanitz, H. Hartmann
FULL PAPER
Table 2. Characterization of the bridged phenoxazinium perchlorates 1 and 24؊31
Compd. R1
R2
R3
R4
Yield [%] Starting
(method) compd.
M. p. [°C]
Emp. formula
(mol. mass)
calcd.
C
found
H
N
S
1a
C2H5 C2H5
H
H
H
H
31 (A)
40 (A)
42 (A)
5 ؉ 6
5 ؉ 6
5 ؉ 6
5 ؉ 6
> 360
C20H20N3O5Cl 57.49 4.82
(417.9) 57.78 5.07
C21H22N3O5Cl 58.40 5.13
(431.9) 58.51 5.10
C22H24N3O5Cl 59.26 5.43
(445.9) 59.16 5.41
C22H24N3O5Cl 59.26 5.43
(445.9) 59.48 5.66
C22H20N3O5Cl 59.80 4.56
(441.9) 60.04 4.58
C23H22N3O5Cl 60.60 4.86
(455.9) 60.43 4.93
C24H24N3O5Cl 61.34 5.15
(462.9) 61.12 5.04
C24H24N3O5Cl 61.34 5.15
(462.9) 61.04 4.98
C25H23N4O5Cl 60.67 4.68
(494.9) 60.36 4.98
C28H30N3O7Cl 60.49 5.44
(556.0) 60.16 5.67
C30H34N3O7Cl 61.69 5.87
(584.1) 61.40 5.97
10.06
10.10
9.73
9.50
9.42
9.25
9.42
9.19
9.51
9.67
9.22
8.95
8.94
9.09
8.94
9.20
11.32
11.53
7.56
7.43
7.19
6.94
12.56
12.41
1b
C2H5 C2H5 CH3
C2H5 C2H5 C2H5
C2H5 C2H5 CH3
265Ϫ268
287Ϫ289
240Ϫ243
1c
1d
CH3 32 (A)
24a
24b
24c
24d
24e
24f
24g
25
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
H
H
H
H
27 (F)
35 (F)
28 (F)
14 ؉ 22a, 22b 335 (dec.)
14 ؉ 22j, 22k
14 ؉ 22c, 22d 233Ϫ235
CH3
C2H5
42 (F)
53 (B)
14 ؉ 22e, 22f
14 ؉ 8c
14 ؉ 22g
> 360
CH3
CH3 32 (F)
> 360
(CH2)2CN
H
H
H
H
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
59 (F)
14 ؉ 22h
>360
(CH2)5COOH
25 (F)
28 (B)
45 (B)
14 ؉ 22i
14 ؉ 8f
14 ؉ 8g
180Ϫ184
223Ϫ224
(CH2)5COOC2H5
H
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
12 (F)
16 (A)
45 (A)
57 (F)
10 (F)
10 (F)
14 ؉ 23a, 23b > 280 (dec.) C21H19N4O5Cl 56.96 4.32
(442.9)
56.53 4.42
63.31 4.52
62.87 4.85
26
C2H5 C2H5
C2H5 C2H5
5 ؉ 15
5 ؉ 17
315Ϫ318
298Ϫ301
C20H17N3O3S
(379.4)
11.07 8.45
10.96 8.30
9.16
27
C23H24N3O5Cl 60.33 5.28
(457.9)
C25H24N3O5Cl 62.31 5.02
(481.9) 62.20 5.30
C28H28N3O5Cl 64.43 5.41
(522.0) 64.96 5.70
C22H18N3O7SCl 52.44 3.60
(503.9) 52.11 3.89
C24H26N3O5Cl 61.08 5.55
(471.9) 60.86 5.92
60.50 5.53
9.16
28
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
14 ؉ 19a, 19b > 360
14 ؉ 20a, 20b > 360
8.72
8.79
29
8.05
7.80
30
14 ؉ 21b
> 360
> 360
8.34
8.54
8.90
8.86
6.36
6.51
31
1 (E)
80 (G)
14 ؉ 18
32
Remarkably, method E also proved successful for the
preparation of the simply bridged phenoxazinium perchlor-
ate 31. This compound was obtained by heating an equimo-
lar amount of 8-hydroxyjulolidine 14 with its nitrophen-
ylazo derivative 18a in ethanolic solution containing some
perchloric acid.
An alternative route G for preparing the phenoxazinium
perchlorate 31 was found by allowing 8-hydroxyjulolidine
(14) to react with nitrous acid in acetic anhydride at room
temperature rather than in the usually used acetic acid. In
the course of this procedure, the indaminium salt 33 was
produced, which could be isolated in satisfactory yield as
the perchlorate by adding diethyl ether to the reaction mix-
ture. Nevertheless, refluxing of the resulting mixture for a
Scheme 5
few minutes also led to formation of the bridged phenoxa- stituted 4-arylazonaphthalene derivative 22j. Instead of fur-
zine perchlorate 31 from its precursor 33. Clearly, the initial nishing the corresponding sulfonamido-substituted naph-
step in this reaction is the formation of the 8-acetoxyjulolid- thoxazinium salt, only the naphthoxazinium salt 24a, lack-
ine 32 from the starting 8-hydroxyjulolidine (14). Sub- ing an arylsulfonyl group, was produced. This compound
sequently, the acetoxy compound 32 is transformed into the could also be obtained by condensing 8-hydroxyjulolidine
corresponding nitroso derivative, which, as recently demon- (14) with the 4-arylazo-1-naphthylamine 22a. The arylsul-
strated,[17] undergoes condensation with its precursor 32 to fonyl moiety is clearly eliminated in the course of the con-
give the indaminium salt 33.
densation of 14 with 22j, probably in the form of an arylsul-
A peculiarity was observed upon condensation of the finic acid. This finding is in contrast to the reaction of the
bridged aminophenol derivative 14 with the sulfamido-sub- sulfonyl-bridged 4-arylazo-1-naphthylamine derivative 21b
926
Eur. J. Org. Chem. 1999, 923Ϫ930

Preparation and Characterization of Bridged Naphthoxazinium Salts
FULL PAPER
with 8-hydroxyjulolidine (14), where condensation leads to the fluorescence intensity of each compound studied was
the sulfonyl-bridged naphthoxazinium salt 30.
set at 100% at 20°C.
A further peculiarity was observed upon condensation of
the N-(5-carboxypentyl)-substituted 4-nitroso-1-naphthyl-
amine 8f obtained by nitrosation of N-(5-carboxypentyl)-1-
naphthylamine 6f with 8-hydroxyjulolidine (14), according
to method B. In ethanol solution, the ethoxycarbonylpen-
tyl-substituted naphthoxazinium perchlorate 24g was ob-
tained, whereas in acetic acid the carboxypentyl-substituted
naphthoxazinium perchlorate 24f was produced instead.
The structures of the naphthoxazinium salts 24؊30 were
confirmed on the basis of elemental-analysis data and by
1H-NMR spectroscopy. In Table 3, 1H-NMR-spectroscopic
data for several of the prepared naphthoxazines are pre-
sented. The low-field shifts of the protons in the ortho posi-
tions of the benzo moieties at about δ ϭ 8.20Ϫ8.90 are
particularly characteristic of these compounds.
As expected, the prepared naphthoxazinium perchlorates
are intensely coloured and exhibit a strong fluorescence, the
wavelength and intensity of which is somewhat dependent
on their substitution pattern. Thus, as can be seen in Table
4, all the prepared naphthoxazinium salts exhibit long-
wavelength absorptions between 605 and 670 nm. Similarly,
the positions of the fluorescence maxima vary between 645
and 712 nm. The StokesЈ shift between the absorption and
emission maxima is, in most cases, rather small, amounting
to about 20 nm. Only for the sulfonamido-substituted
naphthoxazines 27 and 30 as well as for the alkylene-
bridged naphthoxazinium salt 29 does the shift exceed twice
this value.
The spectral properties of phenoxazinium salts have been
extensively studied by Stuzka et al.[18] and more recently
by Drexhage et al.[19] The longest-wavelength absorption
maxima of these compounds are found at around 630Ϫ660
nm, i.e. at shorter wavelengths than those of the compounds
studied here. Evidently, annelation of the phenoxazinium
chromophore by a benzo moiety leads to a bathochromic
shift of about 30 nm. Remarkably, the completely bridged
phenoxazinium salt 31 absorbs at almost the same wave-
length as most of the naphthoxazinium salts 24Ϫ30, indi-
cating that bridging of the phenoxazine chromophore leads
only to a small spectral shift.
Figure 1. Dependence of the fluorescence intensities of several
naphthoxazinium salts plotted against reciprocal temperatue; data
measured in dichloromethane; the temperature dependence of the
absorption spectra was neglected; λmax ϭ λex; Figure 1a, 24d: filled
triangle, 28: filled rhomb, 24c: filled circle, 30: filled square; Figure
1b, 1d: filled triangle, tip downwards 1c: filled triangle, tip upwards,
26: filled circle, 28: filled square
The fluorescence intensities collected in Table 4, which
are given as relative intensities compared to that of com-
pound 28 (taken as 100%), also merit some comment. In
It can readily be seen that the studied compounds show
all cases, the intensities are lower than that of the standard markedly different temperature dependences of their fluor-
28, in accordance with the fact that all the studied com- escence intensities. For the julolidine-bridged naphthoxazi-
pounds have an essentially rigid molecular framework, nium salts 24c, 28, and 30 with an NH group at their naph-
which, as known,[20] prevents non-radiative deactivation tho moieties, a rather small dependence is observed in the
processes and thereby gives rise to low fluorescence quan- interval 20Ϫ120°C. On the other hand, for the non-bridged
tum yields. The moderate quantum yield exhibited by most naphthoxazinium salts, e.g. for compounds 1d, 1e, 26, and
of the studied naphthoxazinium salts most probably stems 27, as well as for the dimethyl- and carboxyalkyl-substituted
from other types of non-radiative deactivation processes, naphthoxazinium salts 24d, 24f and 24g, much more pro-
such as the ISC process.
nounced temperature dependences are observed. Although
In order to gain a deeper insight into this behaviour, vari- some of these compounds have bridged alkylene groups in-
able-temperature measurements of the fluorescence spectra corporated into their chromophoric systems, their fluor-
of some of the naphthoxazinium salts were carried out (see escence intensities decrease significantly with increasing
Figure 1). For ease of comparison of the obtained results, temperature. Clearly, the flexible alkyl groups linked at their
Eur. J. Org. Chem. 1999, 923Ϫ930
927

A. Kanitz, H. Hartmann
FULL PAPER
1
Table 3. H-NMR-spectral data of selected naphthoxazinium perchlorates
[a]
[b]
[c]
[a]
[b]
[c]
[b]
[c]
[b]
[c]
Compd.
R3
R4
24b
a
b
c
8.27
7.87
7.73
8.77
(d)
(t)
e
f
g
h
i
e
f
g
h
i
e
f
g
h
i
e
f
g
h
i
e
f
g
h
i
g
h
i
7.13
2.91
1.99
3.63
7.55
7.14
2.88
1.98
3.61
7.51
6.88
2.83
1.96
3.57
7.37
6.93
2.87
1.99
3.58
7.42
8.86
2.82
1.96
3.60
7.35
1.98
3.52
2.74
1.98
3.66
10.05
(s)
CH3
3.44
(s)
CH3
3.44
(s)
(m)
(m)
(m)
(s)
(t)
d
(d)
24e
24f
24g
25
a
b
c
8.42
7.90
7.80
8.73
(d)
(t)
(s)
CH2
CH2
CN
3.92
3.01
(t)
(t)
H
H
H
H
9.31
9.37
9.38
8.54
(s)
(s)
(s)
(s)
(m)
(m)
(m)
(s)
(t)
d
(d)
a
b
c
8.41
7.87
7.75
8.63
(d)
(t)
(s)
CH2
3.57
1.51
2.26
12.02
(t)
(m)
(m)
(m)
(s)
[CH2]3
CH2
(m)
(t)
(t)
d
(d)
COOH
(s)
a
b
c
8.43
7.86
7.84
8.68
(d)
(t)
(s)
CH2
3.58
1.62
2.33
(m)
(m)
(t)
(q)
(1)
(s)
(m)
(m)
(m)
(s)
[CH2]3
CH2
(t)
d
(d)
COOCH2 4.04
CH3
H
1.15
8.54
a
b
c
8.92
7.92
8.99
7.35
(dd)
(t)
(dd)
(s)
(s)
(m)
(m)
(m)
(s)
d
28
a
b
c
d
e
f
8.27
7.85
7.75
8.61
7.36
2.83
(d)
(t)
(m)
(m)
(t)
(m)
(t)
(d)
(t)
(d)
(s)
j
k
l
(m)
[a]
[b]
[c]
Assignments in accordance with the given formulae. Ϫ Chemical shift in ppm. Ϫ Multiplicity.
Table 4. Absorption and emission data of bridged phenoxazinium perchlorates 1 and 24؊31 measured in dichloromethane solution
Compd.
R1
R2
R3
R4
λmax (log ε)
λF (ΦF,%)[a]
1a
C2H5
C2H5
C2H5
C2H5
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
C2H5
C2H5
Ϫ
Ϫ
Ϫ
C2H5
C2H5
C2H5
C2H5
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
C2H5
C2H5
Ϫ
Ϫ
Ϫ
H
H
645 (4.49)
643 (4.98)
645 (5.08)
669 (5.09)
664 (4.19)
667 (5.13)
668 (5.01)
687 (5.21)
669 (5.03)
669 (5.03)
668 (5.06)
654 (4.81)
605 (4.81)
642 (4.92)
671 (5.25)
675 (4.84)
634 (5.35)
668 (5.35)
663 (47)
665 (42)
666 (40)
687 (35)
687 (5)
1b
CH3
H
1c
1d
C2H5
H
CH3
CH3
H
24a
24b
24c
24d
24e
24f
24g
25
H
CH3
H
H
679 (64)
683 (68)
701 (65)
688 (52)
684 (48)
681 (27)
673 (32)
645 (60)
668 (51)
688 (100)
712 (35)
677 (42)
677 (42)
C2H5
CH3
CH3
H
[CH2]2CN
[CH2]5COOH
H
[CH2]5COOC2H5
H
H
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
H
26
Ϫ
27
Ϫ
Ϫ
Ϫ
Ϫ
28
29
30
31
Ϫ
Ϫ
Ϫ
[a]
Relative quantum yield, referenced to the quantum yield of compound 28 (100%).
928
Eur. J. Org. Chem. 1999, 923Ϫ930

Preparation and Characterization of Bridged Naphthoxazinium Salts
FULL PAPER
ium perchlorate 33 was precipitated, which, if desired, could be
isolated in 54% yield; m.p. 163Ϫ165°C. Ϫ UV (CH2Cl2): λmax (log
ε) ϭ 723 nm (4.62). Ϫ H NMR ([D6]DMSO): δ ϭ 1.89 (m, CH2,
8 H), 1.90 (s, 6 H, CH3CO), 2.62 (t, 8 H, CH2), 3.60 (t, 8 H, NCH2),
7.10 (s, 2 H, CH). Ϫ C28H32ClN3O8 (574.03): calcd. C 58.59, H
5.62, N 7.32; found C 59.06, H 5.83, N 6.68. Ϫ By refluxing the
aforementioned reaction mixture for 30 min and then cooling it,
crystalline benzoxazinium perchlorate 31 was deposited. It was fil-
tered off and recrystallized from nitromethane; yield 80%, m.p. >
360°C. Ϫ 1H NMR ([D6]DMSO): δ ϭ 1.95 (m, 8 H, CH2), 2.82
chromophoric systems facilitate effective non-radiative pro-
cesses, thereby diminishing the proportion of radiative pro-
cesses in the total deactivation cascade. Consequently, the
presence or otherwise of non-rigid groups on the naphtha-
lene or benzene moieties of the naphthoxazinium salts is
largely irrelevant.
A further interesting observation is the dependence of the
absorption and emission properties of the bridged phenox-
azinium salts 24Ϫ31 on the polarity and the pH of the sol-
1
vent used, especially if there is a free proton on one of their (m, 8 H, CH2), 3.57 (m, 8 H, NCH2), 7.35 (s, 2 H, CH). Ϫ
C24H26ClN3O5 (471.94): calcd. C 61.08, H 5.55, N 8.90; found C
60.86, H 5.92, N 8.86.
terminal amino groups. Thus, by the addition of bases to
solutions of such salts, strong hypsochromic effects, ac-
companied by partial or complete loss of their fluorescence
ability, may be observed. For example, the absorption maxi-
mum of the bridged naphthoxazine derivative 28, which is
found at about 670 nm in aqueous ethanol at pH ϭ 4, is
shifted to about 500 nm by increasing the pH value to
above 9. Hence, the phenoxazinium perchlorates 24Ϫ31 can
also be used as acid-base indicators. Details concerning this
feature will be published elsewhere in due course.
Acknowledgments
The authors thank Bayer AG, Leverkusen, for generous finan-
cial support.
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Received September 17, 1998
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930
Eur. J. Org. Chem. 1999, 923Ϫ930