Synthesis and use of clickable bay-region tetrasubstituted perylene tetracarboxylic tetraesters and a perylene monoimide diester as energy acceptors

Article abstract of DOI:10.1039/c4nj01565g

Two novel bay-region chlorine- or phenoxy-substituted perylene tetracarboxylic tetrapropargylesters (PTTEs) and a phenoxy-substituted perylene monoimide dipropargylester (PMIDE) were synthesized, photophysically characterized, and decorated with energy donating coumarin chromophores by means of microwave-assisted Cu(I)-catalyzed 1,3-dipolar cycloaddition reactions.

Full text of DOI:10.1039/c4nj01565g

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Synthesis and use of ‘‘clickable’’ bay-region
tetrasubstituted perylene tetracarboxylic
tetraesters and a perylene monoimide diester as
energy acceptors†
Cite this:DOI: 10.1039/c4nj01565g
Edanur Aydin, Bilal Nisanci, Murat Acar, Arif Dastan and O¨ zgur Altan Bozdemir*
¨
Received (in Montpellier, France)
11th September 2014,
Accepted 21st October 2014
Two novel bay-region chlorine- or phenoxy-substituted perylene tetracarboxylic tetrapropargylesters
(PTTEs) and a phenoxy-substituted perylene monoimide dipropargylester (PMIDE) were synthesized,
photophysically characterized, and decorated with energy donating coumarin chromophores by means
of microwave-assisted Cu(I)-catalyzed 1,3-dipolar cycloaddition reactions.
DOI: 10.1039/c4nj01565g
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be implemented for the fine tuning of device performances in novel
nanoelectronic devices.
Introduction
In recent years, perylene tetracarboxylic tetraesters (PTTEs),
The development of artificial systems capable of collecting
being close relatives of perylene bisimide (PBI) dyes, have and transferring light energy into suitable energy absorbing
attracted great attention among researchers on account of their sites continues to be the subject of a great number of research
high absorption coefficients in the visible region and their good activities pursuing the ultimate goals of mimicking nature’s
fluorescence properties.1,2 The much better solubility of bay- photosynthetic reaction centers and producing efficient solar
region-unsubstituted PTTEs in common organic solvents, compared energy concentrators.6 The efficient transfer of solar energy in
to that of similar PBIs, allows for facile purification and easy the form of electronic energy transfer (EET) can be accomplished
functionalization at the bay-region by means of bromination with systems consisting of rationally designed energy donor and
and nitration.1 Subsequent nucleophilic aromatic substitution energy acceptor chromophores. In this manner, dendrimers
or transition metal-catalyzed coupling reactions carried out on offer one of the most efficient synthetic structures for the
these derivatives have opened up novel pathways for the synthesis arrangement of energy donor chromophores around energy
of more extended aromatic structures.2 In addition to these types acceptors, so as to channel the light energy after its collection
of applications, their high propensity for self-aggregation into from a light source. To date, several light-harvesting dendrimers
one-dimensional supramolecular polymers and columnar liquid have been synthesized by exploiting well-known dye molecules,7
crystals has also been demonstrated.3 Currently used PTTE among which several members of the rylene dyes played important
derivatives bear one or two substituents at the bay-region2 and roles both as energy donors and acceptors.8 However, to the best of
more recently, a couple of derivatives with four chlorine atoms our knowledge, although there is an example for the use of perylene
were employed as intermediates en route to other perylene tetraesters in light-harvesting dendrimers,8g bay-region tetra-
structures.4 It is obvious that increasing the number of substituents substituted PTTE and PMIDE derivatives have never been
placed at the bay-region would be an important contribution to the considered as acceptor cores in dendritic energy transfer systems.
chemistry of this class of fluorescent dyes as it may lead to In this study, for the first time, two novel tetrasubstituted PTTE
improved photophysical properties. Another interesting structure derivatives and a PMIDE derivative with propargyloxy ester func-
possessing a perylene skeleton is the perylene monoimide diester tionalities were constructed to explore their behaviors as energy
(PMIDE).5 As the electron-withdrawing ability of these compounds acceptors in light-harvesting systems.
lies in between that of PBIs and PTTEs, they have the potential to
Results and discussion
Department of Chemistry, Ataturk University, Erzurum, 25240, Turkey.
In the construction of the target light harvesters, we employed a
E-mail: oaltanbozdemir@atauni.edu.tr
convergent approach to attach well-known 4-methyl-7-alkoxy-
† Electronic supplementary information (ESI) available: Experimental procedures,
characterization of new compounds, and spectra. See DOI: 10.1039/c4nj01565g
coumarin energy donor chromophores via microwave-assisted
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Cu(I)-catalyzed 1,3-dipolar cycloaddition, relying on the fact was reacted with a mixture of propargyl bromide and propargyl
that ‘‘click chemistry’’ has been one of the most reliable means alcohol in DMF at 60 1C for 4 h in the presence of DBU. After
for the synthesis of dendrimers.9 As shown in Scheme 1, our chromatographic purifications, perylene tetraphenoxy tetra-
synthetic studies commenced with the synthesis of the first propargyl ester 8 and perylene tetraphenoxy monoimide bis-
core energy acceptor molecule 1,6,7,12-tetrachloroperylene- propargyl ester 9 were obtained in 40% and 35% yield from 5,
3,4,9,10-tetracarboxylicpropargyl ester 4. 1,6,7,12-tetrachloro- respectively. Employing the same microwave-assisted alkyne-
perylenetetracarboxylic acid dianhydride 3 was reacted with a azide cycloaddition reaction, between compounds 2 and 8 or 2
mixture of propargyl bromide and propargyl alcohol in DMF at and 9, in the final step resulted in the formation of LH-2 and
60 1C in the presence of a strong base DBU, to synthesise 4. In LH-3. After chromatographic purification, each target molecule
the last step, this alkyne-functionalized PTTE 4 and compound was obtained in 90% and 95% yield, respectively.
2 were reacted in a microwave reactor using a solvent mixture
It should be noted that among the perylenetetracarboxylic
(1/1/2, H2O/EtOH/CHCl3) at 65 1C in the presence of sodium acid derivatives, PTTEs are the weakest electron acceptors as a
ascorbate and CuSO4 for 1 h, affording LH-1 in 90% yield after result of the poor orbital interactions between the ester carbonyls
chromatographic purification. To obtain our phenoxy substituted and the perylene ring, compared to the imide carbonyls of PBIs.
longer wavelength light-harvesting structures LH-2 and LH-3, PMIDEs, on the other hand, are stronger electron acceptors than
we first synthesized the tetraphenoxy-perylene bisimide 5 by PTTEs, while they are weaker than PBIs. Accordingly, absorption
following a literature procedure.3d A partial basic hydrolysis and emission wavelength maxima of these compounds follow the
reaction was then carried out in the presence of KOH in t-butanol at same trend; PTTEs being the shortest wavelength absorbers and
reflux temperature for 5 h.10 This reaction, after acidic work-up, emitters. One of the strategies frequently employed in order to shift
apart from the starting material resulted in the formation of the absorption and emission maxima of fluorescent dyes to the red
dianhydride 6 and monoimide-monoanhydride 7 as a mixture, end of the visible spectrum is to attach electron-donating function-
which was directly used in the next step without further alities at suitable positions in order to achieve maximum conjuga-
purification. Following the same protocol as above, this mixture tion. If we take the perylene-3,4:9,10-tetra(n-butoxy)tetracarboxylic
Scheme 1 Synthesis of the propargylated perylene derivatives and their conversion into light-harvesting systems LH-1, LH-2, and LH-3.
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acid tetraester 1 as the parent PTTE molecule (labs = 471 nm, of the peripheral chromophores at 315 nm is evident from the
lems = 516 nm) for our comparisons, it is obvious that adding near complete quenching of the coumarin centered fluorescence
substituents at the bay region would increase the solubility of at 378 nm, compared to the emission from the model compound
the resulting compounds and, depending on the electron- 2 with an equal absorption intensity (Fig. 1a). Also, a comparison
withdrawing or -releasing abilities of the substituents, would of the emission intensity of LH-1 at 499 nm with the PTTE 4 reveals a
alter the absorption and emission maxima of the PTTEs 10-fold increase, demonstrating a powerful antenna effect (Fig. 1a).
(Table 1). As expected, a hypsochromic shifting in the absorp- It should be noted here that this donor unit, with a quantum
tion and emission maxima for compound 4 (labs = 459 nm, yield of less than 1%, can be referred to as a ‘‘dark donor’’;
lems = 499 nm) was observed due to the presence of electron- however, when it is excited, the excitation energy is transferred to
withdrawing chlorine substituents, while a bathochromic shifting the acceptor faster than the other quenching pathways.11
was detected for 8 (labs = 492 nm, lems = 534 nm) due to the
Similar measurements were carried out for LH-2. In this
attachment of electron-releasing phenoxy substituents. For PMIDE 9, system, absorption features characteristic of 2 and PTTE 8 are
it is not surprising that the presence of only one imide group is observed in the absorption spectrum (ESI,† Fig. S2). The
sufficient to endow longer wavelength absorption and emission excitation of the coumarin part at 315 nm resulted in a strong
maxima (labs = 540 nm, lems = 572 nm) in comparison to PTTEs.
fluorescence, with nearly a 3.1-fold increase in the emission
In order to assess the efficiency of electronic energy transfer, intensity at 534 nm compared to the emission of the reference
several steady-state and time-resolved spectroscopic measure- dye PTTE 8, which was accompanied by a complete quenching
ments were carried out on each light-harvesting system (Table 1, of the coumarin part (Fig. 1b). This somewhat smaller increase
Fig. 1 and 2, and the ESI† Fig. S1–S6). The absorption spectrum in the acceptor emission is due to the presence of vibronic
of LH-1 appears as a summation of transitions emanating from transitions observed at higher energies in PTTE 8 and LH-2
coumarin 2 and PTTE 4 (ESI,† Fig. S1).
(300–350 nm region), leading to a relatively intense fluorescence
That an efficient electronic energy transfer takes place between emanating from the possibility of direct excitation of the PTTE
the coumarin donors and the PTTE acceptor unit upon excitation part in LH-2 at 315 nm.
Table 1 Photophysical data for the compoundsa
labs (nm)/emax
(Mꢀ1 cmꢀ1
J/1014
Compound
)
lems (nm)
t (ns)/lexc (nm)
w2
FF/lexc (nm)
Mꢀ1 cmꢀ1 nm4
Ro (nm)
E (%)
kT(r)/nsꢀ1
1
2
4
471 (32 410)
320 (10 968)
459 (18 587)
516
378
499
3.6 (457)
0.6 (337)
1.8 (457)
1.08
0.98
0.91
1.00b (450)
0.09c (315)
0.16b (450)
0.04c (315)
0.10c (315)
0.57b (496)
0.20c (315)
0.25c (315)
0.30b (496)
LH-1
8
459 (18 744)
492 (29 180)
499
534
1.5 (337)
5.7 (457)
0.95
1.05
1.86
2.54
1.73
2.46
2.54
2.43
90
93
87
16.4
22.0
11.4
LH-2
9
492 (29 265)
540 (20 853)
534
572
5.4 (337)
5.9 (500)
0.95
0.93
LH-3
540 (20 679)
572
5.4 (337)
1.01
0.10c (315)
a
All spectra were recorded as dilute solutions in CHCl3. labs/lems: maximum absorption/emission wavelengths. lexc: excitation wavelength.
¨
t: fluorescence lifetime. FF: fluorescence quantum yield. Ro: Forster distance. J: spectral overlap integral. E: energy transfer efficiency. kT(r):
energy transfer rate constant. 0.1 M aqueous fluorescein solution (FF = 0.95) was used as a reference. 0.5 M aqueous quinine sulfate solution
b
c
(FF = 0.55) was used as a reference.
Fig. 1 (a) Fluorescence emission spectra of compounds 2, 4 and LH-1 upon excitation at 315 nm in CHCl3. The concentrations of compounds 2 and 4
were adjusted so that they have equal absorbances at 320 nm and 459 nm to LH-1. (b) Fluorescence emission spectra of compounds 2, 8 and LH-2 upon
excitation at 315 nm in CHCl3. The concentrations of compounds 2 and 8 were adjusted so that they have equal absorbances at 320 nm and 492 nm to
LH-2. (c) Fluorescence emission spectra of compounds 2, 9 and LH-3 upon excitation at 315 nm in CHCl3. The concentrations of compounds 2 and 9
were adjusted so that they have equal absorbances at 320 nm and 540 nm to LH-3.
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Fig. 2 Absorption (black) and excitation (red) spectra of (a) LH-1, (b) LH-2, and (c) LH-3, normalized at the absorption maxima of the core acceptor units
(459 nm for LH-1, 492 nm for LH-2, and 540 nm for LH-3). The blue lines represent the efficiency of the percentage energy transfer as a function of the
excitation wavelength.
In LH-3, where only two donor coumarin units are present, between the donor and acceptor chromophores, ignoring the
the absorption spectrum is again a combination of transitions other common quenching pathways. In order to correctly
from the coumarin 2 and PMIDE 9 units, covering a broad determine the energy transfer efficiency, one has to compare
wavelength range stretching from nearly 600 nm to 200 nm the absorption and excitation spectra of the light-harvesting
(ESI,† Fig. S3). It is apparent that the excitation of LH-3 at system – normalized at the acceptor absorption wavelength
315 nm leads to an increased fluorescence at 572 nm as a result maximum – over the entire spectral range, in order to be sure
of an energy transfer, revealing itself as a 2.4-fold enhanced that the harvested photons by the donor are quantitatively
fluorescence compared to the emission intensity of the reference transferred to the acceptor unit. Indeed, this way of determining
dye PMIDE 9 at equal concentrations (Fig. 1c).
energy transfer efficiency has been proven more reliable by many
In order to investigate the likelihood of intermolecular energy researchers as it gives directly the ratio of the number of photons
transfer between the components of light-harvesters and to absorbed by the donor molecules to the number of excitations
confirm that the observed energy transfer is intramolecular in generated in the acceptor.12
nature, suitable donor–acceptor mixtures – representing each
When we applied this method to our light-harvesting systems,
light-harvester as a combination of separate entities – were in each case, we observed a poor match between the excitation –
prepared and subjected to the same spectroscopic measurements acquired for the respective acceptor emission maximum – and
(ESI,† Fig. S4–S6). Hence, the excitation of mixtures of donor and donor absorption regions of the spectrum (Fig. 2). In contrast to
acceptor molecules (2 and 4, 2 and 8, and 2 and 9) at the donor the values calculated by means of donor quantum yields and
absorption maximum (315 nm) revealed no intermolecular lifetimes, we determined 25%, 24%, and 13% efficiency of energy
energy transfer between individual chromophores, as evidenced transfer for LH-1, LH-2, and LH-3, respectively. Similar to the
by the low intensity of the acceptor emissions in each case and many other dendritic light-harvesters constructed by means of
the absence of coumarin quenching.
flexible bonding units,12b these low values must be due to the
Table 1 gives valuable photophysical parameters which can presence of various nonradiative quenching pathways in these
be used for estimation of the efficiency of energy transfer in conformationally flexible supramolecules, as we did not observe
all light-harvesting systems obtained in this study: acceptor any aggregation or photodecomposition in these systems after
emission lifetimes (t) and fluorescence quantum yields (FF) several fluorescence measurements. Nevertheless, up to 10-fold
increase compared to each acceptor model compound when fluorescence intensity increments in the presence of coumarin
excited at the donor site (315 nm), whereas donor lifetimes and donor groups can safely be regarded as a sign of an efficient
quantum yields decrease to nearly zero, indicating an electronic transfer of energy within these light-harvesters.
energy transfer. The fluorescence decays of LH-1, LH-2, and
LH-3 (ESI,† Fig. S19–S26) were found to be single-exponential with w2
¨
values smaller than 1.2, as a sign of good fit. The Forster radii (Ro)
Conclusions
determined for all compounds are very close to each other as
predicted from their structural similarity. Due to the close proximity In summary, we have demonstrated here that bay-region tetra-
of donor and acceptor units, fast energy transfer rates (k(r)) were substituted perylene tetraester and perylene monoimide diester
calculated based on the fluorescence intensity data for LH-1, LH-2, derivatives can be prepared with reactive ester functionalities
and LH-3, and the values are 1.64 ꢁ 1010
s
ꢀ1, 2.20 ꢁ 1010
s
ꢀ1, and which are ready to be exploited in the construction of various
1.14 ꢁ 1010
s
ꢀ1, respectively. The energy transfer efficiencies were functional supramolecular systems, such as light-harvesting
then calculated as 90% for LH-1, 93% for LH-2, and 87% for LH-3. dendrimers or biolabels, by employing fast, microwave-assisted
One of the possible pitfalls of using donor quantum yields click chemistry. As evaluated by various spectroscopic techniques,
and lifetimes in calculating energy transfer efficiencies is the excitation energy can be channeled into these novel dyes when they
preassumption that the changes in these values are merely take part in light-harvesting systems and they have the potential to
related to the intramolecular energy transfer taking place be used as donor sites if suitable donor–acceptor combinations are
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designed. Additionally, self aggregation abilities and liquid crystal- refractive index of the medium, r is the distance between the
linity properties are other important features of these derivatives, donor and acceptor, and tD is the lifetime of the donor in the
on which work by ourselves is in progress.
absence of the acceptor. K2 is usually assumed to be equal to 2/3.
The overlap integral (J(l)) expresses the degree of spectral overlap
between the donor emission and the acceptor absorption, kT(r) is
the rate of energy transfer from donor to acceptor.
Experimental
General
Syntheses
Compounds 213 and 314 were synthesized following procedures
reported in the literature. All chemicals and solvents were purchased
from Sigma-Aldrich and used without further purification. All
solvents were dried and distilled before use. Reactions were
monitored by thin layer chromatography using Merck TLC Silica
gel 60 F254 and the plates were inspected using 254 nm UV-light
Synthesis of compound 4. 1,8-Diazabicyclo[5,4,0]undec-7-ene
(114 mL, 0.76 mmol) and propargyl alcohol (88 mL, 1.52 mmol)
were added to a stirred solution of 3 (100 mg, 0.19 mmol) in
DMF (3.5 mL) at 60 1C and the resulting mixture was stirred for
30 min. Then, a solution of propargyl bromide (80% in toluene,
115 mL, 1.52 mmol) in DMF (0.5 mL) was added dropwise and the
solution was stirred for 3 h at the same temperature. After the
completion of the reaction, the crude product was precipitated
in water (50 mL) and the solid was filtered out using a G4 glass
filter. The solid obtained was dissolved in CH2Cl2 (30 mL) and
washed with water (2 ꢁ 10 mL) and brine. The organic phase was
dried over Na2SO4 and concentrated in vacuo. The residue was
purified by thin layer chromatography (TLC) with CH2Cl2 to
1
and/or by acquiring H-NMR spectra. Column chromatography
was performed over Merck Silica gel 60F (70–230 mesh ASTM).
The 1H- and 13C-NMR spectra were recorded on a Varian-400 or a
Bruker-400 spectrometer in CDCl3 using tetramethylsilane as the
internal reference. All spectra were recorded at 25 1C and
coupling constants ( J values) are given in Hz. Chemical shifts
are given in parts per million (ppm). Abbreviations used to
define the multiplicities are as follows: s = singlet; d = doublet;
t = triplet; q = quartet; hept = heptet; m = multiplet; br = broad.
Mass spectra were recorded on an Agilent Technologies 6530
Accurate-Mass Q-TOF LC/MS. Microwave reactions were per-
formed in a CEM Discover LabMate 200W microwave reactor.
Absorption spectrometry was performed using a Shimadzu
spectrophotometer. Steady-state fluorescence measurements
were conducted using a Shimadzu RF-5301PC spectrofluorom-
eter. Fluorescence decays for the lifetime measurements were
carried out by means of a LaserStrobe Model TM-3 lifetime
fluorophotometer from Photon Technology International (PTI).
Photophysical calculations. Quantum yield measurements
and calculations were performed using fluorescein (FF = 0.95,
0.1 M aqueous solution) and quinine sulfate (FF = 0.55, 0.5 M
aqueous solution) as standard dyes. The following formula was
used for the calculations:
1
afford 4 as a yellow solid (91 mg, 0.13 mmol, 65%). H NMR
(400 MHz, CDCl3, 298 K): d = 8.20 (s, 4H), 5.04–4.99 (m, A part of
the AB system, 4H), 4.97 (dd, B part of the AB system, J = 15.6,
2.4 Hz, 4H), 2.61 (t, J = 2.4 Hz, 4H). 13C NMR (101 MHz, CDCl3,
298 K): d = 166.2, 134.1, 133.0 (2C), 129.5, 127.8, 123.3, 76.9, 76.3,
53.8. HR-ESI-MS: m/z calcd: 715.9599; found: 715.9590.
Synthesis of LH-1. Compound 4 (50 mg, 0.07 mmol), 2 (134 mg,
0.55 mmol), CuSO4ꢂ5H2O (17 mg, 0.07 mmol) and sodium ascorbate
(7.4 mg, 0.04 mmol) were dissolved in a solvent mixture of CHCl3
(2 mL)/EtOH (1 mL)/H2O (1 mL) in a microwave reaction vial.
The reaction mixture was stirred under microwave irradiation at
65 1C for 1 h. The reaction was cooled to room temperature and
the solvent was removed under reduced pressure. The residue
was purified by thin layer chromatography (TLC) (7% MeOH/
CH2Cl2) to afford LH-1 as a yellow solid (105 mg, 0.07 mmol,
1
ꢀ
ꢁꢀ ꢁꢀ
ꢁ
90%). H NMR (400 MHz, CDCl3, 298 K): d = 8.10 (s, 4H), 8.05
R
I
n2
1 ꢀ 10OD
F ¼ FR
(s, 4H), 7.42 (d, J = 8.7 Hz, 4H), 6.82–6.76 (m, 8H), 6.08 (s, 4H),
5.48 (d, A part of the AB system, J = 12.7 Hz, 4H), 5.44 (d, B part of
the AB system, J = 12.7 Hz, 4H), 4.85 (t, J = 5.0 Hz, 8H), 4.45
(t, J = 5.0 Hz, 8H), 2.31 (s, 12H). 13C NMR (101 MHz, CDCl3, 298 K):
d = 166.4, 160.9, 160.5, 155.0, 152.3, 142.1, 133.6, 132.6, 129.7,
127.3, 126.0, 125.6, 122.9, 114.3, 112.4, 112.0, 101.8, 66.6, 59.2, 49.6,
18.6. HR-ESI-MS: m/z calcd: 1696.2801; found: 1696.2784.
2
IR
nR
1 ꢀ 10OD
where F is the fluorescence quantum yield, I is the integrated
fluorescence intensity, n is the refractive index of the solvent,
and OD is the optical density (absorption). The subscript R
refers to the reference fluorophore of known quantum yield.
¨
The Forster distances (Ro), energy transfer efficiencies (E),
Syntheses of compounds 8 and 9. A solution of KOH (4.8 g,
85.5 mmol) in H2O (2 mL) was added dropwise to a stirred
solution of compound 5 (480 mg, 0.44 mmol) in isopropanol
(30 mL) and the resulting mixture was stirred at 85 1C for 5 h.
The dark green reaction mixture was cooled to room tempera-
ture and glacial acetic acid (50 mL) was added. The mixture was
stirred for an additional 1 h at 50 1C. The crude product was
precipitated in water (50 mL) and the solid was collected using a
G4 glass filter, washed with water (3 ꢁ 10 mL) and dissolved in
CH2Cl2 (30 mL). The organic phase was dried over Na2SO4 and
and energy transfer rate constants (kT(r)) were calculated using
the formulae below:15
Ro = 0.211(K2nꢀ4FD J(l))1/6 (in Å)
6
FDA
FD
Ro
6
E ¼ 1 ꢀ
¼
Ro þ r6
ꢀ
ꢁ
6
1
Ro
r
kTðrÞ ¼
tD
¨
where Ro stands for the Forster distance, FD is the quantum concentrated in vacuo. This product was used in the next step
yield of the donor in the absence of the acceptor, n is the without further purification. 1,8-Diazabicyclo[5,4,0]undec-7-ene
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(299 mL, 2.00 mmol) and propargyl alcohol (230 mL, 4.00 mmol) (s, 2H), 7.85 (s, 2H), 7.63 (s, 2H), 7.37 (d, J = 8.2 Hz, 2H), 7.33 (t, J = 8.0
were added to a stirred solution of the above product mixture Hz, 1H), 7.19–7.14 (m, 8H), 7.02–6.98 (m, 4H), 6.83 (d, J = 8.5 Hz, 8H),
(430 mg) in DMF (7 mL) at 60 1C. After stirring for 30 min at 6.73–6.71 (m, 4H), 6.05 (s, 2H), 5.25 (s, 4H), 4.71 (t, J = 5.0 Hz, 4H),
60 1C, a solution of propargyl bromide (80% in toluene, 303 mL, 4.36 (t, J = 5.0 Hz, 4H), 2.60 (m, 2H), 2.28 (s, 6H), 1.03 (d, J = 6.5 Hz,
4.00 mmol) in DMF (1 mL) was added and the reaction mixture 12H). 13C NMR (101 MHz, CDCl3, 298 K): d = 167.5, 163.2, 160.9,
was stirred for 3 h at the same temperature. The crude product 160.6, 155.4, 155.0, 154.2, 152.3, 145.6, 142.5, 135.4, 133.1, 130.7,
was precipitated in water (150 mL) and the solid was filtered out 130.1, 129.9, 129.8, 129.3, 125.8, 125.2, 124.3, 124.26, 123.8, 122.2,
using a G4 glass filter. The solid residue was washed with water 121.0, 120.6, 120.2, 119.7 (2C), 119.5, 118.4, 114.3, 112.5, 112.1,
(3 ꢁ 10 mL), dissolved in CH2Cl2 (50 mL) and the organic phase 101.8, 66.6, 58.8, 49.5, 29.7, 29.0, 24.0, 18.6. HR-ESI-MS: m/z calcd for
was dried over Na2SO4 before being concentrated in vacuo. The [M + H+]: 1504.4801; found: 1504.4898.
residue was purified by column chromatography (SiO2/CH2Cl2 :
Hexanes: 60 : 40). The first fraction was compound 9 (158 mg,
0.154 mmol, 35%). H NMR (400 MHz, CDCl3, 298 K): d = 8.15
1
Acknowledgements
(s, 2H), 7.66 (s, 2H), 7.35 (t, J = 7.8 Hz, 1H), 7.23–7.15 (m, 10H),
The authors would like to thank the Ataturk University Research
7.06–6.98 (m, 4H), 6.88–6.85 (m, 8H), 4.79–4.78 (m, 4H), 2.62
Fund for its support of this project (2011/375).
(hept, J = 6.8 Hz, 2H), 2.41 (t, J = 2.5 Hz, 2H), 1.03 (d, J = 6.7 Hz,
12H). 13C NMR (101 MHz, CDCl3 298 K): d = 166.9, 163.3, 155.4,
155.3, 155.1, 154.3, 145.6, 135.4, 133.1, 130.9, 130.7, 129.9, 129.8,
129.6, 129.4, 128.8, 124.33, 124.31, 123.8, 122.2, 121.1, 121.0,
References
120.6, 119.8, 119.7, 118.4, 77.1, 75.5, 53.0, 29.0, 24.0. HR-ESI-MS:
m/z calcd: 1013.3200; found: 1013.3237. The second fraction was
compound 8 (180 mg, 0.19 mmol, 40%). 1H NMR (400 MHz,
CDCl3, 298 K): d = 7.69 (s, 4H), 7.27–7.23 (m, 8H), 7.08 (t, J =
7.4 Hz, 4H), 6.91–6.88 (m, 8H), 4.85–4.83 (m, 8H), 2.46 (t, J =
2.4 Hz, 4H). 13C NMR (101 MHz, CDCl3 298 K): d = 167.2, 155.7,
153.7, 135.7, 131.1, 130.0, 129.0, 124.3, 121.5, 119.9, 118.9, 77.4,
75.6, 53.1. HR-ESI-MS: m/z calcd: 948.2207; found: 948.2255.
Synthesis of LH-2. Compound 8 (16 mg, 0.017 mmol), 2
(32.5 mg, 0.13 mmol), CuSO4ꢂ5H2O (4.2 mg, 0.017 mmol) and
sodium ascorbate (3 mg, 0.015 mmol) were dissolved in the
mixture of solvents CHCl3 (2 mL)/EtOH (1 mL)/H2O (1 mL) in a
microwave reaction vial and the reaction mixture was stirred
under microwave irradiation at 65 1C for 1 h. Then the reaction
mixture was cooled to room temperature, the solvent was
removed under reduced pressure and the residue was purified
by thin layer chromatography (TLC) (6% MeOH/CH2Cl2) to
afford dendrimer LH-2 as a yellow solid (29 mg, 0.015 mmol,
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1
90%). H NMR (400 MHz, CDCl3, 298 K): d = 7.90 (s, 4H), 7.62
(s, 4H), 7.40–7.36 (m, 4H), 7.20–7.16 (m, 4H), 7.04–7.00 (m, 4H),
6.80 (d, J = 7.7 Hz, 8H), 6.76–6.73 (m, 8H), 6.07 (d, J = 1.1 Hz,
1H), 5.29 (s, 8H), 4.76 (t, J = 5.1 Hz, 8H), 4.40 (t, J = 5.1 Hz, 8H),
2.29 (d, J = 1.1 Hz, 12H). 13C NMR (101 MHz, CDCl3, 298 K): d =
167.5, 160.9, 160.5, 155.5, 154.9, 153.3, 152.3, 142.5, 135.3,
129.7, 129.2, 125.7, 125.2, 124.0, 121.3, 119.4, 119.2, 118.5,
114.2, 112.4, 112.2, 101.7, 66.5, 58.7, 49.4, 18.6. HR-ESI-MS:
m/z calcd: 1928.5408; found: 1928.5458.
Synthesis of LH-3. Compound 9 (14 mg, 0.014 mmol), 2
(13 mg, 0.054 mmol), CuSO4ꢂ5H2O (1.7 mg, 0.007 mmol) and
sodium ascorbate (1.2 mg, 0.006 mmol) were dissolved in the
mixture of solvents CHCl3 (2 mL)/EtOH (1 mL)/H2O (1 mL) in a
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was complete, the solvent was removed under reduced pressure and
the residue was purified by thin layer chromatography (TLC) (4%
MeOH/CH2Cl2) to afford dendrimer LH-3 as a pink solid (20 mg,
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1
0.013 mmol, 95%). H NMR (400 MHz, CDCl3, 298 K): d = 8.12
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