Synthesis, physicochemical and optical characterization of novel fluorescing complex: O-phenylenediamine-benzoin

Article abstract of DOI:10.1007/s10895-010-0808-9

The complex of o-phenylenediamine (o-PDA) and benzoin (BN) was synthesized adopting solid state reaction by mixing of their melt together followed by chilling. The phase diagram study shows the formation of a complex in 1:1 molar ratio with congruent melt

Full text of DOI:10.1007/s10895-010-0808-9

J Fluoresc (2011) 21:1255–1263
DOI 10.1007/s10895-010-0808-9
ORIGINAL PAPER
Synthesis, Physicochemical and Optical Characterization
of Novel Fluorescing Complex: o-Phenylenediamine—Benzoin
Y. Dwivedi & Shiva Kant & S. B. Rai & R. N. Rai
Received: 3 April 2010 /Accepted: 29 December 2010 /Published online: 15 January 2011
#
Springer Science+Business Media, LLC 2011
Abstract The complex of o-phenylenediamine (o-PDA) and
benzoin (BN) was synthesized adopting solid state reaction
by mixing of their melt together followed by chilling. The
phase diagram study shows the formation of a complex in
1:1 molar ratio with congruent melting point and two
eutectics lying on either side of complex. The formation of
complex was confirmed using the FTIR, NMR, mass
spectroscopy, powder XRD and DSC studies. The optical
properties of the parent component, their complex and few
other compositions nearby the complex were studied using
absorption and laser luminescence techniques. The signifi-
cantly higher green/yellow emission was noted with newly
synthesized complex as compared to that of their parents as
well as other compositions of o- PDA and BN.
nonlinear optical, electro-optic, semiconductors, lasers and
superconductor devices has prompted researchers to ex-
plore the variety of novel organic materials of specific
properties for specific applications [1–5]. Apart from the
conventional synthesis of organic materials, the technique
of molecular complexation has been developed as one of
the designing tools in molecular crystal engineering [6] and
this technique has been found capable to produce the
promising optical organic materials as light emitting diode
of different colors including white light [7]. However, very
limited efforts have been made to synthesize molecular
complexes based on interaction between two molecules
adopting solid state reaction, and exploring the concept of
phase diagram [8]. Studies of physicochemical properties of
binary materials are very rare. Nevertheless, optical
properties of some of the complexes have shown sensitivity
to polarity, which is used as a probe to study the
microenvironmental changes of the host as the polarity,
influences the Stoke’s shift of the complex.
.
.
.
Keywords Solvent free synthesis Eutectic Fluorescence
.
.
Phase diagram Green light emission Charge transfer
complex
.
.
.
.
PACS 87.64.k 95.75.Fg 42.62Fi 78.00.oo 78.47.Jc
Generally, in excited states the separation of charges is
different to that of charge distribution of complex in their
ground state that is one of the root causes for various
transformations of chemical and biological complex [9–
12]. Further electron donor-acceptor molecules have been
found ideal for charge transfer process [13]. These
complexes are useful for the study of solvation dynamics
[14], nonlinear optical properties [15], in laser applica-
tions [16] and have also been used as fluorescence probes
[17, 18].
Phenylenediamine (PDA) is found in ortho, meta and
para isomeric forms and is used in syntheses of commercial
hair dyes, polyamides, maleimides and agricultural pesti-
cides. Particularly, polymerised o-phenylenediamine (o-
PDA) is used for various applications such as for
immobilization of bioactive materials, electrocatalysis,
Introduction
The potential application of organic materials for their
versatile uses in fabrication of variety of devices such as
:
Y. Dwivedi S. B. Rai
Laser and Spectroscopy Laboratory, Physics Department,
Banaras Hindu University,
Varanasi, India 221005
:
S. Kant R. N. Rai (*)
Department of Chemistry, Banaras Hindu University,
Varanasi, India 221005
e-mail: rn_rai@yahoo.co.in

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J Fluoresc (2011) 21:1255–1263
corrosion inhibition, and as electrochromic materials [19].
On the other hand benzoin (BN) is employed for photo-
catalyst, chelating and other applications [20]. The o-PDA
has two amino groups and BN has a carbonyl group
therefore the probability of interaction between electron
donor and electron acceptor group are very high. The work
started with thought that the complex formed would be
interesting for various applications. Thus, the o-PDA and
BN have chosen for the investigations in detail.
In this paper, detail of investigations concerning the
identification of specific composition of molecular
complex via establishing phase diagram between o-PDA
and BN are reported. For the determination of suitable
composition that forms the complex, the phase diagram
has been studied in detailed however for the synthesis of
material, solid state reactions has been employed. For the
confirmation of complex formation, powder XRD, DSC,
FTIR, NMR and mass spectroscopy techniques are used.
We also report the structural, thermal and optical proper-
ties of the newly synthesized complex and for comparison
the properties have been compared with the parent
components.
atmosphere. The UV absorption spectra of the parent
molecules and their complex were recorded in solution of
EtOH solvent, using JASCO V-670 absorption spectropho-
tometer in the range 200–2,300 nm. The fluorescence
measurements were carried out using forth (266 nm) and
the third (355 nm) harmonics of Nd:YAG laser (Spitlight
600, Innolas, Germany) as an excitation source. Laser beam
was focused onto the sample using convex lens (focal length
~8 cm) and the spot size at sample was ~100 μm. To detect
the dispersed luminescence, emission from sample was
collected in perpendicular direction to that of on the slit of
computer controlled Trix monochromator iHR320 equipped
with grating blazed at 500 nm and PMT (model 1424 M).
The resolution of monochromator was ~0.2 nm. All
measurements were taken at identical conditions and at
ambient temperature (26 2 °C).
Phase-diagram
The phase diagram of o-PDA and BN system was studied
using thaw melt method and the phase diagram was
established in melting temperature vs composition [21]. In
this method, the mixture of the two compounds covering
entire range of compositions were prepared and their melts
were homogenized together by continuous shaking,
followed by chilling in ice cold water. The melting
temperature of each composition was recorded using a
melting point apparatus attached with a precision ther-
mometer ( 0.5 °C).
Experimental Section
Complex Synthesis and Experimental
The starting material o-phenylenediamine (S.D. fine
chemicals, India) was purified by zone refining technique,
while benzoin compound (Sigma Aldrich) was purified by
crystallization from CCl4. The purity of each compound
was checked by comparing their melting points. The
complex of the BN and o-PDA has been synthesized by
the application of solid state reaction under chilling and
homogenization process, in which parent components
were taken in various molar compositions. The composi-
tions were melted slightly above (4 °C) the melting
temperature of the parents. The molten mixture of the
both parents was homogenized and chilled in ice cooled
water (5 °C). The homogenization and chilling process
were repeated up to four times for the completion of
reaction.
Infrared spectra of parent components and their complex
were measured in transmittance mode in the region 400–
4000 cm-1 by dispersing and palletizing in KBr. The
resolution of FT-IR spectrometer [Perkin Elmer RX-1] was
2.0 cm-1. Baseline corrections were introduced whenever
needed. The mass spectrum of the complex was recorded on
Micromass Quattro II system, Micromass, UK while NMR
spectra were recorded on FTNMR-JOEL AL300 system.
The Differential Thermal Calorimetry (DSC) curve has been
recorded using Mettler TA 4,000 machine under N2 gas
Results and Discussions
Thermal Analysis
The phase diagram of o-PDA and BN has been established
between freshly prepared entire range of compositions of
two compounds and their respective melting points were
determined and the diagram has been depicted in Fig. 1.
The diagram shows the formation of a molecular complex
(A) with congruent melting point having two eutectics E1
and E2 on either side. The composition mole fraction of o-
PDA in E1, E2, and the complex are 0.35, 0.80 and 0.50,
respectively. It is evident from the figure that the melting
point of BN decreases with the addition of o-PDA, and
attains a minimum value at the first eutectic point E1.
Further addition of o-PDA causes the melting point to rise
and attain a maximum at A. The diagram shows that the
addition compound (A) melts congruently i.e. the compo-
sitions of liquid and the solid phases are identical.
Onwards, addition of o-PDA beyond causes a decrease in
melting temperature and attains a minimum at second
eutectic point E2. At eutectic temperatures, the two solid

J Fluoresc (2011) 21:1255–1263
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spectrum of complex, the peak for NH2 proton of o-PDA
(3.37 ppm) is absent. Also the peak for carbonyl carbon of
benzoin (198.88 ppm) is disappeared in 13C of complex.
Apart from these changes, a new signal peak is observed at
157.62 ppm, which could be due to the azomethine carbon
(C=N), this finding indicates the formation of complex. The
detail peak analysis is as:
1
2, 3-Diphenyl-1, 2-dihydro-quinoxaline H NMR (CDCl3,
300MHz) [δ 4.42 (s, 1H, NH), δ 5.68 (s, 1H, CH), δ 6.51-
6.48 (d, 2H, ArH), δ 6.82-7.77 (m, 2H, ArH),δ 7.03-6.98
(m, 2H, ArH), δ 7.50-7.35 (m, 6H, ArH), δ 7.93-7.90 (m,
2H, ArH)], 13C NMR (300 MHz, CDCl3) [δ 157.62,
140.64, 137.02, 134.93, 133.03, 130.17, 129.14, 128.64,
128.37, 128.23, 128.06, 127.07, 126.55, 118.91, 113.73,
54.67].
The mass spectrum of the complex shows the molecular
ion peak (m/z) corresponding to its relative abundance
which are 285 (M+1, 100), 286 (M+2, 24), 283 (M-1, 30),
208 (26), 207 (14), 167 (10), 388(7). The fragmentation of
the parents lead to the 2, 3-Diphenyl-1, 2-dihydro-
quinoxaline complex as the main fragmentation path is
shown in Fig. 3. The mass spectra provided further vital
clue in elucidation of the structure of the complex
formation. The most probable structure and the reaction
mechanism that could be assigned using NMR and mass
spectroscopy are shown in Fig. 3.
Fig. 1 Phase diagram of o-PDA and BN system, established between
different compositions of o-PDA and BN and their respective melting
point
phases and a liquid phase are in equilibrium. The eutectic
reactions may be, schematically, represented as:
L
S1 + S2
The melting temperatures of E1, E2 and A were found to
be 118, 90, and 138 °C, respectively. It was also noted that
the composition of complex as well as immediate adjacent
compositions to the complex solidify late even in ice cold
water. This observation of late solidification has reflected in
XRD where the crystallinity of the complex was found to
be poor.
(b) Powder XRD
In order to understand the nature of the complex whether
parent components are associated to form a new complex or
forming a mechanical mixture, X-ray powder diffraction
patterns of the complex and the parent components, o-PDA
The thermal properties and stability of BN, o-PDA and
their complex have been studied and their DSC curves are
depicted in Fig. 2. The heat of fusion values of BN, o-PDA
and complex are found to be 40.3, 26.3 and 11.8 kJ mol−1
respectively. The DSC curve of the complex shows a single
broad peak and the peaks corresponding to melting
temperatures of pure BN and o-PDA compound are not
found in the curve. The melting point of the complex is
substantially higher than that of the parent compounds. The
higher melting point and existence of a single peak for the
complex indicates that the complex formed is of single and
pure nature, which could be considered as a new species.
Structural Analysis
(a) NMR and mass spectroscopy
The NMR (1H and 13C) spectrum of BN, o-PDA and the
Fig. 2 Differential scanning calorimetric curve of the BN, o-PDA and
their complex
complex has been recorded in CDCl3 solvent. In 1H

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Spectroscopic Properties
Absorption Analysis
(i) UV-Visible absorption
The optical absorption spectra of BN, o-PDA and the
complex have been recorded in the range of UV-Vis. region
(200–900 nm) in EtOH solution and have shown in Fig. 5.
The UV/Vis. Absorption spectrum of BN shows three peaks
at 217 nm, 238 nm and 258 nm which ascribed to the
π→π* transitions due to the presence of the phenyl ketone
group (Ar-C=O), in which the carbonyl group is conjugated
with the benzene ring. The bands observed in absorption
spectrum of o-PDA are found in agreement as reported by
Manoharan et al. [22]. The bands at 220 and 238 nm are
attributed due to the π→π* transition while a strong band
at 295 nm appears due to the amino group [23].
The observed red shift in complex is related to the
structural changes due to the interaction of o-PDA and BN
in EtOH. It is considered that when o-PDA interact with the
BN, water molecule is being removed and the nitrogen
atom of amino group of o-PDA is attached with the C atom
and getting converted to C=NR'NH2, consequently the
electron density of the C=O bond reduces, which causes a red
shift in absorption [24, 25]. This finding is in accordance
with the fact that de-protonation of amino group gives red
shifted absorption maxima [26–29]. Another interesting
observation is that the peak corresponding to the amino
group at 295 nm in o-PDA reduces significantly in complex
which indicates the reduction of the number of amino groups
(–NH2) in the complex.
Fig. 3 The reaction mechanism for the complex formation
and BN, were recorded and depicted in Fig. 4. In the powder
XRD pattern of benzoin, the bragg peaks has been indexed
to the monoclinic cell (a=18.69, b=5.774, c=10.41Å, and
β=105.55°) and compared using JCPDS data card 30-1542.
The powder X-Ray diffraction pattern of o-PDA has also
shown the monophase crystalline structure as the reported
values in JCPDS data file 04-0238.
In XRD pattern of the complex several new peaks were
observed which belongs to neither of the parent components.
This study infers the formation of new molecular complex of
entirely different nature. This finding supports the phase
diagram study where the complex formation has inferred.
In BN absorption spectrum, two weak bands appear at
285 and 326 nm which ascribed as n→π* transitions. These
bands become intense and broad in complex and suffer a
Fig. 5 UV/Vis absorption spectra of BN, o-PDA and complex in
Fig. 4 XRD patterns of BN, o-PDA and their complex
EtOH solution

J Fluoresc (2011) 21:1255–1263
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small bathocromic shift in solvents and this shift differs
with polarity of solvent. Typically, in a charge-transfer
transitions, an increase in the polarity of the medium leads
to a Stokes shift of the absorption maximum. The detail of
bathochromic shift is discussed in luminescence section of
the manuscript.
1,482 cm−1 is associated with the vibrations of the C-N-H
group mixed with C-C stretching and CH bending. A strong
band observed at 1,343 cm−1 results from the interaction
between the N-H and C-H bending and C-N stretching
vibrations. The band observed between 1,112 and
1,214 cm−1 is attributed to CH bending vibrations. The
peaks at 1,243 and 1,247 cm−1 are associated with the C–N
stretching in the solution and solid samples, respectively.
Infra-red absorption spectrum of BN was also found in
agreement with data reported earlier [31] and a broad band
of -OH vibration at 3,382 cm−1 in solution was observed.
However in solid, two bands at 3376.6 and 3414.7 cm−1
with comparatively weak intensity are observed and they
due to –OH vibrations. The additional broadening observed
in solution was expected due to the strong interaction of BN
with host (EtOH). An intense and well-defined peak
observed at 1,680 cm−1 is due to the stretching vibration
of carbonyl group. The peak at 1,205 cm−1 is due to the C-
O vibrations in solid and solution. The FT-IR study of
complex has inferred important information about the
structural changes occurred due to interaction between BN
and o-PDA. The spectrum shows that there are few bands
which are either shifted or invisible in comparison to their
parent molecules, and also some peaks of BN and o-PDA
are present, with a change in intensity, in the spectrum of
complex. Among these bands, the strong absorption band
due to carbonyl (~1,680 cm−1) of BN is found to be absent
and a new sharp band corresponding to C=N group
(~1,605 cm−1) is appears in solid [15]. These drastic
changes indicate the structural changes of the complex to
that of parent components.
(ii) IR absorption
FT-IR absorption spectra of BN, o-PDA and their
complex have been recorded in the range of 400–
4000 cm−1 in solution (EtOH) as well as in solid (Fig. 6).
However to record the solid IR absorption samples were
dispersed in KBr and palletized. The validity of the peaks
assigned for the three compounds have also been verified
by theoretical calculation, which are carried out using
Density Functional Theory (DFT) with B3LYP/6-311G*
basis set. The recorded FT-IR spectrum of o-PDA was
found to be in good agreement with the spectrum as
reported by Ohmasa et al. [30]. In the FT-IR spectrum of
the solid o-PDA, the bands at 3386 cm−1 and 3364 cm−1 are
due to –NH2 group, which are the characteristic symmetric
and asymmetric -N-H stretching vibrations. The broad
peaks around 3,188 and 3,289 cm−1 can be assigned for
the N–H stretching vibration of the –NH2 group. On the
other hand in solution these N-H bands are buried in the broad
–OH vibration peak due to the presence of EtOH. Particularly,
in case of solid the N-H stretching modes are usually observed
sharper than O-H stretching modes. The band observed in the
2,800–3,100 cm−1 region is the characteristic νCH bands of
the aromatic ring vibrations.
Bands observed at 1630.2 and 1633.4 cm−1 are due to
the N-H wagging in solution and solid, respectively. The
bands observed between ~1,590 and ~1,620 cm−1 are
ascribed to C=C stretching mode. The intense band at
Fluorescence Analysis
Fluorescence spectra of BN, o-PDA and their complex have
been recorded under 266 and 355 nm excitations and they
are discussed separately as follows:
(i) Excitation with 266 nm
Fluorescence spectrum of BN, o-PDA and their complex
recorded under 266 nm laser excitations and the spectra
thus obtained were shown in Fig. 7. Solid o-PDA emits
strong (green) emission at 538 nm radiation (FWHM
~50 nm) while the BN give very weak emission at
500 nm which is difficult to record. When the BN and o-
PDA in 1:1 ratio are mixed in EtOH solvent, it gives strong
asymmetrical yellow band (574.83 nm) with large Stock
shift (~308 nm). It was noted that the emission of complex
was markedly red shifted (~35 nm) compared to pure o-
PDA emission. An interesting observation is that the
emission of complex enhances in both, 2.5 times in solid
and 3.2 times in solution as compared to maximum
emission recorded with o-PDA in solid and solution form.
Fig. 6 FT-IR spectrum of BN (1, 2), o-PDA (3, 4) and Complex (5, 6)
in EtOH solution and solid, respectively

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Fig. 7 Fluorescence spectrum of BN, o-PDA and their complex
formed in EtOH solution and solid under 266 nm photon excitation
Fig. 8 Fluorescence spectrum of o-PDA and their complex in EtOH
solution and solid under 355 nm photon excitation
To get the maximum fluorescence intensity, the concen-
tration of binary (BN and o-PDA) was optimized and 1:1
ratio of BN and o-PDA emission was found to be
maximum.
with the case of molecular compounds (considering a single
entities), it may be called intramolecular charge transfer
absorption bands.
(ii) 355 nm excitation
In fact, Nagakura et al. showed in an earlier report that
strong absorption bands observed in a number of mole-
cules containing the nitro or carbonyl group can be
interpreted as intramolecular charge-transfer absorption
bands [32–34]. This improves extinction corresponding to
355 nm consequently enhanced fluorescence intensity. For
comparison a visualized emissions of parents and the
complex under 355 nm excitations at uniform conditions
such as concentrations and laser power etc. is depicted in
Fig. 9.
Charge transfer fluorescence transitions are sensitive to
the polarity and the dielectric constant of the solvent.
Variation in wavelength of maximum absorption and
fluorescence have been plotted in terms of Lippert-Mataga
solvent polarity parameter Δf, which is the function of
On excitation with 355 nm laser photons, o-PDA and
BN yield weak band at 519 and 493 nm respectively, due to
their small absorption coefficient in 355 nm region.
However fluorescence spectrum of the complex reveals a
drastic enhancement (ten times) in emission intensity
compare to 266 nm excitation (Fig. 8). The enhancement
in the emission intensity of complex is larger in solution
compared to solid.
The emission of the complex is much higher with
355 nm excitation compared to the emission observed with
266 nm. A large red shift of ~30 nm is noted in solution on
355 nm excitation compared to solid similar to the emission
pattern observed in 266 nm excitation. The solvatochromic
properties of the complex are correlated with electronic
spectra of complex taking in different solvent of different
polarities viz. hexane, carbon tetrachloride, ethanol, tetra
hydofluoron, acetone, acetonitrile, Dimethylformamide,
and water. Table 1 lists the wavelength of maximum
absorption and fluorescence along with the Stocks shifts
of complex in different polar solvents. It was noted that
with the increase of polarity of solvent the emission band
significantly shifted towards red. The observed large
shifting can be explained as: when an electron donating
group (amino group), and an electron accepting group
(carbonyl group) combine with each other directly or
through a bridge of conjugated double bonds, the migration
of electrons are possible from former to the latter, as a result
of this the complex gives rise a special absorption band
totally different from the parent components. By analogy
Table 1 Wavelength of maximum UV-Vis absorption and fluores-
cence and corresponding Stoke’s Shift of complex in different polar
solvents
Solvent
Absorption
λmax (nm)
Fluorescence
λmax (nm)
Stoke’s shift
Δν (cm−1
)
Carbon Tetrachloride
Tetrahydrofluron
Acetone
398
400
398
402
394
404.8
407
504
544
532
573
547
553
552
6676
6618
6329
7424
7099
6620
6454
Ethenol
Acetonitrile
Dimethylformamide
Water

J Fluoresc (2011) 21:1255–1263
1261
peaks. This indicates that Δμ is positive i.e. the dipole
moment of the complex studied here increases on excita-
tion. Also, the large magnitude of Stokes shift indicates that
the excited state geometry is different from that of the
ground state geometry. It is a general observation that an
increase in the Stoke’s shifts with the polarity shows the
increment in the dipole moment. The full width at half
maximum (FWHM) of absorption band and fluorescence
bands in polar solvent is broader and it also varies linearly
with their polarity.
For the molecules in which the fluorescence and the
absorption bands appears with the same excited and ground
ꢀ
ꢁ
max
max
flu
states, the Stoke shift Δu ¼ u ꢀ u
is expected to
abs
follow a linear relation with Δf [37]:
Fig. 9 A visualized observation for comparison of emissions between
the parents BN, o-PDA and their complex under 355 nm excitations
ꢀ
ꢁ
2
Δu ¼ Δu0 þ 2 me ꢀ mg =hca03
ð2Þ
where μe = excited state dipole moment, μg = ground state
dipole moment, h = plank constant, c = light velocity, a0 =
Onsager cavity radius of interaction.
The values of the Onsagar cavity radii (ao) were
calculated from the molar volume of molecules using the
Suppan’s equation [38]:
static dielectric constant ε and the refractive index of the
solvent and are related as [35, 36]:
ÂÀ
Á À
ÁÃ
Δf ¼ ½ð" ꢀ 1Þ=ð2" þ 1Þꢁ ꢀ n2 ꢀ 1 = 2n2 þ 1
ð1Þ
Both the spectra show the linear variation with the
polarity of the solvents.
However the fluorescence spectra are observed to be
highly sensitive to the solvent polarity, compared to the
absorption spectrum as the slope of the fluorescence plot is
(slope=0.207) higher than the slop of absorption plot
(slope=0.0145) Fig. 10. This large difference suggests that
the excited state of the complex is significantly polar
compare to the ground state.
1=3
ao ¼ ð3M=4pdNÞ
ð3Þ
where δ is the density of the solute molecule, M is the
molecular weight of solute and N is the Avogadro number.
The Lippert-Mataga plot for Stokes shift clearly demon-
strates the solvent polarity sensitive behavior of the
complex. A large Stokes shifted emission is observed in
different solvents, suggesting the higher charge transfer in
the excited state than in the ground state. From the slope of
the plot, the value μe of complex is estimated and found to
be ~7.0625 D keeping μg=2.6763 D (value obtained from
quantum chemical calculation method) and a0=22Å. Such
a high μe value speculated to the S1 state of the complex
shows strong intramolecular charge transfer (ICT) charac-
ter. By separating μe in protic and aprotic solvents, it was
noted that the excited state dipole moment in protic solvents
(μe~5.52 D) is higher than in aprotic solvents (μe~5.41 D).
This indicates the specific hydrogen bonding interaction
between solute-solvent which might be causing an enhance-
ment in the ICT character for the complex. Similar hydrogen
bonding effects on the charge transfer characteristic of other
probe molecules have also been found in literature [39].
The red shift of emission peaks with change of polarity
of solvents are predominant than the shifts in absorption
Conclusion
Fig. 10 Lippert-Mataga plots of absorption; fluorescence and Stock’s
shift against the solvent polarity function (Δf) of complex in (1) CCl4,
(2) THF, (3) Acetone, (4) DMF, (5) Ethenol and (6) Acetonitrile
solvents
A novel complex of o-phenylenediamine and benzoin has
been synthesized adopting solid state reaction by mixing
their melt together followed by chilling. The phase diagram

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been determined by establishing the phase diagram in the
entire range of compositions of two compounds. The
complex formation was confirmed by studying the FTIR,
NMR, mass spectroscopy, powder XRD and DSC techni-
ques. The optical properties of the individual and the
complex have been evaluated using UV-Vis absorption and
laser fluorescence techniques. The complex was noted to
give intense green/yellow emission as compared to their
parents. It was noted that the emission is stronger in
complex composition (1:1) than other compositions of BN
and o-PDA. Absorption and the laser fluorescence of the
complex show its higher sensitivity to the polarity of the
solvents. Spectral shift in absorption/emission band and
enhancement in emission intensity is proposed due to the
intramolecular charge transfer in complex.
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Acknowledgements Authors would like to thanks BRNS, DAE,
India for financial support. One of the authors (Y. Dwivedi) would like
to thanks to CSIR (New Delhi, India) for Senior Research Fellowship.
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