Microwave Assisted Synthesis, Optical Properties and Physicochemical Investigations on the Powerful Fluorophore: Donor (D) -π-Acceptor (A) Chalcone

Article abstract of DOI:10.1007/s10895-016-1909-x

(2E)-3-[4-(dimethylamino)phenyl]-1-(2-hydroxyphenyl)prop-2-en-1-one (DPHP) was synthesized by the reaction 4(dimethylamino) benzaldehyde with 1-(2-hydroxyphenyl) ethanone under microwave irradiation. Structure of DPHP was conformed by ¹H and

Full text of DOI:10.1007/s10895-016-1909-x

J Fluoresc
DOI 10.1007/s10895-016-1909-x
ORIGINAL ARTICLE
Microwave Assisted Synthesis, Optical Properties
and Physicochemical Investigations on the Powerful Fluorophore:
Donor (D) -π-Acceptor (A) Chalcone
Salman A. Khan1 & Abdullah M. Asiri1,2 & Faisal M. S. Aqlan1
Received: 12 May 2016 /Accepted: 15 August 2016
#
Springer Science+Business Media New York 2016
Abstract (2E)-3-[4-(dimethylamino)phenyl]-1-(2-
hydroxyphenyl)prop-2-en-1-one (DPHP) was synthesized by
the reaction 4(dimethylamino) benzaldehyde with 1-(2-
hydroxyphenyl) ethanone under microwave irradiation.
conjugated system with dipolar a group that means electron
donating (D) and electron withdrawing (A) groups [1].
Conjugated dipolar organic molecules containing electron do-
nating (D) and electron withdrawing (A) groups have been
widely examined for their prospective applications as organic
optical materials [2]. Donor (D) - acceptor (A) substituted chro-
mophores such as OCH3, N-(CH3)2 are donor and NO2, CN,
C = O, are acceptor groups, intramolecular charge transfer
(ICT) from the donor group to acceptor group by the pi bonds
plays a important role in determining the optical properties [3].
Among various conjugated systems, long (polyene) chains
have proven to be of particular importance due to their efficient
electron delocalization [4], push–pull functionalization through
synthetic tenability, large two-photon-absorption cross-sections
rendering their use in the field of material sciences such as
optical limiting [5], optical switching [6], electronic devise
[7], polymer coating [8], second order and third order non
linear optical properties [9]. Physicochemical and
photophysical properties such as long singlet lifetime excitation
coefficient, stokes shift, oscillator strength, transition dipole
moment, fluorescence quantum yield, photochemical quantum
yield, and excimer emission [10] These important applications
stimulated our interest in the design and characterization of new
organic molecules based on D–π–A architectures. Many reac-
tion have been reported for the synthesis of donor–π– acceptor
chromophores such as Knoevenagel condensation [11], Diels-
Alder Reaction [12], aldol-condensation [13], Claisen-Schmidt
reaction [14], Suzuki coupling reaction [15]. Aldol condensa-
tion is one of the most important reactions for the synthesis of
the choromophores (chalcones). Chalcone (trans-1,3-diaryl-2-
propen-1-one) is also known as α, β-unsaturated ketones are
natural products belong to flavonoid, are considered as inter-
mediate in the flavonoids biosynthesis, and are widespread in
plants [16, 17]. Its also used as intermediate for the formation of
various heterocyclic organic molecules such as pyrazolines,
1
Structure of DPHP was conformed by H and 13C NMR, FT-
IR, EI-MS spectral studies and elemental analysis. The electron-
ic absorption and fluorescence spectra of DPHP have been stud-
ied in solvents of different polarities, and the data were used to
study the solvatochromic properties such as extinction coeffi-
cient, stokes shift, oscillator strength, transition dipole moment,
fluorescence quantum yield and photochemical quantum yield.
The absorption maximum and fluorescence emission maximum
was observed red shift when increase solvent polarity n-Hexane
to DMF. DPHP undergoes solubilization in different micelles
and may be used as a probe and quencher to determine the
critical micelle concentration (CMC) of CTAB and SDS.
.
.
Keywords DPHP Solvatochromic Fluorescence quantum
.
.
yield Photochemical quantum yield CMC
Introduction
Donor (D) - acceptor (A) chromophore is known as dipolar
organic molecule. Molecules having the long pi (π) bond
* Salman A. Khan
sahmad_phd@Yahoo.co.in
1
Department of Chemistry, Faculty of Science, King Abdulaziz
University, P.O. Box 80203, Jeddah 21589, Saudi Arabia
2
Center of Excellence for Advanced Materials Research (CEAMR),
King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi
Arabia

J Fluoresc
pyrimidines, pyridines, quinolines etc. [18, 19]. The existence
of the α,β-unsaturated ketone moiety in chalcones is a com-
mon part found in a large number of biological active com-
pounds [20]. Therefore, Chalcone derivatives from nature or
synthetic origin exhibit diverse pharmacological activities, such
as antimicrobial, antitumor, anticancer, anti-inflammatory and
anti-amoebic [21–23]. Donor and acceptor group containing
chalcones can be used as dipolar chromophores and enhance
the application in the field of material sciences as well as in the
field of medicinal chemistry [24]. Due to numerous application
of chalcones, in this paper we synthesized a novel donor -
acceptor chlcone ((2E)-3-[4-(dimethylamino) phenyl]-1-(2-
hydroxyphenyl) prop-2-en-1-one) (DPHP) by the reaction
4(di-methyl-amino) benzaldehyde with 1-(2-hydroxyphenyl)
under microwave irradiation and its physicochemical and
photophysical studies.
microwave oven for 55 s. (at 210 W, i.e. 30 % microwave
power). When the reaction was found to be complete, the
reaction mixture was cooled in an ice bath and the product
thus formed was filtered, washed with ethanol followed by
washing with water till the washings were neutral and recrys-
tallized by distilled ethanol and chloroform.
Light yellow solid: Mp. 178 °C; Yeild: 73 %; EIMS m/z
(rel. int.%): 269 (68) [M+1]+; IR (KBr) vmax cm−1: 3065
(C-H), 2920 (C-H), 1620 (C=O), 1522 (C=C), 1268 (C-N);
1H NMR (600 MHz, CDCl3) δ: 13.20 (s, 1H, OH), 7.96 (d,
1H, CH = CH, J = 15.6 Hz), 7.61 (d, 1H, CHaromatic,
J=6.0 Hz),7.50 (d, 1H, CHaromatic, J=2.8 Hz), 7.49 (d,
1H, CHaromatic, J=1.8 Hz), 7.48 (dd, 1H, CHaromatic,
J=2.4 Hz), 7.04 (d, 1H, CHaromatic, J=6 Hz), 6.96 (d,
1H, CH = CH, J = 15.6 Hz), 6.75 (d, 1H, CHaromatic,
J=6.0 Hz), 3.09 (s, 6H, N-(CH3)2; 13C-NMR (CDCl3) δ:
193.52 (C = O), 163.51, 152.20 (C-β), 146.48, 130.86,
129.38, 122.61 (C-α), 120.41, 118.59, 118.51, 114.47,
111.99, 40.25; Anal.calc. for C17H17NO2: C, 76.39, H,
6.41, N, 5.24; Found: C, 76.31, H, 6.36, N, 5.18
(Scheme 1).
Experimental
Chemicals and Reagents
T h e 4 ( d i m e t h y l a m i n o ) b e n z a l d e h y d e , 1 - ( 2 -
hydroxyphenyl)ethanone and sodium hydroxide were pur-
chased from Acros Organic. Other reagents and solvents
(A.R.) were obtained commercially and used without further
purification, except dimethylformamide (DMF), ethanol and
methanol.
Result and Discussion
Characterization of DPHP
The purified DPHP was characterized by the EI-MS m/z
1
Apparatus
(rel. int.%), FT-IR, H-NMR, 13C-NMR and elemental anal-
ysis. FT-IR spectra of DPHP show that a characteristic band
at 1668 cm−1 of the ν (C=O) peak for ethanone that is
shifted to a lower frequency of 1620 cm−1 for DPHP. It is
reasonable to assume that this is due to the conjugation of
the π-electrons on the benzene moiety with those on the
Melting points were recorded on a Thomas Hoover capillary
meltingapparatuswithoutcorrection.FT-IRspectrawererecord-
ed on a Nicolet Magna 520 FT-IR spectrometer. 1H-NMR and
13C-NMR experiments were performed in CDCl3 on a Brucker
DPX 600 MHz spectrometer using Tetramethylsilane (TMS) as
internal standard at room temperature. UV–vis electronic ab-
sorption spectra were acquired on a Shimadzu UV-1650 PC
spectrophotometer. Absorption spectra were collected using a
1 cm quartz cell. Steady state fluorescence spectra were mea-
sured using Shimadzu RF 5301 PC spectrofluorophotometer
with a rectangular quartz cell. Emission spectra were monitored
at right angle. All fluorescence spectra were blank subtracted
before proceeding in data analyses.
1
ethylene moiety in the enon linkage. In the H-NMR spec-
tra, assignments of the signals were based on chemical shift
1
and intensity pattern. H-NMR spectra of DPHP show two
doublets at 7.96 ppm (J=15.6) for the CH=C and 6.96 ppm
(J=15.6 Hz) for the CO=CH indicating that the ethylene
moiety in the enon linkage is in the trans-conformation,
conforming the formation of DPHP. 13C-NMR (CDCl3)
spectrum of DPHP was recorded in CDCl3 and spectral
signals are in good agreement with the probable structures.
The carbonyl carbon of the DPHP generally appears at δ
193.52 in 13C NMR spectra. The α- and β- carbon atoms
with respect to the carbonyl group give rise to characteristic
signals at δ 122.61 for (C- α) and δ152.20 for (C- β) re-
spectively. Details of 13C-NMR spectra of DPHP are pre-
sented in the “Experimental” section. Finally, characteristic
peaks were observed in the mass spectra of DPHP by the
molecular ion peak. The mass spectrum of DPHP shows a
molecular ion peak (M+.) at m/z 269.
Synthesis (2E)-3-[4-(dimethylamino)phenyl]
-1-(2-hydroxyphenyl)prop-2-en-1-one (DPHP)
To a solution of 4(dimethylamino) benzaldehyde (1.0 g,
0.0067 mol) and 1-(2-hydroxyphenyl) ethanone
(0.0067 mol) in dry ethanol (20 ml) taken in a beaker
(100 ml), a catalytic quantity of sodium hydroxide (0.05 g)
was added and the reaction mixture was heated inside a

J Fluoresc
O
H
Scheme 1 Synthesis of DPHP
O
O
H3C
H3C
OH
NaOH
EtOH
CH
3
N
+
OH
N
H C
3
CH
3
Spectral Behavior of DPHP in Different Media
at the carbonyl oxygen is enhanced in the ICT excited
state. While as type (b) hydrogen bonding is weakened
on photoexcitation, because the charge densities at the
N-CH3 decrease in the excited state.
The steady state absorption and fluorescence parameters
of 1 × 10−5 mol dm−3 DPHP recorded in various non- po-
lar, polar aprotic and polar protic solvents are summarized
in Table 1. The absorption and emission spectra of DPHP
are shown in Figs. 1 and 2, respectively. As seen in Fig. 1,
the electronic absorption band of DPHP undergoes red
shifts with increasing solvent polarity (ca 35 nm on going
from n-Heptane to DMF). This feature indicates a strong-
ly allowed π-π* transition with intramolecular charge
transfer characters from dimethyl amino group (electron
donor group) to keto phenyl (electron acceptor group). As
shown in Fig. 2 the fluorescence spectrums suffer more
bathochromic shift with increasing the solvent polarity.
The red-shift in the emission spectrum from 490 nm in
n-Heptane to 526 in DMF observably indicates the inten-
sively photoinduced intramolecular charge transfer (ICT)
takes place with in the molecule in the singlet excited
state. The marginal deviations in data points for alcoholic
solvents are assigned to solute-solvent hydrogen bonding
interaction which causes an extra red shift in the observed
spectra [25] (Table 1).
The energy of absorption (Ea) and emission (Ef) spectra
of the DPHP in different solvents correlated with the em-
pirical Dimroth polarity parameter ET (30) [26] of the
solvent (Fig. 3). A linear correlation between the energy
of absorption and emission versus polarity of solvents was
obtained (Eqs. 1 and 2), The energy of emission spectrum
in protic solvents fall on a separate line indicates that
hydrogen bonding interaction is present along with the
dipolar interaction and plays a significant role in deter-
mining the position of the energy of emission band im-
plying potential application of these parameters to probe
the microenvironment of DPHP.
Ea ¼ 75:17–0:1032 Â ETð30Þ
Ef ¼ 68:28–0:257 Â ETð30Þ
ð1Þ
ð2Þ
Determination of Oscillator Strength and Transition
Dipole Moment
Scheme 2 presents the simplified description of hydro-
gen bonding of DPHP. Type (a) hydrogen bonding is
strengthened in the excited state, since the charge density
The solvatochromic performance of DPHP allows to establish
the difference in the dipole moment between the excited
Table 1 Spectral data and
Solvent
Δf
ETN
ET (30)
Kcal
λab
λem
ε M -
f
μ 12
Debye
Φf
fluorescence quantum yield (φf)
of dye (DPHP) in different
solvents
Δν
(nm) (nm) 1cm−1
(cm−1
)
mol−1
DMF
0.263
0.305
0.299
0.274
0.217
0.255
0.404 43.8
0.654 51.9
0.762 55.4
0.570 49.2
0.259 39.1
0.390 40.7
0.472 45.6
0.164 36
0.210 37.4
31.1
445
437
433
433
437
439
438
426
435
410
526
553
558
543
495
495
496
493
492
490
38990
33420
35900
31100
34780
2577
0.53 7.06
0.64 7.69
0.74 8.23
0.58 7.29
0.37 5.85
0.37 5.86
0.37 5.85
0.37 5.77
0.29 5.34
0.41 5.96
3460
4800
5181
4678
2681
2577
2670
3191
2663
3982
0.66
0.33
0.19
0.49
0.033
0.032
014
EtOH
MeOH
PrOH
CHCl3
CH2Cl2
Acetonitrile 0.304
35940
29200
27000
26100
Dioxan
THF
0.274
0.148
0.0014
0.11
0.10
0.041
n-Hexane

J Fluoresc
0.40
0.36
0.32
0.28
0.24
0.20
0.16
0.12
0.08
0.04
0.00
a
HOR
OH
DMF
EtOH
MeOH
PrOH
CH3Cl
CH2Cl2
CH3CN
Dioxane
THF
O
H3C
H3C
N
b
HOR
Scheme 2 Hydrogen bonding of DPHP with alcoholic solvents
n-Hexane
Δνss is the Stokes shifts of the DPHP in different solvents
were deliberate, as shown in Table 1, using the following
equation [30]:
350 375 400 425 450 475 500 525 550
Wavelength (nm)
Δνss ¼ νab−νem
ð5Þ
Fig. 1 Electronic absorption spectra of 1 × 10−5 mol dm−3 of DPHP in
where Δνss is the difference between λmax of the νab and νe
different solvents
m
indicate the wavenumbers of absorption and emission maxima
(cm−1) respectively.
singlet and the ground state (Δμ=μe – μg). This variation can
be obtained using the simplified Lippert- Mataga equation as
follows [27, 28]:
The change in dipole moments (Δμ) between the excited
singlet and ground state were calculated from the slope of plot
of Stokes shifts (Δνss ) and orientation polarizability of the
solvent (Δf) as 4.70 Debye for DPHP respectively Fig. 4, pos-
itive value indicating that the excited sate is more polor than
the ground state.
The change in transition dipole moments (Δμ12) between
the excited singlet and ground state of DPHP in various sol-
vents were calculated as in Table 1, using the Eq. 6 [31].
ꢀ
ꢁ
2
2 μe − μg
Δνst ¼
Δf ¼
Δf þ Const:
ð3Þ
ð4Þ
hca3
D −1
2D þ 1
n2−1
2n2 þ 1
−
f
where Δνst is known as Stokes–shift which decreasing with
decreasing the solvent polarity indicating to week stabilization
of the excited state in non polar solvents. Δf is the orientation
polarizability of the solvent, μe and μg are the dipole moments
in the excited and ground state, respectively which measures
both electron mobility and dipole moment of the solvent mol-
ecule. c is the speed of light in vacuum, a is the Onsager cavity
radius and h is Planck’s constant, n and ε are the refractive
index and dielectric constant of the solvent respectively in
Eq. 3. The Onsager cavity radius was chosen to be 4.2 Å
because this value is comparable to the radius of a typical
aromatic fluorophore [29].
2
μ12
¼
ð6Þ
4:72 Â 10−7 Â Emax
where Emax is the maximum energy of absorption in cm−1 and
f is the oscillator strength.
The oscillator strength (f), can be calculated using the fol-
lowing equation:
Z
ꢀ ꢁ
f ¼ 4:32 Â 10−9 ε ν dν
ð7Þ
where ν represents the numerical value of wavenumber
(cm−1) and ε is the extinction coefficient (Lmol−1cm−1).
68
66
64
120
100
DMf
EtOH
MeOH
PrOH
CH3Cl
CH2Cl2
CH3CN
Dioxan
THF
n-Hexane
62
60
58
56
54
52
50
E
Ef
a
80
60
40
20
0
32
36
40
44
48
52
56
450 475 500 525 550 575 600 625 650 675
ET (30) kcal mol -1
Wavelegth (nm)
Fig. 2 Emission spectra of 1 × 10−5 mol dm−3 of DPHP in different
solvents (λ ex = 430 nm)
Fig. 3 Plot of energy of absorption (Ea) and emission (Ef) versus ET(30)
of different solvents

J Fluoresc
5500
5000
4500
4000
3500
3000
2500
a
b
c
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0 min
15 min
30 min
45 min
60 min
90 min
120 min
150 min
180 min
210 min
240 min
300
350
400
450
500
550
600
0.20
0.22
0.24
0.26
0.28
0.30
0.32
Wavelength (nm)
F
Fig. 4 Plot of ΔF versus Stokes shift (Δυ)
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0 min
5 min
Oscillator strength values of DPHP in various solvents were
calculated from the Eq. 7 and reported in Table 1, [32].
ET (30) and ENT is the empirical Dimroth polarity parameter
of DPHP was also premeditated according to the following
equation.
10 min
15 min
20 min
25 min
30 min
35 min
40 min
ET ðsolventÞ−30:7
ETN
¼
ð8Þ
ð9Þ
250
300
350
400
450
500
550
32:4
Wavelength (nm)
28591
λmax
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
ET ðsolventÞ ¼
0 min
1 min
2 min
3 min
4 min
5 min
6 min
7 min
8 min
9 min
10 min
11 min
12 min
where λmax corresponds to the peak wavelength (nm) in the
red region of the intramolecular charge transfer absorption of
the DPHP dye.
Fluorescence Quantum Yield of DPHP
300
350
400
450
500
550
The fluorescence quantum yield (φf) was measured using the
optically diluted solution to avoid reabsorption effect (absor-
bance at excition wave relative method with solution of 9, 10-
diphenylanthralene (DPA) in DMF as reference standard. The
Wavelength (nm)
Fig. 6 Effect of irradiation (λex = 430) on the electronic absorption
spectrum of 1 × 10−5 mol dm−3 in (a) DMSO (b), CH2Cl2 (c) CCl4
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
following relation has applied to calculate the fluorescence
quantum yield [33]:
È
À
ÁÉ
F
1−exp −Aref ln10
f1−expð−As ln10Þg  n2r
 n2s
ðsÞ
n
φf ðsÞ ¼ ϕf ðrÞ
ð10Þ
F
ðref Þ
where F denotes the integral of the corrected fluorescence
spectrum, A is the absorbance at the excitation wavelength,
and n is the refractive index of the medium. The subscripts “s”
and “r” refer to sample and reference, respectively.
The fluorescence quantum yield (ϕf) of DPHP depends
strongly on the solvent properties (Table 1). The fluores-
cence quantum yield can be correlated with ET(30) of the
solvent, where ET(30) is the solvent polarity parameter
30
35
40
45
50
55
ET(30) Kcal mol-1
Fig. 5 Plot of ϕf versus ET (30) of different solvents

J Fluoresc
45
40
35
30
25
20
15
10
5
36
33
30
27
24
21
18
15
0
475 500 525 550 575 600 625 650 675 700
0.0000 0.0004 0.0008 0.0012 0.0016
Wavelength (nm)
-3
Fig. 7 Emission spectrum of 1 × 10−5 mol dm−3 of DPHP at different
[CTAB] mol dm
concentrations of CTAB, the concentrations of CTAB at increasing
Fig. 9 Plot of If versus the concentration of CTAB
emission intensity are 0.0, 2 × 10−4, 4 × 10−4 6 × 10−4, 8 × 10−4
,
,
10 × 10−4, 12 × 10−4, 16 × 10−4 and 18 × 10−4 mol dm−3 (λ ex = 430 nm)
Photoreactivity of DPHP in Different Solvents
introduced by Reichardt [34] Fig. 5. ϕf increases with
increase in the polarity of the solvent (n-Hexane to
CH3CN) (expressed as ET(30); reaching maximum in po-
lar aprotic solvents like in DMF with a drop on further
increase in the solvent polarity such as in alcoholic sol-
vents. The increase in ϕf (negative solvatokinetic effect)
with charge transfer character was explained by several
mechanisms such as proximity effect and conformational
changes. Hydrogen bonding between solvent molecules
and the carbonyl group of fluorophore is accounted for
the reduction of ϕf in highly protic alcoholic solvents
due to enhanced radiationless processes. The reduction
in ϕf going from DMF to polar protic solvents like
MeOH and EtOH (positive solvatokinetic effect) can be
attributed to strong ICT interaction, the ϕf value decrease
strongly in highly proton donor solvents (PrOH > EtOH >
MeOH). This effect is due to inter molecular hydrogen
bonding interaction between solvent and excited dyes.
The photoreactivity of DPHP has been studied in different
solvents, namely DMSO, CH2Cl2 and CCl4. Upon irradiation
of a 1×10−5 mol dm−3 of DPHP at 430 nm the absorbance of
DPHP decreased with increasing the irradiation time until a
photostationary state was reached. As shown in Fig. 6, no new
absorption appeared which suggests the absence of a photo-
product. The net photochemical quantum yields (ϕc) of the
DPHP in DMSO, CH2Cl2 and CCl4. are 0.00038, 0.0011
and 0.0085 respectively, which indicates that the DPHP dye
is more photostable in DMSO than in CH2Cl2, and CCl4. It
seems that the photodecomposition of DPHP in chloro-
methane solvents takes place by electron transfer from the
excited dye molecule to solvent according to a well known
mechanism [35].
ðDPHPÞ →1ðDPHPÞ*
absorption of light
ð11Þ
fluorescence ð12Þ
1
ðDPHPÞ*→DPHP þ hυ
1
ðDPHPÞ* þ CHnCl4‐n→1½DPHP…:CHnCl4‐nŠ* exciplex ð13Þ
20
18
16
14
12
10
8
22
20
18
16
14
6
12
4
CMC
2
10
8
0
475 500 525 550 575 600 625 650 675 700
6
Wavelength (nm)
Fig. 8 Emission spectrum of 1 × 10−5 mol dm−3 of DPHP at different
4
0.000
0.004
0.008
0.012
0.016
concentrations of SDS, the concentrations of SDS at increasing emission
[SDS] mol dm-3
intensity are 0.0, 2 × 10−3, 4 × 10−3, 6 × 10−3, 8 × 10−3, 10 × 10−3
,
12 × 10−3, 16 × 10−3 and 18 × 10−3 mol dm−3 (λ ex = 430 nm)
Fig. 10 Plot of If versus the concentration of SDS

J Fluoresc
h
i
δ
1
DPHP…:CHnCl4‐nð*→ÞDPHP:þ
…
:−δCHnCl3‐n
electron transfer
ð14Þ
Figs. 9 and 10, thus DPHP can be employed as a probe and
quencher to determine the CMC of a surfactants.
h
i
d
d
DPHP:þ
…
:−dCHnCl3‐n →DPHP:þ Cl−þ CHnCl3‐n
contact ion pair
:
Conclusion
ð15Þ
It is proposed that the electron transfer from the excited
(2E)-3-[4-(dimethylamino)phenyl]-1-(2-hydroxyphenyl)prop-
2-en-1-one (DPHP) was synthesized by the reaction
4(dimethylamino) benzaldehyde with 1-(2-hydroxyphenyl)
ethanone under microwave irradiation. DPHP dye displays
red shift in its fluorescence spectrum as solvent polarity in-
creases. Moreover, the resulting red shift was observed in polar
protic solvents due to intermolecular hydrogen bonding be-
tween solute and solvent. The hydrogen bond with solvent
enhances the radiationless processes of excited molecule.
DPHP dye displays photodecomposition in chloromethane sol-
vents via electron transfer from excited DPHP to solvent lead-
ing to formation of contact ion pair. DPHP dye undergoes
solubilization in different micelles and may be used in the de-
termination of CMC of surfactants (e.g. SDS and CTAB) and it
can be used as quencher or probe for dyes.
singlet DPHP to CHnCl4-n within transient excited charge
transfer complex (exciplex) is the main primary photochemi-
cal process. It leads to the DPHP radical cation, a chloride ion
and a chloromethyl radical in a solvent cage. The formation of
a contact ion pair usually occurs by electron transfer from
excited donor to the electron acceptor depending on the elec-
tron affinity (EA) of acceptor.
Effect of Surfactant on Emission Spectrum of DPHP
A positively charged and cetyltrimethyl ammonium bromide
(CTAB) and negatively charged sodium dodecyl sulphate
(SDS) surfactants were selected for evaluating the emission
behavior of the DPHP dye. The two specified surfactants were
chosen because ionic charges possessed by DPHP dye can be
influenced by the positively charged CTAB and negatively
charged SDS. Thus, the charge attraction accounts for the
DPHP emission behavior. Fluorescence emission spectra of
DPHP in the absence and presence of CTAB and SDS were
measured. Fluorescence intensities of DPHP increase when
increasing the concentration of CTAB from 2×10−4 up to
1.8×10−3 M as shown Fig. 7. Such enhancement in the fluo-
rescence intensity of 1×10−5 M DPHP at fixed concentrations
with an increase in the CTAB concentration may likely be
ascribed to the association mechanism of DPHP with CTAB.
The fluorescence intensity of DPHP is quenched with an in-
Acknowledgments The authors are thankful to the Chemistry
Department and the Center of Excellence for Advanced Materials
Research at King Abdulaziz University for providing research facilities.
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crease of the SDS concentration (2×10−3 up to 1.8×10−2
M
Moreover, more significant reductions were noticed in fluo-
rescence intensities of DPHP with SDS. The quenching of
DPHP upon increasing SDS concentration can likely be as-
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