The synthesis and proton-induced spectral switching of a novel azine dye and its boron complex

Article abstract of DOI:10.1016/j.dyepig.2010.04.006

An azine dye and its boron complex were synthesized and their structures were confirmed using elemental analysis, UV-Vis, fluorescence, mass and ¹H NMR spectroscopic techniques. The effects of protonation/deprotonation on the absorption and emission characteristics of the two dyes were determined. The observed effects of pH upon the colour of the dyes were interpreted in terms of electron density distribution and intramolecular charge transfer.

Full text of DOI:10.1016/j.dyepig.2010.04.006

Dyes and Pigments 87 (2010) 268e271
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis and proton-induced spectral switching of a novel
azine dye and its boron complex
,
a
c
b,
Sung-Hoon Kim a , Seon-Yeong Gwon , S.M. Burkinshaw , Young-A Son
*
**
a Department of Textile System Engineering, Kyungpook National University, Daegu 702-701, South Korea
b Department of Advanced Organic Materials and Textile System Engineering, Chungnam National University, Daejeon 305-764, South Korea
c University of Leeds, Leeds LS2 9JT, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
An azine dye and its boron complex were synthesized and their structures were confirmed using
elemental analysis, UVeVis, fluorescence, mass and 1H NMR spectroscopic techniques. The effects of
protonation/deprotonation on the absorption and emission characteristics of the two dyes were deter-
mined. The observed effects of pH upon the colour of the dyes were interpreted in terms of electron
density distribution and intramolecular charge transfer.
Received 18 March 2010
Received in revised form
15 April 2010
Accepted 16 April 2010
Available online 24 April 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Azine dye
Boron complex
Protonation/deprotonation
Color change
HOMO/LUMO
Donoreacceptor
1. Introduction
2. Experimental
Azine dyes have attracted attention as potential coordinating
ligands [1e9] and offer several biological applications, including
the preparation of chemically modified electrodes (CME’s) for the
amperometric detection of the reduced form of the coenzyme
NaDH, mono and binuclear cationic complexes as DNA probes and
identification of cells using the positive myeloperoxidase reaction
[1,4,10e13]. This work concerns the synthesis of a novel azine dye 5
and corresponding boron complex 6, as such boron complexes
characteristically display strong absorption and sharp emission
peaks in high quantum yield [2,14,15]. The color switching ability of
the dyes, induced by protonation and deprotonation, was deter-
mined and interpreted in terms of the transformation of the
donoreacceptoredonor (DeAeD) configuration [16e19] of the
azine dye to a DeA molecular architecture (Scheme 1), as evidenced
by changes in the corresponding electron density distribution
within the azine dye.
2.1. Characterisation
Elemental analyses were recorded using a Carlo Elba Model 1106
analyzer, mass spectra were recorded on a Shimadzu QP-1000 and
FAB mass spectra were obtained using a JMS700. 1H NMR spectra
were obtained using a Varian Inova 400 MHz FT-NMR employing
TMS as internal standard. UVeVis absorption spectra were recor-
ded on an Agilent 8453 spectrophotometer and fluorescence
spectra were measured using a Shimadzu RF-5301PC spectropho-
tometer. Fluorescence quantum yields were determined using
fluorescein (FF ¼ 0.90, acetonitrile as the solvent) as reference.
Quantum chemical calculations based on DFT were carried out
using the Dmol3 module installed in a Materials Studio 4.4 package
(Accelrys Inc.) [20,21], employing PerdeweBurkeeErnzerhof (PBE)
functions of generalized gradient approximation (GGA) level [22].
Chemicals were purchased from Aldrich; all solvents were analyt-
ically pure and were used without drying or purification. The
effect of protonation and deprotonation on the azine dyes was
determined by the step-wise addition of a 1 ꢀ 10ꢁ5 molLꢁ1 aq
solution of tetrabutyl ammonium hydroxide or 1 ꢀ 10ꢁ5 molLꢁ1 aq
HCl solution.
* Corresponding author. Tel.: þ82 53 950 5641; fax: þ82 53 950 6617.
** Corresponding author. Tel.: þ82 42 821 6620; fax: þ82 42 823 3736.
E-mail addresses: shokim@knu.ac.kr (S.-H. Kim), yason@cnu.ac.kr (Y.-A. Son).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.04.006

S.-H. Kim et al. / Dyes and Pigments 87 (2010) 268e271
269
OHC
N
D
A
D
H2N NH2
2
H
C
CHO
OH
N
NH2
4
N
N
N
OH
OH
3
1
5
H+
BF3O(CH2CH3)2
D
A
D
D
D
A
A
H+
N
N
H
N H
N
N
N
N
N
N
OH
O
B
F
O
B
F
F
F
5a
6
6a
Scheme 1. Synthetic route used.
2.2. Synthesis (Scheme 1)
CH3CN were investigated. Upon the addition of acid, the main
absorption peak at 380 nm decreased and a new peak at 460 nm
appeared; simultaneously, fluorescence emission intensity
decreased (Fig. 1). The observed acid-induced changes in the
absorption and emission behavior of 5 can be attributed to
protonation of the dye 5a. The observed changes in emission and
2.2.1. Compound 3
Salicylaldehyde 1 (0.9 g, 8.2 mmol) and hydrazine 2 (caution:
may pose explosion hazard, especially if heated; incompatible with
sources of ignition, light, shock, strong oxidizing agents, strong
acids, metal oxides; 2.67 g, 53.3 mmol) were dissolved in 4 ml of
methanol with stirring. After the formation of a white dispersion,
the reaction mixture was filtered under reduced pressure and the
ensuing white solid was washed in hexane and dried.
1.0
a
Yield 70%. 1H NMR(400 MHz) DMSO-d6:
d 5.42 (s, 2H, eNH2),
0.8
0.6
0.4
6.87 (t, J ¼ 7.32 Hz, 1H), 6.92 (d, J ¼ 7.8 Hz, 1H), 7.06 (d, J ¼ 7.56 Hz,
1H), 7.18 (t, J ¼ 7.32 Hz, 1H), 11.09(s, 1H, eOH). Mþ ¼ 136.
2.2.2. Dye 5
3 (0.5 g, 3.7 mmol) and 4-dimethylamino-benzaldehyde 4
(0.55 g, 3.7 mmol) were dissolved in 60 ml of methanol and the
reaction mixture was refluxed for 7 h at the end of which time,
a yellow solid precipitated. The yellow solid (5) was filtered, dried
and chromotographed on silica gel.
[H+]
[OH-]
[H+] [OH-]
0.2
Yield 77%. 1H NMR(400 MHz) DMSO-d6:
d 3.00 (s, 6H), 6.76
(d, J ¼ 8.32 Hz, 2H), 6.92e6.98 (m, 2H), 7.33 (t, J ¼ 7.56 Hz, 1H), 7.58 (d,
J¼ 7.84 Hz,1H), 7.68(d, J¼ 8.36 Hz, 2H), 8.60 (s,1H), 8.85 (s,1H),11.53 (s,
1H, eOH). EA: anal. calcd. C16H17N3O: C; 71.89, H; 6.41, N; 15.72. found
C; 71.78, H; 6.55, N; 15.42%. Mþ ¼ 267 Quantum Yield: FF ¼ 0.007.
0.0
300
350
400
Wavelength (nm)
450
500
b
2.2.3. Dye 6
160
120
80
40
0
5 (0.1 g, 0.37 mmol) was dissolved in 10 ml of toluene under N2;
10 ml of triethylamine was added to the reaction solution at room
temperature and BF3O(CH2CH3)2 (0.7 ml, 5.55 mmol) was then
added over 10 min. The ensuing orange solid was filtered under
reduced pressure, washed using distilled water, dried and chro-
motographed on silica gel.
[H+] [OH-]
Yield: 76% 1H NMR (400 MHz, CDCl3):
d 3.08 (s, 6H), 6.69 (d,
J ¼ 9.08 Hz, 2H), 6.99 (t, J ¼ 7.8 Hz, 1H), 7.10 (d, J ¼ 8.32 Hz, 1H), 7.42
(d, J ¼ 7.8 Hz, 1H), 7.56 (t, J ¼ 8.6 Hz, 1H), 7.71 (d, J ¼ 8.84 Hz, 2H),
8.61(s, 1H), 8.96 (s, 1H). EA: anal. calcd. C16H16BF2N3O: C 60.98, H
5.12, N 13.33, Found C 60.95, H 5.24, N 13.11%. FAB mass:
Mþ ¼ 315.1. MHþ ¼ 154(matrix base peak, 2-nitrobenzylalcohol)
Quantum Yield: FF ¼ 0.04.
400
450
500
550
600
650
700
3. Results and discussion
Wavelength (nm)
Fig. 1. Absorption and emission changes for a 1 ꢀ 10ꢁ5 M solution of 5 in CH3CN
The effects of protonation and deprotonation on the colori-
metric, chemosensing properties of a 1 ꢀ 10ꢁ5 M solution of 5 in
imparted by protonation and deprotonation.

270
S.-H. Kim et al. / Dyes and Pigments 87 (2010) 268e271
absorption (i.e., transformation of 5 to 5a) was reversible by
adjustment of pH.
Fig. 2 shows the effect of pH on the absorption and emission
properties of the boron complex-azine dye chromophore 6 from
which it is apparent that similar results were obtained to those
secured using 5 insofar as the absorption peak at 395 nm decreased
and a new absorption peak at 460 nm appeared. In the case of the
boron complex 6, the maximum absorption peak shifted from
380 nm, which was identical to that found for 5, to 395 nm; the new
absorption peak at 460 nm was also the same as that observed for
dye 5. Once again, adjustment of the pH resulted in reversible
emission and absorption imparted by protonation/deprotonation.
Software was used to calculate the electron density distribution
and related energy potential of the pushepull, intramolecular
charge transfer operating in both the donoreacceptoredonor
(DeAeD) and donoreacceptor (DeA) configurations of 5 and 5a.
From Fig. 3 it is apparent that that in the HOMO state, the electron
density of 5a is greater in the benzene ring which bears the eOH
and eN(CH3)2 groups, namely the donor moieties. However, in the
LUMO state of 5, the electrons in the donor moieties are fewer and
the electron density within the acceptor units is greater. Thus,
DeAeD intramolecular charge transfer determines the chromo-
genic properties of 5.
Fig. 3. Electron distribution of HOMO and LUMO energy levels in 5 and 5a.
However, different characteristics were observed in the case of
the protonation/deprotonation of 5. The addition of acid to a solu-
tion of 5 converts the DeAeD configuration to a DeA molecular
system. In the protonated derivative, 5a, the protonated dime-
thylamine groups cannot act as a donor and, therefore, electron
density is highest within the donor part of the HOMO state and
within the acceptor part of the LUMO state (Fig. 3).
The energy potential values of 5 in both HOMO and LUMO states
were compared. As shown in Fig. 1, protonation shifted the
absorption band bathochromically in the DeA configuration, the
corresponding energy levels being: HOMO (ꢁ2.349)/LUMO
(ꢁ4.548) in the DeAeD configuration and HOMO (ꢁ7.345)/LUMO
(ꢁ5.682) in the DeA configuration. The low excitation energy gap
of 1.663 for the DeA system obtained for 5a fitted well with the
observed maximum absorption wavelengths in terms of the
decrease in the peak at 380 nm and the increase in the peak at
460 nm.
1.2
a
1.0
0.8
0.6
4. Conclusions
[H+]
[OH-] [H+] [OH-]
0.4
0.2
0.0
A novel azine dye and its boron complex were synthesized and
their effect of pH on absorption/emission character were studied
and interpreted using electron density distribution software. Upon
the addition of acid, the main absorption peak of 5 at 380 nm
decreased and a new peak at 460 nm appeared. In the case of the
born complex, 6, the absorption peak at 395 nm decreased and
a new absorption band at 460 nm appeared. The maximum
absorption peak of dye 6 shifted from 380 nm, which was identical
to that observed for 5, to 395 nm. The donoreacceptoredonor
(DeAeD) configuration of 5 was transformed by the addition of
acid to a DeA configuration. The electron distributions of both the
HOMO and LUMO energy states were computationally calculated
and showed that the lower energy gap for 5a fitted well with the
observed maximum absorption wavelengths.
300
350
400
450
500
550
600
Wavelength (nm)
b
160
120
80
Acknowledgements
[H+] [OH-]
This work was supported by the Basic Science Research Program
through the National Reserch Foundation (NRF) grant funded by
the Korea government (MEST) (No. 2010-0001885).
40
References
0
400
450
500
550
600
650
700
[1] Godara M, Maheshwari R, Varshney S, Varshney AK. Synthesis and charac-
terization of some new coordination compounds of boron with mixed azines.
Journal of the Serbian Chemical Society 2007;72(4):367e74.
[2] Loudet A, Burgess K. BODIPY dyes and their derivatives: syntheses and
spectroscopic properties. Chemical Reviews 2007;107(11):4891e932.
Wavelength (nm)
Fig. 2. Absorption and emission changes of a 1 ꢀ 10ꢁ5 M solution of 6 in CH3CN with
imparted by protonation and deprotonation.

S.-H. Kim et al. / Dyes and Pigments 87 (2010) 268e271
271
[3] Guskos N, Paschalidis DG, Majszczyk J, Typek J, Maryniak M. Photoacoustic
study of a new neodymium(III) hydrazone complex. Materials Science-Poland
2005;23(4):1029e34.
[4] Sheng R, Wang R, Kiu W, Wu X, Wu S. A new colorimetric chemosensor for
Hg2þ based on coumarin azine derivative. Sensors and Actuators B: Chemical
2008;128(2):507e11.
[5] Gunnlaugsson T, Leonard JP, Murray NS. Highly selective colorimetric naked-
eye Cu(II) detection using an azobenzene chemosensor. Organic Letters
2004;6(10):1557e60.
[6] Bamfield P. Chromic phenomena: technological application of colour chem-
istry. Cambridge, UK: The Royal Society of Chemistry; 2001.
[7] Thorfinnur G, Lee TC, Raman P. Cd(II) sensing in water using novel aromatic imi-
nodiacetate based fluorescent chemosensors. Organic Letters 2003;5(22):4065e8.
[8] Moon SY, Cha NR, Kim YH, Chang SK. New Hg2þ selective chromo- and flu-
oroionophore based upon 8-hydroxyquinoline. Journal of Organic Chemistry
2004;69(1):181e3.
[13] Bodtke A, Pfeiffer WD, Ahrens N, Langer P. Horseradish peroxidase (HRP)
catalyzed oxidative coupling reactions using aqueous hydrogen peroxide: an
environmentally benign procedure for the synthesis of azine pigments.
Tetrahedron 2005;61(46):10926e9.
[14] Zhou Y, Xiao Y, Chi S, Qian X. Isomeric boronꢁfluorine complexes with
donorꢁacceptor architecture: strong solid/liquid fluorescence and large
stokes shift. Orgnic Letters 2008;10(4):633e6.
[15] 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(5):1515e66.
[16] Li X, Kim SH, Son YA. Optical properties of donor-
p-(acceptor)n merocyanine
dyes with dicyanovinylindane as acceptor group and triphenylamine as donor
unit. Dyes and Pigments 2009;82(3):293e8.
[17] Reichardt C. Solvents and solvent effects in organic chemistry. 3rd ed.
Weinheim: Wiley-VCH; 2003.
[18] Reichardt C. Solvatochromic dyes as solvent polarity indicators. Chemical
Reviews 1994;94(8):2319e58.
[19] Pradhan B, Pal AJ. Organic photovoltaic devices: concentration gradient of
donor and acceptor materials in the molecular scale. Synthetic Metals
2005;155(3):555e9.
[9] JanzenMC, Ponder JB, BaileyDP, IngisonCK, SuslickKS. Colorimetricsensor arrays
for volatile organic compounds. Analytical Chemistry 2006;78(11):3591e600.
[10] Malinauskas A, Niaura G, Bloxham S, Ruzgas T, Gorton L. Journal of Colloid and
Interface Science 2000;230(1):122e7.
[11] Chandra M, Sahay AN, Pandy DS, Tripathi RP, Saxena JK, Reddy VJM, et al.
Potential inhibitors of DNA topoisomerase II: ruthenium(II) poly-pyridyl and
pyridyl-azine complexes. Journal of Organometallic Chemistry 2004;689
(13):2256e67.
[12] Bodtke A, Pfeiffer WD, Ahrens N, Langer P. Peroxidase catalyzed formation of
azine pigmentsda convenient and sensitive method for the identification of
human cells with positive myeloperoxidase reactivity. Bioorganic & Medicinal
Chemistry Letters 2004;14(6):1509e11.
[20] Delley B. An all-electron numerical method for solving the local density
functional for polyatomic molecules. Journal of Chemical Physics 1990;92
(1):508e17.
[21] Delley B. From molecules to solids with the DMol3 approach. Journal of
Chemical Physics 2000;113(18):7756e64.
[22] Boese AD, Handy NC.
A new parameterization of exchange-correlation
generalized gradient approximation functional. Journal of Chemical Physics
2001;114(13):5497e503.