Physical properties of 8-substituted 5,7-dichloro-2-styrylquinolines as potential light emitting materials

Article abstract of DOI:10.1002/jccs.200700198

Derivatives of 5,7-dichloro-2-styrylquinoline (1), modified at position 8 of quinoline moiety with a methyl ether (4, DCSQM) or acetate (5, DCSQA), were synthesized and investigated. Both compounds exhibited high thermal stability (Td > 320 °C). The UV-vis absorption of DCSQM and DCSQA varied only slightly in different solvents, whereas the emission spectra showed pronounced red shifts with increasing solvent polarity, suggesting the intramolecular charge transfer character of the emission state. Compounds 4 and 5 can emit lights from blue to green color in different solvents. The solvent polarity dependent electronic transitions are attributed to efficient intramolecular charge transfer (ICT) processes, in which the HOMOs and LUMOs are localized on the styrene-based ring and the quinoline-based moiety, respectively. The quinoline-based LUMO provides compelling evidence that the first reduction site occurs on the electron-deficient quinoline moiety.

Full text of DOI:10.1002/jccs.200700198

Journal of the Chinese Chemical Society, 2007, 54, 1387-1394
1387
Physical Properties of 8-Substituted 5,7-dichloro-2-styrylquinolines as
Potential Light Emitting Materials
Grace Shiahuy Chena (
), Rahul Subhash Talekar,b Ken-Tsung Wongc (
) and Ji-Wang Chernb,* (
),
Liang-Chen Chic (
)
aDepartment of Applied Chemistry, Providence University, Shalu 433, Taiwan, R.O.C.
bSchool of Pharmacy, National Taiwan University, Taipei 100, Taiwan, R.O.C.
cDepartment of Chemistry, National Taiwan University, Taipei 106, Taiwan, R.O.C.
Derivatives of 5,7-dichloro-2-styrylquinoline (1), modified at position 8 of quinoline moiety with a
methyl ether (4, DCSQM) or acetate (5, DCSQA), were synthesized and investigated. Both compounds
exhibited high thermal stability (Td > 320 °C). The UV-vis absorption of DCSQM and DCSQA varied
only slightly in different solvents, whereas the emission spectra showed pronounced red shifts with in-
creasing solvent polarity, suggesting the intramolecular charge transfer character of the emission state.
Compounds 4 and 5 can emit lights from blue to green color in different solvents. The solvent polarity de-
pendent electronic transitions are attributed to efficient intramolecular charge transfer (ICT) processes, in
which the HOMOs and LUMOs are localized on the styrene-based ring and the quinoline-based moiety,
respectively. The quinoline-based LUMO provides compelling evidence that the first reduction site oc-
curs on the electron-deficient quinoline moiety.
Keywords: Optical materials; Crystal structure; Electronic structure; Density functional theory.
INTRODUCTION
Since the discovery of tris(8-quinolinolato)aluminum
ents had excellent electroluminescent properties and could
also be used as chemosensors.7 It was reported that ether
derivatives of 8-HQ enhanced the fluorescence due to the
blockage of excited-state intramolecular proton transfer
(ESIPT) from 8-OH to the N atom8 while ester derivatives
of 8-HQ exhibited weak fluorescence from the radiation-
less n ® p* transition due to the carbonyl oxygen lone pair
adjacent to the fluorophore.9 The fluorescence pattern of
8-HQ was also affected by halo substituents at the 5- and
7-positions.10 The electron affinity of the 8-HQ would be
increased by introducing chloro substituents at the 5- and
7-positons. A linkage of the electron-defficient quinoline
to the electron-rich trimethoxyphenyl ring via a p-conju-
gated spacer would form a D-p-A system. The aim of the
present work was to exploit the physical properties of this
new class of fluorescent quinoline-based styryl systems.
(AlQ3)1 and poly(p-phenylene-vinylene) (PPV)2 as electro-
luminescent materials, a great deal of effort has been de-
voted to the synthesis of novel emitters. Among them, p-
conjugated donor-acceptor (D-p-A) organic molecules that
feature efficient intramolecular charge transfer (ICT) have
attracted much attention.3 The chromophores are usually
composed of a p-conjugation system such as polyenes as
linkers connecting an electron donor and an electron accep-
tor. Chemical modification of the conjugated backbones al-
lows efficient manipulation of physical properties that are
important for determining the characteristics of light emis-
sion, namely the band gap and the electronic behavior.4
For material research, numerous styryl compounds
have been investigated due to their photonic and electronic
properties.3 Quinoline is an electron-deficient system with
good thermal stability.5 Theoretical studies have demon-
strated that molecular orbitals governing electrolumines-
cence of AlQ3 are localized on an 8-phenoxide oxygen of
quinolinolates.6a Recent studies revealed that several 8-hy-
droxyquinoline (8-HQ) derivatives with various substitu-
EXPERIMENTAL
Synthesis of 5,7-dichloro-8-methoxy-2-methylquinoline
(2)
Commercially available 5,7-dichloro-8-hydroxy-2-
* Corresponding author. E-mail: chern@jwc.mc.ntu.edu.tw

1388 J. Chin. Chem. Soc., Vol. 54, No. 6, 2007
Chen et al.
methylquinoline (1, 2.28 g, 0.01 mol) was added to a mix-
ture of THF (25 mL), aqueous NaOH solution (1.5 g NaOH
in 3 mL H2O) and TBAB (0.15 g). CH3I (1.88 mL, 0.03
mol) was added, and the resulting yellow mixture was
stirred at 40 °C for 30 h.11 The mixture was then extracted
with ether (3 ´ 25 mL), and the organic layers were dried
over MgSO4. Removal of solvent yielded a crude product
that was purified by column chromatography (hexane/ethyl
acetate 4:1), giving the methyl ether 2 as a yellowish solid
(83%). Rf 0.25 (hexane/ethyl acetate 4:1); Mp 151°C; IR
2943, 1581, 1509, 1131 cm-1; 1H NMR (400 MHz, CDCl3)
d 8.42 (d, J = 8.8 Hz, 1H), 7.72 (d, J = 8.8 Hz, 1H), 7.62 (d,
J = 16.2 Hz, 1H), 7.53 (s, 2H), 7.35 (d, J = 16.2 Hz, 1H),
6.86 (s, 1H), 4.2 (s, 3H), 3.92 (s, 6H), 3.88 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 156.5, 153.3, 151.2, 143.5,
139.2, 135.8, 133.8, 131.8, 127.8, 127.2, 127.0, 126.2,
125.2, 119.9, 104.6, 62.5, 61.0, 56.3. MS ESI: 419.9 (M +
H); Anal. Calcd for C21H19NCl2O4: C, 60.01; H, 4.56; N,
3.33. Found: C, 59.98; H, 4.65; N, 3.28.
1
(KBr) 3024, 1588, 966, 681 cm-1; H NMR (400 MHz,
Synthesis of 8-acetoxy-5,7-dichloro-2-[2-(3,4,5-trimeth-
oxyphenyl)vinyl]quinoline (5)
CDCl3) d 8.34 (d, J = 8.6 Hz, 1H), 7.53 (s, 1H), 7.36 (d, J =
8.6 Hz, 1H), 4.13 (s, 3H), 2.77 (s, 3H); 13C NMR (100
MHz, CDCl3) d 160.2, 151.0, 143.3, 133.4, 126.8, 126.6,
126.2, 124.6, 123.0, 62.3, 25.6; MS ESI: 242.3 (M + H);
Anal. Calcd for C11H9NCl2O: C, 54.57; H, 3.75; N, 5.79.
Found: C, 54.50; H, 3.71; N, 5.75.
To a solution of 1 (0.45 g, 2.0 mmol) in acetic anhy-
dride (10 mL) was added 3,4,5-trimethoxybenzaldehyde
(0.58 g, 3 mmol). The mixture was heated at reflux for 48 h
under argon. After evaporation under vacuum, the oily res-
idue was chromatographed on silica gel (hexane/ethyl ace-
tate 3:2) to provide a solid, which was recrystallized from
hexane/ethyl acetate to yield 5 as a yellow solid (81%). Rf
0.16 (hexane/ethyl acetate 4:1); Mp 178 °C; IR (KBr)
Synthesis of 8-acetoxy-5,7-dichloro-2-methylquinoline
(3)
1
Acetic anhydride (1 mL, 10 mmol) was added to a so-
lution of 1 (2.28 g, 10 mmol) in pyridine (50 mL) at 0 °C.12
After stirring for 6 h, pyridine was removed by evapora-
tion, and 3 M HCl (50 mL) was added to the residue. The
aqueous solution was extracted with CHCl3, and the or-
ganic layer was washed with water, dried over MgSO4, and
evaporated under vacuum. The residue was purified by col-
umn chromatography (hexane/ethyl acetate 4:1) and re-
crystallized from ethyl acetate to yield 3 as a yellow solid
(91%). Rf 0.20 (hexane/ethyl acetate 4:1); Mp 105-106 °C
(lit.13 103.5-105 °C); IR (KBr) 2945, 1770, 1618, 1120
cm-1; 1H NMR (200 MHz, CDCl3) d 8.26 (d, J = 8.6 Hz,
1H), 7.56 (s, 1H), 7.30 (d, J = 8.6 Hz, 1H), 2.69 (s, 3H),
2.51 (s, 3H); 13C NMR (100 MHz, CDCl3) d 168.4, 161.1,
142.5, 141.5, 132.9, 128.8, 126.7, 126.1, 124.1, 123.3,
25.4, 20.5; MS ESI: 269.7 (M + H).
2940, 1775, 1578, 1131, 961 cm-1; H NMR (400 MHz,
CDCl3) d 8.38 (d, J = 8.8 Hz, 1H), 7.65 (d, J = 8.8 Hz, 1H),
7.55 (s, 1H), 7.54 (d, J = 16.2 Hz, 1H), 7.15 (d, J = 16.2 Hz,
1H), 6.79 (s, 2H), 3.9 (s, 6H), 3.88 (s, 3H), 2.56 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 168.4, 157.3, 153.3, 142.9,
142.2, 139.3, 136.2, 133.4, 131.7, 129.0, 127.5, 127.2,
126.5, 124.9, 120.7, 104.7, 61.0, 56.2, 20.7; MS ESI: 447.9
(M + H); Anal. Calcd for C22H19NCl2O5: C, 58.94; H, 4.27;
N, 3.12. Found: C, 58.81; H, 4.34; N, 3.07.
X-Ray crystallography
Single-crystal diffraction data for DCSQA were col-
lected on a NONIUS KappaCCD diffractometer with Mo
radiation (l = 0.71073 Å) at 295(2) K. No significant decay
was observed during the data collection. Data were pro-
cessed on a PC using the SHELXTL software package. The
structure was solved and refined by full-matrix least squares
on F2 values. Hydrogen atoms were fixed at calculated po-
sitions and refined using a riding mode. Crystal data and
experimental details are listed in Table 1.
Synthesis of 5,7-dichloro-8-methoxy-2-[2-(3,4,5-tri-
methoxyphenyl)vinyl]quinoline (4)
To a mixture of 2 (0.5 g, 2.2 mmol) in acetic anhy-
dride (11 mL) was added 3,4,5-trimethoxybenzaldehyde
(0.65 g, 3.3 mmol). The mixture was heated at reflux for 48
h under argon and then concentrated in vacuo. The oily res-
idue was chromatographed on silica gel (hexane/ethyl ace-
tate 4:1) to provide a solid, which was recrystallized from
hexane/ethyl acetate to yield 4 as a yellowish solid (76%).
Rf 0.18 (hexane/ethyl acetate 4:1); Mp 180 °C; IR (KBr)
Composition analysis and optical measurement
Ultraviolet-visible (UV-vis) spectra were measured
on a Hitachi UV-160 spectrophotometer and corrected for
background due to solvent absorption. Photoluminescence
(PL) spectra were obtained using a Hitachi F-4500 fluores-
cence spectrophotometer upon excitation at the maximum

2-Styrylquinolines as Light Emitting Materials
Table 1. Crystal data of DCSQA
J. Chin. Chem. Soc., Vol. 54, No. 6, 2007 1389
ning calorimeter, the sample was first heated (20 °C/min) to
the melting point, quenched with liquid nitrogen, and glass
transition temperature (Tg) was recorded by heating (10
°C/min) the quenched sample. Thermogravimetric analysis
(TGA) was used to measure the decomposition tempera-
ture (Td); this procedure was similar to that for Tg measure-
ment.
empirical formula
formula weight
temperature
C22H19Cl2NO5
448.28
295(2) K
wavelength
0.71073 Å
crystal system
space group
orthorhombic
P212121
unit cell dimensions
a = 5.3050(2) Å, b = 12.2153(5) Å,
c = 31.6620(13) Å
2051.84(14) Å3
4
volume
Z
density (calculated)
absorption coefficient
F(000)
crystal size
range for data collection
limiting indices
Computational Method
Calculations were carried out with the GAUSSIAN
9814 program installed on an SGI Origin 3800 computer.
The hybrid B3LYP functional (DFT)15 was used in cooper-
ation with the 6-31G* basis set. All the structures were op-
timized by applying the Berny algorithm using redundant
internal coordinates.16 Numerical vibrational frequencies
were carried out for the confirmation of a stable minimum
structure obtained.
1.451 mg/m3
0.351 mm-1
928
0.2 ´ 0.15 ´ 0.10 mm3
1.79 to 27.47o
-5 £ h £ 6, -11 £ k £ 15,
-40 £ l £ 41
reflections collected
independent reflections
absorption correction
8554
4296 (Rint = 0.0470)
Semi-empirical from equivalents
max. and min. transmission 0.996 and 0.934
refinement method
full-matrix least-squares on F2
RESULTS AND DISCUSSION
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2s (I)]
R indices (all data)
4296/0/272
1.074
R1 = 0.0581, wR2 = 0.1270
R1 = 0.1178, wR2 = 0.1623
0.255 and -0.295 eÅ-3
A straightforward synthesis of the quinoline-based
styrenes is oulined in Scheme I. 5,7-Dichloro-8-hydroxy-
quinaldine (1) was methylated to its methyl ether 2,11 which
then underwent a condensation reaction with 3,4,5-trimeth-
oxybenzaldehyde in acetic anhydride to give the desired
DCSQM (4). The DCSQA (5) was obtained directly by the
same condensation reaction of 1 with 3,4,5-trimethoxy-
benzaldehyde in acetic anhydride. The vinylic protons with
JHH values of 16 Hz in the 1H-NMR spectra indicated the
vinylene bridge in an E disposition. Compound 3, the 8-
acetoxy derivative of 1, was prepared for comparison.
The X-ray structure of DCSQA (Fig. 1) confirms the
E configuration of the olefinic bond. The quinoline ring
and the styryl moiety are situated in ideal coplanarity with
the acetoxy group twisted out of the best plane. The meth-
oxy groups at the 3¢- and 5¢-positions of the trimethoxy-
phenyl ring are coplanar with the best plane while the one
at the 4¢-position angles out to minimize the steric repul-
sion with the neighboring methoxy groups. The same ge-
ometry has been seen in other 3,4,5-trimethoxyphenyl de-
rivatives.17 The selected bond lengths are listed in Table 2.
DCSQM and DCSQA exhibited high thermal stabil-
ity with Td values of 321 °C and 330 °C, respectively, as
evaluated by TGA (Table 3). The glass transition tempera-
tures (Tg) of DCSQM and DCSQAwere determined as 35.7
°C and 55 °C, respectively, by DSC under a nitrogen atmo-
largest diff. peak and hole
absorption wavelength in the same solvent after saturation
with argon. Measurements of quantum yields were per-
formed using coumarin I as a reference, and degassed di-
chloromethane was used as solvent. Cyclic voltammetry
(CV) analyses were performed in 1.0 mM of substrate us-
ing a Princeton Applied Research potentiostat 273A. All
oxidation CV measurements were carried out in anhydrous
CH2Cl2 containing 0.1 M tetrabutylammonium hexafluoro-
phosphate (nBu4NPF6) as a supporting electrolyte, and all
reduction CV measurements were performed in anhydrous
THF containing 0.1 M tetrabutylammonium perchlorate
(nBu4NClO4) as a supporting electrolyte, purging with ar-
gon prior to conducting the experiment. A carbon electrode
(oxidation) or a glassy carbon electrode (reduction) was
used as a working electrode, and a platinum wire served as
a counter electrode. All potentials were recorded versus
Ag/AgCl (sat’d) as a reference electrode. Ferrocenium/fer-
rocene redox occurs at Eo’ = +0.54 V vs. Ag/AgCl (sat’d)
in CH2Cl2/nBu4NPF6 and at Eo’ = +0.63 V vs. Ag/AgCl
(sat’d) in THF/nBu4NClO4. Analyses of differential scan-
ning calorimetry (DSC) were performed using a TA Instru-
ment DSC-2920. On a low-temperature difference scan-

1390 J. Chin. Chem. Soc., Vol. 54, No. 6, 2007
Chen et al.
Scheme I Synthesis of DCSQM (4) and DCSQA (5)
Cl
Cl
Cl
O
CH3I, NaOHaq, TBAB
THF, 40oC, 30 h
(CH3CO)2O, pyridine
0oC to rt, 6 h
Cl
N
CH3
Cl
N
CH3
Cl
N
CH3
OCH3
OH
O
2 (83%)
1
3 (91%)
CH3
3,4,5-trimethoxybenzaldehyde
(CH3CO)2O, reflux, 48 h.
3,4,5-trimethoxybenzaldehyde
(CH3CO)2O, reflux, 48 h.
Cl
Cl
OCH3
OCH3
OCH3
Cl
N
Cl
N
OCH3
O
O
OCH3
OCH3
4, DCSQM
(76%)
CH3
OCH3
5, DCSQA
(81%)
sphere. The low Tgs might reflect the nonplanarity of the
4-methoxy group on the trimethoxyphenyl ring and the
acetoxy group on the quinoline moiety, as revealed in the
X-ray structure of DCSQA. The crystal lattice shows close
and extensive p-p stacking and the dipolar orientation is in
the opposite direction to allow for the dipole-dipole inter-
actions.
The absorption spectra of DCSQM and DCSQA in
CHCl3 solution were examined to investigate the electronic
Table 2. Selected bond lengths (Å) for DCSQA
atom(1)-atom(2) distance (Å) atom(1)-atom(2) distance (Å)
Cl(1)-C(1)
Cl(2)-C(3)
O(1)-C(10)
O(1)-C(9)
O(2)-C(10)
O(3)-C(16)
O(4)-C(17)
O(5)-C(18)
N(1)-C(7)
N(1)-C(8)
C(8)-C(9)
1.719(4)
1.734(4)
1.371(5)
1.386(5)
1.189(5)
1.354(5)
1.380(5)
1.361(5)
1.327(5)
1.366(5)
1.410(6)
C(1)-C(2)
C(1)-C(9)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(4)-C(8)
C(5)-C(6)
C(6)-C(7)
C(7)-C(12)
C(13)-C(14)
C(12)-C(13)
1.397(6)
1.366(6)
1.367(6)
1.422(6)
1.402(6)
1.413(6)
1.364(6)
1.417(7)
1.466(6)
1.475(6)
1.316(6)
Table 3. Photophysical, thermal, and electrochemical properties of
DCSQM and DCSQA
DCSQM
DCSQA
lmax (nm)a
emax (nm)a
Td (°C)
Tg (°C)
Tm (°C)
ff
354
465
321
36
181
0.44
3.20
355
474
330
55
177
0.52
3.22
b
me/mg
a 5.0 ´ 10-5 M in CHCl3.
Fig. 1. Single X-ray crystal structure (a) and the mo-
lecular packing diagram (b) of DCSQA.
b Calculated from the slopes of two plots in Fig. 4.22

2-Styrylquinolines as Light Emitting Materials
J. Chin. Chem. Soc., Vol. 54, No. 6, 2007 1391
properties. Both compounds had similar absorption spectra
with maxima around 354 nm in CHCl3 (Fig. 2), attributed
to p-p* transition of the conjugated system. The bathochro-
mic shift of DCSQM and DCSQA relative to 2 and 3 dem-
onstrated that p-electron delocalization along the vinylene
bridge was enhanced between the electron-rich trimeth-
oxyphenyl moiety and the electron-deficient quinoline
ring.18,19 DCSQM and DCSQA were highly fluorescent in
CHCl3 with the maximum peaks at 465 nm and 474 nm, re-
spectively. The quantum yields of DCSQM and DCSQA in
CH2Cl2 were determined as 0.44 and 0.52, respectively.20
The absorption of DCSQM and DCSQA varied only
slightly in different solvents. However, the emission spec-
tra showed pronounced red shifts with increasing solvent
polarity for both DCSQM and DCSQA (Fig. 3). The red
shift also caused a broadening of the emission band upon
an increase in the solvent polarity. The solvent-dependent
emission characteristics may result from the dipolar inter-
action with the polar solvents, suggesting the ICT character
of the emission state. Changing the solvent from toluene to
acetonitrile led to a 54-nm and 64-nm red shift for DCSQM
and DCSQA, respectively. This result indicates that DCSQM
and DCSQA are more polar in the excited state than in the
ground state. In agreement with our approach, both com-
pounds with D-p-A structural character are thus involved
in the ICT from the trimethoxyphenyl ring to the quinoline
ring. As shown in Fig. 4a, the linear correlation between
the Stokes shift (na - nf) and the solvent polarity parameter
F1 [(e - 1)/(2e + 1) - (n2 - 1)/(2n2 + 1)] for DCSQM and
DCSQA is in good agreement with the Lippert-Mataga
Fig. 2. Absorption and normalized photoluminescence
spectra for 2 × 10-5 M of 2, 3, DCSQM, and
DCSQA in CHCl3.
Fig. 3. Normalized photoluminescence spectra for 2 ×
10-5 M of DCSQM (a) and DCSQA (b) in differ-
ent solvents.
Fig. 4. (a) Plot of (na - nf) versus F1 = (e – 1)/(2e + 1) – (n2 – 1)/(2n2 + 1). (b) Plot of (na + nf) versus F2 = (e – 1)/(2e + 1) + (n2 –
1)/(2n2 + 1).

1392 J. Chin. Chem. Soc., Vol. 54, No. 6, 2007
Chen et al.
equation.21 This result indicates that these compounds may
have close structures in the ground and excited states and
there are intermolecular interactions between the solvent
and molecules in the excited state. The related plot of (na +
nf) versus F2 [(e - 1)/(2e + 1) + (n2 - 1)/(2n2 + 1)] also
shows a linear correlation (Fig. 4b).22,23 The ratios of the
excited state dipole moment to the ground state dipole mo-
ment (me/mg) are, thus, calculated by the slopes as 3.20 and
3.22 for DCSQM and DCSQA, respectively.
To further characterize the structural features and mo-
lecular orbitals, we carried out a theoretical approach using
density functional theory at the B3LYP/6-31G* level. The
most stable structure of DCSQA (5a, Fig. 6) in the ground
state is in accord with that in the solid state; the two out-of-
plane moieties, 4¢-methoxy and 8-acetoxy groups, are on
the same side of the best plane. Interestingly, the structure
in which the two groups are on the opposite side is 3.75
kcal/mol higher in energy than the most stable structure. As
in the case of the crystal structure of DCSQA, planar p-con-
jugation is observed in both 4a and 5a, with the 4¢-methoxy
group deviating by 83° and 96°, respectively, from the plane
of the trimethoxyphenyl moiety. The 8-methoxy group of
4a and the 8-acetoxy group of 5a also angle out of the best
plane by 68° and 74°, respectively, to minimize the lone
pair repulsion between the O and N atoms.
Cyclic voltammetry was conducted to probe oxida-
tion and reduction potentials and the stability of the oxi-
dized and reduced forms. DCSQM and DCSQA had irre-
versible oxidation potential peaks at 1.21 and 1.24 V (Fig.
5), respectively, indicating that the resultant radical cations
were not electrochemically stable. Two reduction poten-
tials were detected for DCSQM and DCSQA; the first re-
duction is irrevesible, whereas the second one is quasi-re-
versible. Due to its electron deficiency, the quinoline moi-
ety may provide a site for reduction in this D-p-A system.
Apparently, the introduction of methoxy or acetoxy as a C8
substituent of quinoline performs a pronounced effect on
the electrochemical behavior. The more electron-donating
character of the -OCH3 group leads DCSQM to exhibit a
lower oxidation potential and a higher reduction potential.
As indicated by the potential onsets, the 8-substituted meth-
oxy and acetoxy groups effectively perturb the LUMO en-
ergy level with a small effect on the HOMO energy level.
The HOMOs and LUMOs of DCSQM and DCSQA
involve the same localizations (Fig. 7): the HOMOs are lo-
calized on the styrene-based structure and the LUMOs are
p* orbitals with contributions from nearly the entire mole-
cule, with a larger contribution from the quinoline moiety.
The quinoline-based LUMO provides compelling evidence
that the first reduction site occurs on the electron-deficient
quinoline moiety. Based on the orbital diagrams, the elec-
tronic transitions of DCSQM and DCSQAcan be attributed
Fig. 5. Comparison of cyclic voltammograms (CV) of
DCSQM (blue) and DCSQA (red). CVs were
performed in THF with 0.1 M of nBu4NClO4 as
a supporting electrolyte for reduction and in
CH2Cl2 with 0.1 M of nBu4PF6 as a supporting
electrolyte for oxidation. A glassy carbon elec-
trode served as the working electrode. Scan rate
= 100 mV/s.
Fig. 6. The optimized structures of DCSQM (4a) and
DCSQA (5a) at the B3LYP/6-31G* level.

2-Styrylquinolines as Light Emitting Materials
J. Chin. Chem. Soc., Vol. 54, No. 6, 2007 1393
Received March 6, 2007.
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7. (a) Jotterand, N.; Pearce, D. A.; Imperiali, B. J. Org. Chem.
2001, 66, 3224. (b) Shults, M. D.; Imperiali, B. J. Am. Chem.
Soc. 2003, 125, 14248. (c) Pearce, D. A.; Jotterand, N.;
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5160.
CONCLUSIONS
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DCSQM and DCSQA were synthesized via a simple
Knoevenagel condensation and emitted blue light in solu-
tion. X-ray structures showed that DCSQA is essentially
planar, with the 4¢-methoxy and 8-acetoxy groups angled
out of the plane; extensive intermolecular p-p stacking in-
teractions were also revealed. The solvent polarity depend-
ent emissions together with the styryl-localized HOMOs
and quinoline-localized LUMOs indicated that the elec-
tronic transitions could be attributed to an efficient intra-
molecular charge transfer from the trimethoxyphenyl ring
to the quinoline moiety. Electrochemical properties re-
vealed the importance of structural modification on the
quinoline moiety upon the physical properties by introduc-
ing C8 substituents with different electronic characters.
The derivatives of 5,7-dichloro-2-styrylquinoline may
present a new class of potential light emitting materials.
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ACKNOWLEDGEMENTS
Financial support was provided by the National Sci-
ence Council, Taiwan, ROC (NSC93-2323-B-002-015 and
NSC93-3112-B-002-021). We thank The National Center
for High-Performance Computing, Taiwan, for computer
resources.
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the refractive indices for sample and reference, respectively,
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1)/(2e + 1) - (n2 – 1)/(2n2 + 1)] + K where na and nf are the
peak absorption and emission frequencies (cm-1), me and mg
are the dipole moment in the excited and ground state, h is
the Planck’s constant, c is the speed of light, a is the Onsager
cavity radius, and K is a constant. The related equation: (na +
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2
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1)] + K’ where K’ is a constant.
the expression, ff = (Asam/Aref) ´ (aref/asam) ´ (nsam/nref)2 ´ f1 ,
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f
where Asam and Aref are the areas under the corrected fluores-
cence spectrum for sample and coumarin 1, asam and aref are
the absorbances of sample and coumarin 1, nsam and nref are