N. Nagarajan et al. / Journal of Photochemistry and Photobiology B: Biology 127 (2013) 212–222
213
the antibacterial and antifungal activities of the compounds were
also explored.
where yA,F denotes a solvent-dependent physicochemical property
of absorbance and fluorescence in a given solvent and y the statis-
0
tical quantity corresponding to the value of the property in the gas
phase. SP (solvent polarisability), SdP (solvent dipolarity), SA and SB
represent independent solvent parameters accounting for various
types of solute–solvent interactions. aSA, bSB, cSP and dSdP are adjust-
able coefficients that reflect the sensitivity of physical property y in
a given solvent to the various solvent parameters.
2
. Experimental section
2.1. Reagents and instruments
All the chemicals were commercially available and they were
used without further purification. 1H NMR and C NMR were re-
13
corded on a Bruker Avance 400 (400 MHz) NMR spectrometer.
Dimethylsulfoxide (DMSO-d6) and CDCl were used as solvent
3
and tetramethylsilane (TMS) as internal standard. Mass spectra
were obtained on a FDMS, VG Instruments ZAB-2 mass spectrom-
eter. X-ray crystallographic diffraction data were collected on a
Bruker SMART APEX-II CCD diffractometer at room temperature
2
2
.2. Synthesis
0
.2.1. General procedure for the synthesis of 4,4 -pyridine-2,6-
-pyridine-3,5-diyldibenzaldehyde (4)
0
diyldibenzaldehyde (3) and 4,4
The corresponding dibromopyridine (1 or 2) (1 g, 4.2 mmol)
were treated with 4-formylphenylboronic acid (1.33 g, 8.86 mmol),
using graphite-monochromated Mo K
a radiation (k = 0.71073 Å).
3 4 2 3
Pd[PPh ] (0.487 g, 0.42 mmol), K CO (3.4 g, 25.2 mmol) in 5:1
Integration and cell refinement were carried out using Bruker
mixture of THF and water and stirred at 70 °C under nitrogen
atmosphere for 12 h and TLC was used to check the completion
of the reaction. The product was extracted with DCM, dried over
SAINT. The structures were solved by direct methods (SHELXS
2
8
6/SHELXS 97) and refined by full-matrix least squares on F using
SHELXL 97. All non-hydrogen atoms were refined anisotropically.
MERCURY was used for all graphical representation of the results.
UV–Vis spectra were recorded at room temperature in quartz cuv-
2 4
Na SO and the compound was purified by column chromatogra-
phy (silica gel 60–120 mesh, hexane/EtOAc) (9:1 v/v) as a eluent
to afford the desired compound 3 or 4 [28].
ettes using JASCO V360 spectrophotometer for chloroform (CHCl
ethylacetate (EtOAc), tetrahydrofuran (THF), dichloromethane
DCM), ethanol (EtOH), methanol (MeOH), acetonitrile (MeCN),
3
),
0
2
.2.2. 4,4 -Pyridine-2,6-diyldibenzaldehyde (3)
(
1
Yield: 66%, H NMR (400 MHz, CDCl
3 H
): d 7.83–7.85 (d, 2H),
N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO)
solutions. Fluorescence spectra were obtained from PerkinElmer-
LS55 spectrofluorometer in the above mentioned solvents. Solvents
of the highest available quality (Spectroscopic or HPLC grade) were
used. Emission spectra were recorded by exciting the samples at
their absorption maximum unless otherwise mentioned. All the
experiments were performed at room temperature at a concentra-
7
2
1
.91–7.95 (t, 1H), 8.02–8.04 (d, 4H), 8.31–8.33 (d, 4H), 10.11 (s,
13
H);
3 C
C NMR (400 MHz, CDCl ): d 120.33, 127.54, 130.16,
36.62, 138.05, 144.54, 155.62, 191.95.
0
2
.2.3. 4,4 -Pyridine-3,5-diyldibenzaldehyde (4)
1
Yield: 69%, H NMR (400 MHz, CDCl
3 H
): d 7.82 (d, 2H, 7.6 Hz),
ꢀ
5
7
2
1
.90 (t, 1H, 8 Hz), 8.01 (d, 4H, 8.4 Hz), 8.31 (d, 4H, 8 Hz), 10.09 (s,
tion of 10 M. Quantum yield of the dyes were calculated by fol-
lowing standard procedure and using 9, 10-diphenylanthracene
1
3
H);
3 C
C NMR (400 MHz, CDCl ): d 120.44, 127.65, 130.27,
36.27, 136.71, 138.16, 144.65, 155.74, 192.06.
(U
f
= 0.95 in ethanol) as Ref. [23] by using the following equation:
2
I
I
S
ꢁ OD
R
ꢁ nS
U
f
¼
U
R
ð1Þ
and I
2.2.4. General procedure for the synthesis of bis-[4-(4,5-diphenyl-1H
imidazol-2-yl)-phenyl]-pyridines (2PBI and 3PBI)
2
ꢁ n
R
R
ꢁ OD
S
where
U
R
is the fluorescence quantum yield of reference, I
S
R
4
A mixture of NH OAc (1.07 g, 13.9 mmol), benzil (0.73 g,
are the area of the sample and reference under the emission spec-
trum, OD and OD are the optical density at the excitation wave-
length of the reference and sample, n and n are refractive index
of solvent of sample and reference. In all measurements, the optical
density of solutions does not exceed 0.1. The electrochemical prop-
erties were investigated by cyclic voltammetry (CV) in DMF by
3.48 mmol), and 3 or 4 (0.5 g, 1.74 mmol) in AcOH (6 ml) were re-
fluxed for 4 h. The mixture was poured into cooled water and fil-
tered, washed with water, dried in vacuo and the compound was
purified by column chromatography (silica gel 60–120 mesh, hex-
ane/EtOAc) (4:1 v/v) as a eluent to afford the target compound 2PBI
and 3PBI as a colorless solid.
R
S
S
R
6
using 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF )
as supporting electrolyte. The experiments were performed at room
temperature (1 mM concentration) with a three-electrode cell con-
sisting of a platinum wire as an auxiliary electrode, a saturated Ag/
2
(
.2.5. 2,6-Bis-[4-(4,5-diphenyl-1H imidazol-2-yl)-phenyl]-pyridine
2PBI)
Yield: 60%, mp: 227–230 °C, 1H NMR (400 MHz, DMSO-d
6
): d
H
+
Ag reference electrode and a platinum working electrode.
7
3
.32 (d, 4H, 7.2 Hz), 7.38 (m, 8H), 7.56 (d, 8H, 7.2 Hz), 8.02 (s,
The multiple linear regression approach of Kamlet–Taft [24,25]
and Catalán [26,27] new generalized solvent polarity scale (four
parameter) has been used to correlate UV–Vis absorption and
emission energies with an index of the solvent dipolarity/polariz-
13
H), 8.27 (d, 4H, 8.4 Hz), 8.37 (d, 4H, 8.8 Hz), 13.01 (s, 2H);
): d
27.21, 127.79, 128.23, 128.41, 128.64, 130.84, 138.19, 138.32,
45.08, 155.18, 171.96; MS (HRMS) m/z: calculated 667.2736,
C
NMR (400 MHz, DMSO-d
1
1
6
C
118.98, 125.17, 125.51, 126.98,
ability which is a measure of the solvent’s ability to stabilize a
+
found 668.2812 (MH) .
⁄
charge or dipole through nonspecific dielectric interactions (
p
or
SP/SdP), and indices of the solvent’s hydrogen-bond donor strength
or SA) and hydrogen-bond acceptor strength (b or SB) according
to the following equations:
2
(
.2.6. 3,5-Bis-[4-(4,5-diphenyl-1H imidazol-2-yl)-phenyl]-pyridine
3PBI)
Yield: 60%, mp: 215 °C, 1H NMR (400 MHz, DMSO-d
(broad, 12H), 7.55 (d.8H, 7.6 Hz), 8.03 (d, 4H, 8.4 Hz), 8.25) (d,
H, 8.4 Hz), 8.49 (m, 1H), 8.98 (s, 2H), 12.80 (s, 2H); 13C NMR
400 MHz, DMSO-d ): d 119.48, 125.67, 126.01, 127.48, 127.71,
(a
6 H
): d 7.35
yA;F ¼ y þ a
pꢂ
ꢁ
pꢂ þ b
ðKamlet—Taft equationÞ
a
ꢁ
a
þ c
b
0
4
(
1
1
ꢁ
b
ð2Þ
ð3Þ
6
C
28.29, 128.73, 128.91, 129.14, 131.34, 138.69, 138.82, 145.58,
yA;F ¼ y þ aSA ꢁ SA þ bSB ꢁ SB þ cSP ꢁ SP þ dsdP
0
55.68, MS (HRMS) m/z: calculated 667.2736, found 668.2810
ꢁ
SdP ðCatalan equationÞ
+
(
MH) .