Synthesis and optical chromic properties of new barbituric acid based dye molecules having push-π-pull system

Article abstract of DOI:10.1080/15421406.2011.599761

Since the molecular structures based on donor-π-acceptor dye shows good optical absorption and emission properties by push-pull chromophore system, donor-π-acceptor dyes have been intensively studied as functional key materials. In this study, the new don

Full text of DOI:10.1080/15421406.2011.599761

Mol. Cryst. Liq. Cryst., Vol. 550: pp. 240–249, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.599761
Synthesis and Optical Chromic Properties of New
Barbituric Acid based Dye Molecules Having
Push-π-Pull System
SU-HO KIM,1 YOUNG-SUNG KIM,1 DO-HYUN LEE,2
AND YOUNG-A SON1,∗
1BK21 FTIT, Department of Advanced Organic Materials and Textile System
Engineering, Chungnam National University, Daejeon, 305-764, S. Korea
2Korea Dyeing Technology Center, Daegu, 703-804, S. Korea
Since the molecular structures based on donor-π-acceptor dye shows good optical ab-
sorption and emission properties by push-pull chromophore system, donor-π-acceptor
dyes have been intensively studied as functional key materials. In this study, the new
donor-π acceptor dyes were designed, synthesized and characterized. The absorption
and fluorescence emission spectra of these dyes, being related with chromic color
changes, were determined with the several solvents of widely different polarities. The
electron energy states of dyes were also characterized by theoretical calculations.
Keywords donor-π-acceptor; chromic properties; HOMO/LUMO; energy transfer;
push- π-pull; electron energy
Introduction
Recently, considerable efforts have been focused on the study of donor-π-acceptor dye sys-
tem. Donor-π-acceptor dyes have attracted great attentions in opto-electronic applications
[1–3]. The power conversion efficiency, photo-stability and absorption/emission properties
are greatly influenced by donor-π-acceptor dye structural system. In order to obtain higher
opto-chromic efficiency of organic dye materials, the design of dye molecular structures
such as strong donor and acceptor substituent, is very of importance in the area of dye
synthesis and chemistry. If the π-conjugated chromophores contain strong terminal donor
and acceptor groups, it is more effective for elucidating the enhancement of absorption and
emission intensity.
In this context, barbituric acid has been greatly enjoyed as a useful fragment in donor-
acceptor dye structural system, because barbiturate group has been considered as strong
electron-withdrawing moiety. Furthermore, the conjugation system within the barbituric
acid is also effective between carbonyl groups and nitrogen atoms [4–5]. As a donor unit,
triphenylamine and carbazole moieties are widely considered to be electron rich groups
[6–7] and selected in this experimental work.
In this study, we have also designed and synthesized new chromic dye materials,
having donor-π-acceptor system. Barbituric acid is used as a strong electron-withdrawing
∗Corresponding author. E-mail: yason@cnu.ac.kr
240

Dye Molecules Having Push-π-Pull System
241
group, and triphenylamine and carbazole moiety are considered as strong electron-donating
groups. The corresponding absorption and fluorescence emission behaviors with chromic
effects were determined with several solvent media having different polarities.
Experimental
Analysis and Measurement
1H-NMR spectra were recorded on an NMR spectrometer JEOL-AL400 operating at 400
MHz. Chemical shifts were referenced to internal Me4Si (TMS). The absorption and fluo-
rescence spectra were measured with an Agilent 8453 spectrophotometer and a Shmadzu
RF-5301PC fluorescence spectrophotometer, respectively. The elemental analyses were
measured on a Thermo Fisher Scientific-Flash EA 1112 Automatic elemental analyzer.
Electron distributions and energy potentials were calculated with Material Studio 4.3.
Cyclic voltammograms were examined with a Versa STAT3 using three-electrode conven-
tional electro chemical cell. Cyclic voltammetry test was conducted in an CH2Cl2 solution
containing tetrabutlyammonium hexafluorophosphate electrolyte. The working electrode
was a glassy carbon. The counter electrode was a platinum wire. The scan rate was com-
monly 100 mV/s.
Synthesis
Aldehyde intermediates such as 4-(diphenylamino) benzaldehyde (2) and 4-(9H-carbazol-
9-yl) benzaldehyde (3) were synthesized according to previously described method [8–11].
The synthetic procedure of dye 1 and 2 is illustrated in Figure 1.
Dye 1
A mixture of barbituric acid (1) (0.31 g, 0.002 mol) and 4-(diphenylamino)-benzaldehyde
(2) (0.54 g, 0.002 mol) in acetic anhydride (5 ml) was refluxed for 3 h. The reaction
was cooled to room temperature and the solid particles were filtered. The product was
then purified by recrystallization with acetic acid to give 0.48g with 59% yield. 1H NMR
(CDCl3) : 8.43 (s, 1H); 8.24–8.22 (d, 2H); 7.38–7.34 (t, 4H); 7.29–7.19 (d, 6H); 6.95–6.92
(t, 2H); 3.40 (s, 6H). MS m/z: 411 (M+). Anal. Calcd. For C25H21N3O3: C, 72.98; H, 5.14;
N, 10.21; Found: C, 73.06; H, 4.65; N, 10.06.
Dye 2
A mixture of barbituric acid (1) (0.31 g, 0.002 mol) and 4-(9H-carbazol-9-yl)benzaldehyde
(3) (0.54 g, 0.002 mol) in acetic anhydride (15 ml) was refluxed for 3h. The reaction
was cooled to room temperature and the solid particles were filtered. The product was
then purified by recrystallization with acetic acid to give 0.46 g with 57% yield. 1H NMR
(CDCl3) : 8.64 (s, 1H); 8.42–8.39 (d, 2H); 8.15–8.13 (d, 2H); 7.75–7.73 (d, 2H); 7.58–7.56
(t, 2H); 7.45–7.44 (t, 2H); 7.34–7.26 (t, 2H); 3.42 (s, 6H). MS m/z: 409 (M+). Anal. Calcd.
For C25H19N3O3: C, 73.34; H, 4.68; N, 10.26; Found: C, 72.84; H, 4.64; N, 9.90.
Results and Discussion
The synthetic procedure of dye 1 and 2 is illustrated in Figure 1. Optical chromic properties
of the donor-π-acceptor dyes were prepared, using strong electron-withdrawing unit (1)
and strong electron-donating units (2, 3).

242
S.-H. Kim et al.
Figure 1. Synthetic routes of the dye 1 and 2.
The λmax,abs and λmax,em values of dye 1 and 2 in various solvents and ET(30) values
are listed in Table 1. ET(30) is an empirical parameter of solvent polarity. Namely, the
transition energy for pyridinium-N-phenoxide betain dye, expressed in kcal mol−1, is used
as a polarity parameter. It is possible to determine the chromic effects using nearly 362
different solvents [12–13].
Absorption spectra in various solvents with dye 1 and 2 are shown in Figure 2. All
synthesized donor-π-acceptor dyes showed good solubility with CCl4, toluene, CH2Cl2,
Table 1. λmax,abs and λmax,em values of dye 1 and 2 in various solvents and ET(30) values
Dye 1
Dye 2
ET(30)
Solvent
λmax
λem
λmax
λem
(kcal mol−1
)
CCl4
Toluene
THF
EA
CH2Cl2
466
463
458
457
471
469
540
557
575
570
579
579
430
428
413
411
426
423
485
509
559
559
569
569
32.4
33.9
37.4
38.1
40.7
41.3
1,2-dichloroethane

Dye Molecules Having Push-π-Pull System
243
Figure 2. Absorption spectra of dye 1 and 2.
1,2-dichloroethane, ethyl acetate and THF. None of any noticeable effect on absorption has
been monitored in various solvent polarities, being shifted within the range of 15 nm.
The fluorescence spectra and emission maximum of dye 1 on ET(30) solvent polarity
parameters are shown in Figure 3. The dependence of emission maximum of dye 1 on
ET(30) solvent polarity parameters was exhibited to almost linear function. From dye 1,
this result indicates the positive fluorescence solvatochromism with increasing solvent
polarity. We also investigated fluorescence solvatochromic properties of dye 2 in similar
method with dye 1. From the findings of dye 2, very similar fluorescence solvatochromic
effects were observed as indicated in dye 1 (Figure 4). All prepared donor-π-acceptor dyes
can be proposed to show the positive fluorescence solvatochromism with the increasing
solvent polarity.
The corresponding results of fluorescence solvatochromism are reflected by large
bathochromic shift of their fluorescence emission maxima with increasing solvent polarity.

244
S.-H. Kim et al.
Figure 3. Fluorescence emission spectra of dye 1 in various solvents (a) and plot of emission maxima
of dye 1 versus solvent polarity parameter ET(30) (b).
From results of Figure 3 and Figure 4, it is proposed that all dyes showed the positive
fluorescence solvatochromism effect, being stable emitting state in polar solvent media. In
particular, dye 2 showed higher intensity of emission in non-polar solvent such as CCl4 and
toluene. However, the emission intensity of dye 1 and 2 decreased with increasing solvent
polarity, because the fluorescence quenching behavior of some aromatic hydrocarbons can
be occurred when they have radical ion formation with solvent polarity [14–15].

Dye Molecules Having Push-π-Pull System
245
Figure 4. Fluorescence emission spectra of dye 2 in various solvents (a) and plot of emission maxima
of dye 2 versus solvent polarity parameter ET(30) (b).
To gain further insight into the geometrical shape and HOMO/LUMO energy levels of
dye 1 and 2, the geometrical structure and molecular orbital calculations were performed
using a Material Studio 4.3 suite. All the theoretical calculation was based on DMol3
program. Figure 5 shows the electron distributions and the HOMO/LUMO energy level
of dye 1 and 2. A strong migration of intramolecular charge transfer (ICT) for all dyes
is observed from donor units (triphenylamine and carbazole moietes) to acceptor unit
(barbituric acid).

246
S.-H. Kim et al.
Figure 5. Electron distributions and HOMO/LUMO energy levels of dye 1 and 2.
From the findings, the fluorescence emission intensity of dye 1 showed weak values
in various solvents with compared to dye 2. It can be explained that due to geometrically
twisted molecular shape of dye 1, the intramolecular repulsion effect increased and loss of π-
conjugation and fluorescence intensity then occurred. Thus, the carbazole donor compound
of dye 2 is more effective than triphenylamine donor compound of dye 1. Fluorescence
emission images of dye 1 and 2 in various solvents were shown in Figure 6. Especially,
dye 2 showed evident fluorescence solvatochromic effects, which are well agreed with the
previous finding and explanation.
Further electrochemical properties were calculated with cyclicvoltammetry (CV) mea-
surement. Using CV measurement, we found the oxidation peak at 0.85 V(onset, dye 1)
and 0.87 V(peak, dye 2). The resulting cyclicvoltammogram was summarized in Figure 7.

Dye Molecules Having Push-π-Pull System
247
Figure 6. The Fluorescence emission photographs of dye 1 and 2 in several solvents.
In addition, the energy potentials of oxidation onset peak and absorption band gap were
used to calculate empirical HOMO/LUMO energy levels. The following equation was used
[16].
HOMO (or LUMO) (eV) = −4.8 − (Epeak or onset − E1/2 (Ferrocene)
)
The HOMO and LUMO levels were calculated to be −5.23 eV and −3.06 eV respectively
for dye 1, and −5.25 eV and −2.72 eV respectively for dye2. The HOMO/LUMO values
that are computationally calculated and Determined with cyclic voltammograms of dye 1
and 2 are listed in Table 2. The potential energy levels of dye 1 and 2 showed the similar
Table 2. HOMO/LUMO values of dye 1 and 2
Determined with cyclic
Computationally calculated
voltammograms
Dye
HOMO
LUMO
ꢀE
HOMO
LUMO
ꢀE
1
2
−5.023
−5.306
−3.182
−3.509
1.84
1.79
−5.23
−5.25
−2.92
−2.72
2.31
2.53

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S.-H. Kim et al.
Figure 7. Cyclic voltammograms of dye 1 and 2 measured in CH2Cl2.
characteristic patterns from the values of computational calculation and electrochemical
measurement.
Conclusions
In this study, we have synthesized new D-π-A type dyes based on barbituric acid as an
acceptor unit and triphenylamine and carboazole as donor units. Dye 1 and 2 indicated
the positive fluorescence solvatochromism with increasing solvent polarity. However the
fluorescence emission intensity of dye 1 showed weak values in various solvents with

Dye Molecules Having Push-π-Pull System
249
compared to dye 2. It can be explained that due to geometrically twisted molecular shape,
the intramolecular repulsion effect increased and loss of π-conjugation and fluorescence
intensity then occurred. The Dye 2 in several solvents with different colors and fluorescent
emission can be easily observed by the naked eyes.
Acknowledgment
“This research was supported by a grant from the Fundamental R&D Program for Core
Technology of Materials funded by the Ministry of Knowledge Economy, Republic of
Korea”
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