Pyrene-naftylamide bifluorophore for spectra-converting media

Article abstract of DOI:10.1007/s10895-009-0558-8

New bifluorophore containing pyrene as an excitation energy donor and naphtylamide as an acceptor is synthesized and its optical properties are studied. It is founded that excitation spectrum of the bifluorophore is almost the sum of its constituents-pyrene and naftylamide. At the same time, in the luminescence spectrum there only the peak of acceptor luminescence is observed, which indicates the effective radiationless energy transfer from the donor to the acceptor. This is also proved by time resolved measurements of bifluorophore decay. The decay rate was calculated from decay curve and appear to be 0.25 hc^-1. The same value obtained from the Foerster's theory is almost by an order as high. It indicates that Foerster's does not applicable in this particular case. Instead, we have to use the electron excitation density functions approach.

Full text of DOI:10.1007/s10895-009-0558-8

J Fluoresc (2010) 20:315–320
DOI 10.1007/s10895-009-0558-8
ORIGINAL PAPER
Pyrene-Naftylamide Bifluorophore for Spectra-Converting Media
Alexander F. Adadurov & Yurii A. Gurkalenko &
Piotr N. Zhmurin
Received: 6 May 2009 /Accepted: 30 September 2009 /Published online: 14 November 2009
#
Springer Science + Business Media, LLC 2009
Abstract New bifluorophore containing pyrene as an
excitation energy donor and naphtylamide as an acceptor
is synthesized and its optical properties are studied. It is
founded that excitation spectrum of the bifluorophore is
almost the sum of its constituents—pyrene and naftylamide.
At the same time, in the luminescence spectrum there only
the peak of acceptor luminescence is observed, which
indicates the effective radiationless energy transfer from the
donor to the acceptor. This is also proved by time resolved
measurements of bifluorophore decay. The decay rate was
calculated from decay curve and appear to be 0.25 нс−1.
The same value obtained from the Förster’s theory is almost
by an order as high. It indicates that Förster’s does not
applicable in this particular case. Instead, we have to use
the electron excitation density functions approach.
their chromophores parts separately and emit at the longest
wavelength.
Because of their special properties, bifluorophores are
widely used in various applications. Thus, for instance,
during recent two decades, there has been a great
emergence of interests in the development of fluorescent
probes for various metal cations. In the paper [3] a novel
bifluorophore bearing one 2,3-naphthocrown-6 and two
coumarin amide units is described as a FRET-based
fluorometric sensor for F− and Cs+ ions. In [4] a new
fluorogenic sensor capable of illustrating metal ion-
triggered FRET changes has been presented. Based on the
FRET changes, this bifliorophore, bearing coumarin-
fluorescein moieties, provides a selective sensor for Cu2+
and Hg2+ ions.
The recently developed tunable dye lasers in the visible
are obtained by incorporation of stable laser organic dyes
into glasses [5]. It thus becomes necessary to continuously
search for new systems and synthesize new laser dyes
covering a wide spectral range of excitation. Specific
bifluorophores based on laser dyes can solve this problem
[6, 7].
.
.
Keywords Photoluminescence Spectra converting
Bifluorophore
Introduction
Bifluorophore is a substance comprises at least two
fluorescent dye moieties covalently linked via a linker
group. The dyes are selected so that the emission spectrum
of a first (donor) dye overlaps the absorption of a second
dye, thereby allowing fluorescent resonance energy transfer
(FRET) [1, 2] to occur between the dyes. As the result,
bifluorophores absorb at more wide band comparing to
Almost the same problem arises in luminescent solar
concentrators (LSC) [8] especially when organic photo-
voltaic cells are used. In [9] an organic cell fabricated of
zinc-phtalocyanine and C60 is described. This solar cell
have its main absorption in the wavelength range between
600 and 800 nm. Below 600 nm, the low absorption limits
the quantum efficiency. Luminescent concentrators are used
to overcome this limitation by spectrally shifting blue and
green light towards the red and waveguiding it to the solar
cell.
:
:
A. F. Adadurov (*) Y. A. Gurkalenko P. N. Zhmurin
Institute for scintillating materials NAN of Ukraine,
60 Lenin Ave,
In luminescent concentrators the broad spectrum of
the sunlight is taken up by a material absorbing in as
wide as possible spectral range and reemitted in a
Kharkov 61001, Ukraine
e-mail: adadurov@isma.kharkov.ua

316
J Fluoresc (2010) 20:315–320
narrow luminescence. Due to the Stokes shift, the
luminescence occurs always to higher wavelengths as
the absorption, the light can be only redshifted [9, 10].
This luminescence should coincide with the best spectral
response of the solar cell.
tylamide and pyrene molecules. Our goal was to expand the
absorption band of LSC and to provide an effective energy
transfer to the long-wave region.
A promising way to enhance the efficiency of organic
solar cells is to use “antenna systems” of absorber materials
that donate the energy from photons absorbed in the blue
and green spectral ranges to the red absorbing solar cell
materials. When multiple dyes are presented in LSC,
photons are absorbed and re-emitted by increasingly longer
wavelength dyes.
It is commonly assumed that only radiative coupling
occurs between the dye molecules [10]. But about a
quarter of the energy collected in the first dye is lost in
every reemission act. These losses can be reduced if the
effective channel of radiationless energy transfer (FRET)
between dyes exists. It is to be noted that while FRET
between dye molecules can occur with a higher efficiency,
the molecular spacing that is required to realize it (less
than Förster’s radius of energy transfer [1]) could be only
achieved in a heavily-doped matrix. But under high
concentration of a dye, which is necessary to achieve
such small distances, light absorption will be so high that
in this case even statement of the considered problem
loses its sense.
Experimental
The scheme of bifluorophore synthesis is presented in
Fig. 1. It can be schematically divided into the following
stages:
1. (а, С19H10NO4Cl). 4-(6-chloro-1,3-dioxo-2,3-
dihydro-1H-benzo[de]isoquinolin-2-yl)benzoic acid
8.5 g (0.062 mol) of para-aminobenzoic acid is added to
5.0 g (0.021 mol) 4-chlorinenaphtal anhydride in 40 ml of
glacial acetic acid and is heated under boiling temperature
during 4 h. After cooling, the precipitate is filtered, washed
by hot water and methanol, and dried at about 80 °С
temperature. The yield of obtained product is 4.92 g (65%).
Melting temperature Тmelt>300 °С.
2. (b, С19H9NO3Cl2). 4-(6-chloro-1,3-dioxo-2,3-dihydro-
1H-benzo[de]isoquinolin-2-yl)-1-benzenecarbonyl
chloride
30 ml (0.41 mol) of thionyl chloride are added to 2.0 g
(0.0056 mol) of substance “а”, boiled during 2 h, then
surplus thionyl is distilled off and its residue is removed by
azeothrope distillation by dry benzene. Benzene residue is
evaporated for dryness in vacuum under room temperature.
Yield of obtained product—about 2 g (95%).
Therefore the problem is to create cascades of excitation
energy migration in which both donor and acceptor are
placed at small distances and their concentration can be
rather low. Such cascades can be performed in complexes
of covalent binding donor and acceptor molecules, that is,
in bifluorophores [11, 12].
3. (с, C16H11N). 3-Aminopyrene
is obtained by known technique [13] by means of pyrene
nitration by dilute nitric acid in acetic acid with further
reduction of resultant 3-nitropyrene by tin chloride in
hydrochloric acid.
Present work concerns the synthesis and studies of
optical properties of new bifluorophore, based on naph-
O
O
H2N
c
SOCl2
Cl
Cl
N
COCl
N
O
COOH
O
b
a
O
O
N
O
O
N
O
Cl
O
O
NH
N
O
N
H
N
H
d
e
Fig. 1 Synthesis scheme

J Fluoresc (2010) 20:315–320
317
4. (d, C35H19N2O3Cl). 1-[4-(6-chloro-1,3-dioxo-2,3-
dihydro-1H-benzo[de]isoquinolin-2-yl)phenylcar-
boxamido]pyrene.
column chromatography. Purity control of synthesized
compounds was made by ТСХ method on Baker-flex
plates “Silica Gel IB-F”.
2.2 g (0.0101 mol) of 3-aminopyrene (substance “с”) in
small discrete portions are added to suspension of 2.0 g
(0.0054 mol) of the substance “b” in 30 ml of benzene; then
15 ml of pyridine is dripped and mixed under 60 °С during
6 h. The mass is cooled, the precipitate is washed with
methanol and dried. The yield of the product is 2.1 g.
5. (e, C39H27N3O4). 1-[4-(6-morpholino-1,3-dioxo-2,3-
dihydro-1H-benzo[de]isoquinolin-2-yl)phenylcarbox-
amido]pyrene
2 ml of morpholine is dripped to 0.4 g of product
“d” solution in 20 ml of Dimethylformamide (DMFA)
and heated under 90 °С during 3 h. Then the substance
is cooled, 30 ml of methanol is added, the yellow
precipitate is filtered, washed with methanol and dried
under about 80 °С temperature. The obtained product is
passed through a chromatograph column of chloroform
with silica gel. The yield is 0.23 g (7.09% in terms of 4-
(6-chloro-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-2-
yl)-1-benzenecarbonyl chloride (“b”)). Melting temperature
Results
Bifluorophore molecule consists of two luminescent parts
(see Fig. 2) one of them (pyrene) being the energy donor
and the other (naphtylamide)—its acceptor. To determine
optical properties of bifluorophore first of all steady-state
spectra of excitation and luminescence of donor and
acceptor were studied separately. For this end we used
4-morpholino-N-(4-carboxy)-phenylimide naphthalic acid
(substance “f”) as the acceptor and 3-acetylamonopyrene
(substance “g”) as the donor (Fig. 3).
Excitation spectra were registered in a maximum of the
luminescent spectrum of the respective dye. They are
presented in Fig. 4a. It follows from the figure that the
donor emission spectrum with the maximum at 413 nm is
well overlapped by excitation spectrum of the acceptor
parts of the bifluorophore (maximum at 395 nm). This
overlapping makes possible an effective energy transfer
between donor and acceptor parts of the bifluorophore
molecule.
It is seen in the Fig. 4 that the excitation spectrum of
bifluorophore is actually the sum of donor and acceptor
maxima at 362 and 395 nm respectively. The width of
bifluorophore excitation band is widen up to 110 nm (from
325 to 435 nm), which contains the same values for donor
and acceptor parts of bifluorophore molecule. It is to be
note that when bifluorophore is excited at 395 nm, there is
practically no luminescence of its donor part (Fig. 4b). This
Тmelt>300 °С.
Molecular mass of obtained substances was measured by
Varian 1200 L Quadrupole MS Liquid Chromatograph/
Mass Spectrometer chromo-mass-spectrometer (Varian
Inc.). It happened to be equal to 610 which is close to the
expected value (618, substance “e”).
Luminescence spectra of synthesized compounds were
measured in chloroform by means of HORIBA JobinYvon
“FluoroMax-4” fluorimeter, absorption spectra—by
“SPECORD 40” spectrophotometer under 10−6 mol⋅l−1
solution concentration. Silica gel 40–100 μm was used for
Fig. 2 Scheme of bifluorophore
O
Donor
O
O
N
N
HN
O
Acceptor

318
J Fluoresc (2010) 20:315–320
Fig. 3 Substances used to study
acceptor (substance “f”, left) and
donor (substance “e”, right)
separately
O
N
O
O
O
N
H3C
COOH
N
H
behavior of bifluorophore molecules luminescence can be
observed even in very small concentration. In such a way,
any influence of reabsorption effects on donor lumines-
cence is eliminated.
Observed spectrum of bifluorophore fluorescence shows
the existence of an effective channel of radiationless energy
transfer between its donor and acceptor parts. The existence
of such a channel is also proved by time-resolved measure-
ments of bifluorophore decay.
First of all we measured decay curves of a donor and
acceptor separately (see Fig. 5). The measurements were
done for solutions of these substances in dichlorethane, the
concentration being 10−6 M⋅l−1. The figure shows that
decay curves as donor and acceptor are strictly single-
exponentials (10 ns–40 ns and 10 ns–60 ns regions) which
indicates the absence of additional quenching channels. The
lifetime of the exited states of donor and acceptor appear to
be equal to 4.3 ns and 8.2 ns, respectively.
In accordance with Förster theory [14], the radiationless
channel of relaxation in a donor-acceptor system must
cause the change in a donor’s luminescence decay law.
Instead of simple exponent, the following decay depen-
dence on time must be observed:
ꢀ
ꢁ
Z
FðtÞ ¼ exp ꢀt=t0ꢀcD ꢁ gðrÞð1 ꢀ expðwðrÞ ꢁ tÞÞdr
ð1Þ
where CD concentration of donor molecules in a sample
g (r)
pair correlation function of donor-acceptor
mutual spatial distribution
1,0
a)
w (r)
rate of radiationless energy transfer between
donor and acceptor located at r distance:
0,8
0,6
1
3
2
s
wðrÞ ¼ 1=t0ðR0=RÞ
ð2Þ
0,4
0,2
τ0
s
lifetime of the donor in the absence of the acceptor
power, determined by the degree of multipolarity
of interaction. For dipole-dipole interaction s=6
0,0
280 300 320 340 360 380 400 420 440 460 480 500
, nm
0
-2
-4
-6
Donor
1,0
=4.3ns
τ
b)
0,8
2
0,6
0,4
0,2
0,0
3
60
0
40
20
1
0
-2
-4
-6
Acceptor
=8.2ns
τ
350
400
450
500
550
600
650
700
, nm
0
20
40
60
t, ns
Fig. 4 Excitation a and emission b spectra of donor (1), acceptor (2)
and bifluorophore (3) molecules
Fig. 5 Decay curves of the donor and acceptor

J Fluoresc (2010) 20:315–320
319
R0
critical (Förster) transfer radius, which is
Excitation
Bifluorofore
determined from known expression of spectra
overlapping [14]:
=2ns
τ1
τ2
100
=7ns
ꢅ
ꢂꢃ
ꢄꢆ
R60 ¼ ð9000 ln 10Þk28d 128p5Nn4
Z
ꢁ
"aðnÞIdðnÞnꢀ4dn;
ð3Þ
10
where εa(v) molar extinction of the acceptor
Id (v)
normalized fluorescence spectrum of the
donor
1
0
10
20
30
40
50
t, ns
8d
quantum yield of the donor in the absence of
acceptor
Avogadro’s number
refractive index of the medium
orientation factor, related to mutual
orientation of two interacting dipoles (as a
rule, it is chosen as 2/3).
Fig. 6 Fluorescence decay of the donor part of bifluorophore
N
n
k2
The contribution of the intermolecular component can be
minimized by decreasing the concentration of bifluorophore
in the sample. As it follows from (4), under low
concentration of the bifluorophore, the rate of energy
transfer on the adjacent molecule tends to zero. But it is
impossible to ignore absolutely the intermolecular energy
transfer. Therefore, the observed decay law must have a
two-component character with different decay laws. The
first exponent with 2 ns lifetime can be related with the
quenching of the donor part of bifluorophore molecule by
acceptor parts of the same molecule as well as by the rate of
spontaneous decay. It appears impossible to select the
irregular component from the decay curves because it is
superimposed by “parasitic” luminescence of the acceptor
with 8 ns lifetime. It is the component that provides the
second, “long”, exponent. It is to be noted that the
luminescence of donor part of bifluorophore molecules is
very weak, so to register it we have to use rather long time
to store.
From the “short” part of the donor’s decay curve (Fig. 6)
we can estimate the rate of energy transfer from the donor
to the acceptor, about 0.25 нс-1. The same value can be
obtained in another way. To do so we must know the
Förster radius of transfer which is easily calculated from
absorption and fluorescence spectra according to Eq. (3)
(R0=34 Å in our case) and the distance between donor and
acceptor part which is determined from structural formula
of the bifluorophore molecule (R=10–15Å). Resulting
quenching rate is greater than observed one almost by an
order. It is possible that instrumentation used for decay time
measurement (apparatus half-width of excitation pulse is
~1 ns) does not resolve such a transfer rate, or suggested
approach does not take into account peculiarities of closely
placed chromophores. In the latter case we must use the
electron excitation density functions approach [15].
Decay curve of donor part of bifluorophore is presented
in Fig. 6. It is seen in the figure that decay curve of donor
part of bifluorophore obviously deviate from a single
exponential. It can be fitted by two exponents with 2 ns
and 7 ns lifetimes (10 ns–40 ns region).
It is to be noted that two-exponent fitting is not so
correct when there is a channel of radiationless energy
transfer. Let us consider the bifluorophore solution. Energy
transfer from its donor part can be either to an acceptor,
which is a part of the same molecule (intramolecular
transfer) or to an acceptor part of another molecule in
the solution (intermolecular transfer). Therefore, the
donor-acceptor correlation function must consist of a
regular part gcðrÞ ꢂ dðr ꢀ RdaÞ, which is determined by
covalently linked donor and acceptor, and a random part
grðrÞ ¼ 4pcar2, which is determined by chaotically distrib-
uted bifluorophore molecules in a solution. It means that
observed donor decay dependence on time must be a two-
component one (taking no account to donor’s spontaneous
decay with 4 ns life-time). The first, (regular) component
which relates to energy transfer to the acceptor part of the
same molecule at the distance R0da, is determined by
. ꢇ
ꢈ
6
exponent with linear power t t0 R0=R0 , and the
second, (irregular), component, related with energy transfer
to the acceptor parts of another molecules, must be
da
characterized by root dependence of power on time
pffiffi
ꢂ cd t. Therefore the observed decay dependence on time
must have the following form:
ꢀ
ꢉ
ꢁ
. ꢇ
ꢈ
IðtÞ ꢂ exp ꢀt t0 ꢀ t t0 R0=R0 6 ꢀ gcd t ;
ð4Þ
pffiffi
da
where γ - a numerical coefficient.

320
J Fluoresc (2010) 20:315–320
The quantum yield of our bifluorophore was determined
References
by means of relative measurements. They include the
measurement of the integral of luminescence curves I and
absorption coefficients on the same wavelength for un-
known and reference media. Then the quantum yield 8 is
determined according to:
1. Förster Th (1941) Experimentelle und theoretische Untersuchung
des zwischenmolecularen Uebergangs von. Electronenanregung-
senergiep. Z. Naturforsh. 4A:321–327
2. Lakowicz JR (ed) (1999) Principles of fluorescence spectroscopy.
Plenum, New York
3. Lee MH, Quang DT, Jung HS, Yoon J, Lee C-H, Kim JS (2007)
Ion-Induced FRET on-off in fluorescent Calix[4]arene. J. Org.
Chem 72:4242–4245
4. Lee Su Yeon, Kim HJ, Wua J-S, No K, Kim JS (2008) Metal ion-
induced FRET modulation in a bifluorophore system. Tetrahedron
Letters 49:6141–6144
5. Alekseev NN, Gorelenko AY, Zen'kevich EI, Kalosha II,
Chernook AV (1988) Photonics of a bifluorophore with an
oxazine fragment. J Appl Spectrosc 49:480–485
6. Yariv E, Schultheiss S, Saraidarov T, Reisfeld R (2001) Efficiency
and photostability of dye doped solid-state lasers in different
hosts. Optical Mater. 16:29–38
ꢀ ꢁꢀ
ꢁ
2
ꢇ
ꢈ
I
n
"
r
8 ¼ 8r
ð5Þ
Ir
nr
"
where n, I, 8, ε are the respective refraction coefficient,
integral intensity of luminescence, quantum yield and
absorbance of studied solutions, and nr, Ir, 8r, εr are the
same quantities of reference medium. As the reference
medium we select 2,5-Diphenyloxazole (РРО) solution in
cyclohexane with quantum yield 8r–0.99 [16]. Measurement
shows that the bifluorophore quantum yield is 8 =0.47.
7. Anufrik SS, Tarkovskii VV, Nikitchenko VM (1999) New laser
media based on bifluorophore coumarin molecules. J Appl
Spectrosc 66(3):772–778
8. Reisfeld R, Shamrakov D, Jorgensen CK (1994) Photostable solar
concentrators based on fluorescent glass films. Solar Energy
Mater Solar Cells 33:417–427
Conclusions
9. Koppe R, Saricifici NS, Büchtemann A (2007) Enhancing photon
harvesting in organic cells with luminescent concentrators. Appl.
Phys. Lett. 90:181126-1–181126-3
10. Koeppe R, Bossart O, Calzaferri G, Sariciftci NS (2007)
Advanced photon-harvesting concepts for low-energy gap, organic
solar cells. Sol Energy Mater Sol Cells 91:986–995
11. Gruzinskii VV, Danilova VI, Kopylova TN, Svinarev NV, Barkova
LA, Kukhto AV, Shevchenko A, Mazykina NI (1988) Spectral-
luminescent and generation properties of a bifluorophore based on
para-terphenyl and coumarin. J Appl Spectrosc 49:1235–1239
12. Alekseev NN, Gorelenko AY, Zen'kevich EI, Kalosha II,
Chernook AV (1988) Photonics of a bifluorophore with an
oxazine fragment. J Appl Spectrosc 49:480–485
13. Vollmann H, Becker H, Corell M, Streeck H (1937) Beitriige zur
Kenntnis des Pyrens und seiner Derivate. J. Liebigs Ann. d.
Chem. 531(1):1–159
Synthesized bifluorophore consists of pyrene molecules as
the donor and naphtylamide molecules as the acceptor of
excitation energy. It is shown in the paper that the resulting
absorption spectrum of the bifluorophore is the sum of
donor and acceptor respective spectra. So the total
absorption is increased allowing to utilize more wide part
of the Sun spectrum in a luminescent concentrator (LSC).
Donor emission in a 380–450 nm band (UF—blue) almost
disappears in the bifluorophore being shifted to green-red
band about 500–600 nm. This in turn allows more effective
coupling with the organic photovoltaic cell.
Quantum yield of obtained bifluorophore is rather low
now, about 0.47 and is increasing is the subject of further
investigations.
It is shown in the present work that observed effective
radiationless energy transfer cannot be explained by
Förster’s theory. It can be relate with small distance
between the donor and the acceptor in the bifluorophore.
This problem requires more detailed separate study.
14. Agranovitch VM, Galanin MD (1982) Electronic excitation
energy transfer in condensed matter. North-Holland, New York
15. Bacchiocchi C, Hennebicq E, Orlandi S, Muccioli L, Beljonne D,
Zannoni C (2008) A reduced distributed monopole model for the
efficient prediction of energy transfer in condensed phases. J.
Phys. Chem. B 112:1752–1760
16. Berlman IB (1965) Handbook of fluorescence spectra of aromatic
molecules. Academic, New York