Extended aromatic π-electron conjugated dyes with three azo bonds and either one or two azulen-1-yl moieties in molecule. Synthesis and basicity

Article abstract of DOI:10.1016/j.dyepig.2011.08.002

Azo dyes with either one or two identical or different azulen-1-yl moieties attached to the structure -N₂-C₆H₄-N ₂-C₆H₄-N₂- were prepared, the phenylene ring being either 1,3-1′,

Full text of DOI:10.1016/j.dyepig.2011.08.002

Dyes and Pigments 92 (2012) 1166e1176
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Extended aromatic
p
-electron conjugated dyes with three azo bonds and either
one or two azulen-1-yl moieties in molecule. Synthesis and basicity
*
Alexandru C. Razus, Liviu Birzan , Mihaela Cristea, Victorita Tecuceanu, Cristian Enache
Institute of Organic Chemistry “C. D. Nenitzescu” of Romanian Academy, Spl. Independentei 202 B, P.O. Box 108, 060023 Bucharest 35, Romania
a r t i c l e i n f o
a b s t r a c t
Article history:
Azo dyes with either one or two identical or different azulen-1-yl moieties attached to the structure -N2-
C6H4-N2-C6H4-N2- were prepared, the phenylene ring being either 1,3-10,30 or 1,4-10,40 disubstituted. The
syntheses were accomplished in good yields via mono or bis diazotization of the corresponding anilines
followed by the coupling with unsubstituted or alkyl substituted azulenes in acetic/acetate medium. The
recorded electronic spectra of the synthesized compounds were analyzed and were compared with those
of related compounds. The isosbestic points resulting from protonation of the azo compounds enabled
pKa values to be determined. From these pKa values it is apparent that all studied compounds are very
weak bases. The high solvatochromic property of the compounds with para,para-substituted phenylene
groups reflects the hyperpolarizability of these compounds.
Received 12 May 2011
Received in revised form
26 July 2011
Accepted 1 August 2011
Available online 10 August 2011
Keywords:
Azulene
Azo
Ó 2011 Elsevier Ltd. All rights reserved.
Diazene
Electronic spectra
Basicity
pKa values
1. Introduction
the azulene-1-yl diazenes with one azo bond [26e29], we have
synthesized and studied the bis azo derivative with one or two
The long history of azoaryl dyes, the large diversity of their
possible structure, as well as the important technical applications
of these chromophores has ensured continued interest in these
compounds. For example, they have been investigated as NLO
materials [1e9], optical limiting materials [10], molecular switches
[11], NIR absorbing dyes [12] and as colorimetric sensors [13]. Their
mesomorphic properties [14], solvatochromic behavior [15e17],
electrochemical behavior [18] and surface-relief-grating (SRG)
formation of azo polymer films [19] have also been studied. Various
aromatic or heteroaromatic moieties have been attached to the azo
bond. One aromatic system investigated was the azulen-1-yl group
[20e22]. The interest shown in this group results from its electron
donor strength. Upon attachment at the position 1 in azulene of an
electron acceptor, a pushepull system is obtained stabilized by the
generation of tropylium cation at the seven-membered azulene
ring. This peculiarity enables the use of the azulen-1-yl moiety in
electronic pushepull systems [23], as well as for other molecular
structures with valuable technical purposes, such as photo-
conductor films [24] or in positive dichroic dyes used in guest-host
(GH) liquid crystal displays (LCD’s) [25]. After the investigations of
azulen-1-yl moieties in the molecule, AzN2C6H4N2C6H5 [30] and
AzN2C6H4N2Az [31] (phenylene ring was meta or para disubstituted
and Az represents substituted or unsubstituted azulen-1-yl group).
The interesting physico-chemical properties of the obtained
compounds and the possibility to use them for technical purposes
encouraged us to extend our investigation into azulene compounds
containing poly azophenyl groups such as 1e4 (Scheme 1).
2. Experimental
2.1. Materials and instrumentations
Melting points are uncorrected: Kofler apparatus (Reichert
Austria). Elemental analyses: Perkin Elmer CHN 240B. UV spectra in
methanol and dioxane: Varian Cary 100 spectrophotometer;
values are given in nm, while log has no dimension; the molar
extinction,
, is expressed in Mꢀ1 cmꢀ1 units. 1H- and 13C-NMR:
l
3
3
Bruker Avance DRX4 (1H: 400 MHz, 13C: 100.62 MHz) and Gemini
300 (1H: 300 MHz, 13C: 75.47 MHz), J values are given in Hz, TMS
was used as internal standard in CDCl3 as solvent. Mass spectra:
Varian 1200L Triple Quadrupole LC/MS/MS spectrometer by direct
injection in ESI. For the column chromatography silica gel 60 and
alumina [II-III Brockmann grade, 70e230 mesh ASTM] were used.
* Corresponding author. Tel.: þ4021 3167900; fax: þ4021 3121601.
E-mail address: lbirzan@cco.ro (L. Birzan).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.08.002

A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
1167
Scheme 1. The structures of the mono- and bis-azulenyl tris azo compounds.
was carefully added. This work-up of the reaction mixture was
important for the quantitative extraction of the products and for
avoiding the generation of an emulsion at the extraction. The
products were extracted with DCM. From this point, the work-
up was similar to the above reported procedure.
The dichloromethane (DCM) was distilled over CaH2. The pH values
were measured with an Orion 3 Star pH-meter.
2.2. Syntheses routes
(a) Diazotization in aqueous hydrochloric medium. A mixture of the
aromatic amines, (2 mmol), HCl (32% aq. 2.3 mL) and water
(2 mL) was magnetically stirred and cooled at 0 ꢁC (generally,
the amine was incompletely dissolved). To this mixture a solu-
tion of sodium nitrite (140 mg, 2 mmol) dissolved in water
(2 mL) was added slowly maintaining the temperature under
5 ꢁC. After 10 min, the mixture was added under stirring to the
solution of the azulene (2 mmol), and potassium acetate (6.7 g)
in methanol (50 mL), cooled at 0 ꢁC. The mixture was stirred at
0 ꢁC for 1 h and then neutralized with sodium hydroxide or
carbonate (10%). The solution was diluted with water (100 ml)
and the products were repeatedly extracted with DCM (typically
3 ꢂ100 mL). The organic layers were washed with water, dried
over sodium sulfate and the solvent was removed in vacuum.
The residue was chromatographed on silica gel with n-hexane as
eluent for recovery of the unreacted azulene and the starting
amine, then with DCM for azo derivatives. Due to the incomplete
separation from the starting amine, sometimes for the product
purification a second chromatography on silica gel was neces-
sary. For the bis amino compounds, two equivalents of sodium
nitrite, azulenes and potassium acetate were used.
(b) Diazotization in dichloroacetic acid. To a stirred solution of
aromatic amines (2 mmol) in dichloroacetic acid (8 mL, 12.4 g)
at 0 ꢁC, a solution of sodium nitrite, (140 mg, 2 mmol), dissolved
in water (1 mL) was added slowly, maintaining the temperature
below 5 ꢁC. After 10 min, the mixture was added at 0 ꢁC to the
very well stirred solution of azulene (2 mmol) and potassium
acetate (12 g) in methanol (100 mL). If the potassium acetate
was not completely dissolved, the yields decrease significantly.
The mixture was stirred at 0 ꢁC for 1 h. The pH of the mixture
was adjusted to neutral with a sodium hydroxide solution which
2.3. Reduction of nitro group
A solution of Na2S$9H2O (9.1 g, 37.9 mmol) in water (9.5 mL)
was added in small portions to a stirred solution of the nitro
derivative (25 mmol) dissolved in hot ethanol (20 mL) under N2.
The reaction mixture was heated under reflux for 45 min and then
was cooled and the alcohol was removed in vacuum. The residue
was dissolved in DCM and the solution was washed with water,
dried over sodium sulfate and the solvent was removed in vacuum.
By chromatography on alumina, using as eluent mixture of n-
hexane and DCM (with concentration gradient), the nitro derivative
was first eluted and then the amine.
2.4. Determination of isosbestic points and the pKa values
The bis aromatic diazenes containing two identical or different
azulenyl moieties were dissolved in dioxaneewater: 3-1, obtaining
a w3 ꢂ 10ꢀ5 mol/L solution. Then HCl (0.1 N, aq.) solution was added
with a syringe and the pH values were recorded (4 ꢂ 25
mL, 150 mL,
250 mL, 500 mL,1000 mL). The double protonation was realized adding
concentrated sulfuric acid (1 mL). The pKa values were considered the
pH values for which the absorbance gap of the main visible band
between the neutral and the protonated forms of the compound, DA
represents 50% of its initial value measured in basic medium [21].
2.5. Product characterization
(E)-azulen-1-yl-[3-(3-phenylazophenyl)azophenyl]diazene,
1Az, dark brown crystals, m.p. 160 ꢁC. UVeVis (MeOH): 229 (4.52),

1168
A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
285sh (4.71), 323 (4.65), 429 (4.48). 1H-NMR (CDCl3): 7.36 (t,
3J ¼ 9.7 Hz, 1 H, 5-H), 7.46 (d, 3J ¼ 4.5 Hz, 1 H, 3-H), 7.51 (t,
3J ¼ 9.9 Hz,1 H, 7-H), 7.78 (t, 3J ¼ 9.8 Hz,1 H, 6-H), 7.53e7.54 (m,1 H,
(dioxane): 237 (4.59), 257 (4.47), 300sh (4.60), 364 (4.58), 368 (4.58),
382sh (4.50), 511 (4.75).1H-NMR (CDCl3): 2.67(s, 3 H, Me6), 2.90(s, 3 H,
Me4), 3.42 (s, 3 H, Me8), 7.26 (s, 1 H, 5-H), 7.39 (s, 1 H, 7-H), 7.41 (d,
4
000-H), 7.56 (t, 3J ¼ 6.8 Hz, 2 H, 3000-H, 5000-H), 7.68 (t, 3J ¼ 7.9 Hz, 1 H,
3J ¼ 4.9 Hz,1H,3-H), 7.52(t,3J ¼ 7.6 Hz, 1 H, 4000-H), 7.55(t, 3J ¼ 7.6 Hz, 2
3
3
3
500-H), 7.70 (t, J ¼ 7.9 Hz, 1 H, 50-H), 7.99 (d, J ¼ 7.0 Hz, 3 H, 40-H,
H, 3000-H, 5000-H), 7.97 (d, J ¼ 7.6 Hz, 2 H, 2000-H, 6000-H), 8.02 (dAB
,
2
000-H, 6000-H), 8.08 (d, 3J ¼ 7.8 Hz, 1 H, 400-H), 8.12 (d, 3J ¼ 6.6 Hz, 1 H,
3J ¼ 8.8 Hz, 2 H, 20-H, 60-H), 8.10 (s, 4 H, 30-H, 300-H, 500-H, 50-H), 8.11
(dAB, 3J ¼ 8.8 Hz, 2 H, 200-H, 600-H), 8.20 (d, 3J ¼ 5.0 Hz, 1 H, 2-H). 13C-
NMR (CDCl3): 25.44, 28.61, 29.81,118.8,122.2,122.9,123.1,123.2,123.9,
124.3, 129.2, 131.4, 131.6, 133.9, 134.8, 141.6, 143.8, 147.5, 148.2, 149.1,
152.4, 152.9, 153.7, 154.2, 156.3. MS [ESI]: 483 [M þ 1]. Calcd for
C31H26N6: C, 77.16; H, 5.43; N, 17.41. Found: C, 77.14; H, 5.51; N, 17.35.
(E)-(5-isopropyl-3,8-dimethylazulen-1-yl)-[4-(4-phenyl-
azophenyl)azophenyl]diazene, 2Gu, dark brown crystals, m.p.
212 ꢁC. UVeVis (dioxane): 245 (4.65), 303 (4.48), 368 (4.60), 388sh
(4.53), 540 (4.82). 1H-NMR (CDCl3): 1.39 (d, 3J ¼ 6.9 Hz, 6 H, CHMe),
2.61 (s, 3 H, Me3), 3.10 (hept, 3J ¼ 6.9 Hz, 1 H, CHMe), 3.37 (s, 3 H,
Me8), 7.35 (d, 3J ¼ 10.7 Hz, 2 H, 7-H), 7.48 (dd, 3J ¼ 10.5 Hz, 2 H, 6-H),
7.51 (t, 3J ¼ 7.6 Hz, 1 H, 4000-H), 7.54 (t, 3J ¼ 7.6 Hz, 2 H, 3000-H, 5000-H),
3
600-H), 8.13 (d, J ¼ 6.9 Hz, 1 H, 60-H), 8.37 (d, 3J ¼ 9.0 Hz, 1 H, 4-H),
8.38 (d, 3J ¼ 4.8 Hz, 1 H, 2-H), 8.52 (s, 1 H, 200-H), 8.57 (s, 1 H, 20-H),
9.42 (d, 3J ¼ 9.9 Hz, 1 H, 8-H). 13C-NMR (CDCl3): 116.0, 116.6, 120.2,
123.0, 123.1, 125.4, 125.6, 126.8, 126.9, 129.2, 129.6, 129.7, 131.3,
135.7, 138.6, 139.2, 139.6, 144.0, 144.2, 152.6, 153.4, 153.5, 155.1. MS
[ESI]: 441 [M þ 1]. Calcd for C28H20N6: C, 76.35; H, 4.58; N, 19.08.
Found: C, 76.34; H, 4.59; N, 19.07.
(E)-[3-(3-phenylazophenyl)azophenyl]-(4,6,8-trimethylazulen-
1-yl)diazene, 1TMA, dark brown crystals, m.p. 113 ꢁC. UVeVis
(MeOH): 227(4.55), 253sh (4.71), 316 (4.79), 438 (4.58).1H-NMR: 2.64
(s, 3 H, Me6), 2.87 (s, 3 H, Me4), 3.41 (s, 3 H, Me8), 7.20 (s,1 H, 5-H), 7.33
(t, 3J ¼ 9.8 Hz,1H, 7-H), 7.38(d, 3J ¼ 4.9 Hz,1 H, 3-H), 7.53 (t, 3J ¼ 7.5 Hz,
2 H, 3000-H, 5000-H), 7.55 (t, 3J ¼ 7.8 Hz, 1 H, 4000-H), 7.63 (t, 3J ¼ 7.9 Hz,1 H,
50-H), 7.69 (t, 3J ¼ 7.9 Hz, 1 H, 500-H), 7.95 (ddd, 3J ¼ 7.8 Hz, 4J ¼ 1.1 Hz,
4J ¼ 1.8 Hz, 1 H, 40-H), 7.98 (dd, 3J ¼ 8.0 Hz, 4J ¼ 1.5 Hz, 2 H, 2000-H, 6000-
H), 8.01 (ddd, 3J ¼ 7.9 Hz, 4J ¼ 1.1 Hz, 4J ¼ 1.8 Hz, 1 H, 60H), 8.06 (ddd,
3
3
7.94 (d, J ¼ 8.2 Hz, 2 H, 20-H, 60-H), 7.98 (d, J ¼ 8.3 Hz, 2 H, 2000-H,
6
000-H), 8.08 (s, 4 H, 200-H, 300-H, 500-H, 600-H), 8.09 (d, 3J ¼ 8.8 Hz, 30-H,
50-H), 8.15 (s, 1 H, 4-H), 8.16 (s, 1 H, 2-H). 13C-NMR (CDCl3): 13.09,
24.43, 28.69, 38.19, 122.9, 123.1, 123.8, 124.2, 125.6, 129.2, 129.3,
131.3, 132.5, 135.0, 136.1, 136.4, 143.6, 145.9, 146.4, 148.9, 152.1,
152.8, 153.7, 154.1, 156.4. MS [ESI]: 511 [M þ 1]. Calcd for C33H30N6:
C, 77.62; H, 5.92; N, 16.46. Found: C, 77.58; H, 5.96; N, 16.46.
(E)-azulen-1-yl-[3-(3-azulen-1-ylazophenyl)azophenyl]
diazene, 3Az, dark green crystals, m.p. 171 ꢁC. UVeVis (dioxane):
234 (5.15), 271 (4.95), 336 (4.68), 434 (4.98). 1H-NMR (CDCl3): 7.42
(t, 3J ¼ 9.8 Hz, 2 H, 5-H), 7.45 (d, 3J ¼ 4.5 Hz, 2 H, 3-H), 7.56 (t,
4
3J ¼ 7.8 Hz, 4J ¼ 1.1 Hz, J ¼ 1.8 Hz, 1 H, 400-H), 8.09 (ddd, 3J ¼ 7.8 Hz,
4J ¼ 1.1 Hz, 4J ¼ 1.8 Hz, 1 H, 600-H), 8.19 (d, 3J ¼ 4.9 Hz,1 H, 2-H), 8.44 (t,
4J ¼ 1.9 Hz, 1 H, 20-H), 8.49 (t, 4J ¼ 1.9 Hz, 1 H, 200-H). 13C-NMR (CDCl3):
25.39, 28.58, 29.81, 116.7, 116.8, 118.3, 122.1, 122.8, 123.1, 124.9, 125.2,
125.5, 129.2, 129.5, 129.7, 131.1, 131.6, 133.4, 134.2, 141.0, 147.3, 147.5,
147.9, 149.9, 152.7, 153.5, 155.2. MS [ESI]: 483 [M þ 1]. Calcd for
C31H26N6: C, 77.16; H, 5.43; N, 17.41. Found: C, 77.13; H, 5.47; N, 17.40.
(E)-(5-isopropyl-3,8-dimethylazulen-1-yl)-[3-(3-phenyl-
azophenyl)azophenyl]diazene, 1Gu, dark brown crystals, m.p.
212 ꢁC. UVeVis (MeOH): 229 (4.56), 319 (4.71), 458 (4.59). 1H-NMR
(CDCl3): 1.38 (d, 3J ¼ 6.8 Hz, 6 H, CHMe), 2.64 (s, 3 H, Me3), 3.12
(hept, 3J ¼ 6.9 Hz,1 H, CHMe), 3.41 (s, 3 H, Me8), 7.35 (d, 3J ¼ 10.3 Hz,
2 H, 7-H), 7.49 (dd, 3J ¼ 10.5 Hz, 4J ¼ 1.7 Hz, 1 H, 6-H), 7.51e7.58 (m,
3J ¼ 9.7 Hz, 2 H, 7-H), 7.66 (t, J ¼ 8.0 Hz, 2 H, 50-H), 7.83 (t,
3
3J ¼ 9.9 Hz, 2 H, 6-H), 8.20 (d, J ¼ 8.0 Hz, 2 H, 40-H), 8.26 (d,
3
3J ¼ 7.8 Hz, 2 H, 60-H), 8.32 (d, 3J ¼ 4.5 Hz, 2 H, 2-H), 8.38 (d,
3J ¼ 9.3 Hz, 2 H, 4-H), 8.78 (s, 2 H, 20-H), 9.38 (d, 3J ¼ 9.9 Hz, 2 H, 8-
H). 13C-NMR (CDCl3): 115.6, 120.8, 122.9, 125.4, 127.6, 127.7, 129.1,
129.7, 135.7, 138.9, 140.0, 143.9, 144.8, 149.2, 154.8. MS [ESI]: 491
[M þ 1]. Calcd. for C32H22N6: C, 78.35; H, 4.52; N, 17.13. Found: C,
78.34; H, 4.56; N, 17.10.
3
3 H, 4000-H, 3000-H, 5000-H), 7.64 (t, J ¼ 7.8 Hz, 1 H, 50-H), 7.70 (t,
3J ¼ 7.8 Hz,1 H, 500-H), 7.95 (ddd, 3J ¼ 7.8 Hz, 4J ¼ 1.8 Hz, 4J ¼ 1.0 Hz,1
4
H, 40-H), 7.99 (dd, 3J ¼ 7.4 Hz, J ¼ 1.6 Hz, 2 H, 2000-H, 6000-H), 8.01
(E)-(4,6,8-trimethylazulen-1-yl)-[3-[3-(4,6,8-trimethylazulen-
1-yl)azophenyl] azophenyl]diazene, 3TMA, dark green crystals,
m.p. 234 ꢁC. UVeVis (dioxane): 233 (5.40), 250sh (4.76), 307 (4.58),
312 (4.58), 321 (4.58), 438 (4.71). 1H-NMR (CDCl3): 2.67 (s, 6 H, Me6),
2.90 (s, 6 H, Me4), 3.45 (s, 6 H, Me8), 7.23 (s, 2 H, 5-H), 7.37 (s, 2 H, 7-H),
4
(ddd, 3J ¼ 7.8 Hz, 4J ¼ 1.8 Hz, J ¼ 1.1. Hz, 1 H, 60-H), 8.07 (ddd,
4
3J ¼ 7.9 Hz, 4J ¼ 1.8 Hz, J ¼ 1.1 Hz, 1 H, 400-H), 8.11 (ddd, 3J ¼ 7.8 Hz,
4J ¼ 1.8 Hz, 4J ¼ 1.1 Hz, 1 H, 600-H), 8.18 (d, 4J ¼ 2.0 Hz, 1 H, 4-H), 8.19
4
(s, 1 H, 2-H), 8.44 (t, J ¼ 1.8 Hz, 1 H, 20-H), 8.50 (t, 4J ¼ 1.8 Hz, 1 H,
200-H). 13C-NMR (CDCl3): 13.09, 24.43, 28.69, 38.19, 116.5, 116.8,
122.6, 123.1, 125.5, 125.6, 128.8, 129.2, 129.5, 129.7, 131.3, 132.0,
135.0, 135.9, 136.3, 143.0, 144.5, 145.7, 148.7, 152.6, 153.5, 155.3. MS
[ESI]: 511 [M þ 1]. Calcd for C33H30N6: C, 77.62; H, 5.92; N, 16.46.
Found: C, 77.56; H, 5.97; N, 16.47.
7.41 (d, 3J ¼ 4.8 Hz, 2 H, 3-H), 7.65 (t, J ¼ 7.8 Hz, 2 H, 50-H), 7.97 (d,
3
3
3J ¼ 7.6 Hz, 2 H, 40-H), 8.02 (d, J ¼ 7.8 Hz, 2 H, 60-H), 8.21 (d,
3J ¼ 4.8 Hz, 2 H, 2-H), 8.46 (bs, 2 H, 30-H). 13C-NMR (CDCl3): 25.43,
28.59, 29.76, 116.3, 118.8, 122.2, 125.5, 125.7, 129.6, 131.9, 134.3, 135.1,
141.8, 147.5, 147.7, 148.4, 149.2, 150.0, 155.1. MS [ESI]: 575 [M þ 1].
Calcd for C38H34N6: C, 79.41; H, 5.96; N, 14.62. Found: C, 79.41; H,
5.98; N, 14.61.
(E)-azulen-1-yl-[4-(4-phenylazophenyl)azophenyl]diazene,
2Az, dark brown crystals, m.p. 217 ꢁC. UVeVis (MeOH): 228 (4.32),
286 (4.19), 363 (4.34), 368 (4.34), 374sh (4.32), 494 (4.52). UVeVis
(dioxane): 242 (4.26), 288 (4.18), 365 (4.34), 368 (4.34), 379sh
(4.30), 494 (4.58). 1H-NMR (CDCl3): 7.39 (t, 3J ¼ 9.6 Hz, 1 H, 5-H),
7.48 (d, 3J ¼ 4.5 Hz, 1 H, 3-H), 7.52 (t, 3J ¼ 10.0 Hz, 1 H, 7-H), 7.52 (t,
3J ¼ 6.5 Hz, 1 H, 4000-H), 7.55 (t, 3J ¼ 7.2 Hz, 2 H, 3000-H, 5000-H), 7.80 (t,
(E)-(5-isopropyl-3,8-dimethylazulen-1-yl)-[3-[3-(5-isopropyl-
3,8-dimethylazulen-1-yl)azophenyl]azophenyl]diazene,
3Gu,
dark green crystals, m.p. 335 ꢁC. UVeVis (dioxane): 232 (5.04), 246
(4.93), 248 (4.93), 251 (4.93), 295 (4.76), 339 (4.66), 341 (4.66), 458
(4.84). 1H-NMR (CDCl3): 1.41 (d, 3J ¼ 6.9 Hz,12 H, CHMe), 2.64 (s, 6 H,
Me3), 3.12 (hept, 3J ¼ 6.9 Hz, 2 H, CHMe), 3.42 (s, 3 H, Me8), 7.35 (d,
3J ¼ 10.7 Hz, 2 H, 7-H), 7.48 (dd, 3J ¼ 10.5 Hz, 4J ¼ 1.8 Hz, 2 H, 6-H),
7.64 (t, 3J ¼ 7.8 Hz, 2 H, 50-H), 7.95 (bd, 3J ¼ 7.8 Hz, 2 H, 40-H), 8.00 (bd,
3J ¼ 7.8 Hz, 2 H, 60-H), 8.17 (d, 4J ¼ 1.9 Hz, 2 H, 4-H), 8.20 (s, 2 H, 2-H),
3
3J ¼ 9.8 Hz, 1 H, 6-H), 7.98 (d, J ¼ 7.3 Hz, 2 H, 2000-H, 6000-H), 8.08
(dAB
,
3J ¼ 9.0 Hz, 2 H, 300-H, 500-H), 8.10 (dAB
,
3J ¼ 9.0 Hz, 2 H, 200-H,
600-H), 8.13 (dAB, 3J ¼ 9.0 Hz, 2 H, 30-H, 50-H), 8.15 (dAB, 3J ¼ 9.0 Hz, 2
H, 20-H, 60-H), 8.36 (d, 3J ¼ 4.8 Hz, 1 H, 2-H), 8.37 (d, 3J ¼ 9.0 Hz, 1 H,
4-H), 9.40 (d, 3J ¼ 9.9 Hz, 1 H, 8-H). 13C-NMR (CDCl3): 120.7, 123.1,
123.9, 124.2, 125.4, 127.3, 129.2, 131.4, 135.7, 138.7, 139.6, 139.8,
144.6, 144.7, 152.1, 152.8, 153.7, 154.0, 155.9. MS [ESI]: 441 [M þ 1].
Calcd for C28H20N6: C, 76.35; H, 4.58; N, 19.08. Found: C, 76.30; H,
4.62; N, 19.11.
4
8.45 (t, J ¼ 1.8 Hz, 2 H, 20-H). 13C-NMR (CDCl3): 13.11, 24.47, 28.80,
38.15, 116.3, 122.6, 124.9, 125.6, 128.7, 129.4, 131.9, 135.0, 135.7, 135.9,
142.9,145.0,145.6,148.7,153.6,155.3. MS [ESI]: 631 [M þ 1]. Calcd for
C42H42N6: C, 79.97;H, 6.71;N,13.32. Found: C, 79.98;H, 6.72;N,13.30.
(E)-azulen-1-yl-[4-(4-azulen-1-ylazophenyl)azophenyl]diazene,
4Az, dark green crystals, m.p. 212 ꢁC. UVeVis (dioxane): 230 (4.88),
259 (4.67), 277 (4.64), 332 (4.29), 518 (4.73). 1H-NMR (CDCl3): 7.38 (t,
(E)-[4-(4-phenylazophenyl)azophenyl]-(4,6,8-trimethylazulen-
1-yl)diazene, 2TMA, dark brown crystals, m.p. 218 ꢁC. UVeVis

A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
1169
3J ¼ 9.6 Hz, 2 H, 5-H), 7.47 (d, 3J ¼ 4.4 Hz, 2 H, 3-H), 7.52 (t, 3J ¼ 9.7 Hz,
2 H, 7-H), 7.80 (t, 3J ¼ 9.8 Hz, 2 H, 6-H), 8.12 (dAB, 3J ¼ 9.2 Hz, 4 H, 30-H,
50-H), 8.15 (dAB, 3J ¼ 9.2 Hz, 4 H, 20-H, 60-H), 8.36 (d, 3J ¼ 9.3 Hz, 2 H, 4-
H), 8.37 (d, 3J ¼ 4.8 Hz, 2 H, 2-H), 9.40 (d, 3J ¼ 9.8 Hz, 2 H, 8-H). 13C-
NMR (CDCl3): 120.6, 123.0, 124.0, 125.3, 127.1, 135.7, 138.6, 139.5, 139.7,
144.5,144.6,152.9,155.7. MS [ESI]: 491 [M þ 1]. Calcd. for: C32H22N6: C,
78.35; H, 4.52; N, 17.13. Found: C, 78.32; H, 4.57; N, 17.11.
(E)-(4,6,8-trimethylazulen-1-yl)-[4-[4-(4,6,8-trimethylazulen-
1-yl)azophenyl]azophenyl]diazene, 4TMA, brown crystals, m.p.
264 ꢁC. UVeVis (dioxane): 241 (4.96), 301 (4.87), 332sh (4.67),
514(4.96). 1H-NMR (CDCl3): 2.68 (s, 6 H, Me6), 2.90 (s, 6 H, Me4), 3.43
(s, 6 H, Me8), 7.23 (s, 2 H, 5-H), 7.36 (s, 2 H, 7-H), 7.39 (d, 3J ¼ 5.6 Hz, 2
H, 3-H), 8.01 (d, 3J ¼ 8.7 Hz, 4 H, 20-H, 60-H), 8.09 (d, 3J ¼ 8.4 Hz, 4 H,
30-H, 50-H), 8.20 (d, 3J ¼ 5.6 Hz, 2 H, 2-H). MS [ESI]: 575 [M þ 1].
Calcd for C38H34N6: C, 79.41; H, 5.96; N, 14.62. Found: C, 79.43; H,
5.99; N, 14.58.
(E)-(5-isopropyl-3,8-dimethylazulen-1-yl)-[4-[4-(5-isopropyl-
3,8-dimethylazulen-1-yl) azophenyl]azophenyl]diazene, 4Gu,
dark green crystals, m.p. 284 ꢁC. UVeVis (dioxane): 232 (5.13), 256
(4.99), 287sh (4.78), 337 (4.40), 342 (4.40), 345 (4.40), 353 (4.36),
359 (4.35), 365 (4.31), 565 (4.95). 1H-NMR (CDCl3): 1.40 (d,
3J ¼ 6.9 Hz, 12 H, CHMe), 2.63 (s, 6 H, Me3), 3.12 (hept, 3J ¼ 6.9 Hz, 2
H, CHMe), 3.38 (s, 3 H, Me8), 7.35 (d, 3J ¼ 10.8 Hz, 2 H, 7-H), 7.49 (dd,
3J ¼ 10.6 Hz, 4J ¼ 1.5 Hz, 2 H, 6-H), 7.99 (dAB, 3J ¼ 8.7 Hz, 4 H, 20-H, 60-
H), 8.08 (dAB, 3J ¼ 8.7 Hz, 4 H, 30-H, 50-H), 8.16 (d, 4J ¼ 1.7 Hz, 2 H, 4-
H), 8.18 (s, 2 H, 2-H). 13C-NMR (CDCl3): 13.09, 24.43, 28.69, 38.19,
122.9, 124.0, 125.6, 129.2, 132.3, 135.0, 136.1, 136.2, 143.4, 145.9,
146.0, 148.9, 152.4, 156.1. MS [ESI]: 631 [M þ 1]. Calcd for C42H42N6:
C, 79.97; H, 6.71; N, 13.32. Found: C, 79.95; H, 6.73; N, 13.32.
(E)-azulen-1-yl-[4-[4-(4,6,8-trimethylazulen-1-yl)azophenyl]
azophenyl]diazene, 4AzTMA, dark green crystals, m.p. 235 ꢁC.
(E)-[4-(5-isopropyl-3,8-dimethylazulen-1-yl)]-[4-[4-(4,6,8-
trimethylazulen-1-yl) azophenyl]azophenyl]diazene, 4TMAGu,
dark green crystals, m.p. 320 ꢁC. UVeVis (dioxane): 241 (4.35),
301(4.11), 335 (3.98), 337 (3.98), 341 (3.98), 347 (3.98), 353 (3.95),
558 (4.49). 1H-NMR (CDCl3): 1.40 (d, 3J ¼ 6.9 Hz, 6 H, CHMe), 2.63 (s,
3
0
3 H, Me3 ), 2.68 (s, 3 H, Me6), 2.90 (s, 3 H, Me4), 3.12 (hept, J ¼ 6.9 Hz,
0
1 H, CHMe), 3.39 (s, 3 H, Me8 ), 3.49 (s, 3 H, Me8), 7.23 (s, 1 H, 5-H),
7.37 (d, 3J ¼ 10.6 Hz, 1 H, 70-H), 7.38 (s, 1 H, 7-H), 7.41 (d, 3J ¼ 4.9 Hz, 1
H, 3-H), 7.50 (dd, 3J ¼ 10.6 Hz, J ¼ 1.4 Hz, 2 H, 60-H), 7.99 (dAB
,
4
3J ¼ 8.4 Hz, 2 H, 2000-H, 6000-H; phenylene attached to -N2-Gu), 8.01
(dAB
,
3J ¼ 8.5 Hz, 2 H, 200-H, 600-H; phenylene attached to -N2-TMA),
8.09 (dAB
,
3J ¼ 8.3 Hz, 4 H, 300-H, 500-H, 3000-H, 5000-H), 8.17 (d,
4J ¼ 1.4 Hz, 2 H, 40-H), 8.18 (s, 2 H, 20-H), 8.20 (d, 3J ¼ 5.0 Hz,1 H, 2-H).
13C-NMR (CDCl3): 13.09, 24.43, 25.44, 28.69, 28.60, 29.77, 38.19,
118.6, 122.9, 123.0, 123.9, 124.0, 125.4, 125.6, 129.1, 131.3, 132.1, 133.6,
134.6, 134.9, 136.0, 141.3, 143.4, 146.0, 147.3, 148.0, 148.2, 148.9, 150.0,
152.3, 152.5, 155.8. MS [ESI]: 603 [M þ 1]. Calcd. for C40H38N6: C,
79.70; H, 6.35; N, 13.94. Found: C, 79.68; H, 6.38; N, 13.94.
(E)-azulen-1-yl-[3-(3-azulen-1-ylazophenyl)azophenyl]
diazene N-oxide, or (Z)-(4-azulen-1-ylazophenyl)-(4-azulen-1-
ylazophenyl)imino-oxido-ammonium (IUPAC), 10Az, brown
crystals, m.p. 238 ꢁC. UVeVis (dioxane): 232 (5.16), 280 (5.01), 327
3
(4.86), 430 (5.00). 1H-NMR (CDCl3): 7.35 (t, J ¼ 9.7 Hz, 1 H, 50-H),
7.38 (t, 3J ¼ 9.7 Hz, 1 H, 5-H), 7.46 (d, 3J ¼ 4.6 Hz, 1 H, 30-H), 7.47 (d,
3
3J ¼ 4.6 Hz, 1 H, 3-H), 7.49 (t, J ¼ 9.7 Hz, 1 H, 70-H), 7.52 (t,
3
3J ¼ 9.7 Hz, 1 H, 7-H), 7.65 (t, J ¼ 7.8 Hz, 1 H, 500-H), 7.67 (t,
3
3J ¼ 7.8 Hz, 1 H, 5000-H), 7.76 (t, J ¼ 10.0 Hz, 1 H, 60-H), 7.79
3
(t, 3J ¼ 10.0 Hz, 1 H, 6-H), 8.06 (d, J ¼ 8.0 Hz, 1 H, 400-H), 8.19 (d,
3
3J ¼ 8.0 Hz, 1 H, 4000-H), 8.28 (d, J ¼ 8.0 Hz, 1 H, 600-H), 8.35 (d,
3
3J ¼ 8.0 Hz, 1 H, 6000-H), 8.36 (d, J ¼ 9.3 Hz, 1 H, 40-H), 8.37 (d,
3
3J ¼ 9.3 Hz, 1 H, 4-H), 8.37 (d, J ¼ 4.2 Hz, 2 H, 2-H, 20-H), 8.79 (t,
4
UVeVis (dioxane): 244 (4.56), 262 (4.51), 280sh (4.47), 334 (4.30),
4J ¼ 1.7 Hz, 1 H, 200-H), 8.94 (d, J ¼ 1.9 Hz, 1 H, 2000-H), 9.41 (d,
1
534 (4.79). H-NMR (CDCl3): 2.67 (0s, 3 H, Me6 ), 2.90 (s, 3 H, Me4 ),
3J ¼ 9.9 Hz, 2 H, 8-H, 80-H). 13C-NMR (CDCl3): 115.4, 119.0, 120.2,
120.5, 122.4, 123.9, 125.4, 125.9, 126.1, 126.8, 126.9, 127.2, 127.3,
129.1, 129.3, 135.7, 138.6, 138.7, 139.6, 139.8, 144.0, 144.5, 144.9,
149.4, 154.7. MS [ESI]: 507 [M þ 1]. Calcd. for C32H22N6O: C, 75.87;
H, 4.38; N, 16.59. Found: C, 75.79; H, 4.42; N, 16.62.
0
0
0
0
3.46 (s, 3 H, Me8 ), 7.23 (s, 2 H, 5 -H), 7.36 (s, 2 H, 7 -H), 7.36 (t,
3J ¼ 9.9 Hz, 1 H, 5-H), 7.41 (d, J ¼ 4.8 Hz, 1 H, 30-H), 7.44 (d,
3
3J ¼ 4.6 Hz, 1 H, 3-H), 7.49 (t, 3J ¼ 9.7 Hz, 1 H, 7-H), 7.77 (t, 3J ¼ 9.8 Hz,
1 H, 6-H), 7.97 (dAB, 3J ¼ 8.7 Hz, 2 H, 2000-H, 6000-H; phenylene attached
to -N2-TMA), 8.06 (dAB, 3J ¼ 9.3 Hz, 4 H, 300-H, 500-H, 3000-H, 5000-H), 8.10
(dAB, 3J ¼ 8.7 Hz, 2 H, 200-H, 600-H; phenylene attached to -N2-Az), 8.14
(E)-(4,6,8-trimethylazulen-1-yl)-[3-[3-(4,6,8-trimethylazulen-
1-yl)azophenyl] azophenyl]diazene N-oxide or (Z)-oxido-[4-(4,6,8-
trimethylazulen-1-yl)azophenyl]-[4-(4,6,8-trimethylazulen-1-yl)
azophenyl]imino-ammonium (IUPAC), 10TMA, green crystals, m.p.
(d, J ¼ 4.6 Hz, 1 H, 20-H), 8.32 (d, 3J ¼ 4.7 Hz, 1 H, 2-H), 8.34 (d,
3
3J ¼ 9.4 Hz,1 H, 4-H), 9.35 (d, 3J ¼ 9.7 Hz,1 H, 8-H). 13C-NMR (CDCl3):
25.37, 28.56, 29.74,118.7, 120.6, 123.0, 123.9, 124.0,125.2, 125.4, 127.1,
131.4, 133.7, 134.6, 135.6, 138.6, 139.4, 139.6, 141.4, 144.5, 144.6, 147.4,
148.2, 148.1, 150.0, 152.5, 152.9, 155.6, 155.9. MS [ESI]: 533 [M þ 1].
Calcd. for C35H28N6: C, 78.92; H, 5.30; N, 15.78. Found: C, 78.89; H,
5.34; N, 15.77.
192 ꢁC. UVeVis (dioxane): 232 (5.15), 250 (4.99), 306 (4.60), 315
1
0
(4.58), 445 (4.65). H-NMR (CDCl3): 2.67 (s, 6 H, Me6 and Me6 ), 2.89
0
0
(s, 6 H, Me4 and Me4 ), 3.43 (s, 6 H, Me8 and Me8 ), 7.23 (s, 1 H, 5-H),
7.26 (s, 2 H, 50-H), 7.35 (s, 1 H, 7-H), 7.38 (s, 1 H, 70-H), 7.39 (d,
3J ¼ 4.7 Hz, 1 H, 3-H), 7.40 (d, J ¼ 4.7 Hz, 1 H, 30-H), 7.61 (t,
3
3
(E)-azulen-1-yl-[4-[4-(5-isopropyl-3,8-dimethylazulen-1-yl)
azophenyl] azophenyl]diazene, 4AzGu, dark green crystals, m.p.
189 ꢁC. UVeVis (dioxane): 244 (4.56), 262 (4.51), 280sh (4.47), 334
(4.30), 534 (4.79). 1H-NMR (CDCl3): 1.39 (d, 3J ¼ 6.9 Hz, 6 H, MeCH),
3J ¼ 7.8 Hz, 1 H, 500-H), 7.63 (t, J ¼ 7.8 Hz, 1 H, 5000-H), 7.95 (d,
3J ¼ 8.0 Hz, 1 H, 400-H), 8.07 (d, J ¼ 7.7 Hz, 1 H, 4000-H), 8.19 (d,
3
3J ¼ 7.9 Hz, 1 H, 600-H), 8.20 (d, J ¼ 4.7 Hz, 2 H, 2-H, 20-H), 8.32 (d,
3
3J ¼ 7.6 Hz, 1 H, 6000), 8.71 (s, 1 H, 200-H), 8.83 (s, 1 H, 2000-H). 13C-NMR
(CDCl3): 25.33, 25.36, 28.53, 29.77, 29.82, 115.4, 119.0, 118.2, 118.5,
121.7,123.4,122.1,122.2,125.4,125.7,130.8,131.4,133.3,133.8,129.0,
129.1, 134.8, 141.6, 144.8,147.4, 147.5, 148.1, 149.3, 149.4, 150.0, 154.8.
MS [ESI]: 591 [M þ 1]. Calcd for C38H34N6O: C, 77.26; H, 5.80; N,
14.23. Found: C, 77.22; H, 5.85; N, 14.26.
2.62 (s, 3 H, Me3 ), 3.09 (hept, 3J ¼ 6.9 Hz, 1 H, CHMe), 3.37 (s, 3 H,
0
Me8 ), 7.35 (d, J ¼ 10.2 Hz, 1 H, 7 -H), 7.36 (t, 3J ¼ 9.8 Hz, 1 H, 5-H),
3
0
0
7.46 (d, 3J ¼ 4.5 Hz, 1 H, 3-H), 7.50 (t, 3J ¼ 9.8 Hz, 1 H, 7-H), 7.51 (d,
3J ¼ 10.2 Hz, 1 H, 60-H), 7.77 (t, 3J ¼ 9.9 Hz, 1 H, 6-H), 7.99 (dAB
,
-
3J ¼ 8.7 Hz, 2 H, 2000-H, 6000-H), 8.09 (dAB, 3J ¼ 8.8 Hz, 2 H, 3000-H, 5000
H; phenylene attached to -N2-Gu), 8.09 (dAB, 3J ¼ 9.2 Hz, 2 H, 300-H,
500-H; phenylene attached to -N2-Az), 8.13 (dAB, 3J ¼ 9.0 Hz, 2 H, 200-
(E)-(5-isopropyl-3,8-dimethylazulen-1-yl)-[3-[3-(5-isopropyl-
3,8-dimethylazulen-1-yl) azophenyl]azophenyl]diazene N-oxide,
or (Z)-[4-(5-isopropyl-3,8-dimethylazulen-1-yl)azophenyl]-[4-
(5-isopropyl-3,8-dimethylazulen-1-yl) azophenyl]imino-oxido-
ammonium (IUPAC), 10Gu, brown crystals, dec. without melting.
UVeVis (dioxane): 234 (4.97), 252sh (4.93), 291 (4.60), 298 (4.60),
351 (4.49), 467 (4.88). 1H-NMR (CDCl3): 1.41 (d, 3J ¼ 6.9 Hz, 12 H,
4
H, 600-H), 8.16 (d, J ¼ 1.8 Hz, 1 H, 40-H), 8.17 (s, 1 H, 20-H), 8.34 (d,
3J ¼ 9.7 Hz, 1 H, 4-H), 8.36 (d, 3J ¼ 4.2 Hz, 1 H, 2-H), 9.38 (d,
3J ¼ 9.9 Hz, 2 H, 8-H). 13C-NMR (CDCl3): 13.09, 24.42, 28.70, 38.17,
120.5, 122.8, 123.1, 123.9, 124.1, 125.4, 125.6, 127.1, 129.2, 132.4,
135.0, 135.7, 136.1, 136.2, 138.6, 139.4, 139.7, 143.5, 144.5, 144.6,
145.9, 146.2, 148.9, 152.3, 153.0, 155.6, 156.1. MS [ESI]: 561 [M þ 1].
Calcd. for C37H32N6: C, 79.26; H, 5.75; N, 14.99. Found: C, 79.24; H,
5.78; N, 14.98.
CHMe), 2.63 (s, 6 H, Me3 and Me3 ), 3.11 (hept, 3J ¼ 6.9 Hz, 1 H,
0
3
CHMe), 3.12 (hept, J ¼ 6.9 Hz, 1 H, CHMe0), 3.41 (s, 6 H, Me80and
3
3
0
Me8 ), 7.32 (d, J ¼ 10.7 Hz, 1 H, 7-H), 7.37 (d, J ¼ 10.7 Hz, 1 H, 7 -H),

1170
A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
NH2
1. NaNO2/acid
2. AzRn/AcOK
1Rn
or
2Rn
Yields (%)
1Rn
Rn: Az 74
TMA 79
2Rn
71
5: meta-meta-isomer; 6: para-para-isomer
66
Rn
Gu 90
69
: AzRn
Scheme 2. Azo coupling of diazotized amines, 5 and 6.
7.48 (d, 3J ¼ 10.6 Hz,1 H, 6-H), 7.50 (d, 3J ¼ 10.6 Hz,1 H, 60-H), 7.60 (t,
124.6,124.8,125.5,127.6,135.7,138.8,139.9,151.4,151.9,156.7,160.4.
MS [ESI]: 382 [M þ 1]. Calcd for C22H15N5O2: C, 69.28; H, 3.96; N,
18.36. Found: C, 69.25; H, 3.98; N, 18.38.
3
3J ¼ 7.9 Hz, 1 H, 500-H), 7.62 (t, J ¼ 8.0 Hz, 1 H, 5000-H), 7.92 (d,
3J ¼ 8.1 Hz, 2 H, 400-H), 8.05 (d, 3J ¼ 7.7 Hz, 2 H, 4000-H), 8.14e8.20 (m,
5 H, 2-H, 20-H, 4-H, 40-H, 600-H), 8.30 (dd, 3J ¼ 8.0 Hz, 4J ¼ 1.3 Hz, 1 H,
(E)-[4-(4-nitrophenyl)azophenyl]-(4,6,8-trimethylazulen-1-
yl)diazene, 11TMA, green crystals, m.p. 262 ꢁC (dec). UVeVis
(MeOH): 237 (4.32), 264 (4.28), 310 (4.25), 340 (4.24), 506 (4.54).
1H-NMR (CDCl3): 2.68 (s, 3 H, Me6), 2.90 (s, 3 H, Me4), 3.42 (s, 3 H,
Me8), 7.28 (s, 1 H, 5-H), 7.40 (s, 1 H, 7-H), 7.41 (d, 3J ¼ 4.9 Hz, 1 H, 3-
H), 8.01 (d, 3J ¼ 8.6 Hz, 2 H, 30-H, 50-H), 8.06 (d, 3J ¼ 8.8 Hz, 2 H, 300-
H, 500-H), 8.11 (d, 3J ¼ 8.6 Hz, 2 H, 20-H, 60-H), 8.18 (d, 3J ¼ 4.7 Hz, 1 H,
2-H), 8.40 (d, 3J ¼ 8.7 Hz, 2 H, 200-H, 600-H). 13C-NMR (CDCl3): 25.41,
28.58, 29.75, 119.0, 122.2, 123.1, 123.4, 124.7, 124.8, 131.9, 134.1,
134.7, 141.1, 147.6, 149.9, 151.9, 154.6, 157.2. MS [ESI]: 424 [M þ 1].
Calcd for C25H21N5O2: C, 70.91; H, 5.00; N, 16.54. Found: C, 70.90; H,
5.02; N, 16.55.
4
6
000-H), 8.70 (s, 1 H, 200-H), 8.82 (t, J ¼ 1.9 Hz, 1 H, 2000-H). 13C-NMR
(CDCl3): 13.07, 24.47, 28.74, 28.80, 38.13, 38.16, 115.6, 119.1, 121.5,
123.4, 125.2, 125.5, 125.6, 128.5, 128.6, 129.0, 129.1, 131.8, 132.4,
134.9, 135.0, 135.7, 135.8, 136.0, 136.3, 142.8, 143.3, 144.9, 145.0,
145.4, 146.1, 148.8, 149.4, 153.6, 154.8, 155.0. MS [ESI]: 647 [M þ 1].
Calcd. for C42H42N6O: C, 77.99; H, 6.54; N, 12.99. Found: C, 78.02; H,
6.60; N, 12.95.
(E)-azulen-1-yl-[4-(4-nitrophenyl)azophenyl]diazene, 11Az,
green crystals, m.p. 252 ꢁC. UVeVis (MeOH): 228 (4.32), 278 (4.32),
346 (4.20), 497 (4.53). 1H-NMR (CDCl3): 7.41 (t, 3J ¼ 9.8 Hz, 1 H, 5-
H), 7.48 (d, 3J ¼ 4.5 Hz, 1 H, 3-H), 7.54 (t, 3J ¼ 9.8 Hz, 1 H, 7-H),
7.81 (t, 3J ¼ 9.9 Hz, 1 H, 6-H), 8.08 (dAB, 3J ¼ 9.1 Hz, 2 H, 300-H, 500-H),
8.14 (bs, 4 H, 20-H, 30-H, 50-H, 60-H), 8.36 (d, 3J ¼ 4.7 Hz, 1 H, 2-H),
8.45 (d, 3J ¼ 9.8 Hz, 1 H, 4-H), 8.55 (dAB, 3J ¼ 7.0 Hz, 2 H, 200-H, 600-H),
9.40 (d, 3J ¼ 9.8 Hz, 1 H, 8-H). 13C-NMR (CDCl3): 120.9, 123.2, 123.5,
(E)-(5-isopropyl-3,8-dimethylazulen-1-yl)-[4-(4-nitrophenyl)
azophenyl]diazene, 11Gu, green crystals, m.p. 221 ꢁC. UVeVis
(MeOH): 237 (4.32), 295 (4.25), 297 (4.25), 299 (4.25), 350 (4.14), 352
(4.14), 355 (4.14), 547 (4.52).1H-NMR (CDCl3): 1.40 (d, 3J ¼ 6.8 Hz, 6 H,
H2N
1. Na NO2/HCl
2. AzRn/AcOK
N
N
3Rn
or
4Rn
Yields (%)
3Rn
4Rn
45
0*
50
Rn: Az 87
TMA 91
Gu 93
NH2
*From the reaction results only mono
diazotized compound in 66 % yield
7: meta-meta-isomer; 8: para-para--isomer
Rn
O-
N+
1'
1. Na NO2/HCl
2. AzRn/AcOK
O-
N
N
NH2
H2N
N
N+
N
N
N
1"
1"'
1
9
10; yields (%)
Rn = Az: 65
TMA: 60
Gu: 34
Rn
Scheme 3. Azo coupling of diazotized 7, 8 and 9.

A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
1171
Scheme 4. Stepwise preparation of the para-para diphenylene bis-azulenyl tris azo compounds.
CHMe), 2.61 (s, 3 H, Me3), 3.12 (hept, 3J ¼ 6.9 Hz,1 H, CHMe), 3.36 (s, 3
H, Me8), 7.38 (d, 3J ¼ 10.8 Hz, 2 H, 7-H), 7.51 (d, 3J ¼ 10.4 Hz,1 H, 6-H),
7.97 (dAB, 3J ¼ 8.6 Hz, 2 H, 20-H, 60-H), 8.03 (d, 3J ¼ 8.8 Hz, 2 H, 300-H,
500-H), 8.08 (dAB, 3J ¼ 8.6 Hz, 2 H, 30-H, 50-H), 8.15 (bs, 1 H, 2-H), 8.16
24.41, 28.66, 38.14, 114.7, 122.8, 123.3, 125.2, 125.6, 129.0, 132.1,
134.9, 136.0, 136.8, 143.2, 145.6, 146.0, 148.8, 149.5, 152.5, 155.3. MS
[ESI]: 422 [M þ 1]. Calcd for C27H27N5: C, 76.93; H, 6.46; N, 16.61.
Found: C, 76.94; H, 6.44; N, 16.62.
(bs, 1 H, 4-H), 8.36 (dAB
,
3J ¼ 8.8 Hz, 2 H, 200-H, 600-H). 13C-NMR
(Z)-[4-(4-azulen-1-ylazophenyl)azophenyl]-(4-azulen-1-
ylazophenyl)imino-oxido-ammonium, 15Az, brown crystals,
dec. without melting. UVeVis (dioxane): 211 (5.13), 229 (5.15),
256sh (4.87), 277 (4.75), 346 (4.47), 365 (4.43), 507 (4.86). 1H-NMR
(CDCl3): 7.38 (t, 3J ¼ 9.5 Hz, 1 H, 5-H), 7.40 (t, 3J ¼ 9.6 Hz, 1 H, 50-H),
7.46 (d, 3J ¼ 3.6 Hz, 1 H, 3-H), 7.47 (d, 3J ¼ 3.9 Hz, 1 H, 30-H), 7.51 (t,
(CDCl3): 13.09, 24.40, 28.68, 38.21, 122.9, 123.4, 124.7, 125.6, 129.6,
132.9, 135.1, 136.3, 136.8, 143.9, 146.1, 146.9, 148.5, 149.0, 151.7, 156.1,
157.1. MS [ESI]: 452 [M þ 1]. Calcd for C27H25N5O2: C, 71.82; H, 5.58;
N, 15.51. Found: C, 71.80; H, 5.59; N, 15.54.
4-(4-azulen-1-ylazophenyl)azoaniline, 12Az, dark green crys-
tals, m.p. 210 ꢁC. UVeVis (MeOH): 228 (4.40), 280 (4.23), 396sh
(4.00), 495 (4.54). 1H-NMR (CDCl3): 6.77 (dAB, 3J ¼ 8.8 Hz, 2 H, 200-H,
600-H), 7.35 (t, 3J ¼ 9.8 Hz, 1 H, 5-H), 7.45 (d, 3J ¼ 4.7 Hz, 1 H, 3-H),
3
3J ¼ 9.7 Hz, 1 H, 7-H), 7.53 (t, J ¼ 9.7 Hz, 1 H, 70-H), 7.79 (t,
3
3J ¼ 9.7 Hz, 1 H, 6-H), 7.80 (t, J ¼ 9.7 Hz, 1 H, 60-H), 8.10 (dAB
,
3J ¼ 8.8 Hz, 2 H, 200-H, 600-H), 8.12 (dAB, 3J ¼ 8.8 Hz, 2 H, 3000-H, 5000-H),
8.14 (s, 4 H, 20000-H, 30000-H, 50000-H, 60000-H), 8.36 (d, 3J ¼ 9.3 Hz, 1 H, 4-
H), 8.37 (d, 3J ¼ 4.1 Hz, 2 H, 2-H, 20-H), 8.38 (d, 3J ¼ 9.3 Hz, 1 H, 40-H),
7.48 (t, 3J ¼ 9.8 Hz, 1 H, 7-H), 7.77 (t, 3J ¼ 9.9 Hz, 1 H, 6-H), 7.86 (dAB
,
3J ¼ 8.7 Hz, 2 H, 300-H, 500-H), 8.00 (dAB, 3J ¼ 8.8 Hz, 2 H, 30-H, 50-H),
8.10 (dAB, 3J ¼ 8.8 Hz, 2 H, 20-H, 60-H), 8.35 (d, 3J ¼ 9.5 Hz, 1 H, 4-H),
8.36 (d, 3J ¼ 4.7 Hz, 1 H, 2-H), 9.38 (d, 3J ¼ 9.7 Hz, 1 H, 8-H). 13C-NMR
(CDCl3): 114.2, 119.9, 122.5, 122.8, 124.8, 124.9, 126.4, 135.2, 138.1,
138.6, 139.2, 143.8, 144.1, 146.5, 149.2, 152.6, 154.4. MS [ESI]: 352
[M þ 1]. Calcd for C22H25N5: C, 75.19; H, 4.88; N, 19.93. Found: C,
75.15; H, 4.91; N, 19.94.
8.46 (dAB
,
3J ¼ 8.8 Hz, 2 H, 300-H, 500-H), 8.53 (dAB
,
3J ¼ 8.9 Hz, 2 H,
2
000-H, 6000-H), 9.39 (d, 3J ¼ 9.8 Hz, 2 H, 8-H), 9.40 (d, 3J ¼ 9.7 Hz, 2 H,
80-H). 13C-NMR (CDCl3): 120.6, 120.8, 122.6, 123.1, 123.3, 123.5,
124.3,125.4,125.8,127.1,127.2,127.4,135.7,138.7,138.8,139.4,139.8,
139.9, 144.4, 144.6, 144.7, 149.4, 152.5, 154.3, 155.7, 156.2, 159.6. MS
[ESI]: 611 [M þ 1]. Calcd for C38H26N8O: C, 74.74; H, 4.29; N, 18.35.
Found: C, 74.80; H, 4.35; N, 18.30.
4-[4-(4,6,8-trimethylazulen-1-yl)azophenyl]azoaniline,12TMA,
dark green crystals, dec. without melting. UVeVis (MeOH): 235 (4.43),
297 (4.18), 368 (4.16), 498 (4.58). 1H-NMR (CDCl3): 2.58 (s, 3 H, Me6),
(Z)-[4-[4-(5-isopropyl-3,8-dimethylazulen-1-yl)azophenyl]
azophenyl]-[4-(5-isopropyl-3,8-dimethylazulen-1-yl)azophenyl]
imino-oxido-ammonium, 15Gu, brown crystals, dec. without
melting. UVeVis (dioxane): 250 (4.66), 302 (4.51), 364 (4.43), 366
3
2.66 (s, 3 H, Me4), 3.41 (s, 3 H, Me8), 6.75(dAB, J ¼ 8.8 Hz, 2 H, 200-H, 600-
H), 7.21 (s,1 H, 5-H), 7.34 (s,1 H, 7-H), 7.38 (d, 3J ¼ 4.9 Hz,1 H, 3-H), 7.84
(dAB, 3J ¼ 8.8 Hz, 2 H, 300-H, 500-H), 7.97 (bs, 4 H, 20-H, 30-H, 50-H, 60-H),
8.17 (d, 3J ¼ 4.9 Hz, 1 H, 2-H). 13C-NMR (CDCl3): 25.36, 28.57, 29.73,
114.7, 118.5, 122.1, 123.0, 123.3, 125.2, 131.2, 133.4, 134.3, 141.1, 146.0,
147.3, 147.9, 148.1, 149.6, 149.9, 152.7, 155.1. MS [ESI]: 394 [M þ 1]. Calcd
for C25H23N5: C, 76.31; H, 5.89; N, 17.80. Found: C, 76.30; H, 5.88; N,
17.82.
(4.43), 368 (4.43), 548 (4.91). 1H-NMR (CDCl3): 1.40 (d, 3J ¼ 6.9 Hz,
3
0
0
12 H, CHMe, CHMe ), 2.62 (s, 6 H, Me3, Me3 ), 3.11 (hept, J ¼ 6.9 Hz,
1 H, CHMe), 3.12 (hept, 3J ¼ 6.9 Hz, 1 H, CHMe0), 3.38 (s, 3 H, Me8),
3.39 (s, 3 H, Me8 ), 7.36 (d, 3J ¼ 10.6 Hz, 1 H, 7-H), 7.38 (d,
0
3J ¼ 10.6 Hz, 1 H, 70-H), 7.51 (t, 3J ¼ 9.6 Hz, 4J ¼ 1.7 Hz, 1 H, 6-H), 7.55
4-[4-(5-isopropyl-3,8-dimethylazulen-1-yl)azophenyl]azoa-
niline, 12Gu, dark green crystals, dec. without melting. UVeVis
(MeOH): 230 (4.65), 250 (4.56), 294 (4.29), 400 (4.33), 520 (4.71).
1H-NMR (CDCl3): 1.39 (d, 3J ¼ 6.8 Hz, 6 H, CHMe), 2.61 (s, 3 H, Me3),
Table 1
Diazotization of 4-(4-nitrophenyl)azoaniline, coupling with azulene and reduction
of nitro-derivatives 11 to amine 12 (yields in %).
Compounds
Rn
3.10 (hept, 3J ¼ 6.9 Hz, 1 H, CHMe), 3.36 (s, 3 H, Me8), 6.75 (dAB
,
3J ¼ 8.0 Hz, 2 H, 200-H, 600-H), 7.32 (d, 3J ¼ 10.8 Hz, 2 H, 7-H), 7.46 (d,
Az
83
TMA
75
Gu
94
3
3J ¼ 10.4 Hz, 1 H, 6-H), 7.83 (d, J ¼ 8.0 Hz, 2 H, 300-H, 500-H), 7.95
Diazotization of 4-(4-nitrophenyl)azoaniline
and coupling with AzH
Reduction of compounds 11 to amine 12
(dAB, 3J ¼ 10.0 Hz, 2 H, 20-H, 60-H), 7.97 (dAB, 3J ¼ 10.0 Hz, 2 H, 30-H,
56
60
65
50-H), 8.14 (bs, 1 H, 4-H), 8.16 (bs, 1 H, 2-H). 13C-NMR (CDCl3): 13.07,

1172
A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
Table 2
3, Aldrich catalog) (Scheme 2). Because the amine 5 is not
commercially available, it was synthesized using the protocols
described in the literature for this compound [32,33].
Diazotization of amines 12 and azo coupling with azulenes to compounds 4RnRn0
(yields in %).
Rn0
Rn
Az
The diazotization of amine 6 was performed in the presence of
hydrochloric acid, while dichloroacetic acid was more appropriate
starting from the amine 5 [31]. The coupling with azulene occurred
in situ without the diazonium salt separation. The yields obtained
starting from the aniline with azo groups in the para-position has
always been lower as compared with those for the meta isomer, due
to the mesomeric effect exerted by azo group in diazonium salts.
This effect decreases the positive charge at the diazonium group in
para-position and, therefore, decreases the electrophilic activity of
diazotized amine 6. Nevertheless, yields between 66% and 90%
were obtained for the compounds 1 and 2 (Scheme 2). The coupling
reactions were always accompanied by anilines deamination in
yields ranging from 3 to 5%.
TMA
Gu
Az
TMA
Gu
70
65
90
76
15
56
25
25
22
(dd, 3J ¼ 10.6 Hz, J ¼ 1.7 Hz, 1 H, 60-H), 7.97 (dAB
,
3J ¼ 8.9 Hz, 2 H,
4
2
0000-H, 60000-H), 8.00 (dAB
,
3J ¼ 8.8 Hz, 2 H, 30000-H, 50000-H), 8.07 (dAB
,
3J ¼ 8.9 Hz, 2 H, 200-H, 600-H), 8.10 (dAB, 3J ¼ 8.7 Hz, 2 H, 3000-H, 5000-H),
8.16 (d, 4J ¼ 1.9 Hz, 1 H, 4-H), 8.17 (d, 4J ¼ 1.9 Hz, 1 H, 40-H) 8.17 (bs,
2-H, 2-H, 20-H), 8.44 (dAB
,
3J ¼ 8.8 Hz, 2 H, 300-H, 500-H), 8.51 (dAB
,
3J ¼ 8.8 Hz, 2 H, 2000-H, 6000-H). 13C-NMR (CDCl3): 13.10, 24.42, 28.70,
38.19, 122.5, 122.9, 123.2, 123.4, 124.4, 125.6, 127.0, 127.1, 129.1,
132.6,135.0,135.1,136.1,136.3,137.2,143.3,143.7,145.9,146.3,149.0,
149.2, 151.8, 154.2, 154.8, 156.6, 158.2. MS [ESI]: 751 [M þ 1]. Calcd
for C48H46N8O: C, 76.77; H, 6.17; N, 14.92. Found: C, 76.75; H, 6.21;
N, 14.94.
It must be emphasized that our attempts to obtain and to couple
the diazonium salt starting from the aniline with azo bonds in
ortho-position toward amino group failed due to the generation of
benzotriazoles before coupling could occur.
3.2. Syntheses of 3 and 4 with three azo bonds and two azulene-1-
yl moieties
3. Results and discussion
The syntheses of diazenes 1e4 (Scheme 1) are based on the
nucleophilic character of the 1-position in azulene compounds,
which allows the electrophilic coupling of these non-benzenoid
aromatic hydrocarbons with the desired diazonium salts.
The presence of the second azulen-1-yl moiety in the molecules,
as in the compounds 3 and 4, necessitates more complicated
synthetic routes. These routes are chosen in function of the
symmetry of the synthesized azo compounds, if they possess either
identical or different terminal azulen-1-yl groups (Scheme 3).
For symmetrical molecules, compounds 3Rn and 4Rn, the
synthesis started from the already known 3-(3-aminophenyl)
azoaniline, 7 [34], and 4-(4-aminophenyl)azoaniline, 8 [35] (Scheme
3). The preparation of diamine 7 occurred simultaneously with the
generation of some amount of corresponding azoxy derivative, 9.
This by-product was separated using column chromatographyand it
3.1. Syntheses of the compounds 1 and 2 with three azo bonds and
one azulene-1-yl moiety
Compounds 1 and 2 were prepared by the coupling of azulenes
with diazonium salts obtained from 3-(3-phenylazophenyl)azoa-
niline, 5, and 4-(4-phenylazophenyl)azoaniline, 6 (Disperse Orange
Scheme 5. Diazotization and coupling of compound 14.

A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
1173
Scheme 6. The structures of bis azo compounds containing one or two azulenyl moieties in the molecule.
can be further reduced with Zn/NaOH to 3,30-diaminohy-
drazobenzene, which, exposed to the air, yielded compound 8.
The azoxy compound 9 was used as a starting diamine for the
preparation of the new azoxy dyes 10 (Scheme 3). The azoxy group
did not interfere in the coupling process and also it was compatible
with the azulene moiety, known as very sensitive to common
oxidants.
acetylaminoaniline, instead of the expected compound 13, the
(mono azo)-(mono azoxy) derivative 14 was obtained [37]. Never-
theless, we have synthesized the tris azo azoxy compounds, 15Rn to
prove once more the compatibility between the azoxy group with
an oxidant aptitude and the azulenyl moiety deactivated by an azo
group (Scheme 5).
As emphasized, the coupling of amines with azo group in meta-
position occurred readily, as compared with the para isomer. It is
notable that, contrary to what was observed for para-phenyl-
enediamine, which could not be diazotized and coupled with
azulenes at both amino groups [31], this reaction sequence took
place starting from diamine 8. Another peculiarity of the reaction
was the mono coupling of diamine 8 when the diazonium salt was
reacted with 4,6,8-trimethylazulene and the lack of the disubsti-
tuted product from the experiment.
For the compounds possessing two different azulen-1-yl moie-
ties, two consecutive coupling reactions were used, as depicted in
Scheme 4. Thus, the diazotization of 4-(4-nitrophenyl)azoaniline,
followed by the coupling with azulene generated the compounds
11. These nitro-derivatives were reduced to the corresponding
amines and the sequence diazotization-coupling was performed to
afford the compounds 4RnRn0 (Table 1 and 2).
3.4. The electronic spectra of aromatic dyes 1e4 with three azo
bonds and with one or two azulen-1-yl moieties in molecule;
comparison with the corresponding compounds 16e19 with two azo
bonds
The important effect produced on the electronic spectra by the
presence of (azulen-1-yl)azo moiety as an extended conjugated p-
electron system has already been studied for the molecules with
one or two such moieties attached to one phenylene group,
compounds 16e19 in Scheme 6 [30,31]. The enhancement in
p-
electron conjugation of azulen-1-yl-phenyl diazene by the
supplementary introduction into the molecule of phenylene and
azo groups, as in dyes 1e4, induces an important bathochromic
shift for the lmax of the main visible band (Table 3). These results
indicated that it would be of interest to build dyes with more
extend conjugated
p-electron system as in the new compounds
The diazotization of amine 12(Rn ¼ Az) occurred in the hydro-
chloric acid medium. The amine 12(Rn ¼ TMA) is much less soluble
in this acid, therefore for diazotization a mixture of phosphoric acid
(85%):nitric acid (62%) (3:2 vol) was used [36]. Unfortunately, the
guaiazulenyl moiety present in the structure of amine 12(Rn ¼ Gu)
was oxidized by nitric acid leading to a tarry reaction mixture.
Therefore only phosphoric acid was used but the coupling yields
were significantly lower than it was observed in previous cases.
This protocol was also used for the preparation of the diazenes 4
with Rn ¼ Rn0. By this method, the yields of the compounds 4Az and
4Gu were increased and this route allowed the preparation of
4TMA. Nevertheless, the more advantageous protocol described in
Scheme 3 was used for the synthesis of the dyes 4Az and 4Gu.
1e4, 10 and 15 and to investigate their electronic spectra in
comparison with the spectra of the previously reported compounds
16e17 (Table 3 and 4).
Generally, the bathochromic effect for the compounds with one
azulen-1-yl moiety, 1 and 2 is more intense for the para-substituted
phenylene isomers as for meta ones (Table 3) due to the more
extended
p-electron conjugation for the first compounds. At the
same time, the data in Table 3 outlined that the red shift effect
increases with the number of the 1,4-phenyleneazo groups present
Table 4
lmax of the main visible band (in nm) for the synthesized dyes 1e4 in dioxane:water
3:1 (vol) at pH neutral and acid, as well as at isosbestic point (IP) and the obtained
pKa.
3.3. Attempts to synthesize compounds with four azo bonds and
two azulene-1-yl moieties
Compd. Rn or
Rn/Rn0
lmax
Color in solution
pKa ¼ pHeq
Neutral IP
Acid Neutral Acid
1
2
3
4
Az
TMA
Gu
Az
TMA
Gu
Az
TMA
Gu
Az/Az
Az/TMA
Az/Gu
435
435
458
506
e
465 515 Yellow Red
477 517 Yellow Red-brick 0.75
492 538 Yellow Red
0.50
The attempts to directly obtain bis azo diamine 13, the required
starting reagent for the synthesis of tetra azo derivatives, failed.
When para-di nitrosobenzene was condensed with para-
1.34
0.96
0.98
1.21
515 556 Red
519 560 Red
536 576 Violet
Violet
Violet
Indigo
546
438
439
463
528
550
564
464 511 Yellow Red-brick 0.31
470 518 Yellow Cyclamen 1.58
495 542 Yellow Cyclamen 1.45
Table 3
Absorption maxima of the main visible band of mono azulenic diazenes, Rn ¼ Az
(
lmax in nm in methanol).
553 604 Red
561 607 Red
576 617 Violet
557 586 Violet
597 615 Violet
596 624 Violet
Blue
Blue
Blue
Violet
Blue
Blue
0.74
1.23
1.36
1.71
1.46
1.29
0.74
1.56
1.47
AzN2Pha
422
Bis azo derivatives
Tris azo derivatives
para (or p,p)
Comp. 17Az/469
Comp. 17TMA/484
Comp. 17Gu/517
Comp. 16Az/428
Comp. 16TMA/438
Comp. 16Gu/459
Comp. 2Az/494
Comp. 2TMA/514
Comp. 2Gu/540
Comp. 1Az/429
Comp. 1TMA/438
Comp. 1Gu/458
TMA/TMA 540
TMA/Gu
Gu/Gu
Az
TMA
Gu
559
566
434
441
464
meta (or m,m)
10
468 528 Yellow Red
470 519 Yellow Red
493 539 Yellow Red
a
Az ¼ azulen-1-yl.

1174
A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
Fig. 1. The isosbestic points of several synthesized dyes.
in the molecule. Thus, the bathochromic shift of ca. 25 nm was
found for lmax of the main visible band when 17 is compared with 2,
whereas for the compounds 16 and 1 the values of lmax remained
unchanged.
The inductive effect of the alkyl substituents on azulenyl moiety
enhances the electron density and mobility along the molecule.
Therefore, the bathochromic effect increases with the number of
alkyl groups (Table 3). The alkyl substitution was more effective for
the para isomers, but their effect has also been observed for the
meta isomers.
It is not surprising that for the symmetric bis (azulen-1-yl)azo
systems, 3 and 4 with Rn ¼ Rn0, no significant difference in the lmax
of the main visible band was detected due to the decrease in the
charge polarization, which takes place in 1 and 2. The alkyl
substituents on azulen-1-yl moieties produce a bathochromic shift
for all compounds being more pronounced for the paraepara
isomers and for the guaiazulenyl group.
There are no significant differences in lmax of the main visible
band between the compounds that contains an azoxy group, 10 and
15, and the corresponding compounds only with azo groups, 4. For
the compounds containing one azo or azoxy bond the difference
between the values of the main visible band of these groups is
significant (azobenzene has a lmax ¼ 314 nm, while azoxybenzene
has a lmax ¼ 322 nm in ethanol) [38]. However, this gap decreases
with the increase of the number of azo groups. This behavior can be
explained by an extended conjugation between azo and azoxy
groups when the extra oxygen atom acquires a lower influence on
the whole chromophores.
The very low solubility (at least at some pH values) of several
polyazoazulenes in standard solvents, e.g. water or alcoholewater
mixtures, forced us to choose a solvent mixture which dissolves all
the compounds in both basic and acidic media and, at the same
time, allows an easy recording of pH values. Therefore, the acide
base properties of the dyes 1e4 were studied in dioxaneewater
Fig. 2. The shift of the main visible band with the solvent for the compounds 2Az and 4Az.

A.C. Razus et al. / Dyes and Pigments 92 (2012) 1166e1176
1175
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described in Table 4. As a rule, the obtained pKa values (Table 4)
indicate that all the compounds are very weak bases. Usually, only
the single protonation of dyes 1e4 is observed in relatively strong
acidic medium. However, electron rich azulenes, such as guaiazu-
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protonation. Therefore, in these cases, at lower pH, the protonation
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all the compounds is significantly bathochromic shifted. The
absorption gap between the neutral and strong acid form is higher
in the case of the meta isomers (ca. 80 nm) and lower for para (ca.
55 nm). The azoxy groups behave similarly with the azo groups
even the differences of pKa values of their conjugated acids are
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The high polarizability of paraepara compounds 2 or 4 produces
a strong positive solvatochromic effect. Thus, a bathochromic shift
over 50 nm of the main visible band is obtained for the solutions in
nonpolar solvents, e.g. hexane, as compared with the aprotic polar
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4. Conclusions
The syntheses of meta,meta- and para,para-tris azo compounds,
1e4 was accomplished in good yields by coupling reaction between
corresponding mono- or di-arylamino moieties and azulenes.
When two azulene-1-yl moieties are present in the molecules, they
can be either identically or differently substituted. In our attempt to
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compounds 15 were obtained. The importance of the relative
positions of substituents on phenylene rings, as well as the influ-
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electronic spectra of the investigate dyes, were discussed and
compared with the behavior of the already studied bis azo deriv-
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the investigated tris azoic compounds were recorded. The resulted
pKa values of their conjugated acids proved their very weak
basicity. Our results also suggest the possibility of the double
protonation of some of these compounds. The high solvatochromic
behavior of the compounds 2 and 4 enables us to expect also their
molecular hyperpolarizability.
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Acknowledgments
The financial support of this research, received from the
Ministry of Education and Research, Romania, PN-II No.115/2007, is
gratefully acknowledged.
[28] Razus AC, Birzan L, Surugiu NM, Corbu AC, Chiraleu F. Syntheses of azulen-1-
yl-benzothiazol-2-yl diazenes. Dyes Pigm 2007;74:26e33.
[29]. Razus AC, Birzan L, Cristea M, Ungureanu E-M, Cretu M-S. Investigation on the
correlation between the structure of azulen-1-yl-benzothiazol-2-yl diazenes
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yl moieties. Part 2: The synthesis, characterization, electronic spectra and
basicity of novel, bis aromatic diazenes containing two azulen-1-yl moieties.
Dyes Pigm 2009;82:216e25. and the references therein.
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