Design and synthesis of sulfobetainic diketopyrrolopyrrole (DPP) laser dyes

Article abstract of DOI:10.1039/c2nj40569e

We have devised new diketopyrrolopyrrole dyes soluble in polar solvents. The colors of the dyes have been changed by substituting the 3,6-phenyl residues for thiophene groups. The solubility in polar solvents has been improved by alkylation of a dimethylaminopropyne fragment with a 1,3-sultone giving rise to sulfobetaine moieties. These dyes exhibit strong and broad absorption in the visible range (488 nm for the phenyl-DPP and 578 nm for the thiophene-DPP) and intense fluorescence at, respectively, 554 nm (Φ_F 0.36) and 609 nm (Φ_F 0.19). The phenyl-DPP dye exhibits a maximum broad band lasing efficiency of 14.6% and a maximum narrow band lasing efficiency of 9.5% with a wide tunable range (554 nm to 616 nm) on excitation with a second harmonic of a Q-switched Nd:YAG (532 nm) laser in MeOH/H₂O. The lasing efficiency remains unaffected for hours. The thiophene-DPP dye does not show any lasing action.

Full text of DOI:10.1039/c2nj40569e

New Journal of Chemistry
A journal for new directions in chemistry
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Volume 37 | Number 2 | February 2013 | Pages 253–544
ISSN 1144-0546
PAPER
Soumyaditya Mula,
Raymond Ziessel et al.
Design and synthesis of
sulfobetainic diketopyrrolopyrrole
(DPP) laser dyes
1144-0546(2013)37:2;1-E

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PAPER
Design and synthesis of sulfobetainic
diketopyrrolopyrrole (DPP) laser dyes
Soumyaditya Mula,*a Delphine Hablot,b Krishna K. Jagtap,cd Elodie Heyerb and
Raymond Ziessel*b
Cite this: NewJ.Chem., 2013,
37, 303
We have devised new diketopyrrolopyrrole dyes soluble in polar solvents. The colors of the dyes have been
changed by substituting the 3,6-phenyl residues for thiophene groups. The solubility in polar solvents has
been improved by alkylation of a dimethylaminopropyne fragment with a 1,3-sultone giving rise to
sulfobetaine moieties. These dyes exhibit strong and broad absorption in the visible range (488 nm for the
phenyl-DPP and 578 nm for the thiophene-DPP) and intense fluorescence at, respectively, 554 nm (FF 0.36)
and 609 nm (FF 0.19). The phenyl-DPP dye exhibits a maximum broad band lasing efficiency of 14.6% and a
maximum narrow band lasing efficiency of 9.5% with a wide tunable range (554 nm to 616 nm) on
excitation with a second harmonic of a Q-switched Nd:YAG (532 nm) laser in MeOH/H2O. The lasing
efficiency remains unaffected for hours. The thiophene-DPP dye does not show any lasing action.
Received (in Montpellier, France)
4th July 2012,
Accepted 3rd September 2012
DOI: 10.1039/c2nj40569e
www.rsc.org/njc
and 6, were synthesised and their photo-physical properties were
examined. The dyes were designed to contain phenyl or thiophene
Introduction
The 3,6-diaryl-2,5-dihydro-1,4-diketopyrrolo[3,4-c]pyrrole (DPP)
class of compounds are widely known as high-performance
pigments used in inks, paints, and plastics,1 owing to their
brilliant shades and outstanding photostability. The strong
fluorescence and moderate Stokes shifts of the DPP dyes2 make
them ideal candidates for designing chemosensors,3a light-
emitting diodes,3b dye-sensitized solar cells,3c,d organic thin-
film transistors,4 bulk heterojunction organic solar cells5 and
solid state lasers.6 But their insolubility in common organic
solvents because of strong intermolecular hydrogen bonding
and p–p interactions restricts their use in many applications.
Thus the development of new synthetic routes to improve the
solubility of these dyes is very important.
moieties as the 3,6-diaryl groups in order to provide different
coloured DPP dyes (red and purple respectively). The sulfobetaine
moiety is known to retain its zwitterionic character over a broad
pH range and hence it was attached to the DPP core to improve
the water solubility of the dyes. This strategy was based upon
that developed during a research program aimed at solubilizing
difluoroboron-dipyrromethane dyes (Bodipys) in water.8
Dye lasers are the most versatile and one of the most
successful laser sources known today, contributing significantly
to basic physics, chemistry, biology and other fields. Known
since 1966, liquid dye lasers are expected to have high-efficiency,
low laser threshold, wide wavelength-tunable range and long-
lifetime coherent light sources.9a,b Although various dyes are
known today for use in different wavelength regions,10 the
development of new organic materials having comparable or
superior laser performances in terms of efficiency, tuning range,
photochemical stability and photo-thermal characteristics is an
important goal in dye laser chemistry. In the present study, we
also examined the lasing properties as well as photo-chemical
stability of new DPP dyes. To the best of our knowledge, the DPP
dyes have not been used in liquid dye lasers so far.
Replacement of the lactam N–H protons improves the
solubility,7 yet making them soluble in highly polar medium
still remains a challenge. In the present study, we designed and
developed a novel strategy to make DPP dyes soluble in polar
organic solvents and in aqueous mixtures. Two new DPP dyes, 3
a Bio-Organic Division, Bhabha Atomic Research Centre, Mumbai-400085, India.
E-mail: smula46@yahoo.com
b
´
´
Laboratoire de Chimie Moleculaire et Spectroscopies Avancees (LCOSA), UMR
´
`
´
7515 au CNRS, Ecole Europeenne de Chimie, Polymeres et Materiaux,
25 rue Becquerel, 67087 Strasbourg Cedex 02, France. E-mail: ziessel@unistra.fr,
http://www-lmspc.u-strasbg.fr/lcosa
Results and discussion
Syntheses
c Laser and Plasma Technology Division, Bhabha Atomic Research Centre,
For the synthesis of the target dyes (Scheme 1), dimethylamino-
Mumbai-400085, India
d Department of Chemistry, University of Pune, Pune-411007, India
propyne was coupled with the bromo dyes 111 and 412 respectively,
c
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Fig. 1 (a) 1H NMR spectra of dye 3 in d6-DMSO (S1) at rt and peak attribution.
The insets represent the signal of protons k found in d4-methanol (right hand
side) and expansion of the benzyl protons windows (left-hand side). S2 corre-
spond to residual water. (b) 13C NMR of dye 3 in d6-DMSO.
Scheme 1 Key: (i) Dimethylaminopropyne (3.0 equiv.), benzene, Et3N,
[Pd(PPh3)2Cl2] (10 mol%), CuI (15 mol%), 60 1C, 15 h. (ii) 1,3-Propanesultone
(20 equiv.), DMF, 80 1C, 88 h. (iii) Dimethylaminopropyne (4.5 equiv.), benzene,
Et3N, [Pd(PPh3)2Cl2] (5 mol%), CuI (8 mol%), 60 1C, 15 h. (iv) 1,3-Propanesultone
(20 equiv.), 1,2-dichloroethane, 80 1C, 48 h.
protons integration for each signal. The methylene residue
nearby the sulfonate resonates as a triplet at 2.50 ppm
(Fig. 1a). The carbon spectra presented the expected six signals
for the alkyl atoms, the ethynyl signals at 80.3 and 89.4 ppm and
the expected aromatic CH (five signals) and CC (six signals). The
lactam signal was found at 161.4 ppm (Fig. 1b).
via Sonogashira coupling to furnish compounds 2 and 5. In
order to have reasonable solubility in organic solvents for the
post-functionalization, dyes 1 and 4 carry lipophilic benzyl and
ethylhexyl side chains respectively. The reaction was catalyzed
by a Pd(0) species, generated in situ from a Pd(II) precursor
and CuI. Compounds 2 and 5 were individually reacted with
1,3-propanesultone8 in dimethylformamide or 1,2-dichloro-
ethane to furnish the zwitterions 3 and 6 in 72% and 76%
yields respectively. This is the first application of this strategy to
solubilize DPP dyes. The new dyes 3 and 6 were soluble in polar
solvents including aqueous mixtures and could be purified by
reverse phase (C18-silica) column chromatography. These dyes
were unambiguously characterized by NMR spectroscopy giving
well-defined spectra excluding any formation of aggregates in
DMSO, MeOH or MeOH–water solvents. A typical example is
depicted in Fig. 1 giving a first order spectrum in which the
bridging phenyl rings exhibit two doublets of an AA0BB0 system.
Diagnostic signals are provided by the methylene groups at
5.01 and 4.63 ppm, respectively, assigned to the DPP benzyl and
dimethylaminopropyne residues. This assignment has safely
been made by comparing the chemical shifts of the methylene
Optical properties
The absorption spectral profile of dye 2 in CH2Cl2 was broad and
centred at 488 nm with a moderately high absorption coefficient of
log e = 4.15 (Fig. 2 and Table 1). When excited in the absorption
band at 450 nm dye 2 exhibits an intense fluorescence centered at
544 nm. This emission band is characterized by a vibrational-like
structure which is weakly solvent dependent. The Stokes shift
group in compound 1 and analogues (dCH Ph about 5.0 ppm
2
in each case), and the methylene group in compound 5
and analogues (dCH CRC about 4.70 ppm in each case). The
2
methylene group of the ethylhexyl lateral chain resonates as a
doublet at about 3.90 ppm. The ammonium signal resonate at
3.15 ppm and the sultone signals were found as multiplets
centered at 3.60, 2.50 and 2.10 ppm with the expected four
Fig. 2 Absorption (black line), emission (dashed line) and excitation (dotted
line) spectra of dye 2 in CH2Cl2 at room temperature.
c
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Table 1 Selected optical properties of the DPP dyesa
labs
lem tF
Rad. rate, Non-rad. rate,
c
b
Dyes (nm) e (Mꢀ1 cmꢀ1) (nm) (ns) FF krc (108
s
ꢀ1) knr (108 sꢀ1
)
2
3
6
488
480
576
23 300
17 500
23 000
554 5.0 0.80
554 5.4 0.36
609 2.8 0.19
1.6
0.7
0.7
0.4
1.2
2.9
a
Measured at room temperature in CH2Cl2 for dye 2, in MeOH/H2O
b
(8/2, v/v) for dye 3 and 6. Determined using F = 0.88 for Rhodamine 6G
in ethanol as the reference,17 lexc = 488 nm for dyes 2 and 3, or
determined using F = 0.51 for Cresyl Violet in ethanol as the reference,17
c
lexc = 578 nm for dye 6. Radiative (Rad.) and non-radiative (Non-rad.)
rates were calculated using the following equations: kr = FF/tF, knr
=
(1 ꢀ FF)/tF, assuming that the emitting state is produced with unit
quantum efficiency.
Fig. 4 Absorption (black line), emission (dashed line) and excitation (dotted
line) spectra of dye 6 in MeOH/H2O (8/2, v/v) at room temperature.
(2440 cmꢀ1) revealed significant change in the molecular
structure in the excited state (Fig. 2).13 This is likely due to the
presence of the flexible aromatic side chains which can freely water, forming aggregates with large absorption bands with
rotate along the C–C linking bond. This is in stark contrast to maxima at 500 and 535 nm. An unresolved emission band
Bodipy dyes, which display emission profiles which mirror spanning over 250 nm and peaking about 575 nm was observed
the absorption spectra due to the rigidity of the emitting in water with relatively low fluorescence quantum yields (about
dipyrromethene core.14 The fluorescence spectral profile was 7%). Under these aqueous conditions the excitation spectrum
broad and can be assigned as a single electronic transition. does not match the absorption spectrum. In strong contrast the
The fluorescence quantum yield of dye 2 was high (0.80) and the excitation spectra of dye 3 in MeOH/H2O overlap with the
emission lifetime (5.0 ns) was comparable to those recorded for absorption spectra proving that all transitions participate to
related organic dyes including Bodipys.15 The excitation spectrum the emission detected at 554 nm (Fig. 3).
perfectly matches the absorption spectrum (Fig. 2) excluding the
presence of aggregates or fluorescent impurities.
The absorption and emission profiles of dye 6 in MeOH/H2O
(8/2, v/v) are presented in Fig. 4. Similar spectra were obtained
The substitution of the bromo-phenyl or bromo-thiophene in pure MeOH but dye 6 is insoluble in pure water. The
in compounds 1 and 4 by alkyne substituents has little influence absorption band was quite broad, spanning over 180 nm. The
on the absorption and emissive properties of dyes 2 and 5. Such 3,6-thiophene moieties of 6 extend the delocalization along the
weak effects have also been previously observed in similar thiophene–lactam main axis as previously observed for related
derivatives.11
derivatives.16 Consistent with this, the low energy absorption
The absorption and emission profiles of dye 3, recorded in band of 6 was shifted bathochromically by about 96 nm
pure MeOH or MeOH/H2O (8/2, v/v, Fig. 3), were essentially the compared to that of dye 3 (Table 1). The shape of the emission
same as those of dye 2. Dye 3 had a yellow fluorescence, band was consistent with that expected for a singlet emitter.
although its emission quantum yield (0.36) was about two The emission band was also bathochromically shifted but only
times weaker than that of 2. Importantly, the excited state by 55 nm, which effectively reduced the Stokes shift (941 cmꢀ1
)
lifetime (5.4 ns) of dye 3 in a polar medium was higher than as compared to 3. Dye 6 showed reddish fluorescence but
that of 2 recorded in an aprotic (CH2Cl2) medium (Table 1). It fluorescence lifetime (2.8 ns) and quantum yield (0.19) were
was noticed that dye 3 was not completely soluble in pure also much lower than those of dye 3. The excitation spectrum is
in good agreement with the absorption spectra (Fig. 4).
Lasing characteristics
The lasing characteristics of dye 3 were evaluated in MeOH/H2O
(8/2, v/v) solution. The concentration-dependent broadband
lasing efficiency of dye 3 followed an expected pattern
(Fig. 5), with a maximum lasing efficiency (Z) of 14.6% at a
concentration of 2 mM. However, the narrow-band lasing
efficiency (Zmax = 9.5%) of the dye solution (1.8 mM) in
MeOH/H2O (8/2, v/v), measured at 580 nm (lL) using the second
harmonic of a Q-switched (PRF-10 Hz, pulse width B6 ns)
Nd:YAG (532 nm) laser, was slightly less (Fig. 6). More signifi-
cantly, dye 3 had a much wider wavelength tunability (554 nm to
616 nm), although less efficiency than commercially available
Rh6G. The increased tuning range of dye 3 should be very useful
Fig. 3 Absorption (black line), emission (dashed line) and excitation (dotted
line) spectra of dye 3 in MeOH/H2O (8/2, v/v) at room temperature.
c
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Fig. 8 Time-dependent broadband lasing efficiency of dye 3 in MeOH/H2O
Fig. 5 Broadband lasing efficiency of dye 3 in MeOH/H2O (8/2, v/v) determined
(8/2, v/v).
by pumping with 532 nm radiation of a Q-switched pulsed Nd-YAG laser.
Unfortunately, dye 6 did not produce any lasing action light
on excitation with the second harmonic of a Q-switched (PRF-
10 Hz, pulse width B6 ns) Nd:YAG (532 nm) laser. This may be
attributed to the low fluorescence quantum yield, shorter
excited state lifetime and smaller Stokes shift with respect to
dye 3. The small Stokes shift would increase the ground state
absorption (GSA) of the dye molecules at the high concen-
tration used for the lasing experiments. Based on the above
results, dye 3 was chosen for studying the photo-chemical
stability.
Photostability of dye 3
Fig. 6 Narrow band lasing efficiency of dye 3 in MeOH/H2O (8/2, v/v) deter-
mined by pumping with 532 nm radiation of a Q-switched pulsed Nd-YAG laser.
The time dependent broadband lasing efficiencies of dye 3 is
shown in Fig. 8. The lasing efficiency remained unchanged over
2 h of exposure but started decreasing gradually thereafter.
Even then, the lasing efficiency dropped by only 9% of its initial
value after 4 h of exposure. These results clearly demonstrated
that dye 3 is very stable under lasing conditions, promising for
its long term use as a laser dye.
for its applications. The slope efficiency of the dye at lL with a
threshold pump energy of 3 mW was 8.5% (Fig. 7).
It is important to mention that the aqueous mixture is
always preferred over pure organic solvents as large amounts
of solvent are required in a dye laser. This is for making safer
dye lasers in terms of fire hazard, environmental pollution, and
easy treatment and disposal of wastes. Also, due to the weaker
dependence of its refractive index on temperature (dn/dT),
water has higher photothermal figure of merit (F).18 The high
F value of water is particularly beneficial with high repetition-
rate dye lasers to reduce the divergence of the dye laser beam.
Conclusions
Using a new strategy for the synthesis of DPP dyes soluble in
polar solvents (alcohol or alcohol/water), two differently
coloured-dyes were synthesized and their optical properties
were evaluated. It provides the evidence that approach via
sultone-chemistry gives rise to modified DPPs possessing good
water solubility combined with useful optical properties. It will
certainly have impact on functional dyes community especially
on research focused on fluorescence imaging. One of the dyes,
compound 3, showed a maximum narrow-band lasing effi-
ciency of 9.5% and its wide wavelength tunability coupled with
a very high stability under lasing conditions makes it a promis-
ing fluorophore for further investigations. Although dye 6 did
not exhibit lasing behaviour, the present studies have estab-
lished the efficacy of the strategy for developing laser dyes
soluble in alcohol or aqueous alcohols. Further work is dedi-
cated to the replacement of the benzyl or ethylhexyl lateral
chains with water compatible solubilising chains such as
polyethyleneglycol.
Fig. 7 Dye laser slope efficiency of dye 3 at lL in MeOH/H2O (8/2, v/v).
c
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Experimental
General details
with EtOAc (3 ꢁ 10 mL) and finally with Et2O (3 ꢁ 10 mL). The
residue was purified on a RP18 column, eluting first with H2O +
1% TFA, followed by H2O + 1% TFA/THF (H2O/THF = 9/1 to 7/3)
to furnish dye 3 (89.0 mg, 72%). 1H NMR (400 MHz, d6-DMSO),
d (ppm): 2.03–2.15 (m, 4H), 2.53 (t, J = 6.9 Hz, 4H), 3.15 (s, 12H),
3.57–3.69 (m, 4H), 4.63 (s, 4H), 5.01 (s, 4H), 7.13 (d, J = 7.4 Hz,
4H), 7.19–7.37 (m, 6H), 7.80 (AB sys, JAB = 8.2 Hz, nOd = 37.0 Hz,
8H); 13C NMR (100.6 MHz, d6-DMSO), d (ppm): 19.0, 44.5, 47.6,
49.9, 54.1, 62.9, 80.3, 89.4, 109.5, 123.1, 126.2, 127.1, 128.1,
128.5, 128.7, 132.1, 137.1, 147.3, 161.4; ESI-MS in H2O/MeOH +
1% TFA, positive mode, m/z (%): 875.3 (100), 438.1 (45, doubly
charged). Anal. calcd for C48H50N4O8S2 + H2O: C, 64.55; H, 5.87;
N, 6.27%. Found: C, 64.38; H, 5.65; N, 6.09%.
The 1H and 13C spectra were recorded at room temperature with a
200 MHz, 300 MHz, or 400 MHz spectrometer, using perdeuterated
solvents as the internal standards. The 1H and 13C chemical shifts
are given in ppm relative to the residual protiated solvent or the
solvent, respectively. The FT-IR spectra were recorded as thin solid
layers using an apparatus equipped with an ATR ‘‘diamond’’
apparatus. The steady-state emission and excitation spectra were
recorded with a spectrofluorimeter (Fluoromax-4 Horiba Jobin
Yvon). All fluorescence spectra were corrected. The following equa-
tion was used to determine the relative fluorescence quantum yield:
f(X) = (AS/AX)(FX/FS)(nX/nS)2f(S)
Compound 5. To a degassed solution of 3,6-bis(5-bromothien-2-
yl)-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione 4
(138.8 mg, 0.203 mmol) and [Pd(PPh3)2Cl2] (7.1 mg,
0.010 mmol) in benzene/Et3N (15 mL/5 mL) were added CuI
(3.1 mg, 0.016 mmol) and 1-dimethylamino-2-propyne (100 mL,
0.929 mmol, 4.5 equiv.). The reaction mixture was heated at
60 1C overnight. The concentrated residue was purified by
column chromatography on silica gel by eluting with CH2Cl2/
EtOH (gradient from 100 to 90/10) to give dye 5 (115.9 mg,
83%). 1H NMR (300 MHz, CDCl3), d (ppm): 0.85 (t, 6H, J =
7.4 Hz), 0.88 (t, 6H, J = 7.9 Hz), 1.18–1.40 (m, 16H), 1.81–1.90
(m, 2H), 2.39 (s, 12H), 3.55 (s, 4H), 3.97 (d, 2H, J = 7.4 Hz), 3.98
(d, 2H, J = 7.9 Hz), 7.28 (d, 2H, J = 4.1 Hz), 8.82 (d, 2H, J = 4.1 Hz);
13C NMR (75 MHz, CDCl3), d (ppm): 10.6, 14.1, 14.1, 23.2, 23.7,
28.5, 30.3, 39.3, 44.4, 46.2, 49.0, 78.4, 93.5, 108.9, 128.4, 130.2,
133.1, 135.5, 139.7, 161.7. ESI-MS in CH2Cl2 + 1% TFA, positive
mode, m/z (%): 687.3 (100). Anal. calcd C40H54N4O2S2: C, 69.93;
where A is the absorbance at the excitation wavelength (in the
range 0.01–0.1 a.u.), F is the area under the corrected emission
curve, n is the refractive index of the solvents (at 25 1C) used in
measurements, and the subscripts S and X represent standard
and unknown, respectively. The following standards were used:
Rhodamine 6G (Fem = 0.88 in ethanol) and Cresyl Violet (Fem
=
0.51 in ethanol) as the references.17 The luminescence lifetimes
were measured with a spectrofluorimeter equipped with a
R928 photomultiplier and a pulsed diode, connected to a delay
generator, without using any filter for excitation. The emission
wavelengths were selected by a monochromator. The lifetimes
were deconvoluted with the adequate software, using a light-
scattering solution (LUDOX) for the instrument response.
Syntheses
Compound 2. To a degassed solution of 2,5-dibenzyl-3,6-bis- H, 7.92; N, 8.16%. Found: C, 69.74; H, 7.62; N, 7.85%.
(4-bromophenyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione 1 (220.0 mg, Compound 6. As described earlier, reaction of 1,3-propanesultone
0.35 mmol) and [Pd(PPh3)2Cl2] (25.0 mg, 0.04 mmol, 0.1 equiv.) in (300 mL, 3.419 mmol, 20.0 equiv.) with dye 5 (116.0 mg, 0.169 mmol,
benzene/Et3N (22 mL/10 mL) were added CuI (10.0 mg, 0.05 mmol) 1.0 equiv.) in 1,2-dichloroethane (12 mL) at 80 1C for 2 days, followed
and 1-dimethylamino-2-propyne (114 mL, 1.06 mmol, 3.0 equiv.). by the usual isolation and chromatography (RP18 column, eluting
After heating the reaction mixture at 60 1C overnight, it was brought with H2O/THF + 1% TFA (H2O/THF = 8/2 to 7/3) afforded dye 6
to room temperature, filtered through a pad of Celite, and concen- (124.0 mg, 76%). 1H NMR (400 MHz, MeOD), d (ppm): 0.82–0.90 (m,
trated under reduced pressure. The resultant solid taken in CH2Cl2 12H), 1.19–1.34 (m, 16H), 1.71–1.77 (m, 2H), 2.28–2.34 (m, 4H),
(10 mL) was washed with aqueous saturated NaCl (20 mL) and then 2.94–2.97 (m, 4H), 3.29 (s, 12H), 3.73–3.78 (m, 4H), 3.90 (d, 4H, 3J =
extracted with CH2Cl2 (3 ꢁ 50 mL) and dried over MgSO4. After 7.2 Hz), 4.72 (s, 4H), 7.61 (d, 2H, 3J = 4.1 Hz), 8.64 (d, 2H, 3J = 4.1 Hz).
concentration in vacuo, the residue was purified by column chro- 13C NMR (100 MHz, MeOD), d (ppm): 10.9, 14.3, 14.4, 20.2, 23.7,
matography (silica gel, eluting with CH2Cl2 followed by 5–15% 24.0, 24.8, 26.7, 29.4, 29.5, 30.7, 31.2, 31.3, 33.0, 33.1, 35.4, 40.4, 43.1,
EtOH/CH2Cl2) to furnish dye 2 (174.0 mg, 78%). 1H NMR (400 44.5, 46.9, 51.3, 56.3, 58.7, 61.9, 64.5, 70.4, 72.3, 72.4, 84.9, 85.7, 85.7,
MHz, CDCl3), d (ppm): 2.37 (s, 12H), 3.49 (s, 4H), 4.99 (s, 4H), 110.4, 126.6, 133.3, 136.0, 136.1, 136.8, 140.7, 162.4. ESI-MS in H2O/
7.15–7.35 (8 line-m, 12H), 7.61 (AB sys, JAB = 7.6 Hz, nOd = 97.3 Hz, MeOH + 1% TFA, positive mode, m/z (%): 931.3 (100), 466.3 (15,
10H); 13C NMR (100.6 MHz, CDCl3), d (ppm): 14.2, 22.7, 24.9, 29.1, doubly charged). Anal. calcd for C46H66N4O8S4 + 2H2O: C, 57.12; H,
29.4, 29.7, 31.9, 44.1, 44.3, 45.8, 48.4, 48.7, 53.5, 63.4, 65.3, 69.7, 73.7, 7.29; N, 5.79%. Found: C, 56.89; H, 7.03; N, 5.56%.
84.9, 88.1, 110.1, 126.5, 126.7, 127.2, 127.5, 128.9, 129.0, 132.1, 137.3,
Lasing studies
148.3, 162.7. ESI-MS in CH2Cl2 + 1% TFA, positive mode, m/z (%):
630.2 (100), 573.2 (35). Anal. calcd for C42H38N4O2: C, 79.97; H, 6.07; The lasing study of dye 3 in MeOH/H2O (8/2) was carried out using a
N, 8.88. Found: C, 79.82; H, 5.79; N, 8.64%.
narrow-band dye laser set-up, transversely pumped by the second
Compound 3. To a stirred solution of dye 2 (89.0 mg, harmonic (at 532 nm) output of a Q-switched pulsed Nd:YAG laser at
0.14 mmol) in anhydrous 1,2-dichloroethane (20 mL) under a repetition rate of 10 Hz with B6 mJ pulse energy and 5–7 ns fwhm
argon was added 1,3-propanesultone (124 mL, 1.40 mmol). After pulses. A schematic of the dye laser setup is shown in Fig. 9. The dye
heating the reaction mixture at 60 1C for 15 h, it was brought to laser was set up in Littrow configuration (with a grating of 2400 lines
room temperature, centrifuged, and the precipitate was washed per mm) a with 25 ꢁ 4-prism pre-expander. The pump and dye laser
c
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NJC
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Fig. 9 Dye laser setup used for lasing experiments.
powers were measured by the same power meter (OPHIR). The dye
solution of 3 (O.D. = 0.66 at 532 nm, 1 mm cell) in MeOH/H2O (8/2,
v/v) was used to determine the lasing efficiency. The tuning curve of
the dye solution was obtained by scanning the wavelength of dye
laser through the gain profile of dye, and measuring the average
pump and dye laser powers with a power meter. For determining the
pump laser threshold (LT) and slope efficiency (Zs) of the dye
solution, the power of the dye laser, while tuning the laser wave-
length at the peak of the respective gain curves, was measured as a
function of input pump power at 532 nm.
Photostability studies
The photostability of dye 3 was measured from the change in its
lasing efficiency. For this, a MeOH/H2O (8/2, v/v) solution of dye
3 was exposed to the second harmonic of a Nd:YAG (532 nm)
laser for 4 h and the lasing efficiencies were measured at
different times (0–240 min).
Acknowledgements
We sincerely thank and acknowledge Dr A. K. Ray (BARC, India)
for his help during lasing experiments and Prof. S. Chattopad-
hyay (BARC, India) for his help in preparation of the manuscript.
The CNRS and ECPM are also acknowledged for providing,
respectively, financial support and research facilities.
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