Synthesis and characterization of novel (oligo)thienyl-imidazo-phenanthrolines as versatile π-conjugated systems for several optical applications

Article abstract of DOI:10.1016/j.tet.2008.07.043

A series of new heterocyclic chromophores 3-6 were synthesized in moderate to excellent yields by condensation of 5,6-phenantroline-dione with formyl-thiophene derivatives 1-2 in the presence of ammonium acetate in glacial acetic acid. These chromophores possess an (oligo)thienyl π-conjugated system attached to an imidazo-phenanthroline moiety. These derivatives were evaluated concerning their solvatochromic properties, thermal stabilities, and molecular optical nonlinearities.

Full text of DOI:10.1016/j.tet.2008.07.043

Tetrahedron 64 (2008) 9230–9238
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and characterization of novel (oligo)thienyl-imidazo-phenanthrolines
as versatile
p-conjugated systems for several optical applications
,
Rosa M.F. Batista a, Susana P.G. Costa a, M. Belsley b, Carlos Lodeiro c, M. Manuela M. Raposo a
*
a Centro de Qu´ımica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal
b Departamento de F´ısica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal
c
´
ˆ
REQUIMTE, Departamento de Quımica, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, 2829-516 Monte de Caparica, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 May 2008
Received in revised form 9 July 2008
Accepted 11 July 2008
Available online 17 July 2008
A series of new heterocyclic chromophores 3–6 were synthesized in moderate to excellent yields by
condensation of 5,6-phenantroline-dione with formyl-thiophene derivatives 1–2 in the presence of
ammonium acetate in glacial acetic acid. These chromophores possess an (oligo)thienyl
p-conjugated
system attached to an imidazo-phenanthroline moiety. These derivatives were evaluated concerning
their solvatochromic properties, thermal stabilities, and molecular optical nonlinearities.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
p-Conjugated systems
Thiophene
Imidazole
Phenanthroline
Solvatochromic probes
Hyper-Rayleigh scattering (HRS)
Thermal stability
Nonlinear optics (NLO)
1. Introduction
Oligothiophenes behave as very efficient electron relays almost
comparable to polyenes; thiophene has a lower resonance energy
The design and synthesis of organic chromophores as nonlinear
optical (NLO) materials has been the focal point of a large amount of
recent research in great part due to the potential advances in the
fields of optical communication, information processing, frequency
doubling and integrated optics that could be realized by materials,
which display strong second order optical nonlinearities together
with robust material properties.1 Donor–acceptor substituted het-
eroaromatic compounds have attracted widespread interest be-
cause it has been experimentally and theoretically demonstrated
that they increase the second-order molecular NLO properties of
push–pull chromophores with respect to the corresponding aryl
analogues. It has also been demonstrated that the electron density
than that of benzene, and oligothiophenes have been shown to
produce larger values of the molecular hyperpolarizability, . The
larger nonlinearities were attributed to the bathochromic effect of
sulfur, the partial decrease of aromatic character, and an increased
b
p
-overlap between the thiophene units. Oligophenylenes attain
a rapid saturation beyond the terphenyl unit, whereas oligothio-
phenes have a strong tendency to increase as the number of
b
thiophene units increases. Aside from the electron transmission
efficiency, another merit of oligothiophenes is their inherent sta-
bility from which thiophene-based donor (D)–acceptor (A) chro-
mophores should benefit.4 Moreover, these push–pull systems are
also excellent solvent polarity indicators due to their positive sol-
vatochromism.4b–e,g–j This type of compounds can therefore be
applied in electro-optical devices.1
of the
p-conjugated system plays a major role in determining
second-order NLO response.2 Electron excessive/deficient hetero-
cycles act as auxiliary donors/acceptors when they are connected to
donating/withdrawing groups, and the increase of donor/acceptor
Triaryl(heteroaryl)-imidazole2e,5 and benzimidazole6 based
chromophores have received increasing attention due to their
distinctive linear and nonlinear optical properties and also due to
their excellent thermal stability in guest–host systems. Imidazole
derivatives can be further substituted on the nitrogen atom so that
the electron density of the chromophore can be changed. This
functionalization will remove the possibility of tautomerism and
strength leads to substantial increase in
b
values.3
* Corresponding author.
E-mail address: mfox@quimica.uminho.pt (M.M.M. Raposo).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.07.043

R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
9231
introduces a new potentially useful chemical variable for the op-
2. Results and discussion
2.1. Synthesis
timization of NLO activity of the chromophore (e.g., introduction of
groups with suitable electronic properties). The imidazole ring can
be easily tailored to accommodate functional groups, which allows
the covalent incorporation of the NLO chromophores into poly-
amides leading to NLO side chain polymers.5a,d,7 For the practical
application of second-order NLO materials, not only a high hyper-
polarizability but also good thermal stability is required. In this
respect, promising candidates are (benz)imidazole derivatives,5,6 as
well as conjugated (oligo)thiophenes.4 Despite all these promising
properties for NLO applications, only a few publications concerning
the synthesis and characterization of NLO chromophores based on
triaryl(heteroaryl)-imidazoles can be found in the available
literature.2e,5a–e,h,m
Due to their optoelectronic properties, aryl-imidazo-phenan-
throlines play important roles in materials science and medicinal
chemistry.8–10 Therefore, they have found application as ligands for
the synthesis of metal complexes of ruthenium(II), copper(II),
cobalt(II), nickel (II), manganese(II), and several lanthanides espe-
cially for nonlinear optical (NLO) applications,8a–c,g while in me-
dicinal chemistry they are important building blocks for the
synthesis of proton, anion, and cation sensors9 or as ligands for
ruthenium(II) and platinum(II) complexes with important and di-
verse biological applications such as probes of DNA structure or
new therapeutic agents due to their capacity to bind or interact
with DNA.10
New material properties can be achieved when new conjugated
systems are composed by different heterocyclic nuclei, which
allow the fine tuning of important physical and/or photophysical
properties. As a result of the optical and conductive properties,
conjugated materials containing thiophene, imidazole, and phe-
nanthroline heterocycles have found many applications including
those described above.4,5,8–10
Owing to synthetic difficulties, most of the NLO imidazoles de-
veloped so far, namely 2,4,5-triaryl(heteroaryl)-imidazoles, only
possess short conjugation pathways (spacers) such as phenyl,
thienyl or thiazolyl.2e,5a–e,h,m Our approach to the design of new
2.1.1. Synthesis of formyl-(oligo)thiophenes 1–2
The formylation of thiophene and oligothiophene derivatives is
usually achieved through two methods: the Vilsmeier reac-
tion,4a,b,13 (or by a modified procedure of the Vilsmeier formylation
using DMF/POCl3 in dichloroethane14) or by metalation followed by
formyldelithiation using DMF.4a,b,15 More recently, palladium cat-
alyzed cross-coupling reactions, have also been used in the
synthesis of formyl-functionalized (oligo)thiophenes.4c,d,h,i
In order to compare the effect of the electronic nature of one or
two imidazo-phenanthroline moieties on the optical properties of
linear or angular oligothienyl-imidazo-phenanthrolines 3–6, for-
myl-oligothiophenes 1–2 containing one or two formyl groups
were used as precursors of phenanthrolines 3–6. Compounds 1b,e,f
and 2b were prepared using two different methods of synthesis:
metalation followed by reaction with DMF (1b and 2b) or through
Suzuki cross-coupling reactions (1e,f).
Therefore, 5-formyl-2-methoxythiophene 1b was synthesized
using our recently reported procedure.4b The metalation of
2-methoxythiophene was carried out using 1.2 equiv of n-BuLi in
dry ether at 0 ꢀC for 1 h. Subsequently, the organolithium derivative
was converted to the corresponding formylthiophene by addition
of 1.2 equiv of DMF followed by refluxing the mixture for 1 h, with
a 73% yield.
Recently, we have demonstrated that 5-alkoxy- and 5-N,N-di-
alkylamino-2,20-bithiophenes are selectively lithiated at the
a-po-
sition of the thiophene ring giving only the mono-formylated
derivatives, 50-formyl-5-alkoxy- or 50-formyl-5-N,N-dialkylamino-
2,20-bithiophenes, when equimolar amounts of bithiophene and
DMF were used.4b In order to obtain the diformyl bithiophene 2b an
excess of the metalation reagent (2 equiv) and also of DMF (2 equiv)
were used. Instead of the diformyl derivative 2b, as the only
product, we obtained a mixture of two compounds (confirmed by
1
TLC and H NMR). The metalation of 5-methoxy-2,20-bithiophene
p
-conjugated systems for several potential optical applications is
using 2 equiv of n-BuLi in dry ether at 0 ꢀC for 1 h followed by
reaction with 2 equiv of DMF by refluxing the mixture for 1 h
produced a mixture of the two formylated derivatives: 50-formyl-5-
methoxy-2,20-bithiophene4b in 42% yield and 5-methoxy-4,50-
diformyl-2,20-bithiophene 2b in 31% yield. The methoxy group in
phenyl or benzyl derivatives is known as a moderately strong ortho
directing substituent with electron withdrawing properties in
metalation reactions.15d,16 In 5-methoxy-2,20-bithiophene 2b, the
methoxy group also demonstrated an ortho directing effect on
the thiophene ring. Consequently, formylation at position 4 of
the bithiophene moiety, ortho to the methoxy group was also
observed for 5-methoxy-2,20-bithiophene giving the diformylated
derivative 2b.
based on the use of electron-rich five-membered heteroaromatics
such as thiophenes and imidazoles in the conjugation pathway,
combined with electron deficient heterocycles such as phenan-
throline, which also acts as an acceptor group due to the deficiency
of electron density on the ring C atoms. Furthermore, the planarity
and the extension of conjugation of the phenanthroline moiety
with imidazole and oligothienyl units lead to an increase of the
overall conjugation. Additionally to the structural characteristics
described above they exhibit also high thermal stabilities making
them interesting for several applications in materials
chemistry.2e,11
To the best of our knowledge, this is the first report on the
synthesis and evaluation of the solvatochromic and optical (linear
and nonlinear) properties of (oligo)thienyl-imidazo-phenanthro-
line derivatives. We are aware of only one article that reports the
Compounds 1a and 1c were commercially available. The syn-
thesis of 50-formyl-2-methoxy-2,20-bithiophene 1d and 4-formyl-
5-piperidino-2,20-bithiophene 2a has been reported by us, recently,
through metalation followed by reaction with DMF or through
Vilsmeier formylation.4b
synthesis of
a thienyl-imidazo-phenanthroline derivative in
which the thiophene ring was linked to the imidazo-phenan-
throline moiety through its position 3. This compound was used
as ligand on the synthesis of a polypyridyl ruthenium complex as
effective coating agent for the synthesis of gold or silver
nanocomposites.8f
2.1.2. Synthesis of (oligo)thienyl-imidazo-phenanthrolines 3–6
Mono- or diformyl (oligo)thiophenes 1–2 with the formyl
group at
a, b or a and b positions of the thiophene ring were
Following our interest in heterocyclic derivatives for several
optical applications (e.g., NLO, OLED’s, etc.)4b–e,g–k,12 we now report
the synthesis and characterization of the thermal and optical
used as precursors of linear and angular phenanthrolines 3–6 in
order to evaluate the effect of the position of the phenanthroline
group on the optical properties of these chromophores. There-
fore, compounds 3–6 with either thienyl, bithienyl or terthienyl
moieties (substituted with H, alkoxy or N,N-dialkylamino donor
groups) linked to the imidazo-phenanthroline system were syn-
thesized in moderate to excellent yields (41–92%, Table 1)
properties of the new
p-conjugated systems 3–6, containing
a functionalized oligothienyl
p-conjugated bridge linked to the
imidazo-phenanthroline system, which is original and different
from other related reports.8–10

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R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
Table 1
2.2. UV–visible study of phenanthrolines 3–4
Yields, IR absorption and 1H NMR data of phenanthrolines 3–6
All the compounds with the exception of bis-phenanthrolines
5–6 were soluble enough to allow the UV–visible study. The elec-
tronic spectra of phenanthrolines 3–4, recorded in dioxane solu-
tions (10ꢁ4 M) showed an intense lowest energy charge-transfer
absorption band in the UV–visible region (Tables 2 and 3). The
position of this band was strongly influenced by the structure of the
Entry Formyl-
Oligothienyl-
R1
n
Yield IR
(%)
n
dH
a
oligothiophene phenanthroline
(cmꢁ1
)
(ppm)b
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
3a
3b
3c
3d
3e
4
H
MeO
H
MeO
H
d
1
1
2
2
3
2
2
2
90
92
88
76
83
79
41
80
3430
3435
3437
3400
3426
3435
3421
3430
13.84
13.25
13.91
13.90
Not visible
13.93, 14.00
Not visible
Not visible
compounds, for example, by the length of the p-conjugated bridge,
2a
2b
5
6
Piperidino
MeO
by the electronic nature of the groups (H or methoxy) substituted
on the oligothienyl moiety, and also by the number of the imidazo-
phenanthroline moieties substituted on the (oligo)thienyl
conjugated system.
a
For the NH stretching band (recorded in KBr).
For the NH proton of the imidazole ring for compounds 3–6 (DMSO-d6).
b
Remarkable differences in energy occur upon conversion of
formyl-oligothiophenes 1–2 to phenanthrolines 3–6. For example,
formyl-thiophene 1a (lmax¼281.5 nm) is shifted 55 nm (phenanthro-
line 3a, lmax¼336.5 nm). In the case of introduction of two imidazo-
phenanthroline moieties, the position of the absorption band, e.g., for
diformyl-thiophene 1f (lmax¼365.5 nm) is shifted 52.5 nm (phenan-
throline 4, lmax¼336.5 nm, Table 3, entries 1 and 6, respectively).
The reason for the red shift in the investigated compound 3b
through the Radziszewski reaction17 of 5,6-phenanthroline-dione
with formyl-thiophene derivatives 1–2 and ammonium acetate in
refluxing glacial acetic acid for 15 h (Scheme 1) in order to
evaluate also the effect of the nature of the
p-conjugated bridge
on the optical (linear and nonlinear) properties of chromophores
3–6.
In the 1H NMR spectra of imidazo-phenanthroline derivatives
signals at about 13.25–13.91 ppm for compounds 3 were detected.
All signals appeared as broad singlets and were attributed to N–H in
the imidazole moiety. A broad correlation could be observed be-
tween the donor properties of the oligothienyl group attached to
position 2 of the imidazole nucleus and the chemical shift of the
nitrogen proton of the imidazole ring in compounds 3 (Table 1). In
fact, from the data in Table 1, one may infer that an increase in the
chemical shift of the NH proton in the 1H NMR spectra results from
a decrease in the electron donating nature of the (oligo)thiophene
moiety. The NH was also identified by IR spectroscopy as a sharp
(lmax¼346 nm) relative to the unsubstituted thienyl-imidazo-phe-
nanthroline 3a (lmax¼336.5 nm) was the strong inductive and con-
jugative effect of the alkoxy substituent (Table 3, entries 1 and 2,
respectively). In general, the stronger the donor and/or acceptor
group,thesmallertheenergydifferencebetweengroundandexcited
states, and the longer the wavelength of absorption. Comparison of
the electronic absorption spectra of thienyl-imidazo-phenanthro-
line 3a (lmax¼336.5 nm) with bithienyl-imidazo-phenanthroline
3c (lmax¼383.5 nm) and terthienyl-imidazo-phenanthroline 3e
(
lmax¼411.5 nm) revealed that an increase in the number of
band within the spectral region of 3400–3437 cmꢁ1
.
thiophene units that constitutes the
p
conjugated bridge causes
H
N
3a R1 = H, n = 1
3b R1 = MeO, n = 1
3c R1 = H, n = 2
3d R1 = MeO, n = 2
3e R1 = H, n = 3
R1
S
N
N
n = 1-3
N
1a-e
R1
CHO
S
N
n = 1-3
N
H
N
4
N
S
N
S
N
H
1a R1 = H, n = 1
1b R1 = MeO, n = 1
1c R1 = H, n = 2
1d R1 = MeO, n = 2
1e R1= H, n = 3
1f
N
N
O
O
N
N
NH4OAc/AcOH/reflux
+
1f R1 = CHO, n = 2
S
N
R3
S
5
N
2a
NH
S
S
R1
R3
N
S
2
N
R2
2b
H
N
MeO
N
2a R1=Piperidino, R2=CHO,R3=H
2b R1=MeO, R2=CHO, R3=CHO
N
S
6
N
N
NH
N
N
Scheme 1. Synthesis of phenanthrolines 3–6 by condensation of 5,6-phenanthroline-dione with formyl (oligo)thiophenes 1–2 in the presence of ammonium acetate in glacial
acetic acid.

R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
9233
Table 2
Solvatochromic data [lmax (nm) and nmax (cmꢁ1) of the charge-transfer band] for phenanthrolines 3–4 in selected solvents with
p
*
values by Kamlet et al.18a
Solventa
p
*
Compound
3a
3b
3c
3d
3e
4
lmax
nmax
lmax
nmax
lmax
nmax
lmax
nmax
lmax
nmax
lmax
nmax
EtOH
0.54
333.0
336.5
337.0
336.0
337.0
30,030
29,717
29,673
29,761
29,673
339.0
346.0
348.0
356.5
357.5
29,498
28,902
28,736
28,050
27,972
377.0
383.5
381.0
386.0
388.0
26,525
26,075
26,246
25,906
25,773
389.0
393.0
391.0
393.0
394.0
25,706
25,445
25,575
25,445
25,380
406.0
411.5
410.0
419.0
420.0
24,630
24,301
24,390
23,866
23,809
413.0
418.0
413.8
421.0
427.8
24,213
23,923
24,166
23,753
23,375
Dioxane
CHCl3
DMF
0.55
0.7618b
0.88
DMSO
1.00
a
Solvents used as received.
a dramatic red shift of the charge-transfer band. This observation
clearly indicates that the incorporation of thiophene units in push–
pull compounds enhances their charge-transfer properties. The
influence of the number of imidazo-phenanthroline moieties is
demonstrated by comparison of the absorption maxima of com-
pounds 3c and 4 as the longest wavelength transition is shifted
from 383.5 nm in 2,20-bithiophenimidazo[4,5-f][1,10]phenanthro-
line 3c to 418.0 nm in 2,20-bithiophene-5,50-bis-imidazo[4,5-
f][1,10]phenanthroline 4.
view of the strong solvatochromism, the good correlation with p
*
values for the 5 solvents investigated and the long wavelength
absorption in the visible range, compounds 3b (Dnmax¼1526 cmꢁ1),
3c
(
(
Dnmax¼752 cmꢁ1),
3e
(
Dnmax¼821 cmꢁ1),
and
4
Dnmax¼838 cmꢁ1), appear to be quite reliable solvent polarity in-
dicating dyes.
2.4. Nonlinear optical properties and thermal stability of
phenanthrolines 3–6
2.3. Solvatochromic behavior of phenanthrolines 3–4
We have used the hyper-Rayleigh scattering (HRS) method19 to
measure the first hyperpolarizability
using the 1064 nm fundamental wavelength of a Q-switched
Nd:YAG laser. Dioxane was used as solvent, and the values were
b of phenanthrolines 3–4
Several studies have demonstrated that the replacement of
a benzene ring by a less aromatic heterocycle in typical donor–
acceptor chromogens of the same chain length and bearing the
same D–A pair results in a significant bathochromic shift (in a given
solvent) of the visible absorption spectra. This red shift obtained,
for example, with thiophene, thiazole and pyrrole rings suggests an
increase of molecular hyperpolarizability, according to theoretical
NLO studies. Experimental data confirmed this positive effect, in
particular, for the five-membered heterocycles mentioned
above.4c–e,g–i,6h,11 In order to investigate whether compounds 3–4
could act as suitable probes for the determination of solvent po-
larity, we carried out a study of the absorption spectra of com-
pounds 3–4 in five selected solvents (ethanol, dioxane, chloroform,
DMF, and DMSO) of different solvation character (Table 2). The
wavelength maxima lmax and wavenumber maxima nmax of com-
b
measured against a reference solution of p-nitroaniline (pNA)20 in
order to obtain quantitative values, while care was taken to prop-
erly account for possible fluorescence of the dyes (see Section 4 for
more details). Compounds 3a and 3b displayed exceptionally large
amounts of fluorescence near the second harmonic wavelength of
532 nm, leading to rather large uncertainties in the corresponding
hyperpolarizabilites. The static hyperpolarizability (b0) values were
calculated using a simple two-level model neglecting damping.
They are therefore only indicative and should be treated with
caution (Table 3).
From Table 3 it is obvious that the increase of the donor strength
of the group substituted on the thiophenic or bithiophenic moieties
resulted both in red-shifted absorption maxima and enhanced
pounds 3–4 are listed in Table 2 and were compared with
p
*
values
b
values for phenanthrolines 3b and 3d (R¼OMe), compared to
for each solvent, determined by Kamlet et al.18 Phenanthrolines 3–4
exhibited positive solvatochromism with respect to their CT
absorption band, i.e., the position of the absorption maximum
shifted to longer wavelengths as the polarity of the solvent in-
creased due to a greater stabilization of the excited state relative to
the ground state with an increase in the polarity of the solvent. In
derivatives 3a and 3c (R¼H) (Table 3, entries 1–4). Although the
uncertainties in the values for the b are rather high, a comparison of
the respective
b
values for 3a (26ꢂ10ꢁ30 esu), 3c (46ꢂ10ꢁ30 esu),
and 3e (320ꢂ10ꢁ30 esu) suggests that an increase in the number of
thiophenic nuclei4g linked to the imidazo-phenanthroline moiety
leads to progressively larger nonlinearities (Table 3, entries 1, 3, and
Table 3
UV–visible absorption for formyl-(oligo)thiophenes 1–2 and phenanthrolines 3–6,
b
and b0 values and Td data for phenanthrolines 3–6a
Entry
Formyl-
oligothiophene
UV–vis.
Oligothienyl-
phenanthroline
R1
n
UV–vis.
b
/10ꢁ30
b0/10ꢁ30
Td
lmax (nm)a
lmax (nm)a (log
3)
(esu)b
(esu)c
(ꢀC)d
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
2a
2b
d
281.5
309.0
349.5
375.5
396.0
365.5
335.6
367.0
d
3a
3b
3c
3d
3e
4
5
6
pNA
H
MeO
H
MeO
H
d
1
1
2
2
3
2
2
2
d
336.5 (4.36)
346.0 (3.84)
383.5 (4.45)
393.0 (4.44)
411.5 (4.43)
418.0 (3.84)
de
26 (þ63, ꢁ26)
110 (ꢃ40)
46 (ꢃ43)
170 (ꢃ40)
320 (ꢃ60)
d
14
57
19
67
110
d
441
341
451
423
467
690
389
725
d
Piperidino
MeO
d
df
d
de
df
d
352.0
16.9
8.5
a
Experimental hyperpolarizabilities and spectroscopic data measured in dioxane solutions.
All the compounds are transparent at the 1064 nm fundamental wavelength.
b
c
d
e
f
Data corrected for resonance enhancement at 532 nm using the two-leveꢁl 1model with b0
¼
b
[1ꢁ(lmax/1064)2][1ꢁ(lmax/532)2]; damping factors not included 1064 nm.21
Decomposition temperature (Td) measured at a heating rate of 20 ꢀC min under a nitrogen atmosphere, obtained by TGA.
Due to insolubility it was not possible to obtain the UV–visible spectrum.
Due to insolubility it was not possible to obtain the first hyperpolarizability,
b value.

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R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
5, respectively).With the exception of bis-phenanthrolines 5–6 all
the compounds were soluble in most common organic solvents.
Therefore, only the latter two compounds were not soluble enough
to permit HRS evaluation.
spectrophotometer. Elemental analyses were carried out on a Leco
CHNS 932 instrument. Mass spectrometric analyses were per-
formed at ‘C.A.C.T.I. – Unidad de Espectrometria de Masas’, Uni-
versity of Vigo, Spain.
All the oligothienyl-imidazo-phenanthrolines 3–6 are ther-
mally stable, high melting materials, with melting points above
320 ꢀC. Thermal stability of compounds 3–6 was estimated by
thermogravimetric analysis (TGA), measured at a heating rate of
20 ꢀC minꢁ1 under a nitrogen atmosphere. The results obtained
revealed the exceptional thermal stability for all compounds,
which could be heated up to Td¼341–467 ꢀC (phenanthroline de-
rivatives 3a–e) or 389–725 ꢀC (bis-phenanthroline derivatives
4–6). The increase of the number of thiophenic units, e.g., as in 3c
(Td¼451 ꢀC) and 3e (Td¼467 ꢀC) and especially the incorporation
All the solvents were of spectrophotometrical grade. Light
petroleum refers to solvent boiling in the range 40–60 ꢀC.
Compounds 1a and 1c were commercially available. The syn-
thesis of formyl-oligothiophenes 1d and 2a was described
elsewhere.4b
4.2. Procedures for the synthesis of formyl- derivatives 1b
and 2b via metalation with n-BuLi followed by reaction
with DMF
of
a second phenanthroline moiety, e.g., comparison of 3c
(Td¼451 ꢀC) with 4 (Td¼690 ꢀC), leads to highly thermal stable
4.2.1. Synthesis of 5-formyl-2-methoxythiophene (1b)
materials.
A 2.5 M solution of n-BuLi in hexanes (0.44 mL, 1.1 mmol) was
added dropwise under Ar at 0 ꢀC to a stirred solution of 2-
methoxythiophene (1.0 mmol) in anhydrous diethyl ether. The
reaction mixture was then stirred for 1 h at 0 ꢀC and was allowed
to stand 15 min at room temperature. DMF (0.05 mL, 1.0 mmol)
dissolved in anhydrous diethyl ether (2 mL) was added dropwise
at room temperature. The mixture was heated at reflux for 1 h.
The mixture was poured into water (20 mL) and extracted with
ethyl acetate (3ꢂ50 mL). The combined organic extracts were
washed with H2O (100 mL), dried with MgSO4 and the solvent
was evaporated under reduced pressure to give the crude 5-for-
myl-2-methoxythiophene 1b, which was purified by ‘flash’ chro-
matography on silica with increasing amounts of diethyl ether in
light petroleum as eluent. Compound 1b was obtained as a brown
3. Conclusions
For the first time, a variety of donor–acceptor substituted phe-
nanthrolines 3 and 5 and bis-phenanthrolines 4 and 6 have been
synthesized, in moderate to excellent yields from easily available
formyl-oligothiophenes 1–2 and low cost commercially available
reagents, using simple and convenient procedures.
These materials exhibit good solvatochromic properties, ex-
ceptional thermal stabilities but modest NLO responses. The chro-
mophore nonlinearities depend primarily on the length of the
p-conjugated bridge and secondarily on the type of substituents on
the (oligo)thienyl moiety.
Our results concerning the nonlinear optical properties of
phenantrolines 3–6 showed that, the resultant values for the
oil (95%). UV (dioxane): lmax nm (log
IR (liquid film) 2931, 1657 (C]O), 1540, 1478, 1418, 1338, 1231,
1211, 1052, 988, 782 cmꢁ1 1H NMR (CDCl3)
3.97 (s, 3H, OCH3),
6.32 (d, 1H, J¼4.5 Hz, 3-H), 7.49 (d, 1H, J¼4.2 Hz, 4-H), 9.63 (s, 1H,
3) 309.0 (3.95), 253.0 (3.57).
n
hyperpolarizability
b
are modest. Moreover, the hyper-
.
d
polarizability of some compounds (especially compounds 3a and
b
3c) have rather high relative uncertainties due to the fact that the
detected signals were relatively small and the amount of fluores-
cence was high. Although imidazo-phenanthroline derivatives
have been of interest in the field of coordination chemistry for
a number of years8–10 only platinum and ruthenium complexes of
aryl-imidazo-phenanthroline have been reported so far from dif-
ferent perspectives, mainly directed at studies of interactions with
DNA. Therefore, some of the new phenanthrolines 3–6, due to
their fluorescence, could be used for other interesting optical ap-
plications such as proton, anion, and cation sensors with envi-
ronmental, biological, and medicinal applications and also as
ligands for the synthesis of several metal complexes for diverse
applications which are already underway.22
CHO). 13C NMR (CDCl3)
d 60.49, 106.29, 130.03, 137.65, 175.90,
182.28. MS (EI) m/z (%): 142 (Mþ, 13), 141 (10), 99 (11), 86 (65), 84
(100), 71 (13). HRMS: (EI) m/z (%) for C6H6O2S; calcd 142.0089;
found 142.0093.
4.2.2. Synthesis of 4,50-diformyl-5-methoxy-2,20-bithiophene (2b)
A 2.5 M solution of n-BuLi in hexanes (2.16 mL, 5.4 mmol) was
added dropwise under Ar at 0 ꢀC to a stirred solution of 2-
methoxythiophene (2.70 mmol) in anhydrous diethyl ether. The
reaction mixture was then stirred 1 h at 0 ꢀC and was allowed to
stand for 15 min at room temperature. DMF (0.42 mL, 5.4 mmol)
dissolved in anhydrous diethyl ether was added dropwise at room
temperature. The mixture was heated at reflux for 1 h. The mixture
was poured into water (20 mL) and extracted with ethyl acetate
(3ꢂ50 mL). The combined organic extracts were washed with H2O
(100 mL), dried with MgSO4, and the solvent was evaporated under
reduced pressure to give a mixture of 5-methoxy-50-formyl-2,20-
bithiophene and 4,50-diformyl-5-methoxy-2,20-bithiophene 2b,
which was purified by ‘flash’ chromatography on silica with in-
creasing amounts of diethyl ether in light petroleum as eluent. The
first compound eluted was 5-methoxy-50-formyl-2,20-bithiophe-
ne4b (42%). The second compound eluted was 4,50-diformyl-5-
methoxy-2,20-bithiophene 2b as a green solid (27%). Mp: 170–
4. Experimental
4.1. General
Reaction progress was monitored by thin layer chromatography
(0.25 mm thick precoated silica plates: Merck Fertigplatten Kie-
selgel 60 F254), while purification was effected by silica gel column
chromatography (Merck Kieselgel 60; 230–400 mesh). NMR spec-
tra were obtained on a Varian Unity Plus Spectrometer at an op-
erating frequency of 300 MHz for 1H NMR and 75.4 MHz for 13C
NMR or a Bruker Avance III 400 at an operating frequency of
400 MHz for 1H NMR and 100 MHz for 13C NMR using the solvent
peak as internal reference. The solvents are indicated in parenthesis
172 ꢀC. UV (dioxane): lmax nm (log
(liquid film) 1665 (C]O), 1553, 1523, 1501, 1386, 1270, 1237, 1224,
3) 367.0 (4.80), 242.0 (4.75). IR
n
1179, 1066, 1000, 973, 858, 827, 797, 666 cmꢁ1 1H NMR (CDCl3)
.
d
4.17 (s, 3H, OCH3), 7.16 (d, 2H, J¼3.9 Hz, 40-H), 7.46 (s, 1H, 3-H),
before the chemical shift values (
d
relative to TMS and given in
7.67 (d, 1H, J¼4.2 Hz, 30-H), 9.86 (s, 1H, CHO), 9.93 (s, 1H, CHO). 13C
ppm). Melting points were determined on a Gallenkamp apparatus
and are uncorrected. Infrared spectra were recorded on a BOMEM
MB 104 spectrophotometer. UV–vis absorption spectra (200–
NMR (CDCl3) d 62.48, 121.79, 122.18, 123.34, 123.80, 137.18, 141.76,
146.13, 176.51, 182.08, 182.32. MS (EI) m/z (%): 252 (Mþ, 100), 237
(73), 209 (9), 153 (13), 137 (15), 127 (5), 109 (6). HRMS: (EI) m/z (%)
for C11H8O3S2; calcd 251.991488; found 251.990697.
800 nm) were obtained using
a
Shimadzu UV/2501PC

R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
9235
4.3. General procedure for the synthesis of formyl-
(oligo)thiophenes 1e,f through Suzuki cross-coupling
6.49 (d, 1H, J¼4.2 Hz, 40-H), 7.58 (d, 1H, J¼4.2 Hz, 30-H), 7.78–7.82
(m, 2H, 5-H and 10-H), 8.80 (dd, 2H, J¼8.4 and 1.8 Hz, 4-H and 11-
H), 9.01 (dd, 2H, J¼6.0 and 1.8 Hz, 6-H and 9-H), 13.25 (s, 1H, NH).
2-Bromo-5-formylthiophene and 5-bromo-2,20-bithiophene
(1.2 mmol) were coupled to 5-formylthiophene boronic acid
(1.6 mmol), in a mixture of DME (15 mL) and aqueous 2 M Na2CO3
(1 mL) and Pd(PPh3)4 (6 mol %) at 80 ꢀC under an argon atmosphere
for 5–12 h. After cooling the mixture was filtered. Ethyl acetate and
a saturated solution of NaCl were added and the phases were
separated. The organic phase was washed with water (3ꢂ50 mL)
and an aqueous solution of NaOH (10%). The organic phase obtained
was dried (MgSO4), filtered and solvent removal gave a crude
mixture, which was submitted to column chromatography on silica
with increasing amounts of diethyl ether in light petroleum as el-
uent, affording the coupled products 1e,f.
13C NMR (DMSO-d6)
d 60.36, 105.04, 119.02, 119.18, 123.16, 123.39,
124.90, 125.94, 129.44, 129.64, 135.29, 143.23, 143.44, 146.62,
147.70, 167.50. MS (FAB) m/z (%): 333 ([MþH]þ, 100), 332 (Mþ, 33),
307 (17), 289 (12), 155 (20), 154 (63). HRMS: (FAB) m/z for
C18H13N4OS; calcd 333.0810; found 333.0808.
4.4.3. 2-(20,200-Bithiophene)-imidazo[4,5-f][1,10]phenan-
throline (3c)
Orange solid (88%). Mp >320 ꢀC. UV (dioxane): lmax nm (log
3)
383.5 (4.45), 288.0 (4.23), 249.0 (4.35). IR (KBr)
1572, 1489, 1426, 1401, 1353, 1231, 1130, 1094, 1028, 926, 805, 739,
721, 686 cmꢁ1. 1H NMR (DMSO-d6) 7.14–7.20 (m,1H, 400-H), 7.45 (d,
n 3437 (NH), 3071,
d
1H, J¼3.9 Hz, 30-H), 7.48 (dd, 1H, J¼3.2 and 1.2 Hz, 300-H), 7.60 (dd,
1H, J¼4.8 and 1.2 Hz, 500-H), 7.76–7.82 (m, 2H, 5-H and 10-H), 7.84
(d, 1H, J¼3.9 Hz, 40-H), 8.84 (d, 2H, J¼7.5 Hz, 4-H and 11-H), 9.00–
9.08 (m, 2H, 6-H and 9-H), 13.90 (s, 1H, NH). 13C NMR (DMSO-d6)
4.3.1. 5-Formyl-2,20:50200-terthiophene (1e)
Orange solid (63%). Mp: 141.8–143.1 ꢀC. UV (dioxane): lmax nm
(log 3) 396.0 (4.06), 267.0 (3.48). IR (KBr) n 3095, 2959, 1728, 1650
(C]O), 1459, 1285, 1223, 1048, 833, 795, 708 cmꢁ1. 1H NMR (CDCl3)
d 123.35, 124.89, 126.28, 127.05, 128.60, 129.54, 131.80, 134.40,
d
7.06 (m, 1H, 400-H), 7.13 (d, 1H, J¼3.9 Hz, 300-H), 7.23–7.25 (m, 2H,
135.92, 138.13, 140.55, 143.62, 145.76, 147.93. MS (EI) m/z (%): 384
(Mþ, 26), 192 (5), 147 (7), 138 (7), 99 (7), 63 (11), 62 (100). HRMS:
(EI) m/z for C21H12N4S2; calcd 384.0503; found 384.0521.
40-H and 500-H), 7.28–7.29 (m, 2H, 30-H and 3-H), 7.68 (d, 1H,
J¼3.9 Hz, 4-H), 9.87 (s, 1H, CHO). MS (FAB) m/z (%): 276 ([MþH]þ,
27), 275 (Mþ, 26), 167 (22), 154 (38). HRMS: (FAB) m/z (%) for
C
13H9OS3; calcd 275.9737; found 275.9745.
4.4.4. 2-(500-Methoxy-20,200-bithiophene)-imidazo[4,5-f]-
[1,10]phenanthroline (3d)
4.3.2. 5,50-Diformyl-2,20-bithiophene (1f)
Brown solid (76%). Mp >320 ꢀC. UV (dioxane): lmax nm (log
3)
Orange solid (40%). Mp: 215.9–217.2 ꢀC. UV (dioxane): lmax nm
393.0 (4.44), 276.5 (4.33), 249.0 (4.39). IR (KBr)
n 3400 (NH), 3078,
(log 3) 365.5 (4.45), 290.0 (3.71), 260.0 (3.69). IR (KBr) n 3097, 2922,
1655 (C]O), 1511, 1437, 1385, 1277, 1225, 1053, 889, 799, 751,
2935, 1655, 1573, 1501, 1425, 1351, 1250, 1200, 1131, 1091, 1052,
1029, 991, 925, 805 cmꢁ1. 1H NMR (DMSO-d6)
d 3.90 (s, 3H, OCH3),
676 cmꢁ1
.
1H NMR (CDCl3)
d
7.77 (d, 2H, J¼4.2 Hz, 30-H and 3-H),
6.37 (d, 1H, J¼4.2 Hz, 400-H), 7.14 (d, 1H, J¼4.2 Hz, 300-H), 7.26 (d, 1H,
J¼3.9 Hz, 30-H), 7.79 (d, 1H, J¼3.9 Hz, 40-H), 7.80–7.90 (m, 2H, 5-H
and 10-H), 8.75–8.90 (m, 2H, 4-H and 11-H), 9.00–9.10 (m, 2H, 6-H
8.05 (d, 2H, J¼3.9 Hz, 40-H and 4-H), 9.93 (s, 2H, 2ꢂCHO). 13C NMR
(CDCl3) d 126.46, 136.91, 143.84, 144.82, 182.55. MS (EI) m/z (%): 223
(Mþþ1, 20), 222 (Mþ, 100), 220 (78), 192 (20), 149 (13), 133 (22), 83
(16). HRMS: (EI) m/z (%) for C10H6O2S2; calcd 221.9809; found
221.9815.
and 9-H), 13.90 (s, 1H, NH). 13C NMR (DMSO-d6)
d 60.38, 105.23,
112.76, 118.65, 121.92, 122.75, 122.97, 126.78, 129.26, 130.39, 135.35,
138.72, 143.49, 145.67, 147.62, 165.45. MS (EI) m/z (%): 414 (Mþ, 4),
384 (6), 186 (15), 165 (20), 151 (28), 137 (31), 123 (37), 110 (48), 98
(98), 97 (55), 84 (92), 83 (100), 68 (63). HRMS: (EI) m/z for
4.4. General procedure for the synthesis of (oligo)thienyl-
imidazo-phenanthrolines 3–6
C22H14N4OS2; calcd 414.0609; found 414.0620.
A
mixture of formyl-(oligo)thiophene (1.2 mmol), NH4OAc
4.4.5. 2-(20,200:500,2%-Terthiophene)-imidazo[4,5-f]-
[1,10]phenanthroline (3e)
(20 mmol), and 1,10-phenanthroline-5,6-dione (1 mmol) in glacial
acetic acid (20 mL) was stirred and heated at reflux for 4 h. The
mixture was then cooled to room temperature and the product
precipitated during neutralization with NH4OH (5 M). The pre-
cipitate was filtrated, washed with water and diethyl ether,
recrystalized from methanol and dried at 50 ꢀC in vacuo to give the
pure product.
Brown solid (83%). Mp >320 ꢀC. UV (dioxane): lmax nm (log
3)
411.5 (4.43), 393.0 (4.44), 275.0 (4.31), 253.0 (4.41). IR (KBr)
n 3426
(NH), 3071, 2926, 2851, 1723, 1655, 1565, 1487, 1391, 1271, 1131,
1029, 926, 792, 738 cmꢁ1 1H NMR (DMSO-d6)
. d 7.10–712 (m, 1H,
4%-H), 7.30–7.41 (m, 4H, 30-H, 300-H, 400-H and 3%-H), 7.55 (dd, 1H,
J¼4.2 and 1.2 Hz, 5%-H), 7.77–7.82 (m, 3H, 40-H, 5-H and 10-H),
8.80–8.84 (m, 2H, 4-H and 11-H), 8.97–8.99 (m, 2H, 6-H and 9-H).
4.4.1. 2-Thiophenimidazo[4,5-f][1,10]phenanthroline (3a)
13C NMR (DMSO-d6)
d 121.71, 123.18, 123.31, 124.48, 125.10, 125.55,
Yellow solid (90%). Mp >320 ꢀC. UV (dioxane): lmax nm (log
3
)
125.90, 126.63, 127.34, 128.50, 129.54, 130.52, 131.88, 133.39, 134.05,
134.86, 135.87, 136.83, 138.05, 141.07, 143.49, 144.04, 146.78, 147.49.
MS (FAB) m/z (%): 467 ([MþH]þ, 16), 466 (Mþ, 7), 441 (15), 391 (18),
316 (34), 288 (46), 154 (23). HRMS: (FAB) m/z for C25H15N4S3; calcd
467.0459; found 467.0446. C25H14N4S3: calcd C 64.35, H 3.02, N
12.01, S 20.62; found C 64.28, H 3.07, N 12.12, S 20.79.
336.5 (4.36), 282.5 (4.46), 247.0 (4.40). IR (KBr)
n
3430 (NH), 1668,
1561, 1295, 1237, 1130, 1075, 923, 853–795, 736 cmꢁ1
.
1H NMR
(DMSO-d6)
d
7.27–7.29 (m, 1H, 40-H), 7.76 (dd, 1H, J¼4.8 and 1.2 Hz,
30-H), 7.82 (br s, 2H, 5-H and 10-H), 7.90 (dd, 1H, J¼4.0 and
1.2 Hz, 50-H), 8.84 (br s, 2H, 4-H and 11-H), 9.02 (dd, 2H, J¼4.4 and
1.2 Hz, 6-H and 9-H),13.84 (s,1H, NH). 13C NMR (DMSO-d6)
d 119.06,
123.29, 126.07, 126.25, 128.31, 129.53, 133.39, 135.51, 143.54, 146.24,
147.81. MS (EI) m/z (%): 303 (Mþþ1, 15), 302 (Mþ, 100), 301 (9), 193
(5). HRMS: (EI) m/z for C17H10N4S; calcd 302.0626; found 302.0623.
4.4.6. 2-(20,200-Bithiophene)-bis[imidazo[4,5-
f][1,10]phenanthroline] (4)
Orange solid (79%). Mp >320 ꢀC. UV (dioxane): lmax nm (log
3)
418.0 (3.84), 321.0 (3.49), 262.0 (3.79). IR (KBr)
n 3435 (NH), 3065,
4.4.2. 2-(50-Methoxy-20-thiophene)-imidazo[4,5-f]-
1651, 1563, 1481,1427,1352, 1232,1131, 1029, 927, 805, 739 cmꢁ1. 1H
[1,10]phenanthroline (3b)
NMR (DMSO-d6)
d
7.68 (d, 1H, J¼4.0 Hz, 30-H or 40-H), 7.73 (d, 1H,
Dark red solid (92%). Mp >320 ꢀC. UV (dioxane): lmax nm (log
3
)
J¼4.0 Hz, 30-H or 40-H), 7.80–7.90 (m, 6H, 30-H, 40-H, 2ꢂ5-H and
2ꢂ10-H), 8.80–8.88 (m, 4H, 2ꢂ4-H and 2ꢂ11-H), 9.00–9.08 (m, 4H,
2ꢂ6-H and 2ꢂ9-H), 13.93 (s, 1H, NH), 14.00 (s, 1H, NH). 13C NMR
346.0 (3.84), 285.5 (3.93). IR (KBr)
n
3435 (NH), 1651, 1504, 1200,
3.97 (s, 3H, OCH3),
1087, 968, 799, 730 cmꢁ1. 1H NMR (DMSO-d6)
d

9236
R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
(DMSO-d6)
d
123.42, 123.62, 125.95, 127.31, 127.94, 129.70, 130.00,
Rayleigh signal that arises from dioxane was taken into account
according to the expression
134.49, 136.42, 137.49, 144.74, 145.28, 148.09. MS (FAB) m/z (%): 603
([MþH]þ, 5), 460 (7), 413 (8), 307 (36), 289 (18), 232 (24), 155 (30),
154 (100). HRMS: (FAB) m/z for C34H19N8S2; calcd 603.1174; found
603.1165. C34H18N8S2: calcd C 67.76, H 3.01, N 18.59, S 10.64; found
C 67.65, H 3.09, N 18.63, S 10.75.
ꢀ
D
E
D
Eꢁ
I2 ¼ G Nsolvent bs2olvent þ Nsolute b2solute Iu2
u
where the factor G is an instrumental factor that takes into account
the detection efficiency (including geometrical factors and linear
absorption or scattering of the second harmonic light on its way to
the detector) and local field corrections. The brackets indicate an
average over the spatial orientations of the molecules.
4.4.7. 2-(500-Piperidino-20,200-bithiophene)-imidazo[4,5-f]-
[1,10]phenanthroline (5)
Brown solid (41%). Mp >320 ꢀC. IR (KBr)
n
3421 (NH), 3061,
2932, 2851, 2797, 2363, 1665, 1572, 1493, 1445, 1376, 1124–1020,
803, 740, 691 cmꢁ1. 1H NMR (DMSO-d6 with TFA-d)
1.80–2.10 (m,
We took particular care to avoid reporting artificially high
hyperpolarizibilities due to a possible contamination of the hyper-
Rayleigh signal by molecular fluorescence near 532 nm. Measure-
ments were carried out using two different interference filters with
different transmission pass bands centered near the second har-
monic at 532 nm. The transmission band of the narrower filter (CVI
model F1.5-532-4) was 1.66 nm (full width at half maximum) with
a transmission of 47.6% at the second harmonic, while the corre-
sponding values for the wider filter (CVI model F03-532-4) were
3.31 nm, with a transmission of 63.5% at the second harmonic. The
transmission of each filter at the second harmonic wavelength was
carefully determined using a crystalline quartz sample. We assume
that any possible fluorescence emitted from the solutions is es-
sentially constant over the transmission of both interference filters.
Then by comparing the signals obtained with the two different
filters we can determine the relative contributions of the hyper-
Rayleigh and possible fluorescence signals. More concretely the
overall detected signal can have contributions from both the second
harmonic signal and any possible fluorescence that is emitted
within the passband of the filter. Denoting SNB as the actual signal
measured (after correction for the solvent contribution) using the
‘narrow’ (CVI model F1.5-532-4), we have
d
6H, 3ꢂCH2), 2.20–2.60 (m, 4H, 2ꢂNCH2), 7.21 (br s, 1H, 40-H), 7.40–
7.60 (m, 1H, 500-H), 8.41–8.60 (m, 4H, 400-H, 300-H, 5-H and 10-H),
9.42–9.57 (m, 4H, 4-H, 6-H, 9-H and 11-H). MS (FAB) m/z (%): 468
([MþH]þ, 23), 467 (Mþ, 10), 307 (26), 289 (17), 232 (61), 157 (96),
154 (100). HRMS: (FAB) m/z for C26H22N5S2; calcd 468.1317; found
468.1317. C26H21N5S2: calcd C 66.78, H 4.53, N 14.98, S 13.71; found
C 66.71, H 4.62, N 15.05, S 13.59.
4.4.8. 2-(50-Methoxy-20,200-bithiophene)-bis[imidazo[4,5-f]-
[1,10]phenanthroline] (6)
Dark brown solid (80%). Mp >320 ꢀC. IR (KBr)
n
3430 (NH), 3071,
2917, 1631, 1481, 1424, 1398, 1316, 1226, 1017, 805, 738, 720 cmꢁ1. 1H
NMR (DMSO-d6 with TFA-d) 4.28 (s, 1H, OCH3), 8.12–8.27 (m, 6H,
d
2ꢂ5-H, 2ꢂ10-H, 30-H and 40-H), 9.01–9.29 (m, 9H, 2ꢂ4-H, 2ꢂ11-H,
2ꢂ6-H, 2ꢂ9-H and 300-H). MS (FAB) m/z (%): 633 ([MþH]þ, 4), 316
(10), 308 (10), 307 (38), 289 (18), 288 (14), 155 (30), 154 (100).
HRMS: (FAB) m/z for C35H21N8OS2; calcd 633.1280; found 633.1279.
C
35H20N8OS2: calcd C 66.44, H 3.19, N 17.71, S 10.14; found C 66.36,
H 3.27, N 17.75, S 10.30.
4.5. Nonlinear optical measurements for compounds 4–5
using the hyper-Rayleigh scattering (HRS) method19a
u
SNB ¼ TNBS2 þ ANBSF
while the corresponding signal obtained using the ‘wide’ (CVI
model F03-532-4) band interference filter is
Hyper-Rayleigh scattering (HRS) was used to measure the first
hyperpolarizability
b of response of the molecules studied. The
experimental set-up for hyper-Rayleigh measurements is similar to
that presented by Clays et al.19a The incident laser beam came from
a Q-switched Nd:YAG laser operating at a 10 Hz repetition rate with
approximately 10 mJ of energy per pulse and a pulse duration
(FWHM) close to 12 ns at the fundamental wavelength of 1064 nm.
The incident power could be varied using a combination of a half
wave-plate and Glan polarizer. The incident beam was weakly fo-
cused (beam diameter w0.5 mm) into the solution contained in
a 5 cm long cuvette. The hyper-Rayleigh signal was collimated us-
ing a high numerical aperture lens passed through an interference
filter centered at the second harmonic wavelength (532 nm) before
being detected by a photomultiplier (Hamamatsu model H9305-
04). The current pulse from the photomultiplier was integrated
using a Stanford Research Systems gated box-car integrator (model
SR250) with a 25 ns gate centered on the temporal position of the
incident laser pulse. The hyper-Rayleigh signal was normalized at
each pulse using the second harmonic signal from a 1 mm quartz
plate to compensate for fluctuations in the temporal profile of the
laser pulses due to longitudinal mode beating. Dioxane was used as
u
SWB ¼ TWBS2 þ AWBSF
Here S2u is the second harmonic signal incident on the filters while
SF is the average fluorescence signal over the passband of the filters.
We assume the fluorescence component is broad enough that the
average fluorescence signal is essentially identical for both filters.
The transmissions TNB and TWB are, respectively, the transmission of
the ‘narrow’ and ‘wide’ band interference filters at the second
harmonic wavelength (47.6% and 63.5%), while ANB and AWB rep-
resent the area under the respective filter’s transmission curve. The
transmission curves were obtained using a dual-beam spectro-
photometer with slits adjusted to give 0.1 nm resolution. We
obtained values of 1.29 nm and 2.18 nm for ANB and AWB, re-
spectively. Solving the above equations for S2 and SF we arrive at
the following expression for the actual hyper-Rayleigh and fluo-
rescence contribution to the signal obtained using the narrow band
interference filter:
u
ꢂ
ꢃ
SNBAWB ꢁ SWBANB
TNBAWB ꢁ TWBANB
u
S2NB
¼
TNB
a solvent, and the
b values were calibrated using a reference solu-
tion of p-nitroaniline (pNA)19b also dissolved in dioxane at a con-
centration of 1ꢂ10ꢁ2 M (external reference method). The
hyperpolarizability of pNA dissolved in dioxane is known from
EFISH measurements carried out at the same fundamental wave-
length.20 The concentrations of the solutions under study were
chosen so that the corresponding hyper-Rayleigh signals fell well
within the dynamic range of both the photomultiplier and the box-
ꢂ
ꢃ
SWBTNB ꢁ SNBTWB
TNBAWB ꢁ TWBANB
This allows us to determine whether fluorescence is present and to
reliably correct for its presence provided that the integrated con-
tribution is less than 80% of the total detected signal within the
temporal gate of the box-car integrator (25 ns). The resultant values
SFNB
¼
ANB
car integrator. All solutions were filtered (0.2
mm porosity) to avoid
spurious signals from suspended impurities. The small hyper-

R.M.F. Batista et al. / Tetrahedron 64 (2008) 9230–9238
9237
Bradamante, S.; Facchetti, A.; Klein, C.; Pagani, G. A.; Redi-Abshiro, M.; Wort-
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for the hyperpolarizability and the associated uncertainties are
reported in Table 3. The uncertainties have been calculated using
the measured variances in the signals obtained using the narrow
and wide band filters for both the compound and the background
obtained from the measurements on pure dioxane and the pNA
reference solution. Measurements for compound 3c and especially
compound 3a have rather high relative uncertainties due to the fact
that detected signals were relatively small and the amount of
fluorescence is high. Once the fluorescence and the background
from the dioxane solvent are discounted, the remaining contribu-
tion is not much greater than the combined the statistical fluctu-
ations of the signals from the compound and references.
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When using the ‘narrow’ band filter the estimated fraction of
the total detected signal due to fluorescence together with the
estimated experimental uncertainty is listed in the following table:
Compound
SFNB=SNB
3a
3b
3c
3d
3e
0.87 (þ0.13, ꢁ0.66)
0.59 (ꢃ0.24)
0.73 (ꢃ0.51)
0.59 (ꢃ0.10)
0.63 (ꢃ0.07)
The higher level of uncertainty for compounds 3a and 3c is also
reflected in the estimated uncertainty of the fluorescence contri-
bution for these compounds.
4.6. Thermogravimetric analysis of compounds 3–6
Thermogravimetric analysis of samples was carried out using
a TGA instrument model Q500 from TA Instruments, under high
purity nitrogen supplied at a constant 50 mL minꢁ1 flow rate. All
samples were subjected to a 20 ꢀC minꢁ1 heating rate and were
characterized between 25 and 800 ꢀC.
Acknowledgements
ˆ
Thanks are due to the Fundaça˜o para a Ciencia e Tecnologia
´
(Portugal) for financial support through Centro de Quımica – Uni-
versidade do Minho (project PTDC/QUI/66250/2006, PhD grant to
´
R.M.F. Batista SFRH/BD/36396/2007) and Departamento de Fısica
´
(Universidade do Minho) and Departamento de Quımica (FCT-UNL)
REQUIMTE.
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