Synthesis, optical characterization and crystal and molecular X-ray structure of a phenylazojulolidine derivative

Article abstract of DOI:10.1016/j.dyepig.2011.09.001

The synthesis, spectroscopic characterization, and X-ray crystal structure of [4-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-ylazo)-phenyl]- methanol azodye are reported. A 37-47 nm bathochromic shift has been observed by comparison with analogou

Full text of DOI:10.1016/j.dyepig.2011.09.001

Dyes and Pigments 92 (2012) 1177e1183
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis, optical characterization and crystal and molecular X-ray structure
of a phenylazojulolidine derivative
,
a
b
Nadia Barberoa, Claudia Baroloa, Domenica Marabellob , Roberto Buscaino , Giuliana Gervasio ,
*
,
Guido Viscardia
**
a Department of General Chemistry and Organic Chemistry and NIS, Interdepartmental Centre of Excellence, University of Torino, C.so M. d’Azeglio 48, I-10125 Torino, Italy
b Dipartimento di Chimica IFM and CrisDi (Centro Interdipartimentale Cristallografia Diffrattometrica), Università di Torino, Via Pietro Giuria 7, I-10125 Torino, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 July 2011
Received in revised form
2 September 2011
Accepted 5 September 2011
Available online 22 September 2011
The synthesis, spectroscopic characterization, and X-ray crystal structure of [4-(2,3,6,7-tetrahydro-
1H,5H-pyrido[3,2,1-ij]quinolin-9-ylazo)-phenyl]-methanol azodye are reported. A 37e47 nm bath-
ochromic shift has been observed by comparison with analogous azodyes where diethylamino or
dimethylamino groups act as donor moiety in agreement with the larger electronic donating properties
of julolidine. The azobenzene skeleton adopts a planar trans-configuration and intra- and inter-molecular
hydrogen bonds have been detected. A correlation between the spectroscopic and the molecular features
has been attempted.
Keywords:
Azodyes
Ó 2011 Elsevier Ltd. All rights reserved.
Dipolar dyes
X-ray analysis
Crystal structure
H bond
Nonlinear optics (NLO)
1. Introduction
nitrogen atom, that allows a more efficient delocalization of the
electron lone pair. Second harmonic generation efficiency confirmed
In recent decades, organic colour chemistry is undergoing very
exciting developments as a result of the opportunities presented by
dye applications in high technology fields [1]: electronic devices
[2,3], linear and non-linear optics (NLO) [4], sensors [5,6], fluores-
cent probes [7,8], biomedical uses [9e12] and solar cells [13,14].
Owing to the importance of functions performed by dyes, beyond
the simple provision of colour, they are in general referred as
“functional dyes” [15,16].
Azo compounds in particular are used in the fields of non-linear
optics and optical data storage [17e21]. Their optical and spectro-
scopic properties depend not only on the atomic arrangement in
the molecular structure [22] but also on the crystal packing.
Spectroscopic data (UVeVis) [23,24], proton magnetic resonance
spectra [25], and dipole moments measurements [26] of dipolar
azodyes suggest that julolidine is a particularly powerful electron
donor moiety, thanks to the nearly planar sp2 conformation at the
the larger push-pull nature of dipolar NLO-phores containing juloli-
dine moiety compared with no-cyclic arylamines derivatives [27]. It is
also known that the derivatives of 9-phenylazojulolidine have
a pronounced bathochromic shift of the first band in comparison with
the corresponding derivatives of 4-dimethylaminoazobenzene [24].
This large bathochromic shift is associated with the improved
conjugation of the amino-nitrogen atom with the aromatic ring
brought by the methylene bridges in the julolidine system. A red shift
has also been reported for stilbene dyes [28] where replacing
4-(dimethylamino)phenyl with julolidine lead to an increase of
second order hiperpolarizability (b0) due to the greater
p-electron
donating ability of julolidine.
Despite the interesting results related to azodyes containing
julolidine moiety, no crystallographic data have been published at
the moment even if X-ray analysis can give information about the
planarity of the molecule. Actually, Hallas et al. [26] suggested that
the terminal nitrogen atom in the 9-phenylazojulolidines is
more nearly sp2-hybridized than that in the 4-phenylazo-N,N-
diethylanilines.
* Corresponding author. Tel.: þ39 011 6707504; fax: þ39 011 6707855.
** Corresponding author. Tel.: þ39 011 6707598; fax: þ39 011 6707591.
E-mail addresses: domenica.marabello@unito.it (D. Marabello), guido.viscardi@
unito.it (G. Viscardi).
In the present paper, we report the synthesis, spectroscopic
characterization and single crystal X-ray analysis of the
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.09.001

1178
N. Barbero et al. / Dyes and Pigments 92 (2012) 1177e1183
[4-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-ylazo)-
phenyl]-methanol (1) (Fig. 1), an interesting intermediate for NLO-
dye based on julolidine moiety.
2. Experimental
2.1. Materials
Starting materials as well as synthetic grade solvents were
purchased from Aldrich and used without further purification.
Chromatographic separation was carried out on direct silica gel
(200e300 mesh).
2.2. Synthesis of [4-(2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]
quinolin-9-ylazo)-phenyl]-methanol (1)
Fig. 1. Synthesis of azodye 1.
Table 1
A solution of NaNO2 (6.80 g, 20 ml of water) was added drop-
wise into a mixture of 4-aminophenylmethanol (12.14 g), HCl (36%,
40 ml) and water (100 ml) with vigorous stirring at 273 K. After
30 min of stirring, the diazonium salt solution was filtered and
dropwise added to coupling agent solution, cooled at 273e5 K and
prepared by adding 25 g of julolidine hydrobromide in 750 ml of
water and equimolar quantity of sodium acetate. During the addi-
tion of diazonium salt solution, pH was monitored continuously by
pHmeter owing to maintain the pH 4 by addition of solid sodium
acetate. After 1 h of reaction, solid NaHCO3 was added until
neutralization and the mixture extracted with ethyl acetate. The
organic phases were anhydrified with anhydrous Na2SO4, filtered
and evaporated. The crude solid was purified by flash chromatog-
raphy on silical gel, using petroleum ether/ethyl acetate (70/30 v/v)
mixture as eluent. Dye 1 was obtained as red-violet powder in 55%
yield.
The red crystals suitable for X-ray analysis were obtained by
dissolving the powder in acetonitrile at 60 ꢀC, and slowly cooling
the solution at room temperature with partial slow evaporation of
solvent; m.p. 135e137 ꢀC; 1H-NMR (400 MHz, CDCl3): 1.99 ppm
(m, 4H, H5), 2.81 ppm (t, 4H, H6), 3.27 ppm (t, 4H, H4), 4.73 ppm
(s, 2H, CH2OH); 7.43 ppm (m, 4H, H1 þ H3), 7.78 ppm (d, 2H, H2);
13C-NMR (50 MHz, CDCl3): 21.4; 27.6; 49.9; 64.6; 120.7; 121.9;
122.6; 127.3; 141.6; 142.5; 145.5; 152.6 ppm. MS-EI (m/z): 307 (Mþ),
172 (100%), 142, 107, 91, 77; FT-IR (cmꢁ1): 3340 (OeH), 2927 and
2837 cmꢁ1 (aliphatic CH), 1600 and 1529 (benzene CeC). Elemental
analysis: C19H21N3O Calc: C, 74,24; H, 6,89; N, 13,67; found: C,
74,20; H, 6.90; N, 13.66.
Crystal data, experimental details and refinement parameters for azodye 1.
Empirical formula
C19H21N3O (1)
Formula weight (amu)
Colour/shape
Crystal dimension (mm)
Lattice type, space group
Unit cell dimensions
307.39
Red/prismatic
0.14 ꢂ 0.22 ꢂ 0.42
Monoclinic, P21/c
a ¼ 8.398(1) Å
b ¼ 24.591(4) Å
c ¼ 7.785(1) Å
b
¼ 99.704(3)ꢀ
Volume (Å3)
1584.7(4)
4
Z (number of molecules in unit cell)
Measurement temperature (K)
Density (calculated) (g/cm3)
F(000)
293(2)
1.288
656
0.082
5124
Absorption coefficient (mmꢁ1
Reflection collected
)
Unique reflection
2477
P
P
Rint
h,k,l limits
¼
jjFoj2 ꢁ jFoj2ðmeanÞj= jFoj2
0.0293
ꢁ10 ꢃ h ꢃ 6
ꢁ32 ꢃ k ꢃ 22
ꢁ9 ꢃ l ꢃ 9
1.66/28.30
208
0.0839
0.1941
1.214
q
min./max. deg.
Np (Number of parameters)
P
P
jjFoj ꢁ kjFcjj= jF0j
P
RðFÞ ¼
ꢀ
ꢁ
P
1=2
Rw ¼
ðwFo2 ꢁ Fc2Þ2= wðFo2Þ2
X
ꢀ
Goodness-of-fit ¼
ðwFo2 ꢁ Fc2Þ2=
1=2
ꢁ
ðno: of unique reflections ꢁ no: of parametersÞ
Largest peak and hole in final difference map (eꢁÅ3)
0.20 and ꢁ0.23
Fig. 2. a. Solvatochromism of azodye 1. b. Halochromism of azodye 1.

N. Barbero et al. / Dyes and Pigments 92 (2012) 1177e1183
1179
Fig. 3. Comparison between a) absorption and fluorescence emission spectrum of azodye 1 in DMSO and b) diffuse reflectance and fluorescence emission spectrum on the solid
sample.
2.3. Characterization
atoms were anisotropically refined. All hydrogen atoms have
been located on the last difference Fourier maps and in order to
better refine the structure all but H(8) of the eOH group have
been calculated and refined riding on the connected C atom
(Uiso(H) 1.2 times Ueq(C)). Only the coordinates of H(8) were fixed
at the value found in the last difference Fourier maps, and its Uiso
has been set at 1.5 times Ueq of C(8). Programs used were
SHELXTL [29] for structure solution, refinement and molecular
graphics, Bruker AXS SMART (diffractometer control), SAINT
(integration), SADABS (absorption correction) [30]. Crystallo-
graphic data, experimental details, and refinement parameters
are listed in Table 1.
CCDC 830926 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via www.
ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.
cam.ac.uk, or by contacting The Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: þ44 1223
336033.
The 1H-NMR spectrum was recorded on a Jeol EX400 NMR
spectrometer, while 13C-NMR was recorded on a Brucker AC200
in CDCl3 using CHCl3
(
dH ¼ 7.25 ppm,
d
C ¼ 77.36 ppm) as
reference. Mass spectrum was recorded on a Thermo Finnigan,
EI direct injection, 70 eV. IR spectrum was recorded in the
region of 4000e400 cmꢁ1 using a Shimadzu FT-IR 8400 spec-
trophotometer (KBr pellets). UVeVis spectra were recorded on
a Shimadzu UV-1700 spectrometer using different solvents in
order to investigate the solvatochromic behaviour of dye 1. A
stock solution (3.5 ꢂ 10ꢁ3 M) in dimethylsulphoxide (DMSO)
was prepared and dilutions (3.5 ꢂ 10ꢁ5 M) in tetrahydrofuran
(THF), toluene, dichloromethane, dimethylformamide (DMF),
dimethyl sulfoxide (DMSO) and ethanol were analysed. An hal-
ocromic study has been performed in ethanol solution
(w10ꢁ5 M) by adding different quantities of acidic (HCl, H2SO4,
HBr) water solutions. Diffuse reflectance spectrum was per-
formed on a Cary 5000 UVeViseNIR Spectrophotometer after
dilution with Poly(tetrafluoroethylene).
Fluorescence measurements were recorded using a LS55 Perkin
Elmer spectrofluorimeter equipped with a xenon lampsource and
a 5 mm path length quarz cell. Fluorescence spectrum of dye 1 in
DMSO was recorded in the range of 500e600 nm upon excitation at
470 nm.
Table 2
Selected bond lenghts (Å) and angles (ꢀ) of azodye 1.
C(l)eC(2)
C(l)eC(6)
C(l)eC(7)
C(2)eC(3)
C(3)eC(4)
C(4)eC(5)
C(4)eN(9)
C(5)eC(6)
1.371(5)
1.376(5)
1.520(5)
1.382(5)
1.371(5)
1.379(5)
1.434(4)
1.378(5)
1.408(5)
1.255(4)
1.410(4)
1.388(5)
1.392(5)
1.368(4)
1.409(5)
1.501(4)
1.520(5)
1.499(5)
1.457(4)
1.367(4)
1.445(4)
1.481(5)
1.486(5)
1.496(5)
1.377(5)
1.414(5)
C(1)eC(7)eO(8)
112.6(3)
113.9(3)
113.9(3)
118.5(3)
121.6(3)
119.4(3)
121.5(3)
119.1(3)
109.3(3)
109.1(3)
112.6(3)
122.7(3)
122.2(3)
115.1(3)
113.1(3)
111.9(4)
110.8(4)
118.3(3)
122.5(3)
119.2(3)
122.2(3)
120.2(3)
119.8(3)
120.0(3)
C(4)eN(9)eN(10)
N(9)eN(10)eC(11)
C(22)eC(11)eC(12)
C(13)eC(12)eC(11)
C(12)eC(13)eC(23)
C(12)eC(13)eC(14)
C(23)eC(13)eC(14)
C(13)eC(14)eC(15)
C(16)eC(15)eC(14)
N(17)eC(16)eC(15)
C(23)eN(17)eC(18)
C(23)eN(17)eC(16)
C(18)eN(17)eC(16)
N(17)eC(18)eC(19)
C(18)eC(19)eC(20)
C(19)eC(20)eC(21)
C(22)eC(21)eC(23)
C(22)eC(21)eC(20)
C(23)eC(21)eC(20)
C(21)eC(22)eC(11)
N(17)eC(23)eC(13)
N(17)eC(23)eC(21)
C(13)eC(23)eC(21)
X-ray crystal data have been collected on a Siemens P4
diffractometer equipped with a Bruker APEX CCD detector using
graphite-monochromatized MoK
a
radiation (
l
¼ 0.71073 Å). The
intensities have been semi-empirically corrected for absorption,
using symmetry equivalent reflections and the refinement was
made using full-matrix least-squares on F2. All non-hydrogen
C(7)eO(8)
N(9)eN(10)
N(10)eC(11)
C(11)eC(22)
C(11)eC(12)
C(12)eC(13)
C(13)eC(23)
C(13)eC(14)
C(14)eC(15)
C(15)eC(16)
C(16)eN(17)
N(17)eC(23)
N(17)eC(18)
C(18)eC(19)
C(19)eC(20)
C(20)eC(21)
C(21)eC(22)
C(21)eC(23)
Fig. 4. ORTEP plot (50% probability) of azodye 1.

1180
N. Barbero et al. / Dyes and Pigments 92 (2012) 1177e1183
Table 3
Crystallographic comparison of the azo-skeleton between some azo-compounds with different structure type.
Compound
N1]N2
C1eN1
C2eN2
Angle between
phenyl groups
Ref.
1
2
1.255(4)
1.247(2)
1.434(4)
1.428(2)
1.410(4)
1.428(2)
5.8ꢀ
This work
[36]
planar
3
4
1.276(4)
1.272(4)
1.415(5)
1.414(4)
1.394(5)
1.387(4)
3.45ꢀ
2.44ꢀ
[41]
[41]
5
6
1.260(4)
1.255(3)
1.439(4)
1.431(3)
1.420(4)
1.414(3)
10.3ꢀ
5.5ꢀ
[39]
[39]
7
8
1.263(2)
1.217(3)
1.427(3)
1.442(3)
1.405(3)
1.442(3)
42.2ꢀ
[39]
[40]
0ꢀ
9
1.253(6)
1.454(6)
1.454(6)
76.2ꢀ
[42]
10
11
1.257(7)
1.295(4)
1.460(7)
1.407(5)
1.464(7)
1.371(5)
68.7ꢀ
[47]
[38]
9.4ꢀ
12
1.267(3)
1.427(3)
1.407(3)
planar
[37]
13
14
1.221(3)
1.209(7)
1.490(3)
1.674(7)
1.490(3)
1.674(7)
[45]
[46]

N. Barbero et al. / Dyes and Pigments 92 (2012) 1177e1183
1181
Table 4
3.3. Crystal structure
Intra- and inter-molecular H-bonds geometry for azodye 1.
The ORTEP plot of the molecular structure, with the atom
labelling, of azodye 1 is showed in Fig. 4 and relevant bond lengths
and angles are listed in Table 2.
The azobenzene skeleton adopts a trans-configuration with the
two phenyl rings forming a dihedral angle of 5.8ꢀ, in agreement
with most of the structures of the related azodye molecules
[36e40]. The planarity around N(17) is confirmed. The rough
DeH$$$A
DeH
(Å)
H$$$A
(Å)
D$$$A
(Å)
D-H$$$A
H$$$AeX
(ꢀ)
(ꢀ)
Intramolecular bonds
C(5)eH(5)$$$N(10)
C(12)eH(12A)$$$N(9)
Intermolecular bonds
O(8)eH(8A)$$$N(9)
C(16)eH(16A)$$$O(8)
C(3)eH(3A)$$$O(8)
C(2)eH(2A)$$$O(8)
C(20)eH(20A)$$$N(10)
C(19)eH(19A)$$$N(10)
2.50
2.48
0.930a
0.930a
2.740
2.728
95
96
85
85
2.07
2.56
2.86
2.93
3.14
3.20
1.01
2.971
3.474
3.477
3.514
3.674
3.852
149
157
125
122
131
112
130
109
128
158
115
119
0.970a
0.930a
0.930a
0.970a
0.970a
planarity of this dye may suggest a wide p-electron delocalization,
reflected in a shortness of the NePh bonds and an increase of the
N]N double bond with respect to a molecule without aromatic
groups. This effect on the N]N and NePh bonds should be
enhanced by the electron donor ability of the substituents con-
nected to the aromatic rings.
a
H position calculated and refined riding on the corresponding C atom (see
experimental).
In azodye 1 the N(9)eN(l0) bond distance is 1.255(4) Å, in
agreement with that of azobenzene (1.247(2) Å) [36], and some of
its derivatives [37,38,40,42]. In order to assess the effect of the
presence of a strong donating group (such as julolidine with respect
to standard linear alkylamino), crystallographic features of several
azo-compounds are reported for a comparison in Table 3. The N]N
bond distance can vary widely, and it is difficult to find a strict
correlation with the electron features of the substituents. In
particular, considering the e.s.d.’s of all distance data, biphenyl
azodyes 1e7and 9e12 show a slight elongation of N]N distance
with respect to azodyes 13 and 14, where no aromatic rings is
connected to this bond.
The NePh bond distances, instead, seem to be influenced by the
presence of both donor and acceptor groups. In fact, in compounds
3, 4, 6, 7, 11, 12 a shortness of the NePh bond can be observed when
an electron donor substituent is present in para position with
respect to the azo bond. Also in the azodye 1 this shortness is
detected even if only a donor group is present: the N(10)eC(11) and
C(4)eN(9) bond distances are 1.410(4) and 1.434(4) Å, respectively.
Harada et al. [43] have carried out a crystallographic study on
the particular behaviour of the N]N and NePh bonds at different
temperatures. They have observed an increasing of the N]N bond
length with the decreasing of the temperature from 296 to 90 K and
3. Results and discussion
3.1. Synthesis
The synthetic approach of azodye 1 is reported in Fig. 1.
Conventional diazotation with sodium nitrite and hydrochloric acid
of 4-aminophenylmethanol gave the required diazonium salt that
was reacted with a water solution of julolidine hydrobromide. The
reaction was performed in acidic aqueous solution between 0 and
5 ꢀC and solid sodium acetate was added to obtain the optimal pH
conditions (pH ¼ 4) for the coupling reaction on the tertiary aryl
amine, before and during the addition of diazonium salt solution.
After pH adjustment with sodium bicarbonate, a red solid was
obtained.
3.2. Spectroscopic properties
The UVeVis characterization (reported in Fig. 2) confirmed what
previewed: the presence of the julolidine ring instead of a dimethyl
or diethyl benzene moiety caused a red shift of the maximum of
absorption. The lmax of the julolidine compound is 450 nm in
ethanol versus 410 nm for the dimethyl benzene compound [31]
and 420 nm for the diethyl benzene compound. [32] Moreover,
a positive solvatochromic behaviour is observed (Fig. 2a), ranging
from 440 nm in toluene to 469 nm in DMSO. A complete reversible
bathocromic (þ80 nm) and hypercromic shift (þ100%) of the
justified
this behaviour as an artifact caused by the torsional
vibration of the NePh bonds in crystals. This behaviour can occur
also in the azodye of this work, and cannot put in evidence the
expected lengthening of the N]N.
Intramolecular H-bond of CeH$$$N type [44] (Table 4 and Fig. 4)
have been detected in the azodye 1. The presence of such type of
stabilizing interactions, that contribute to the planarity of the
molecule, has been reported also for the planar azobenzene
derivatives 3, 4 and 11.
In the crystal packing two inter-molecular OeH$$$N and
CeH$$$O hydrogen bonds are noticeable. They involve the same OH
group and connect 3 molecules (Fig. 5 and Table 4). These two types
of interaction are responsible of the formation of layers of parallel
molecules, shown in Fig. 6. In particular O(8)eH(8A)$$$N(9) is
a very short interaction (2.07 Å), responsible for the elongation of
p
/ p
* band were obtained by acidification (HCl and HBr) of
ethanol solution (Fig. 2b) as generally already observed for push-
pull azodye owing to reversible protonation at the azo group [1].
Surprisingly, dye 1 also shows a fluorescence signal, even if
weak, in DMSO with a Stoke’s shift of 72 nm (Fig. 3) and with higher
intensity on the crystalline solid sample (Stoke’s shift of 150 nm). In
fact, it has been proven that pseudo-stilbenes type azobenzenes are
not good emitters, even at low temperature and adsorbed to
surfaces, their non-radiative decay rate overwhelms their radiative
decay [33], unless an hydroxyl group is in orto position with respect
to N]N bond [34,35].
Fig. 5. Representation of OeH$$$N and CeH$$$O inter-molecular hydrogen bonds.

1182
N. Barbero et al. / Dyes and Pigments 92 (2012) 1177e1183
Fig. 6. Representation of the plane of molecules connected towards the OeH$$$N and CeH$$$O inter-molecular hydrogen bonds, with the sandwich
pep stacking interaction
evidenced.
Fig. 7. Representation of the weak CeH$$$O hydrogen bonds that are responsible of the cohesion of the layers of molecules.
the O(8)eH(9) bond (1.01 Å) and for the orientation of H(8) toward
the N(9) atom. The C(16)eH(16A)$$$O(8) hydrogen bond is instead
longer (2.56 Å) and involves an hydrogen atom of one methylene
The azobenzene skeleton adopts a planar trans-configuration;
the influence, however, of the electron donating feature of the
julolidine substituent can be detected only in the shortening of the
NePh bond but not on the lengthening of the N]N bond, probably
due to the torsional vibrations of the azo fragment. The data show
a strong tendency of this compound to form intra and inter-
molecular H-bonds, similar to those found in other azobenzene
derivatives.
group of the julolidine. A sandwich
pep stacking interaction,
involving the C(1)eC(6) ring and the aromatic ring of the julolidine,
is also present in this layer, with a distance between aromatic rings
of 4.083 Å (see Fig. 6).
Other inter-molecular hydrogen bonds (see Fig. 7) involve the
oxygen of the OH group with two hydrogen atoms of benzene
(2.93 and 2.86 Å) and the N(10) with the hydrogens of two
methylene groups of the julolidine (3.20 and 3.14 Å). These two
weaker inter-molecular contacts are responsible of the cohesion
between the previous layers of the molecules. The inter-molecular
hydrogen bonds observed in azodye 1 are common to benzene
azodyes and the lengths found are in agreement with literature
data [22,38].
The obtained results can be useful and important for the design
of functional dyes (i.e. NLO-octopolar dyes, DSC sensitizers etc.)
containing azobenzeneejulolidine moiety.
Acknowledgements
NB, CB, RB and GV acknowledge financial support of this work
by the EU project “Innovasol” grant agreement number 227057-2,
DyeCells project (grant cod. 121) from Ministero dell’Ambiente e
della Tutela del Territorio e del Mare (Italy) and thank Compagnia
di San Paolo and Fondazione CRT for continuous equipment
supply.
4. Conclusions
The synthesis of a julolidine substituted azodye has been per-
formed, its spectroscopic properties, as well as its X-ray crystal
structure have been determined. This is the first X-ray structure of
julolidine azo-compound in literature. Julolidine moiety induces
a large bathochromic shift with respect to diethylamino or dime-
thylamino groups present as donor moiety, confirming the larger
electronic donating properties. Moreover, this dye presents an
unusual detectable fluorescence emission with very large Stoke’s
shift, both in solid state and in solution, even at room temperature.
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