D-π-A solvatochromic charge transfer dyes containing a 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptor

Article abstract of DOI:10.1016/j.dyepig.2009.07.012

The preparation and solvatochromic behavior of novel, intramolecular charge transfer dyes obtained by the condensation of 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran with 4-dimethylamino benzaldehyde and 9-formyljulolidine are described. The absorption and fluorescence emission spectra of the dyes were studied in solvents of differing polarity. The dyes exhibited positive solvatochromism and their solvatochromic properties are discussed with the aid of semiempirical calculations. The HOMO and LUMO values of the dyes were obtained using both cyclic voltammetry and theoretical calculations; the electrochemical results were in agreement with both observed values and theoretical calculations. pH molecular switching was achieved by modulation of intramolecular charge transfer by means of protonation/deprotonation in DMSO solution.

Full text of DOI:10.1016/j.dyepig.2009.07.012

Dyes and Pigments 84 (2010) 169–175
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
D–
p
–A solvatochromic charge transfer dyes containing
a 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptor
,
b
a
c
a
Sung-Hoon Kim a , Sue-Yoen Lee , Seon-Yeong Gwon , Young-A Son , Jin-Seok Bae
*
a Department of Textile System Engineering, Kyungpook National University, Daegu 702-701, South Korea
b Department of Advanced Organic Materials Science and Engineering, Kyungpook National University, Daegu 702-701, South Korea
c School of Chemical and Biological Engineering, Chungnam National University, Daejeon 305-764, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The preparation and solvatochromic behavior of novel, intramolecular charge transfer dyes obtained by
the condensation of 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran with 4-dimethyla-
mino benzaldehyde and 9-formyljulolidine are described. The absorption and fluorescence emission
spectra of the dyes were studied in solvents of differing polarity. The dyes exhibited positive
solvatochromism and their solvatochromic properties are discussed with the aid of semiempirical
calculations. The HOMO and LUMO values of the dyes were obtained using both cyclic voltammetry and
theoretical calculations; the electrochemical results were in agreement with both observed values and
theoretical calculations. pH molecular switching was achieved by modulation of intramolecular charge
transfer by means of protonation/deprotonation in DMSO solution.
Received 14 June 2009
Received in revised form
20 July 2009
Accepted 21 July 2009
Available online 14 August 2009
Keywords:
D–p–A solvatochromic charge transfer dye
Positive solvatochromism
2-Cyanomethylene-3-cyano-4,5,
5-trimethyl-2,5-dihydrofuran
pH molecular switch
Ó 2009 Elsevier Ltd. All rights reserved.
Intramolecular charge transfer (ICT)
Cyclic voltammetry
1. Introduction
electron acceptor that induces significantly high dipole moment,
first-order molecular hyperpolarizability [16,17]. In this present
Solvatochromic D–
p
–A charge transfer dyes attract much atten-
report, we designed the synthesis and the solvatochromic properties
of the D– –A charge transfer dyes containing 2-cyanomethylene-3-
cyano-4,5,5-trimethyl-2,5-dihydrofuran 1 as shown in Scheme 1. The
organic functional dyes with D– –A molecular structure have
attracted much attention because of their inherent nonlinear optical
characteristics, which are highly sensitive to changes in the external
environment such as polarity and pH of media, due to their intrinsic
character [5]. We have previously reported the synthesis and pH-
tion because of their applicability as probes for the determination of
solvent polarity as well as their potential application as colorimetric
chemosensors for volatile organic compounds (VOC) [1,2]. Charge
transfer dyes have also been developed for use as photo- (PL) and
electroluminescent (EL) materials in dye lasers [3,4], sensors [5], dye-
sensitized solar cells [6,7], switchable viscosity probes [8], dual-ion-
switched molecular brakes [9] and optical light emitting diodes
(OLED’s) [10]. Solvatochromism can be defined as the phenomenon
whereby a compound changes colour, either by a change in the
absorption or emission spectra of the molecule, when dissolved in
different solvents [11,12]. Recently, solvatochromic dyes such as pyr-
idinium betain [13] and stilbazolium [14] have been synthesized and
studied. We have been concerned with the solvatochromic behavior
ofBarbituricacidand Meldrum’sacidbased merocyaninedyesand on
the structural features responsible for relative changes in the
magnitude of their spectral shifts [15]. 2-Cyanomethylene-3-cyano-
4,5,5-trimethyl-2,5-dihydrofuran 1 was well adopted as a strong
p
p
induced molecular switching of D–p–A type solvatochromic charge
transfer dyes [18,19]. In this work, pH-induced changes in absorption
and fluorescence spectra of these dyes were also examined.
2. Experimental
Melting points were determined using an Electrothermal IA900
apparatus and were uncorrected. Elemental analyses were recor-
ded on a Carlo Elba Model 1106 analyzer. Mass spectra were
recorded on a Shimadzu QP-1000 spectrometer using electron
energy of 70 eV and direct probe EI method. 1H NMR spectra were
recorded in DMSO-d6 using a Varian Inova 400 MHz FT-NMR using
TMS as internal standard. The UV–Vis absorption spectra were
measured on an Agilent 8453 spectrophotometer. Fluorescence
* Corresponding author. Tel.: þ82 53 950 5641; fax: þ82 53 950 6617.
E-mail address: shokim@knu.ac.kr (S.-H. Kim).
0143-7208/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.07.012

170
S.-H. Kim et al. / Dyes and Pigments 84 (2010) 169–175
O
NC
N
OHC
N
CN
NC
CN
NC
dye 1
2
NC
O
O
NC
OHC
N
N
1
CN
CN
dye 2
3
Fig. 1. Synthetic routes of dye 1 and dye 2.
spectra were measured on a Shimadzu RF-5301PC Fluorescence
spectrophotometer.
Calcd. for C24H22N4O: C, 75.37; H, 5.80; N, 14.65. Found; C, 74.41; H,
5.92; N, 14.41%.
3. Results and discussion
2.1. Materials
3.1. Solvatofluorchromism
4-Dimethylaminobenzaldehyde, julolidine, 3-hydroxy-3-methyl-
2-butanone and malononitrile were purchased from Aldrich. Thr
other chemicals were of the highest grade available and were used
without further purification. All employed solvents were analytically
pure and were employed without any further drying or purification.
2-Cyanomrthylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran 1 was
made by condensation of 3-hydroxy-3-methyl-2-butanone with
malononitrile [20]. 9-Formyljulolidine 3 was synthesized according
to the literature [21]. Dye 1–2 were prepared by the literature
procedure [22–24].
The synthesis of dye 1 and 2 is depicted in Fig. 1.
The target compound dye 1 (with dimethylaminobenzene) and
dye 2(with julolidine moiety) on the terminal phenyl ring of ami-
nophenyl donor were successfully obtained by condensing alde-
hydes 4-dimethylaminobenzaldehyde 2 and 9-formyljulolidine 3
with a strong electron acceptor 2-cyanomrthylene-3-cyano-4,5,5-
trimethyl-2,5-dihydrofuran 1 in ethanol/chloroform (4:1 v/v). The
chemical structures of all the intermediates and dyes were char-
acterized by 1H NMR, MS and elemental analysis. The lmax, abs and
lmax,em values of the solvent-dependent absorption and fluorescent
emission of dye 1 and 2 in various solvents and ET(30) values are
listed in Table 1.
The results show that dye 1 and 2 exhibited strong sol-
vatochromic properties. The absorption and emission spectra of
dye 1 in several solvents having different polarities are shown in
Fig. 2. As the solvent polarity is increased, a bathochromic shift is
observed (i.e., positive solvatochromism), (Fig. 2a). The absorption
maximum showed a shift with solvent polarity, which extended
from 527 nm for xylene to 584 nm for ethanol. The fluorescence
spectra also exhibited a solvent effect (Fig. 2b). The emission
maximum showed shifts with solvent polarity, which extended
from 597 nm for xylene (excited at 510 nm) to 647 nm for DMF
(excited at 510 nm).
2.2. Electrochemical measurement
The redox potentials were measured by cyclic voltammetry on
an VersaSTAT3 model. Cyclic voltammetry experiment was run in an
acetonitrile solution containing tetrabutylammonium hexa-
fluorophosphate electrolyte. The reference electrode, Ag/Agþ was
directly immersed in the reaction cell. The working electrode was
a glassy carbon. The counter electrode was a platinum wire. The
scan rate was commonly 50 mV/s. HPLC grade acetonitrile was used
as purchased and used in the electrochemical redox potential
measurements of these dyes.
2.3. Synthesis of dye 1 and 2
These photophysical properties of dye 1 show a close similarity
to that observed for solvatochromic merocyanine dyes based on
Barbituric acid and Meldrum’s acid [15]. These features indicate
Dye 1 and 2 were prepared from the similar method described
in previous work [22–24]. Structures were confirmed by the
following.
Table 1
2.3.1. Dye 1
lmax, abs and lmax, em values of dye 1 and 2 in various solvents and ET(30) values of
solvents.
Yield 13% : mp 290–292 ꢀC.
1H NMR (DMSO-d6, 400 MHz):
d 1.76 (s, 6H), 3.12 (s, 6H), 6.84 (d,
Solvent
dye 1
dye 2
ET(30)
J ¼ 9.08 Hz, 2H), 6.91 (d, J ¼ 15.84 Hz, 1H), 7.80 (d, J ¼ 9.01 Hz, 2H),
7.95 (d, J ¼ 15.84 Hz, 1H). EI-MS, m/z ¼ 330 Anal. Calcd. for
C20H18N4O: C, 72.71; H, 5.49; N, 16.96. Found; C, 72.16; H, 5.57; N,
17.08%.
(kcal molꢁ1
)
lmax (nm) lem (nm) lmax (nm) laem (nm)
a
Xylene
Toluene
THF
Chloroform
Acetone
DMF
527
551
558
576
565
581
597
602
630
614
638
647
638
639
593
594
606
617
616
629
620
629
632
634
655
650
658
668
660
660
33.1
33.9
37.4
39.1
42.2
43.8
45.6
51.9
2.3.2. Dye 2
Yield 24%: mp 238–240 ꢀC.
1H NMR(DMSO-d6,400MHz):
d
1.71 (s, 6H), 1.88 (q, J¼ 5.24 Hz, 4H),
Acetonitrile 577
Ethanol
584
2.71 (t, J ¼ 6.00 Hz, 4H), 3.40 (t, J ¼ 5.56 Hz, 4H), 6.76 (d, J ¼ 15.48 Hz,
a
2H), 7.39 (s, 2H), 7.86 (d, J ¼ 15.44 Hz, 2H). EI-MS, m/z ¼ 382. Anal.
Excited at 510 nm.

S.-H. Kim et al. / Dyes and Pigments 84 (2010) 169–175
171
0.8
0.6
0.4
0.2
0.0
a
585
5
4
570
555
540
6
7
3
2
8
525
1
30
35
40
45
50
55
450
500
550
600
650
700
ET(kcal/mol)
Wavelength(nm)
b1000
3
645
630
615
600
800
4
600
400
200
0
8
5
6
2
1
7
30
35
40
45
50
55
550
600
650
700
750
ET(kcal/mol)
Wavelength(nm)
Fig. 2. The UV–vis absorption (a) and fluorescence emission spectra (b) of dye 1
(1 ꢂ 10ꢁ5 mol Lꢁ1) in xylene (1), toluene (2), THF (3), CHCl3 (4), acetone (5), DMF (6),
acetonitrile (7), ethanol (8), respectively.
Fig. 4. Plot of absorption and emission maxima of dye 1 of a function of solvent
polarity parameter ET.
a strongly allowed p–p* transition with charge transfer characters.
The intramolecular charge transfer (ICT) interaction, that is from
aminobenzene moiety to the acceptor fragment is strongly
enhanced upon excitation as evidence from the extreme bath-
ochromic shift of the fluorescence maximum in polar solvents. The
positive solvatochromism indicated that dye 1 has a large dipole
moment in the excited state rather than in the ground state.
24.657
debye
Excited
State
ΔE > ΔE'
Ground
State
16.214
debye
Increasing Solvent Polarity
Fig. 5. The UV–vis absorption and fluorescence emission photographs of dye 1 in
Fig. 3. Effect of solvent polarity on the transition energy of dye 1–2.
several solvents.

172
S.-H. Kim et al. / Dyes and Pigments 84 (2010) 169–175
500
a
b
1.2
1.0
0.8
0.6
0.4
0.2
0.0
4
5
2
6
400
1
7
300
4
3
8
2
200
1
3
100
0
5,6,7,8
500
600
Wavelength(nm)
700
550
600
650
700
750
Wavelength(nm)
Fig. 6. The UV–vis absorption (a) and fluorescence emission spectra (b) of dye 2 (1 ꢂ10ꢁ5 mol Lꢁ1) in xylene (1), toluene (2), THF (3), CHCl3 (4), acetone (5), DMF (6), acetonitrile (7),
ethanol (8), respectively.
Pariser-Parr Pople(PPP)-calculated dipole moment (
ground state and first excited singlet states of dye 1 are presented in
Fig. 3.
m
, Debye) in the
3.2. Theoretical calculation and electrochemical properties
of dye 1–2
The dependence of the absorption and emission maximum of
dye 1 on ET(30) solvent polarity parameter can be fitted to almost
linear function (Fig. 4). As the solvent polarity increased, a bath-
ochromic shift observed (i.e., positive solvatochromism).
Fig. 5 shows the UV–Vis absorption and fluorescence emission
photographs of dye 1 in various solvents, dye 1, in several solvents
with different colours and fluorescent emission, can be easily
observed by the naked eyes.
We also investigated solvatochromic properties of dye 2 in
various solvents. Fig. 6 shows the absorption and emission
spectra of dye 2 in a similar range of solvents. Dye 2 shows one
solvent-dependent absorption band in the visible (around
590–630 nm), with a bathochromic shift of 40 nm, when going
from xylene to ethanol (Fig. 6a). Dye 2 also exhibited a large red
shift in emission spectra as solvent polarity increases. (Fig. 6b)
Fig. 7 shows that there is a fairly good relationship between lmax,
For the interpretation of the intramolecular charge transfer
process of dye 1 and 2, the quantum chemical DMol3 approach
was used. All the theoretical calculations were performed by
DMol3 program in the Materials Studio 4.4 package [25,26]
which is the quantum mechanical code using density func-
tional theory. Perdew-Burke-Ernzerhof (PBE) function of
generalized gradient approximation (GGA) level [27] with
double numeric polarization basis set was used to calculate the
energy level of the frontier molecular orbital. Fig. 9 shows the
electron distribution of the HOMO and LUMO energy level of
dye 1 and 2.
Comparison of the electron distribution in the frontier MOs
reveals that the HOMO-LUMO excitation moves the electron
distribution from aminobenzene moiety to the acceptor, which
showed a strong migration of ICT character of dye 1 and 2.
The electrochemical reduction/oxidation behaviors of these
dyes were determined by cyclic voltammetry (CV) in dry CH3CN.
Using this measurement [28], the potentials of the highest oxida-
tion peak and the lowest reduction peak can be used to calculate
lmax, em and the solvent polarity parameter ET(30).
abs,
Fig. 8 shows the UV–Vis absorption and fluorescence emission
photographs of dye 2 in several solvents (Fig. 9).
670
660
650
640
630
630
620
610
600
590
30
35
40
45
50
55
30
35
40
45
50
55
ET(kcal/mol)
ET(kcal/mol)
Fig. 7. Plot of absorption and emission maxima of dye 2 of a function of solvent polarity parameter ET.

S.-H. Kim et al. / Dyes and Pigments 84 (2010) 169–175
173
the HOMO/LUMO energy levels. The following equation (1) can be
used at this determination.
HOMOðorLUMOÞ
ꢂ ðeVÞ [ L4:8L½EoxidationorreductionpeakLE1=2ðFerroceneÞꢃ
(1)
The electronic states (HOMO/LUMO) of dye 1 and dye 2 were
investigated by cyclic voltammetry (CV). As shown in Fig. 10, both of
the dyes; 1 and 2 exhibited oxidation and reduction peaks. The
estimated electron affinity (LUMO level) values for dye 1 and dye 2
were ꢁ3.78 eV and ꢁ4.03 eV, respectively. The ionization potential
(HOMO level) of dye 1 and dye 2 were ꢁ5.78 eV and ꢁ4.79 eV,
respectively. As the first visible absorption of dye 1 and dye 2 caused
by the intramolecular charge transfer character of the transition, the
introduction of julolidine moiety to the D–p–A system produced
a bathochromic shift of 60 nm. Electrochemical results were in
agreement with observed values and theoretical calculation.
3.3. pH-induced switching in electronic absorption
and fluorescence spectra
Fig. 8. The UV–vis absorption and fluorescence emission photographs of dye 2 in
several solvents.
The interaction of the dye 1 and 2 with acid (CF3COOH)/base
((Bu)4N(OH)) was investigated in DMSO solution through spec-
trophotometric titration experiments. Fig. 11 showed the UV–Vis
absorption and fluorescence spectral changes of dye 1 and 2 in
DMSO solution with acid/base.
Upon addition of acid and base to the dye 1 solution, the band at
600 nm progressively decreases. Addition of base results in an
obviously decreased absorbance at 600 nm, while acid induce
much smaller. The color changed from red to colorless. Fluores-
cence spectra (Fig. 11b) also showed a similar result, which is
consistent with that of UV–Vis spectra. On the other hand, no
changes were observed in the absorption and fluorescence spectra
of dye 2 upon addition of acid. While upon addition of base to the
solution of dye 2, absorption and fluorescence intensity decreased
drastically. Upon addition of acid or base, the colorless solution of
dye 1 and 2 became gradually red and recovered completely back to
the initial state. We propose that these spectral changes, with
proton in dye 1, are due to the interaction of the proton and the
electrons of nitrogen atom of the alkylamino moiety. As a result, the
protonation reduces the electron density in the nitrogen atom, thus
the ICT process is not possible any more and absorption and
emission intensity decreased. The addition of OHꢁ to dye 1 and 2
Fig. 9. Electron distribution of the HOMO and LUMO energy levels of dye 1 and 2.
could conceivably lead to carbanion adducts. Actually, the
a
-carbon
1e-5
1e-5
dye 2
dye 1
8e-6
8e-6
6e-6
4e-6
2e-6
0
6e-6
4e-6
2e-6
0
-2e-6
-4e-6
-6e-6
-2e-6
-4e-6
-6e-6
-1.0
-0.5
0.0
0.5
1.0
1.5
-1.0
-0.5
0.0
0.5
1.0
Potential (V)
Potential (V)
Fig. 10. Cyclic voltammetry (CV) of dye 1 and 2 in CH3CN solution: scan rate ¼ 50 mV/s.

174
S.-H. Kim et al. / Dyes and Pigments 84 (2010) 169–175
dye 2
dye 1
a
1.2
a
0.6
0.4
0.2
0.0
0.9
-
+
+
]
[OH ]
[H
]
[H
0.6
-
[OH ]
+
[H
]
-
0.3
0.0
[OH ]
400
500
600
700
400
500
600
700
Wavelength(nm)
Wavelength(nm)
dye 2
dye 1
50
40
30
20
10
0
160
120
80
40
0
b
b
+
-
[H
]
[OH ]
+
-
[H
]
[OH ]
+
-
[H
]
[OH ]
650
700
750
600
650
700
750
Wavelength(nm)
Wavelength(nm)
Fig. 11. The UV–Vis absorption (a) and fluorescence spectral switching (b) of dye 1 and 2 in DMSO solution with protonation/deprotonation.
which has lower electron density in LUMO can interact with OHꢁ as
a nucleophile (LUMO of dye 1 and 2 in Fig. 9).
[5] de Silva AP, Gunaratne HQN, Gunnlaugsson T, Huxley AJM, McCoy CP,
Rademacher JT, et al. Signaling recognition events with fluorescent sensors
and switches. Chemical Reviews 1997;97:1515–66.
[6] Sansregret J, Drake JM, Thomas WRL, Lesiecki ML. Light transport in planar
luminescent solar concentrators: the role of DCM self-absorption. Applied
Optics 1983;22:573–7.
4. Conclusions
[7] Liu B, Zhu W, Zhang Q, Wu W, Xu M, Ning Z, et al. Conveniently synthesized
isophorone dyes for high efficiency dye-sensitized solar cell: tuning photo-
Owing to the presence of a julolidine moiety as a strong donor,
dye 2 exhibited w60 nm red-shifted absorption compared to that of
dye 1. As both dyes exhibited positive solvatofluorchromic prop-
erties in various solvents, the solvatochromic behavior of the dyes
offers application in volatile organic compound (VOCs) detection.
The HOMO and LUMO values obtained using theoretical calcula-
tions were in agreement with those secured from electrochemical
measurement. pH-Induced molecular switching was demonstrated
by modulation of intramolecular charge transfer via protonation/
deprotonation.
voltaic performance by structural modification of donor group in donor–
acceptor system. Chemical Communications 2009:1766–8.
p–
[8] Zhu LL, Li X, Ji FY, Ma X, Wang QC, Tian H. Photolockable ratiometric viscosity
sensitivity of cyclodextrine polypseudorotaxane with light-active rotor graft.
Langmuir 2009;25:3482–6.
[9] Zhang D, Zhang Q, Su J, Tian H. A dual-ion-switched molecular brake based on
ferrocene. Chemical Communications 2009:1700–2.
[10] Zhang XH, Chen BJ, Lin XQ, Wong QTY, Lee CS, Kwong HL, et al. A new family of
red dopants based on chromen-containing compounds for organic lumines-
cent device. Chemistry of Materials 2001;13:1565–9.
[11] Reichardt C. Solvents and solvent effects in organic chemistry. 3rd ed. Wein-
heim, Germany: Wiley-VCH; 2003.
[12] Reichardt C. Solvatochromic dyes as solvent polarity indicators. Chemical
Review 1994;94:2319–58.
ꢀ
[13] Reichardt C, Ro¨chling A, Schafer G. Syntheses and UV–visible spectroscopic
Acknowledgements
properties of two new hydrophilic 2,6-di(carbamoyl)-substituted sol-
vatochromic pyridinium N-phenolate betaine dye. Journal Physical Organic
Chemistry 2003;16:682–90.
This work was supported by the Korean Science and Engineering
Foundation (KOSEF) grant funded by the Korea government (MEST)
(No. R11-2009-0063408). This research was supported by Kyung-
pook National University Fund, 2008.
[14] Coe BJ, Harris JA, Hall JJ, Brunschwig BS, Hung ST, Libaers W, et al. Syntheses
and quadratic nonlinear optical properties of salts containing benzothiazolium
electron-acceptor groups. Chemistry of Matericals 2006;18(25):5907–18.
[15] Wang S, Kim SH. New solvatochromic merocyanine dyes based on barbituric
acid and meldrum’s acid. Dyes and Pigments 2009;80:314–20.
[16] Luo J, Liu S, Haller M, Liu L, Ma H, Jen AKY. Design, synthesis, and properties of
highly efficient side-chain dendronized nonlinear optical polymers for electro-
optics. Advanced Materials 2002;14:1763–8.
References
[1] Bamfield P. Chromic phenomena: technological application of colour chem-
istry. Cambridge, UK: The Royal Society of Chemistry; 2001.
[2] Janzen MC, Ponder JB, Bailey DP, Ingison CK, Suslick KS. Colorimetric sensor
arrays for volatile organic compounds. Analytical Chemistry 2006;78(11):
3591–600.
[17] He M, Leslie TM, Sinicropi JA, Garner SM, Reed LD. Synthesis of chromophores
with extremely high electro-optic activities. 2. Isophorone- and combined
isophorone-thiophene-based chromophores. Chemistry of Matericals
2002;14:4669–75.
[18] Wang S, Kim SH. Photophysical and electrochemical properties of D–
p–A type
[3] Anthonov VS, Hohla KL. Dye stability under excimer-laser pumping. Applied
Physics B 1983;B32:9.
solvatofluorchromic isophorone dye for pH molecular switch. Current Applied
Physics 2009;9:783–7.
[4] Speiser S, Shakkour N. Photoquenching parameters for commonly used laser
dyes. Applied Physics B 1985;B38:191.
[19] Wang S, Kim SH. Proton-induced fluorescent switching of a new 2D–
p–A type
vinylcyanoacetate-pyran dye. Spectrochimica Acta Part A 2009;72:677–81.

S.-H. Kim et al. / Dyes and Pigments 84 (2010) 169–175
175
[20] Melikian G, Rouessac FP, Alexandre C. Synthesis of substituted dicyanome-
thylenedihydrofurans. Synthetic Communications 1995;25:3045–51.
[21] Cai G, Bozhkova N, Odingo J, Berova N, Nakanishi K. CD excitation chirality
method. New red-shifted chromophores for hydroxyl groups. Journal of
American Chemical Society 1993;115:7192–8.
[22] Cho MJ, Kim JY, Kim JH, Lee SH, Dalton LR, Choi DH. Heterocyclic nonlinear
optical chromophores composed of phenothiazine or carbazole donor and 2-
cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptor. Bulletin
of Korean Chemical Society 2005;26:77–84.
[24] Wang H, Lu Z, Lord SJ, Moerner WE, Twieg RJ. Modifications of DCDHF single
molecule fluorophores to impart water solubility. Tetrahedron Letters
2007;48:3417–74.
[25] Delley B. An all-electron numerical method for solving the local density func-
tional for polyatomic molecules. Journal of Chemical Physics 1990;92:508–17.
[26] Delley B. From molecules to solids with the DMol3 approach. Journal of
Chemical Physics 2000;113:7756–64.
[27] Boese AD, Handy NC.
A new parameterization of exchange-correlation
generalized gradient approximation functional. Journal of Chemical Physics
2001;114:5497–503.
[28] Lee HS, Kim JH. Measurement of physical properties of conducting polymers.
Polymer Science and Technology 2007;18:488–95.
[23] Wang H, Lu Z, Lord SJ, Willets KA, Bertke JA, Bunge SD, et al. The influence of
tetrahydroquinone rings in dicyanomethylenedihydrofuran (DCDHF) single-
molecule fluorophores. Tetrahedron 2007;63:103–14.