Synthesis and spectroscopic properties of arene-substituted pyrene derivatives as model compounds for fluorescent polarity probes

Article abstract of DOI:10.1002/1099-0690(200110)2001:20<3819::AID-EJOC3819>3.0.CO;2-W

In this paper, the syntheses of a variety of substituted phenyl pyrenes 5a-n by Suzuki cross-coupling and of two decoupled analogues 10 and 17 are reported. These compounds have been investigated by fluorescence spectroscopy. The solvatochromism of their emission bands (Stokes shift) and the quantum yields in methylcyclohexane and acetonitrile have been determined. Furthermore, the crystal structure of a pyrenyl-tris(2,2′-bipyridine)ruthenium(II) complex 19 is presented.

Full text of DOI:10.1002/1099-0690(200110)2001:20<3819::AID-EJOC3819>3.0.CO;2-W

FULL PAPER
Synthesis and Spectroscopic Properties of Arene-Substituted Pyrene
Derivatives as Model Compounds for Fluorescent Polarity Probes
Matthias Beinhoff,[a] Wilfried Weigel,[b] Martin Jurczok,[b] Wolfgang Rettig,*[b]
Claudia Modrakowski,[a] Irene Brüdgam,[a] Hans Hartl,[a] and A. Dieter Schlüter*[a]
Keywords: Cross-coupling / Pyrene / Fluorescent polarity probes / Solvatochromism
In this paper, the syntheses of a variety of substituted phenyl
pyrenes 5a−n by Suzuki cross-coupling and of two decoupled
quantum yields in methylcyclohexane and acetonitrile have
been determined. Furthermore, the crystal structure of a pyr-
analogues 10 and 17 are reported. These compounds have enyl-tris(2,2Ј-bipyridine)ruthenium(II) complex 19 is pre-
been investigated by fluorescence spectroscopy. The solva- sented.
tochromism of their emission bands (Stokes shift) and the
Introduction
comparison with the dendrimer skeleton, our concept in-
volves so-called volume dummies, which are incorporated
The ultimate goal of this long-term project is to synthe- into those generations not bearing the probes in order to
size spherical dendrimers,[1Ϫ5] in which photoinduced dir- maintain the same steric and chemical microenvironment at
ected charge transfer[6Ϫ9] can take place from the interior each generation.[31]
to the exterior along the dendritic wedges. The intention is
Herein, we describe the synthesis of a series of 1-pyrenyl
to create systems with a relatively long lifetime of the arenes as well as of two model compounds for use as vol-
charge-separated photoexcited state to mimic charge-sep- ume dummies and report their spectroscopic properties in
aration processes in biological photosystems.[10,11] If an a homogeneous solvent environment. As yet, they do not
electron donor is chosen as the core and the dendritic bear functional groups for dendrimer synthesis but are sup-
wedges are equipped with electron acceptors at defined po- posed to serve as model compounds for the rational design
sitions (generations), several electron-transfer (ET) steps of optimized fluorescent polarity probes and dummy build-
should be possible relaying the electron from acceptor to ing blocks to be used in the synthesis of the target dendri-
acceptor, akin to the multi-step ET involved in photosyn- mers.[32]
thesis, provided that there is a free-energy gradient to pro-
vide the necessary driving force.[12Ϫ15] This gradient could
Results and Discussion
be based on polarity. The first step is to clarify whether it is
possible to generate and quantify a solvent-induced polarity
gradient either by structural modifications[16] or by ex-
ploiting position-dependent solvation. If the density gradi-
ent of a dendrimer decreases on going from its interior to
its exterior, as SANS measurements[17] and computational
studies[18,19] have indicated for certain systems, local polar-
ity created by the penetration of polar solvent molecules
would be expected to increase in this direction.[20Ϫ22] This
effect might be quantified by analyzing the fluorescence of
site-specifically incorporated polarity probes based on
solvatochromism.[23,24Ϫ28] In this project, acceptor-substi-
tuted pyrene derivatives that are covalently bound at spe-
cific generations of the dendrimer are employed as fluores-
cence probes.[29,30] Due to the bulkiness of the probes in
Pyrene was chosen as the basic fluorophore because of
its well-documented photochemistry[33] and the ready ac-
cessibility of suitable derivatives. Moreover, the fluorescence
maxima of certain pyrene derivatives show large solvato-
chromic effects,[34Ϫ36] which is an important prerequisite for
site-resolved probing of the local polarity in the interior of
a dendrimer.
A series of pyrenes with the general structure 5
(Scheme 1) was prepared and the photoexcited-state prop-
erties were investigated in methylcyclohexane and acetoni-
trile. Compounds 5 consist of two parts, namely the pyrene
donor and the substituted phenyl group in the 1-position,
which serves as an electron acceptor; this renders the pyrene
a highly polarity-sensitive probe. The electron acceptor be-
ars electron-withdrawing groups of different strengths (R1)
(Table 1). The nature of the electron-withdrawing group was
varied to ascertain which of them gave the largest solva-
tochromic effect. Additional substituents R2 and R3 in the
ortho-positions of the phenyl ring can be expected to influ-
ence the phenyl/pyrenyl rotational barrier due to their steric
demand and thus the accessibility of the charge-separated
[a]
Freie Universität Berlin, Institut für Chemie,
Takustrasse 3, 14195 Berlin, Germany
Fax: (internat.) ϩ49 (0)30/8385 3357
E-mail: adschlue@chemie.fu-berlin.de
[b]
Humboldt Universität zu Berlin, Institut für Physikalische und
Theoretische Chemie,
Bunsenstrasse 1, 10117 Berlin, Germany
Fax: (internat.) ϩ49 (0)30/2093 5574
E-mail: rettig@chemie.hu-berlin.de
Eur. J. Org. Chem. 2001, 3819Ϫ3829
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ193X/01/1020Ϫ3819 $ 17.50ϩ.50/0
3819

W. Rettig, A. D. Schlüter et al.
FULL PAPER
Scheme 1. (a) 1. nBuLi, Et2O, Ϫ78 °C, 30 min, 2. (iPrO)3B, Ϫ78 °C to room temp., 3. Hϩ/H2O; (b) pinacol, 40 °C, 45 min; (c) Pd(PPh3)4,
toluene, 1  Na2CO3, reflux, 16Ϫ20 h
state (Table 1). A few examples with electron-donating sub- quantum correlation (HMQC) NMR. The 2-H and 10-H
stituents on the phenyl ring were also synthesized. Com- protons absorb at δ ϭ 8.7 and 9.2, respectively, which is
pounds 10 and 17 (Schemes 3 and 4) differ from 5b only by remarkably downfield shifted and typical of aryl protons in
a methylene and an ethylene spacer unit, respectively, be- the vicinity of a boronic ester function. The pinacol ester 3
tween the donor and acceptor and were prepared and in- can be stored for months on the laboratory bench without
vestigated as potential volume dummies.
any change, as verified by HPLC.
With the exception of 4e,[46] the bromoarenes 4aϪo used
for the coupling reactions with 3 were either purchased
(4aϪd, 4f, 4h؊k) or were prepared according to literature
procedures. Compound 4e was synthesized according to the
sequence shown in Scheme 2. The product of the regioselec-
tive lithiation of the dibromoxylene 6 at C-5[47] with butyl-
lithium in diethyl ether at Ϫ78 °C was formylated with di-
methylformamide (DMF)[48] to produce the benzaldehyde
7. Reaction of 7 with hydroxylamine and subsequent ther-
mally induced dehydration gave benzonitrile 4e in 39%
yield.[49] Accompanying amounts of non-dehydrated oxime
8 were removed by column chromatography and identified
by NMR spectroscopy and mass spectrometry. The yield of
4e could be increased to 81% by dehydration of 8 to 4e with
carbon disulfide in the presence of aqueous sodium hydrox-
ide.[50]
Synthesis
The most common procedure for aryl/aryl couplings at
the 1-position of pyrenes is the Gomberg reaction of di-
azonium arenes with pyrene.[36Ϫ38] The products are formed
in low yields (5 to 20%) and are accompanied by regioiso-
mers. Suzuki cross-coupling (SCC),[39,40] as the presently
most efficient and widely applicable aryl/aryl coupling reac-
tion, was employed as the key reaction for the coupling of
the donor and acceptor parts of 5. There have only been
two previous reports of the application of SCC to this syn-
thesis.[41,42]
Borylation of the commercially available 1-bromopyrene
1 and subsequent esterification of the crude free boronic
acid 2 with pinacol gave the boronic ester 3 in 80% yield
based on 1 (Scheme 1). Compound 3 was prepared on a
25 g scale. The intermediate free acid 2[41Ϫ45] was not usu-
SCC reactions yielding 5aϪo (Scheme 1) were carried out
ally isolated due to its low solubility, but it was character- under standard conditions using an equimolar ratio of the
ized by NMR spectroscopy and mass spectrometry. All sig- substrates in a heterogeneous solvent system of toluene and
1
nals in the H and 13C NMR spectra of 3 could be unam- 1  aq. Na2CO3 using 2 mol % Pd(PPh3)4 as the catalyst
biguously assigned by applying heteronuclear multiple precursor. The yields and selected spectroscopic data of
3820
Eur. J. Org. Chem. 2001, 3819Ϫ3829

Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes
FULL PAPER
Scheme 2. (a) 1. nBuLi, Et2O, Ϫ78 °C, 30 min, 2. DMF; (b) hydrox-
ylamine hydrochloride, pyridine, toluene, reflux, 2 h; (c) CS2, 3 
NaOH, (nBu)4NHSO4, room temp., 20 h
compounds 5aϪo are summarized in Table 1. The coupling
is sensitive to the substituents R2 and R3 of 4. The greater
the steric demand, the lower the yield. In the case of the
cyano-substituted arenes 5b,d,e, the isolated yields decrease
from 87% (5b) for the unsubstituted para-benzonitrile deriv-
ative to 53% (5d) in the presence of one methyl group in
the position ortho to the bromo function, and decrease fur-
ther to 28% (5e) with a second ortho-methyl group. The
Scheme 3. (a) 4-(Bromomethyl)benzonitrile, AlCl3, CS2; (b) 4-cy-
anobenzoyl chloride, AlCl3, CS2, reflux; (c) 4-bromobenzoyl chlo-
ride, AlCl3, CS2, reflux; (d) NaBH4, AlCl3, THF, reflux, 90 min;
(e) CuCN, DMF, reflux
bulkiness of the pyrene moiety is considered as a possible serted between the donor and acceptor (Scheme 3 and
explanation.[51]
Scheme 4). FriedelϪCrafts alkylation of pyrene 9 with p-
Since benzonitrile 5b was found to be a suitable polarity (bromomethyl)benzonitrile gave a mixture of the regioiso-
probe (see next section), two potential volume dummies 10 mers 10 and 11 in low yield (Scheme 3), from which 10
and 17 were synthesized that also bear the nitrile function could be obtained in analytically pure form. This route was
but differ from 5b by a methylene or ethylene bridge in- nevertheless considered unsatisfactory because of the tedi-
Table 1. Chemical yields, UV absorption, and fluorescence data for the pyrenyl arene derivatives 5aϪo in methylcyclohexane (MCH) and
acetonitrile (AN)
No.[a] R1
R2
R3
yield[b] λabs [nm][c]
λfl [nm]
MCH
∆νSt [cmϪ1 [d]
MCH AN
]
∆γ∆νSt
Φfl
[e]
(%)
MCH
AN
AN
[cmϪ1
]
MCH
AN
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
H
CN
H
CN
CN
CO2Et
CO2Et Me
COMe
NO2
CF3
OMe
OMe
H
H
H
Me
H
H
83
87
342
343
343
342
342
342
342
343
342
344
342
342
342
342
342
343
380, 400 381, 398 3599
3566
5651
4670
4302
3467
5655
4177
7462
4701
3955
3955
3566
3592
4824
6137
Ϫ33
1591
1026
1070
0
1604
1081
1837
1611
96
161
33
13
1050
1697
0.41
0.69
0.21
0.08
0.042
0.49
0.07
0.58
0.81
0.34
0.29
0.072
0.76
0.24
391, 406 427
383, 401 407
381, 388 401
4060
3644
3232
CN 66
H 53
Me Me 28
H
378, 389 378, 389 3467
H
H
H
H
H
H
H
88
46
87
78
85
89
58
390, 404 424
388, 397 399
4051
3096
5625
3090
H
H
H
H
425
461
0.011[f][g] 0.58[g]
342, 356[h] 340, 357[h] 392, 408 429
0.006
0.11
0.17
0.09
0.14
0.38
Ϫ
0.002
0.21
0.32
0.14
0.20
0.66
Ϫ
342
342
342
343
343
344
342
342
342
344
343
344
387, 401 389, 402 3859
383, 403 387, 404 3794
379, 399 380, 399 3533
381, 401 383, 402 3579
Me
OMe
Me Me 37
H
[i]
H
83
78
394
406
411
436
3774
4440
see Scheme 1[j]
[a]
[b]
[c]
Purity of all compounds Ն 99.5% according to HPLC analysis. Ϫ
Yields were not optimized. Ϫ
Only the long-wavelength
[d]
absorption maxima are given. Ϫ Stokes shifts (∆νSt) have been calculated from the maxima of absorption and fluorescence (the mean
value is taken in case of a vibrational structure). Ϫ [e] Fluorescence quantum yield. Ϫ In hexane. Ϫ [g] Ref.[17c]
Ϫ
Shoulder. Ϫ [i] 4,4-
[f]
[h]
Dimethyl-2-oxazoline. Ϫ Spectroscopic data of the corresponding Ru2ϩ complex 19: λabs ϭ 340 and 455 nm, λfl ϭ 642 nm in tetrahy-
[j]
drofuran.
Eur. J. Org. Chem. 2001, 3819Ϫ3829
3821

W. Rettig, A. D. Schlüter et al.
FULL PAPER
Scheme 4. (a) 1. Methyl triphenylphosphonium iodide, THF, 0 °C,
2. nBuLi, 3. 15; (b) 1. 9-BBN, THF, room temp., 8 h, 2. 4-bromo-
benzonitrile, Pd(PPh3)4, 1  Na2CO3, reflux, 16 h; (c) 1. (4-cyano-
benzyl)triphenylphosphonium bromide, KOtBu, THF, room temp.,
30 min, 2. 15, room temp., 2 h, then reflux, 20 h; (d) Mg, Pd/C, n-
propanol, reflux, 24 h
ous recrystallization procedure required. An attempt to ob-
tain 10 by reduction of the FriedelϪCrafts acylation prod-
uct 12 was unsuccessful. Only the corresponding alcohol
(not shown) was obtained. Even though the employed con-
ditions (WolffϪKishner and NaBH4/AlCl3[52]) have been re-
ported to have proved successful in similar cases, the strong
electron-withdrawing effect of the cyano group may hinder
the reduction.[53] Finally, 10 was synthesized in an overall
yield of 40% by FriedelϪCrafts acylation of the pyrene 9
with para-bromobenzoic acid chloride, reduction of the re-
sulting ketone 13[54] with NaBH4/AlCl3, and Rosen-
mundϪvon Braun cyanodehalogenation of 14 with CuCN
in DMF.[55,56]
The ethylene-bridged homologue 17 could be obtained
by two different methods (Scheme 4): (a) Hydroboration of
1-vinylpyrene 16[57,58] with 9-borabicyclo[3.3.1]nonane (9-
BBN) and subsequent SuzukiϪMiyaura coupling[59,60] with
para-bromobenzonitrile gave 17 in moderate yield; (b) Wit-
tig reaction of pyrene aldehyde 15 with the phosphonium
ylide of para-(bromomethyl)benzonitrile in the presence of
KOtBu in tetrahydrofuran gave the stilbene derivative 18 in
92% yield. Its hydrogenation to 17 proceeded quantitatively,
as determined by HPLC. However, in practice, the yield is
Figure 1. Structure and ORTEP[64] plot of the Λ-enantiomer of 19
RuII(bipy)2Cl2 yielded rac-[bis(2,2Ј-bipyridine){5-(pyren-1-
yl)-2,2Ј-bipyridine}ruthenium(II)]
bis(hexafluorophos-
phate) (19) in 83% yield (Figure 1). Suitable crystals of 19
were obtained by slow diffusion of methanol into a dichlor-
omethane solution. The X-ray structural analysis[63] was
carried out at 153 K and revealed that 19 crystallizes with
three molecules of dichloromethane per formula unit. Both
enantiomeric ∆- and Λ-isomers were found in the unit cell
(Figure 1).
UV Absorption and Fluorescence Measurements
The normalized absorption and fluorescence spectra of
reduced by the work-up procedure. Method (b) turned out some of the pyrenyl arenes are depicted in Figure 2. The
to be superior. It avoids the handling of 1-vinylpyrene with spectroscopic data are summarized in Table 1. The absorp-
its propensity to polymerize and allows scale-up to 25 g of tion spectra of all compounds show a single intense band
17.
with a maximum at around 340 nm and log ε values of
Bichromic pyreneϪruthenium(II)Ϫtris(2,2Ј-bipyridine) about 4.5. They resemble those of the parent phenyl pyrene
dyads have attracted some interest in recent years.[61,62] chromophore 5a, except that of 5i, which shows multiple
Some of these complexes show outstanding photophysical absorption bands and a red shift. The negligible solvato-
properties such as reverse triplet-triplet energy-transfer be- chromic shift of the absorption spectra with the solvent po-
2ϩ
tween the two partners. Ru(bipy)3 dyads with either one larity is consistent with a small difference between the di-
1-pyrenyl moiety at the 4-position of one bipy[61] or with pole moments of the FranckϪCondon (FC) excited state
one 1-ethynylpyrenyl moiety at the 5-position of a bipy have and the ground state and suggests a negligible degree of CT
been investigated in detail.[62] To contribute to this field we in the FC excited state, except in the case of 5i. In general,
additionally applied our coupling method to the synthesis the long-wavelength absorption band of the pyrenyl arenes
of 5-(pyren-1-yl)-2,2Ј-bipyridine (5o) (Scheme 1 and corresponds to the S0ϪS1 (π,π*) transition. In the case of
Table 1), the subsequent complexation of which with rac- the nitro derivative 5i, the involvement of a low-lying
3822
Eur. J. Org. Chem. 2001, 3819Ϫ3829

Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes
FULL PAPER
hindered compounds. However, the fluorescent charge-
transfer states in acetonitrile can be rationalized in terms
1
1
of a mixing of Lb and/or La with ET states in various
proportions. A detailed mechanistic study regarding the
properties of the photoexcited state and the kinetics of the
relaxation pathway is under investigation.
The quantum yield of the fluorescence is another import-
ant parameter in examining the ability of pyrenyl arenes to
act as fluorescent probes (Table 1). Moderate to high values
(0.1Ϫ0.8) have been determined for most of the pyrenyl ar-
enes, with larger values being recorded in acetonitrile than
in methylcyclohexane. The low values (Ͻ 0.1) measured for
5d, 5g, and 5l in methylcyclohexane and for 5e, 5i in both
solvents indicate a significant involvement of non-radiative
relaxation pathways.
In the dendrimers, the polarity probes will be applied in
combination with structurally related volume dummies to
maintain the overall structure of the dendrimers. The re-
quirement that the volume dummies should not absorb
light at the wavelengths at which the probe molecules are
excited can be achieved by decoupling the π-electron sys-
tems of the pyrene and arene moieties by introducing a
methylene or ethylene bridge between the two groups. An
example of a suitable combination of a polarity probe and
volume dummy is given by 5b and (4-cyanobenzyl)pyrene
Figure 2. UV absorption and fluorescence spectra of 5a, 5i, 5f, and
5k in methylcyclohexane (MCH) and acetonitrile (AN)
charge-transfer absorption band may be invoked to explain (10). Their UV absorption and fluorescence spectra (Fig-
the low-energy transition extending beyond 400 nm. ure 3) indicate that for wavelengths Ͼ 360 nm a selective
The fluorescence spectra in non-polar solvents such as excitation of the probe, irrespective of the solvent polarity,
methylcyclohexane show a maximum between 380 and should be possible. Corresponding results were obtained for
400 nm (Table 1). They are similar in appearance and in the ethylene-bridged derivative 17.
the position of the maximum to that of phenylpyrene 5a
(Figure 2). The fluorescence spectra are structured in
methylcyclohexane but lose their vibrational structure in
acetonitrile in the case of acceptor-substituted pyrenyl ar-
enes. Solvatochromic measurements were carried out in or-
der to investigate the change in the charge distribution be-
tween the FC and the equilibrated S1 states. The difference
between the energies of the absorption and fluorescence
maxima is given by the Stokes shifts (Table 1). With the
exception of those of 5a, 5j, and 5kϪ5m, the fluorescence
spectra are strongly red-shifted in the polar solvent aceto-
nitrile, i.e. a strong solvatochromic effect is observed with
increasing solvent polarity. It is deduced from these obser-
vations that by introducing an acceptor substituent on the
phenyl group a substantial charge transfer takes place after
excitation and geometrical relaxation of the molecules on
the excited-state surface.
For all the compounds (5cϪ5e, 5g, 5l, 5m) for which the
ground-state dihedral angle between the pyrene and the
phenyl moiety is increased by the introduction of ortho sub-
Figure 3. Comparison of the UV absorption and fluorescence spec-
tra of the cyano-functionalized polarity probe 5b and the corres-
stituents at the phenyl group, a decrease in the Stokes shifts
is observed with respect to the unhindered compound.
Therefore, it can be assumed that the pyrenyl arenes un-
dergo a flattening in the excited state and that the charge-
transfer state is stabilized by mesomeric interactions.
ponding volume dummy 10 in methylcyclohexane (MCH) and ace-
tonitrile (AN)
In the dendrimers, the UV and fluorescence spectra of
the probes and dummies will be superimposed. The ratio of
From the data presented here, no clear conclusion can be the number of probe molecules to the dummy chromoph-
drawn regarding the nature of the relaxation coordinate on ores depends on the number of generations and the struc-
the excited-state surface, especially for the sterically ture of the dendrimer. With increasing number of genera-
Eur. J. Org. Chem. 2001, 3819Ϫ3829
3823

W. Rettig, A. D. Schlüter et al.
FULL PAPER
Experimental Section
General: All chemicals for synthesis were purchased from Aldrich
or Acros Chimica and were used without further purification. Sev-
eral compounds were prepared according to literature procedures
and gave satisfactory NMR and MS data: 4g,[65] 4l,[66] 4m,[67,68]
4n,[69] 4o,[70,71] 6,[47] 13,[54] 15,[72] 16,[57] (4-cyanobenzyl)triphenyl-
phosphonium bromide.[73] Pd(PPh3)4 was prepared according to
ref.[74] and was used without further characterization. Compounds
5a,[75,76] 5h,[36] 5i,[37] 13,[54] and 18[73] are included in the Experi-
mental Section in view of the lack of spectroscopic data in the
literature. All other compounds are new (CAS-online January
2000). Diethyl ether and tetrahydrofuran were distilled from so-
dium/benzophenone ketyl or potassium/benzophenone ketyl; the
toluene used was of p.a. quality. All cross-coupling reactions were
carried out under oxygen-free conditions. Ϫ Melting points: Büchi
SMP 510 (open capillaries, uncorrected values). Ϫ NMR: Bruker
AC 250, AM 270, AMX 500 (1H: CDCl3 at δ ϭ 7.24, 13C: CDCl3
at δ ϭ 77.0 as internal standards, 20 °C). Ϫ MS: PerkinϪElmer
Varian MAT 711, electron-impact (EI) mode. Ϫ IR: Nicolet 5SXC
(FT-IR). Ϫ Elemental analyses: PerkinϪElmer EA 240. Ϫ Column
chromatography: Merck silica gel 60, 0.040Ϫ0.063 mm (230Ϫ400
mesh). Ϫ RP-HPLC: Macherey-Nagel, Nucleosil 7µm C18, UV
detection at 335 nm.
Figure 4. Excitation wavelength dependence of the fluorescence
spectra of a 1:14 mixture of 5b and 10 in acetonitrile, which repre-
sents a realistic ratio in a G4 dendron with the probe introduced
in the first generation; selective excitation of the probe is seen at
λ
exc Ͼ 360 nm
Spectrophotometric grade methylcyclohexane and acetonitrile were
used as solvents for the spectroscopic measurements. For the fluor-
escence measurements, the pyrenyl derivatives 5aϪo, 10, and 17
were purified by preparative HPLC to ensure purities of Ͼ 99.5%.
UV absorption spectra were measured on an ATI UNICAM UV
series UV-02113 spectrometer; fluorescence spectra were recorded
on an AMINCO-Bowman series 2 spectrofluorimeter. They were
tions this ratio will decrease, i.e. the number of the probes
will be considerably smaller than the number of volume
dummies. Figure 4 shows the fluorescence spectra of a mix-
ture of both components in a concentration ratio of 1:14 corrected for instrumental sensitivity. A solution of quinine bisul-
fate in 0.1  H2SO4 (Φf ϭ 0.52)[77] was employed as a standard for
the measurement of the fluorescence quantum yields.
(5b/10) to simulate a dendrimer of the fourth generation.
The fluorescence spectra were recorded with reference to
the excitation wavelength. The spectrum recorded at λexc
340 nm displays the fluorescence maxima of both the probe
and the dummy, whereas the spectra recorded at λexc
360 nm show exclusively the fluorescence spectrum of the
probe.
ϭ
4,4,5,5-Tetramethyl-2-pyren-1-yl-1,3,2-dioxaborolane (3): n-butylli-
thium (2.6 mL of a 1.6  solution in hexane, 4.16 mmol, 1.09
equiv.) was added dropwise. To a solution of 1-bromopyrene
(1.07 g, 3.81 mmol) in tetrahydrofuran (50 mL) at Ϫ78 °C. After
stirring for 30 min at this temperature, triisopropyl borate (1.75
mL, 7.58 mmol, 2.00 equiv.) was added and the solution was al-
lowed to warm to room temperature over a period of 30 min. Then,
5% hydrochloric acid (50 mL) was added, the layers were separated,
and the aqueous phase was extracted with diethyl ether (3 ϫ). The
combined organic phases were treated with 2,3-dimethyl-2,3-bu-
tanediol (pinacol) (1.46 g, 12.35 mmol, 3.24 equiv.) and the solu-
tion was stirred at 40 °C for 45 min until the reaction was complete,
as indicated by the disappearance of the free boronic acid upon
TLC analysis. After removal of the solvent in vacuo, the remaining
dark oil was chromatographed on silica gel (hexane/ethyl acetate,
20:1). Precipitation from dichloromethane/methanol gave 1.06 g
Ͼ
Conclusion
A variety of acceptor- and donor-substituted pyrene de-
rivatives have been synthesized using SCC as the key reac-
tion step. Investigation of their excited states in solvents of
different polarity has shown that, due to the combination
of a moderately strong solvatochromism and a high fluores-
cence quantum yield, the cyano and ester derivatives 5b and (85%) of 3 as a yellowish solid; m.p. 123 °C. Ϫ Rf ϭ 0.24 (hexane/
1
ethyl acetate, 20:1). Ϫ H NMR (500 MHz, CDCl3): δ ϭ 1.55 (s,
5f, respectively, should be especially suitable as fluorescent
probes to report the polarity of the surrounding medium.
Likewise, the volume dummies, i.e. the decoupled deriva-
tives 10 and 17 for the cyano series, should serve their pro-
posed function.
For future probe design, the introduction of additional
acceptor groups on the phenyl ring is envisaged as allowing
further improvement of the properties of these polarity
probes based on solvatochromism caused by charge transfer
in the excited state.
12 H, 12-H), 8.04 (t, J ϭ 7.6 Hz, 1 H, 7-H), 8.09 (d, 3J ϭ 8.8 Hz,
1 H, 4-H), 8.13 (d, J ϭ 8.8 Hz, 1 H, 5-H), 8.21 (d, J ϭ 7.6 Hz,
1 H, 6-H), 8.23 (d, J ϭ 9.0 Hz, 1 H, 9-H), 8.24 (d, J ϭ 7.6 Hz,
1 H, 3-H), 8.26 (d, J ϭ 7.6 Hz, 1 H, 8-H), 8.67 (d, J ϭ 7.6 Hz,
1 H, 2-H), 9.21 (d, 3J ϭ 9.0 Hz, 1 H, 10-H). Ϫ 13C NMR
(126 MHz, CDCl3): δ ϭ 25.0 (C-12), 83.8 (C-11), 124.0 (C-3), 124.3
(C-10b), 124.5 (C-10c), 125.1 (C-6), 125.3 (C-8), 125.6 (C-7), 127.4
(C-4), 127.7 (C-9), 128.0 (C-10), 128.5 (C-5), 130.7 (C-8a), 131.0
(C-5a), 133.4 (C-3a), 133.8 (C-2), 136.4 (C-10a). Ϫ MS (70 eV,
135°C): m/z (%) ϭ 328 (100) [M]ϩ, 313 (1), 270 (5), 255 (13), 228
3
3
3
3
3
3
3
3824
Eur. J. Org. Chem. 2001, 3819Ϫ3829

Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes
FULL PAPER
(56), 202 (7). Ϫ IR (KBr): ν˜ ϭ 3046 (w), 2970 (m), 2926 (w), 1347, solution (3 , 1 mL), toluene (3 mL), and tetra-n-butylammonium
1355, 1371, 1378, 1388 cmϪ1 [s, ArϪB(OH)2]. Ϫ C22H21BO2 hydrogen sulfate (0.14 g, 0.41 mmol). The mixture was stirred for
(328.21): calcd. C 80.51, H 6.45; found C 80.42, H 6.31.
20 h at room temperature. After extractive work-up with toluene,
the residue was chromatographed on silica gel (hexane/ethyl ace-
tate, 10:1). The product was precipitated from dichloromethane/
methanol to give 0.30 g (75%) of the benzonitrile 4e as colorless
crystals.
Pyren-1-ylboronic Acid (2): This compound was obtained by chro-
matographic separation (hexane/ethyl acetate, 20:1, then ethanol)
of the crude product after extractive work-up as described for 3,
followed by precipitation from ethanol; m.p. Ͼ 265 °C. Ϫ 1H NMR
(250 MHz, [D6]DMSO): δ ϭ 8.04 (t, 3J ϭ 7.5 Hz, 1 H, 7-H),
Typical Procedure for the Suzuki Cross-Coupling of 3 and 4a؊o
3
8.14Ϫ8.30 (m, 6 H), 8.35 (d, J ϭ 7.5 Hz, 1 H, 2-H), 8.66 [s, 2 H,
3,5-Dimethyl-4-pyren-1-yl-benzonitrile (5e): After degassing a mix-
ture of 3 (0.36 g, 1.10 mmol), 4e (0.23 g, 1.09 mmol), toluene (20
mL), and aqueous sodium hydroxide solution (1 , 10 mL), the
catalyst precursor Pd(PPh3)4 (25.4 mg, 2 mol%) was added and the
mixture was stirred under reflux for 20 h. The layers were then
separated, the aqueous phase was extracted with toluene (3 ϫ), the
combined organic phases were dried with MgSO4, and the solvent
was evaporated. The residue was purified by column chromatog-
raphy on silica gel (hexane/ethyl acetate, 20:1) to give 0.10 g (28%)
of 5e; m.p. 217Ϫ218 °C. Ϫ Rf ϭ 0.23 (hexane/ethyl acetate, 20:1).
B(OH)2], 8.79 (d, 3J ϭ 9.0 Hz, 1 H, 10-H). Ϫ 13C NMR (63 MHz,
[D6]DMSO): δ ϭ 123.1, 123.7, 124.1 (br), 125.0 (br), 126.0 (br),
126.9 (br), 127.6 (br), 128.6 (br), 130.5, 130.9, 131.5, 131.9 (br),
132.6 (br), 134.1. Ϫ MS (70 eV, 40 °C): m/z (%) ϭ 246 (33) [M]ϩ,
228 (21) [M Ϫ H2O]ϩ, 202 (18) [M Ϫ B(OH)2]ϩ. Ϫ HRMS: m/z
calcd. for C16H11BO2 246.08521; found 246.08921.
4-Bromo-3,5-dimethylbenzaldehyde (7): A solution of 2,5-dibrom-
oxylene 6 (1.90 g, 7.20 mmol) in diethyl ether (20 mL) was treated
with n-butyllithium (4.5 mL of a 1.6  solution in hexane, 1.0
equiv.) at Ϫ78 °C. After stirring for 45 min, N,N-dimethylformam-
ide (1.7 mL, 22.0 mmol, 3.06 equiv.) was added and the solution
was allowed to warm to room temperature. It was then acidified
with 5% hydrochloric acid and extracted with diethyl ether. The
residue obtained after standard work-up was chromatographed on
silica gel (hexane/ethyl acetate, 10:1) and crystallized from diethyl
ether to give 1.21 g (79%) of 7 as colorless crystals; m.p. 67 °C. Ϫ
Rf ϭ 0.49 (hexane/ethyl acetate, 6:1). Ϫ 1H NMR (250 MHz,
CDCl3): δ ϭ 2.46 (s, 6 H), 7.54 (s, 2 H), 9.91 (s, 1 H). Ϫ 13C NMR
(63 MHz, CDCl3): δ ϭ 23.8, 128.8, 132.5, 134.8, 139.5, 191.6. Ϫ
MS (80 eV, 30 °C): m/z (%) ϭ 214 (80) [C9H981BrO]ϩ, 212 (78)
[C9H979BrO]ϩ, 211 (100) [C9H879BrO]ϩ. Ϫ IR (KBr): ν˜ ϭ 1684
cmϪ1 (CO, vs). Ϫ C9H9BrO (213.07): calcd. C 50.73, H 4.26; found
C 50.51, H 4.35.
1
3
Ϫ H NMR (500 MHz, CDCl3): δ ϭ 1.92 (s, 6 H), 7.45 (d, J ϭ
9.0 Hz, 1 H), 7.53 (s, 1 H), 7.71 (d, 3J ϭ 7.5 Hz, 1 H), 7.98 (d, 3J ϭ
9.0 Hz, 1 H), 8.03 (d, 3J ϭ 7.5 Hz, 1 H), 8.13 (s, 1 H), 8.18 (d, 3J ϭ
7.5 Hz, 1 H), 8.23 (d, 3J ϭ 7.5 Hz, 1 H), 8.27 (d, 3J ϭ 7.5 Hz, 1 H).
Ϫ
13C NMR (125 MHz, CDCl3): δ ϭ 20.5, 111.2, 119.3, 123.8,
124.7, 124.9, 125.1, 125.3, 125.5, 126.0, 126.2, 127.3, 127.7, 128.1,
128.2, 130.8, 130.9, 131.2, 134.0, 138.8, 145.4. Ϫ MS (80 eV, 120
°C): m/z (%) ϭ 331 (100) [M]ϩ, 314 (37), 301 (11), 202 (4). Ϫ
C25H17N (331.41): calcd. C 90.60, H 5.17, N 4.23; found C 90.19,
H 5.18, N 4.27.
1-Phenylpyrene (5a): M.p. 93 °C. Ϫ Rf ϭ 0.26 (hexane). Ϫ 1H NMR
(500 MHz, CDCl3): δ ϭ 7.51Ϫ7.72 (m, 5 H), 7.99Ϫ8.27 (m, 9 H).
Ϫ
13C NMR (126 MHz, CDCl3): δ ϭ 124.6, 124.78, 124.84, 124.9,
125.1, 125.2, 126.0, 127.2, 127.4, 127.4, 127.6, 128.3, 128.4, 130.5,
130.6, 130.9, 131.4, 137.7, 141.2. Ϫ MS (70 eV, 110 °C): m/z (%) ϭ
278 (100) [M]ϩ. Ϫ C22H14 (278.35): calcd. C 94.93, H 5.07; found
C 94.48, H 5.02.
4-Bromo-3,5-dimethylbenzonitrile (4e). ؊ (I) From Benzaldehyde 7:
Aldehyde 7 (1.05 g, 4.93 mmol) was dissolved in a mixture of hy-
droxylamine hydrochloride (0.37 g, 5.33 mmol, 1.08 equiv.) and
pyridine (0.81 mL, 10.02 mmol, 2.03 equiv.). After a few minutes,
toluene (5 mL) was added and the solution was heated under reflux
for 2 h in an apparatus fitted with a water trap. The reaction mix-
ture was subsequently extracted with toluene (3 ϫ), the combined
organic phases were dried with MgSO4, and the solvent was evap-
orated. The residue was purified by column chromatography on
silica gel (hexane/ethyl acetate, 10:1). Yield: 39% of 4e. The main
product was 4-bromo-3,5-dimethylbenzaldehyde oxime 8 (see be-
4-(Pyren-1-yl)benzonitrile (5b): M.p. 153 °C. Ϫ Rf ϭ 0.10 (hexane/
1
ethyl acetate, 20:1). Ϫ H NMR (500 MHz, CDCl3): δ ϭ 7.68 (d,
3J ϭ 8.5 Hz, 2 H), 7.81 (d, 3J ϭ 8.5 Hz, 2 H), 7.88 (d, 3J ϭ 7.8 Hz,
1 H), 7.99Ϫ8.23 (m, 8 H). Ϫ 13C NMR (126 MHz, CDCl3): δ ϭ
110.9, 118.9, 124.1, 124.6, 125.5, 126.2, 127.0, 127.2, 128.0, 128.1,
130.7, 131.1, 131.3, 132.0, 135.2, 146. 0. Ϫ MS (70 eV, 315 °C):
ϩ
˜
m/z (%) ϭ 303 (100) [M] , 276 (4), 138 (6). Ϫ IR (KBr): ν ϭ 2224
cmϪ1 (CN, m). Ϫ C23H13N (303.36): calcd. C 91.06, H 4.32, N
1
low); m.p. 144 °C. Ϫ Rf ϭ 0.48 (hexane/ethyl acetate, 6:1). Ϫ H
NMR (250 MHz, CDCl3): δ ϭ 2.43 (s, 6 H), 7.32 (s, 2 H). Ϫ 13C
NMR (63 MHz, CDCl3): δ ϭ 3.7, 110.6, 118.3, 131.0, 133.1, 139.9.
Ϫ MS (80 eV, 40 °C): m/z (%) ϭ 211 (99) [C9H881BrN]ϩ, 209 (100)
4.62; found C 91.11, H 4.59, N 4.53.
2-(Pyren-1-yl)benzonitrile (5c): M.p. 176 °C. Ϫ Rf ϭ 0.10 (hexane/
1
ethyl acetate, 20:1). Ϫ H NMR (500 MHz, CDCl3): δ ϭ 7.55 (t,
[C9H8 BrN] . Ϫ IR (KBr): ν ϭ 2222 cmϪ1 (CN, m). Ϫ C9H8BrN
(210.07): calcd. C 51.46, H 3.84, N 6.67; found C 51.11, H 3.68,
N 6.59.
79
ϩ
˜
3J ϭ 7.5 Hz, 1 H), 7.63 (d, 3J ϭ 7.5 Hz, 1 H), 7.72 (t, 3J ϭ 7.5 Hz,
3
3
1 H), 7.81 (d, J ϭ 10.0 Hz, 1 H), 7.89 (d, J ϭ 7.5 Hz, 1 H), 7.97
3
3
(m, 3 H), 8.12 (s, 2 H), 8.18 (d, J ϭ 7.5 Hz, 1 H), 8.22 (d, J ϭ
7.5 Hz, 1 H), 8.26 (d, J ϭ 8.0 Hz, 1 H). Ϫ 13C NMR (126 MHz,
3
4-Bromo-3,5-dimethylbenzaldehyde Oxime (8): The aldoxime 8 was
isolated as the main product in the synthesis of 4c according to
CDCl3): δ ϭ 113.8, 118.2, 124.2, 124.55, 124.59, 124.8, 125.3,
125.6, 126.2, 127.3, 127.4, 127.9, 128.1, 128.2, 128.8, 130.7, 131.3,
1
route I in 56% yield. Ϫ Rf ϭ 0.20 (hexane/ethyl acetate, 6:1). Ϫ H
131.6, 132.0, 132.3, 133.0, 133.2, 144.8. Ϫ MS (70 eV, 120 °C):
NMR (250 MHz, CDCl3): δ ϭ 2.41 (s, 6 H), 7.26 (s, 2 H), 8.04 (s,
ϩ
1 H). Ϫ 13C NMR (63 MHz, CDCl3): δ ϭ 23.8, 126.5, 129.5, 130.3,
˜
m/z (%) ϭ 303 (100) [M] , 276 (6), 138 (7). Ϫ IR (KBr): ν ϭ
2218 cmϪ1 (CN, m). Ϫ HRMS: m/z calcd. for C23H13N 303.10480;
138.9, 149.7.
Ϫ
MS (80 eV, 50 °C): m/z (%)
ϭ
229 (98)
[C9H1081BrNO]ϩ, 227 (100) [C9H1079BrNO]ϩ.
(228.09).
Ϫ C9H10BrNO
found 303.10623.
3-Methyl-4-(pyren-1-yl)benzonitrile (5d): M.p. 176 °C. Ϫ Rf ϭ 0.10
1
4-Bromo-3,5-dimethylbenzonitrile (4e). ؊ (II) From Benzaldehyde
(hexane/ethyl acetate, 20:1). Ϫ H NMR (500 MHz, CDCl3): δ ϭ
3
3
Oxime (8): Aldoxime 8 (0.40 g, 1.76 mmol) was suspended in a 2.06 (s, 3 H), 7.45 (d, J ϭ 7.5 Hz, 1 H), 7.57 (d, J ϭ 10.0 Hz, 1
3
3
mixture of carbon disulfide (0.75 mL), aqueous sodium hydroxide
H), 7.64 (d, J ϭ 8.5 Hz, 1 H), 7.68 (s, 1 H), 7.79 (d, J ϭ 7.5 Hz,
Eur. J. Org. Chem. 2001, 3819Ϫ3829
3825

W. Rettig, A. D. Schlüter et al.
FULL PAPER
1 H), 8.02 (dd, 3J ϭ 8.5 Hz, 2 H), 8.12 (s, 2 H), 8.18 (d, 3J ϭ 7.94Ϫ8.21 (m, 9 H). Ϫ 13C NMR (63 MHz, CDCl3): δ ϭ 55.4,
3
7.5 Hz, 1 H), 8.23 (d, J ϭ 8.5 Hz, 2 H). Ϫ 13C NMR (126 MHz, 113.9, 124.6, 124.7, 125.0, 125.4, 126.0, 127.25, 127.32, 127.4,
CDCl3): δ ϭ 20.1, 111.5, 119.1, 124.4, 124.58, 124.63, 125.3, 125.5,
126.2, 126.5, 127.3, 127.8, 128.1, 128.4, 129.4, 130.8, 131.0, 131.3,
127.5, 127.7, 128.6, 130.4, 131.02, 131.04, 131.60, 133.6, 137.5,
159.0. Ϫ MS (70 eV, 150 °C): m/z (%) ϭ 308 (100) [M]ϩ, 293 (19),
131.5, 133.4, 134.9, 138.6, 145.8. Ϫ MS (80 eV, 160 °C): m/z (%) ϭ 263 (24). Ϫ HRMS: m/z calcd. for C23H16O 308.120115; found
ϩ
Ϫ1
˜
317 (100) [M] . Ϫ IR (KBr): ν ϭ 2230 cm (CN, s). Ϫ C24H15N 308.12432.
(317.38): calcd. C 90.82, H 4.76, N 4.41; found C 90.77, H 4.86,
N 4.23.
1-(4-Methoxy-2-methylphenyl)pyrene (5l): M.p. 131 °C. Ϫ Rf ϭ 0.53
(hexane/ethyl acetate, 3:1). Ϫ 1H NMR (500 MHz, CDCl3): δ ϭ
2.03 (s, 3 H), 3.92 (s, 3 H), 6.91 (d, 3J ϭ 7.5 Hz, 1 H), 6.95 (s, 1 H),
7.27 (d, 3J ϭ 7.5 Hz, 1 H), 7.74 (d, 3J ϭ 9.0 Hz, 1 H), 7.86 (d, 3J ϭ
7.5 Hz, 1 H), 7.98 (m, 2 H), 8.09 (s, 2 H), 8.14 (d, 3J ϭ 7.5 Hz,
Ethyl 4-(Pyren-1-yl)benzoate (5f): M.p. 129 °C. Ϫ Rf ϭ 0.44 (hex-
ane/ethyl acetate, 6:1). Ϫ 1H NMR (500 MHz, CDCl3): δ ϭ 1.37
3
(t, 3 H), 4.39 (q, 4 H), 7.57 (d, J ϭ 8.0 Hz, 2 H), 7.80Ϫ8.17 (m,
3
1 H), 8.19 (t, J ϭ 7.5 Hz, 2 H). Ϫ 13C NMR (125 MHz, CDCl3):
11 H). Ϫ 13C NMR (126 MHz, CDCl3): δ ϭ 14.4, 61.1, 124.6,
124.8, 124.9, 125.0, 125.8, 126.1, 127.31, 127.34, 127.8, 127.9,
128.4, 129.3, 129.8, 130.6, 130.88, 130.90, 131.4, 136.5, 145.9,
166.6. Ϫ MS (80 eV, 180 °C): m/z (%) ϭ 350 (100) [M]ϩ, 322 (16),
305 (4), 276 (28), 202 (7), 138 (8). Ϫ IR (KBr): ν˜ ϭ 1719 cmϪ1 (CO,
vs). Ϫ HRMS: m/z calcd. for C25H18O 350.13068; found 350.12470.
δ ϭ 20.6, 55.3, 110.9, 115.4, 124.5, 124.8, 124.9, 125.0, 125.5, 125.9,
127.2, 127.3, 127.4, 127.8, 129.3, 130.4, 131.0, 131.4, 131.7, 133.1,
137.1, 138.4, 159.1. Ϫ MS (80 eV, 150 °C): m/z (%) ϭ 317 (100)
[M]ϩ. Ϫ HRMS: m/z calcd. for C24H18O 322.135765; found
322.13369.
1-(4-Methoxy-2,6-dimethylphenyl)pyrene (5m): M.p. 139 °C. Ϫ Rf ϭ
0.54 (hexane/ethyl acetate, 3:1). Ϫ 1H NMR (500 MHz, CDCl3):
δ ϭ 2.46 (s, 6 H), 3.39 (s, 3 H), 7.32 (s, 2 H), 7.95Ϫ8.06 (m, 3 H),
Ethyl 3-Methyl-4-(pyren-1-yl)benzoate (5g): M.p. 131 °C. Ϫ Rf ϭ
0.45 (hexane/ethyl acetate, 6:1). Ϫ 1H NMR (500 MHz, CDCl3):
δ ϭ 1.48 (t, 3 H), 2.12 (s, 3 H), 4.48 (q, 2 H), 7.46 (d, 3J ϭ 7.5 Hz,
1 H), 7.66 (d, 3J ϭ 10.0 Hz, 1 H), 7.84 (d, 3J ϭ 7.5 Hz, 1 H),
7.96Ϫ8.24 (m, 9 H). Ϫ 13C NMR (126 MHz, CDCl3): δ ϭ 14.4,
20.2, 61.0, 124.5, 124.6, 124.7, 124.8, 125.1, 125.3, 126.7, 126.8,
127.3, 127.5, 127.7, 128.5, 129.7, 130.8, 131.0, 131.3, 136.1, 137.3,
3
8.08 (s, 2 H), 8.14Ϫ8.22 (m, 3 H), 8.27 (d, J ϭ 10.0 Hz, 1 H). Ϫ
13C NMR (125 MHz, CDCl3): δ ϭ 16.2, 59.8, 124.5, 124.7, 124.9,
124.9, 125.5, 125.9, 127.18, 127.22, 127.4, 127.5, 128.5, 130.3,
130.7, 131.0, 131.5, 136.6, 137.6, 156.4. Ϫ MS (70 eV, 180 °C):
m/z (%) ϭ 336 (100) [M]ϩ, 321 (23), 306 (15), 276 (10), 138 (7). Ϫ
HRMS: m/z calcd. for C25H20O 336.15141; found 336.151140.
145.5, 166.8. Ϫ MS (80 eV, 180 °C): m/z (%) ϭ 364 (100) [M]ϩ, 336
Ϫ1
˜
(7), 319 (5), 276 (15), 138 (11). Ϫ IR (KBr): ν ϭ 1706 cm (CO,
vs). Ϫ C26H20O2 (364.44): calcd. C 85.69, H 5.53; found C 85.44,
H 5.58.
4,4-Dimethyl-2-[4-(pyren-1-yl)phenyl]-2-oxazoline (5n): M.p. 139 °C.
Ϫ Rf ϭ 0.09 (hexane/ethyl acetate, 6:1). Ϫ 1H NMR (500 MHz,
CDCl3): δ ϭ 1.47 (s, 6 H), 4.18 (s, 2 H), 7.68 (d, 3J ϭ 7.5 Hz, 2 H),
7.93 (d, 3J ϭ 8.0 Hz, 1 H), 7.95Ϫ8.00 (m, 2 H), 8.03 (s, 2 H),
8.09Ϫ8.21 (m, 6 H). Ϫ 13C NMR (125 MHz, CDCl3): δ ϭ 28.4,
67.5, 79.0, 124.5, 124.6, 124.69, 124.73, 124.8, 125.1, 125.9, 126.8,
127.2, 127.5, 127.6, 128.2, 130.4, 130.5, 130.66, 130.69, 131.2,
1-[4-(Pyren-1-yl)phenyl]ethanone (5h): M.p. 184Ϫ185 °C. Ϫ Rf ϭ
0.22 (hexane/ethyl acetate, 6:1). Ϫ 1H NMR (500 MHz, CDCl3):
3
δ ϭ 2.69 (s, 3 H), 7.64 (d, 3J ϭ 8.2 Hz, 2 H), 7.91 (d, J ϭ 7.9 Hz,
1 H), 7.97Ϫ8.21 (m, 10 H). Ϫ 13C NMR (126 MHz, CDCl3): δ ϭ
26.6, 124.6, 124.8, 125.0, 125.3, 126.1, 127.2, 127.2, 127.7, 127.8,
128.2, 128.3, 130.7, 130.9, 131.3, 135.7, 136.1, 146.1, 197.7. Ϫ MS
(70 eV, 315 °C): m/z (%) ϭ 320 (100) [M]ϩ, 305 (6), 276 (51), 138
136.5, 144.1, 161.9. Ϫ MS (70 eV, 175 °C): m/z (%) ϭ 375 (100)
ϩ
[M] . Ϫ IR (KBr): ν ϭ 1644 cmϪ1 (ArϪCϭNϪR, s). Ϫ C27H21NO
˜
(13). Ϫ IR (KBr): ν ϭ 1681 (CO, vs) cmϪ1. Ϫ HRMS: m/z calcd.
(375.46): calcd. C 86.37, H 5.64, N 3.73; found C 86.15, H 5.90,
N 3.64.
˜
for C24H16O 320.120115; found 320.12341.
1
5-(Pyren-1-yl)-2,2Ј-bipyridine (5o): M.p. 172Ϫ173 °C. Ϫ H NMR
1-(4-Nitrophenyl)pyrene (5i): M.p. 206Ϫ207 °C. Ϫ Rf ϭ 0.36 (hex-
ane/ethyl acetate, 6:1). Ϫ 1H NMR (270 MHz, CDCl3): δ ϭ 7.77
3
3
(500 MHz, CDCl3): δ ϭ 7.34 (t, J ϭ 5.0 Hz, 1 H), 7.86 (dt, J ϭ
7.5, J ϭ 1.5 Hz, 1 H), 7.97Ϫ8.25 (m, 10 H), 8.52 (d, J ϭ 8.0 Hz,
4
3
3
3
(d, J ϭ 8.8 Hz, 2 H), 7.93 (d, J ϭ 7.9 Hz, 1 H), 8.00Ϫ8.25 (m,
3
3
3
1 H), 8.61 (d, J ϭ 8.0 Hz, 1 H), 8.75 (d, J ϭ 5.0 Hz, 1 H), 8.97
(d, 4J ϭ 1.5 Hz, 1 H). Ϫ 13C NMR (125 MHz, CDCl3): δ ϭ 120.7,
121.1, 123.8, 124.3, 124.6, 124.7, 124.9, 125.1, 125.4, 126.1, 127.2,
127.5, 127.8, 128.1, 128.6, 130.7, 131.1, 131.3, 133.3, 136.8, 137.0,
138.7, 149.2, 150.4, 154.7, 155.8. Ϫ MS (80 eV, 130 °C): m/z (%) ϭ
356 (100) [M]ϩ. Ϫ HRMS: m/z calcd. for C26H16N2 356.13135;
found 356.13467.
8 H), 8.39 (d, J ϭ 8.8 Hz, 2 H). Ϫ 13C NMR (63 MHz, CDCl3):
δ ϭ 123.6, 124.1, 124.7, 124.9, 125.3, 125.7, 126.3, 127.1, 127.2,
128.1, 128.2, 128.4, 130.7, 131.3, 134.8, 147.0, 148.0. Ϫ MS (80 eV,
250 °C): m/z (%) ϭ 323 (100) [M]ϩ, 276 (46), 138 (12). Ϫ IR (KBr):
ν ϭ 1539 (NϭO [νas], vs), 1342 cmϪ1 (NϭO [νs], vs). Ϫ C22H13NO
˜
(323.34): calcd. C 81.72, H 4.03, N 4.33; found C 81.66, H 4.14,
N 4.19.
4-[(Pyren-1-yl)methyl]benzonitrile (12): Pyrene (7.05 g, 34.86 mmol)
and 4-cyanobenzoyl chloride (5.86 g, 35.41 mmol, 1.02 equiv.) were
dissolved in carbon disulfide (50 mL) and the mixture was cooled
1-(4-Trifluoromethylphenyl)pyrene (5j): M.p. 133 °C. Ϫ Rf ϭ 0.54
(hexane/ethyl acetate, 6:1). Ϫ 1H NMR (250 MHz, CDCl3): δ ϭ
7.72 (d, 3J ϭ 8.0 Hz, 2 H), 7.83 (d, 3J ϭ 8.0 Hz, 2 H), 7.93 (d, 3J ϭ
8.0 Hz, 1 H), 7.97Ϫ8.07 (m, 3 H), 8.09 (s, 2 H), 8.13Ϫ8.23 (m,
3 H). Ϫ 13C NMR (63 MHz, CDCl3): δ ϭ 122.3, 124.6, 124.7,
124.9, 125.1, 125.4, 125.5, 126.2, 126.7, 127.3, 127.8, 128.0, 128.4,
129.2, 129.7, 130.9, 131.0, 131.4, 135.9, 144.9. Ϫ MS (80 eV,
to
0 °C. After the portionwise addition of AlCl3 (6.80 g,
51.00 mmol, 1.46 equiv.), the mixture was heated under reflux over-
night, then poured into ice-water (50 g) and the resulting mixture
was stirred until the color of the organic phase turned from black
to yellow. The layers were then separated, the aqueous phase was
extracted with toluene (3 ϫ), the combined organic phases were
dried with MgSO4, and the solvent was evaporated. The residue
was purified by column chromatography on silica gel (dichloro-
methane) and precipitated from dichloromethane/methanol. Yield:
120 °C): m/z (%) ϭ 346 (100) [Mϩ], 276 (57), 138 (22). Ϫ IR (KBr):
Ϫ1
˜
ν ϭ 1615 (m), 1327 cm (vs, br). Ϫ C23H13F3 (346.35): calcd. C
79.76, H 3.78; found C 79.55, H 3.88.
1-(4-Methoxyphenyl)pyrene (5k): M.p. 160 °C. Ϫ Rf ϭ 0.51 (hexane/
ethyl acetate, 3:1). Ϫ 1H NMR (270 MHz, CDCl3): δ ϭ 3.92 (s, 8.34 g (71%) of 12 as bright-yellow crystals; m.p. 171 °C. Ϫ Rf ϭ
3 H), 7.09 (d, 3J ϭ 8.3 Hz, 2 H), 7.56 (d, 3J ϭ 8.3 Hz, 2 H),
0.21 (hexane/ethyl acetate, 6:1). Ϫ 1H NMR (270 MHz, CDCl3):
3826
Eur. J. Org. Chem. 2001, 3819Ϫ3829

Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes
FULL PAPER
δ ϭ 7.71 (d, 3J ϭ 8.0 Hz, 2 H), 7.91 (d, 3J ϭ 8.0 Hz, 2 H), 4-(Pyren-1-ylmethyl)benzonitrile (10): Bromoarene 13 (3.77 g,
7.96Ϫ8.25 (m, 8 H), 8.39 (d, 3J ϭ 9.5 Hz, 1 H). Ϫ 13C NMR
10.15 mmol) and copper(I) cyanide (4.65 g, 51.92 mmol, 5.12
(63 MHz, CDCl3): δ ϭ 116.1, 117.9, 123.7, 124.19, 124.25, 124.8, equiv.) were suspended in DMF (5 mL) and the mixture was heated
126.2, 126.5, 126.6, 127.0, 127.3, 129.5, 129.7, 130.0, 130.5, 130.6,
at 160 °C overnight. The solvent was then distilled off, the residue
131.0, 131.1, 132.2, 133.7, 142.2, 196.5. Ϫ MS (80 eV, 150 °C): was chromatographed on silica gel (CH2Cl2), and the product was
ϩ
Ϫ1
˜
m/z (%) ϭ 331 (100) [M] . Ϫ IR (KBr): ν ϭ 2229 cm (CN, m).
precipitated from the eluate by adding methanol to give 3.22 g
Ϫ C24H13NO (331.37): calcd. C 86.99, H 3.95, N 4.23; found C (80%) of 10 as a colorless solid; m.p. 141 °C. Ϫ Rf ϭ 0.21 (hexane/
86.86, H 4.02, N 4.00.
ethyl acetate, 6:1). Ϫ 1H NMR (500 MHz, CDCl3): δ ϭ 4.62 (s,
3
3
2 H), 7.13 (d, J ϭ 8.1 Hz, 2 H), 7.39 (d, J ϭ 8.1 Hz, 2 H), 7.72
As the sole product of the reduction of 12 with sodium borohyd-
ride/aluminium chloride in tetrahydrofuran, 4-[hydroxy(pyren-1-
yl)methyl]benzonitrile was obtained; m.p. 133 °C. Ϫ Rf ϭ 0.16
(hexane/ethyl acetate, 3:1). Ϫ 1H NMR (250 MHz, CDCl3): δ ϭ
3
(d, J ϭ 7.5 Hz, 1 H), 7.88Ϫ7.98 (m, 5 H), 8.02 (m, 3 H). Ϫ 13C
NMR (126 MHz, CDCl3): δ ϭ 39.2, 119.0, 123.1, 124.7, 124.9,
125.1, 126.1, 127.2, 127.3, 127.9, 128.1, 128.2, 129.0, 129.2, 130.5,
131.2, 132.2, 132.4, 132.4, 146.7. Ϫ MS (70 eV, 180 °C): m/z (%) ϭ
3
3.39 (s, 1 H, OH), 6.60 (s, 1 H), 7.37 (d, J ϭ 8.3 Hz, 2 H), 7.42
ϩ
317 (100) [M] , 215 (20). Ϫ IR (KBr): ν ϭ 2224 cmϪ1 (CN, vs). Ϫ
˜
3
3
(d, J ϭ 8.3 Hz, 2 H), 7.87 (d, J ϭ 7.8 Hz, 1 H), 7.95Ϫ8.03 (m, 4
C24H15N (317.38): calcd. C 90.82, H 4.76, N 4.41; found C 90.44,
H 4.56, N 4.14.
3
H), 8.06 (d, J ϭ 7.8 Hz, 1 H), 8.10Ϫ8.16 (m, 3 H). Ϫ 13C NMR
(63 MHz, CDCl3): δ ϭ 72.6, 110.7, 118.8, 122.5, 124.5, 124.8,
124.9, 125.0, 125.3, 125.6, 126.1, 127.0, 127.2, 127.8, 128.0, 128.1,
130.3, 131.1, 131.2, 132.0, 135.3, 148.7. Ϫ MS (80 eV, 60 °C): m/z
(%) ϭ 333 (100) [M]ϩ. Ϫ IR (KBr): ν˜ ϭ 2230 cmϪ1 (CN, s). Ϫ
HRMS: m/z calcd. for C24H15NO 333.11536; found 333.11734.
4-[2-(Pyren-1-yl)vinyl]benzonitrile (18): Potassium tert-butoxide
(16.5 g, 147.0 mmol, 1.05 equiv.) was added to a stirred slurry of (4-
cyanobenzyl)triphenylphosphonium bromide (64.0 g, 140.0 mmol,
1.36 equiv.) in dry tetrahydrofuran (250 mL). After stirring the re-
sultant solution for 30 min at ambient temperature, pyrene carbal-
dehyde 15 (23.9 g, 103.4 mmol) was added in a single portion. The
mixture was stirred for 2 h at room temperature and then refluxed
overnight. After the addition of a molar excess of water, the organic
solvent was removed under reduced pressure and the resultant
aqueous mixture was extracted three times with dichloromethane.
The combined organic layers were dried, filtered, and concentrated
to dryness. Column chromatography (hexane/ethyl acetate, 20:1 to
5:1) gave (E/Z)-18 (31.5 g, 92%). The (E)-isomer was separated by
recrystallization from dichloromethane/methanol; m.p. 189 °C. Ϫ
Rf ϭ 0.20 (hexane/ethyl acetate, 6:1). Ϫ 1H NMR (500 MHz,
CDCl3): δ ϭ 7.23 (d, 3J ϭ 16.0 Hz, 1 H), 7.62 (s (!), 4 H), 7.99Ϫ8.08
1-(4-Bromobenzoyl)pyrene (13): M.p. 173 °C (dichloromethane)
[174Ϫ175 °C (acetic acid)[54]]. Ϫ Rf ϭ 0.25 (hexane/ethyl acetate,
1
3
10:1). Ϫ H NMR (250 MHz, CDCl3): δ ϭ 7.59 (d, J ϭ 8.5 Hz,
2 H), 7.74 (d, 3J ϭ 8.5 Hz, 2 H), 8.02 (d, 3J ϭ 7.8 Hz, 1 H),
8.06Ϫ8.25 (m, 7 H), 8.31 (d, 3J ϭ 9.3 Hz, 1 H). Ϫ 13C NMR
(63 MHz, CDCl3): δ ϭ 123.7, 124.3, 124.5, 124.8, 126.0, 126.2,
126.5, 126.9, 127.1, 128.4, 129.0, 129.3, 129.7, 130.6, 131.1, 131.8,
132.0, 132.4, 133.2, 137.5, 197.3. Ϫ MS (80 eV, 150 °C): m/z (%) ϭ
386 (100) [C23H1381BrO]ϩ, 384 (94) [C23H1379BrO]ϩ. Ϫ IR (KBr):
Ϫ1
˜
ν ϭ 1651 cm (CO, vs). Ϫ C23H13BrO (385.26): calcd. C 71.71,
H 3.40; found C 71.59, H 3.35.
1-(4-Bromobenzyl)pyrene (14): Ketone 12 (10.5 g, 27.25 mmol) and
sodium borohydride (5.12 g, 135.3 mmol, 4.97 equiv.) were dis-
solved in tetrahydrofuran (200 mL) and aluminium chloride was
cautiously added at room temperature. The mixture was heated un-
der reflux for 90 min and then poured into ice-water (200 g). The
resulting mixture was extracted with dichloromethane (2 ϫ), the
combined organic phases were dried with MgSO4, and the solvent
was evaporated. The residue was purified by column chromatog-
raphy on silica gel (hexane/ethyl acetate, 20:1) and the product was
recrystallized from dichloromethane/methanol to give 7.60 g (75%)
of 13 as colorless crystals; m.p. 140 °C. Ϫ Rf ϭ 0.37 (hexane/ethyl
3
(m, 3 H), 8.11Ϫ8.15 (m, 2 H), 8.18Ϫ8.20 (m, 3 H), 8.25 (d, J ϭ
3
8.0 Hz, 1 H), 8.40 (d, J ϭ 9.6 Hz, 1 H). Ϫ 13C NMR (126 MHz,
CDCl3): δ ϭ 110.5, 119.0, 122.5, 123.6, 124.8, 125.0, 125.1, 125.4,
125.7, 126.2, 126.9, 127.4, 127.8, 128.0, 128.7, 129.1, 129.4, 130.5,
130.7, 131.4, 131.5, 132.5, 142.0. Ϫ MS (80 eV, 180 °C): m/z (%) ϭ
329 (100) [M]ϩ. Ϫ IR (KBr): ν˜ ϭ 2215 cmϪ1 (CN, s). Ϫ HRMS:
m/z calcd. for C25H15N 329.12045; found 329.12423. Ϫ The (E/Z)
mixture of 18 showed additional signals due to the (Z)-isomer in
1
3
the H NMR spectrum: δ ϭ 6.88 (d, J ϭ 12.0 Hz, 1 H), 7.09 (d,
3J ϭ 8.0 Hz, 2 H), 7.28 (d, 3J ϭ 8.0 Hz, 2 H), 7.47 (d, 3J ϭ 12.0 Hz,
1 H), 7.74 (d, J ϭ 8.0 Hz, 1 H).
1
3
acetate, 10:1). Ϫ H NMR (500 MHz, CDCl3): δ ϭ 4.63 (s, 2 H),
7.05 (d, 3J ϭ 8.1 Hz, 2 H), 7.37 (d, 3J ϭ 8.1 Hz, 2 H), 7.81 (d, 3J ϭ
7.8 Hz, 1 H), 7.97Ϫ8.19 (m, 8 H). Ϫ 13C NMR (126 MHz, CDCl3):
δ ϭ 38.6, 119.2, 123.4, 124.7, 124.8, 124.9, 125.1, 125.1, 125.9,
127.0, 127.4, 128.0, 129.0, 130.3, 130.7, 131.2, 131.5, 133.6, 140.0.
Ϫ MS (70 eV, 120 °C): m/z (%) ϭ 372 (100) [C23H1581Br]ϩ, 370 (98)
[C23H1579Br]ϩ. Ϫ C23H15Br (371.27): calcd. C 74.41, H 4.07; found
C 74.27, H 4.01.
4-[2-(Pyren-1-yl)ethyl]benzonitrile (17): A mixture of 4-[2-(pyren-1-
yl)vinyl]benzonitrile 18 (26.01 g, 78.96 mmol), magnesium (19.27 g,
792.68 mmol, 10.04 equiv.), and 10% Pd/C (3.25 g) in n-propanol
(1500 mL) was heated to reflux for 24 h. The mixture was then
filtered through Celite eluting with tetrahydrofuran. The solvent
was removed from the eluate and the residue was purified by col-
umn chromatography on silica gel (dichloromethane) to give
25.10 g (96%) of 17; m.p. 126 °C. Ϫ Rf ϭ 0.22 (hexane/ethyl acetate,
6:1). Ϫ 1H NMR (500 MHz, CDCl3): δ ϭ 3.16 (t, 2 H), 3.59 (t,
As a side product, the incompletely reduced 1-(4-bromophenyl)-1-
(pyren-1-yl)methanol was obtained; m.p. 156 °C. Ϫ Rf ϭ 0.31 (hex-
ane/ethyl acetate, 3:1). Ϫ 1H NMR (250 MHz, [D6]DMSO): δ ϭ
6.45 (d, 1 H, OH), 6.75 (d, 3J ϭ 4.5 Hz, 1 H), 7.40 (d, 3J ϭ 8.2 Hz,
3
3
2 H), 7.19 (d, J ϭ 8.0 Hz, 2 H), 7.51 (d, J ϭ 8.0 Hz, 2 H), 7.67
2 H), 7.47 (d, 3J ϭ 8.2 Hz, 1 H), 8.02 (t, 3J ϭ 7.6 Hz, 1 H), (d, J ϭ 8.0 Hz, 1 H), 7.98Ϫ8.06 (m, 4 H), 8.10 (d, J ϭ 9.0 Hz, 1
3
3
8.11Ϫ8.33 (m, 7 H). Ϫ 13C NMR (63 MHz, [D6]DMSO): δ ϭ 71.8, H), 8.17Ϫ8.20 (m, 3 H). Ϫ 13C NMR (126 MHz, CDCl3): δ ϭ 34.9,
120.7, 124.1, 124.6, 124.8, 125.6, 125.8, 126.0, 126.3, 127.0, 127.7,
127.8, 128.0, 128.7, 129.7, 129.6, 130.7, 131.4, 131.7, 138.6, 145.04, 127.2, 127.4, 127.5, 128.5, 129.3, 130.0, 130.7, 131.3, 132.1, 134.5,
145.08. Ϫ MS (80 eV, 60 °C): m/z (%) ϭ 388 (31) [C23H15O81Br]ϩ, 147.1. Ϫ MS (80 eV, 120 °C): m/z (%) ϭ 331 (13) [M]ϩ, 215 (100)
37.9, 109.8, 119.0, 122.8, 124.7, 124.9, 125.0, 125.1, 125.9, 126.8,
ϩ
Ϫ1
386 (30) [C23H15O79Br]ϩ, 203 (100) [pyrene ϩ H]ϩ. Ϫ IR (KBr): [M Ϫ CH2PhCN] . Ϫ IR (KBr): νϭ 2224 cm
(CN, m). Ϫ
˜
ν˜ ϭ 3260 (s, br), 3041, 2922, 1588 (m), 1484 (s) cmϪ1. Ϫ HRMS:
m/z calcd. for C23H15BrO 386.03063; found 386.03265.
C25H17N (331.41): calcd. C 90.60, H 5.17, N 4.23; found C 90.49,
H 5.20, N 4.09.
Eur. J. Org. Chem. 2001, 3819Ϫ3829
3827

W. Rettig, A. D. Schlüter et al.
FULL PAPER
[3]
[4]
[5]
[6]
A. W. Bosman, H. M. Janssen, E. W. Meijer, Chem. Rev. 1999,
99, 1665Ϫ1688.
M. Fischer, F. Vögtle, Angew. Chem. Int. Ed. 1999, 38,
885Ϫ905.
A. D. Schlüter, J. P. Rabe, Angew. Chem. Int. Ed. 2000, 39,
864Ϫ883.
rac-[Bis(2,2Ј-bipyridine){5-(pyren-1-yl)-2,2Ј-bipyridine}ruthenium-
(II)](PF6)2 (19): A suspension of 5o (60 mg, 0.17 mmol) and cis/
trans-bis(2,2Ј-bipyridine)dichlororuthenium(II)·xH2O (86 mg) in
aqueous ethanol (30 mL, 1:1, v/v) was refluxed for 19 h. The solvent
was then evaporated and the residue was chromatographed on silica
gel eluting with methanol/2  aq. NH4Cl/nitromethane (7:2:1).
Water was added to the eluate and the resulting mixture was ex-
tracted with chloroform. After evaporation of the chloroform, the
remaining red solid was redissolved in methanol (3 mL) and a sa-
turated solution of NH4PF6 in methanol (2 mL) was added. After
standing overnight, the mixture was centrifuged, the solvent was
decanted off, and the residue was dried in vacuo to give 19 (0.15 g,
For an elegant study on electron transfer in a dendrimer from
´
a porphyrin core through a Frechet-type shell, see: D.-L. Jiang,
T. Aida, J. Am. Chem. Soc. 1998, 120, 10895Ϫ10901.
For the related antenna effect in dendrimers and a comprehen-
[7]
sive survey of methods by which the interiors of dendrimers
´
have been investigated, see: S. Hecht, J. M. J. Frechet, Angew.
Chem. Int. Ed. 2001, 40, 74Ϫ91 and references therein.
D. Gust, T. A. Moore, Adv. Photochem. 1992, 16, 1Ϫ65.
A. K. Burrell, M. R. Wasielewski, J. Porphyrins Phthalocya-
nines 2000, 4, 401Ϫ406.
See, for example: J. Deisenhofer, O. Epp, K. Miri, R. Huber,
H. Michel, Nature 1985, 318, 618Ϫ624.
N. Krauß, W.-D. Schubert, O. Klukas, P. Fromme, H. T. Witt,
W. Saenger, Nat. Struct. Biol. 1996, 3, 965Ϫ973.
For charge transfer, for example in DNA, see: D. Porath, A.
Bezryadin, S. de Vries, C. Dekker, Nature 2000, 403, 635Ϫ638.
C. Aubert, M. H. Vos, P. Mathis, A. P. M. Eker, K. Brettel,
Nature 2000, 405, 586Ϫ590.
[8]
[9]
0.14 mmol, 83%); m.p.
Ͼ 210 °C (decomp.). Ϫ
1H NMR
4
(500 MHz, [D3]acetonitrile): δ ϭ 7.14 (dt, 3J ϭ 6.7, J ϭ 1.5 Hz,
3
3
1 H), 7.40 (m, 5 H), 7.68 (d, J ϭ 5.7 Hz, 1 H), 7.73 (dt, J ϭ 7.5,
[10]
[11]
[12]
[13]
[14]
4J ϭ 1.5 Hz, 1 H), 7.81 (t, J ϭ 6.0 Hz, 2 H), 7.85 (s, J ϭ 2.2 Hz,
3
4
1 H), 7.89 (m, 2 H), 8.00 (d, 3J ϭ 5.7 Hz, 1 H), 8.04Ϫ8.14 (m,
3
4
3
7 H), 8.18 (dt, J ϭ 7.7, J ϭ 1.5 Hz, 1 H), 8.22 (d, J ϭ 8.2 Hz,
3
3
1 H), 8.24 (d, J ϭ 7.7 Hz, 1 H), 8.29 (d, J ϭ 8.2 Hz, 2 H), 8.45
(d, 3J ϭ 8.2 Hz, 1 H), 8.51 (d, 3J ϭ 8.2 Hz, 2 H), 8.61 (d, 3J ϭ
8.2 Hz, 1 H), 8.64 (d, 3J ϭ 8.2 Hz, 1 H), 8.67 (d, 3J ϭ 8.2 Hz, 1 H).
Ϫ
13C NMR (125 MHz, [D3]acetonitrile): δ ϭ 123.6, 124.8, 125.0,
125.1, 125.1, 125.2, 125.8, 126.5, 126.9, 127.5, 127.7, 128.0, 128.2,
128.4, 128.4, 128.5, 128.7, 128.8, 129.3, 129.4, 131.2, 131.3, 132.0,
132.5, 138.3, 138.7, 138.7, 138.9, 139.9, 140.9, 152.6, 152.6, 152.6,
152.7, 152.8, 156.4, 157.6, 157.7, 157.7, 157.8. Ϫ MS (FAB): m/z
(%) ϭ 915 (4) [M Ϫ PF6]ϩ, 770 (1) [M Ϫ 2PF6]ϩ, 614 (2) [M Ϫ
2 PF6 Ϫ bipy]ϩ, 455 (1) [M Ϫ 2 PF6 Ϫ 2 bipy]ϩ, 413 (4)
[Ru(bipy)2]ϩ, 357 (2) [pyrene ϩ bipy]ϩ. Ϫ C46H32F12N6P2Ru
(1059.79): calcd. C 52.13, H 3.04, N 7.93; found C 51.67, H 3.25,
N 7.70.
F. D. Lewis, X. Liu, J. Liu, S. E. Miller, R. T. Hayes, M. R.
Wasielewski, Nature 2000, 406, 51Ϫ53.
[15]
[16]
B. Giese, M. Spichty, ChemPhysChem 2000, 1, 195Ϫ198.
A structural measure would be the construction of dendrimers
from subunits with different polarities in a sequential fashion,
i.e., starting from a non-polar core and continuing through in-
creasingly more polar generations until a highly polar (perhaps
even charged) surface is reached. First steps in this direction
have already been made: L. Shu, A. D. Schlüter, Macromol.
Chem. Phys. 2000, 201, 239Ϫ245.
[17]
[18]
[19]
[20]
[21]
D. Pöschke, M. Ballauff, P. Lindner, M. Fischer, F. Vögtle,
Macromolecules 1999, 32, 4079Ϫ4087.
R. L. Lesanec, M. Muthukumar, Macromolecules 1990, 23,
2280Ϫ2288.
D. Boris, M. Rubinstein, Macromolecules 1996, 29,
7251Ϫ7260.
For different views, see: P. G. de Gennes, H. Hervet, J. Phys.
(Paris) 1983, 44, L351ϪL355.
S. Uppuluri, S. E. Keinath, D. A. Tomalia, P. R. Dvornic, Mac-
X-ray Structure Analysis:[63] Crystals of 19 suitable for X-ray struc-
ture analysis were obtained by slow diffusion of methanol into a
solution of the compound in dichloromethane. A crystal of dimen-
sions 0.65 ϫ 0.53 ϫ 0.20 mm was mounted on tip of a glass fiber
at Ϫ150 °C and placed in the cold nitrogen stream of a Bruker
AXS SMART CCD diffractometer [Mo-Kα radiation (λ ϭ 0.71073
˚
A), graphite monochromator]. To avoid loss of the intercalated
solvent, the data collection was performed at Ϫ120 °C. The crystals
were found to belong to the monoclinic space group (C2/c), a ϭ
romolecules 1998, 31, 4498Ϫ4510.
[22]
[23]
˚
L. Cavallo, F. Fraternali, Chem. Eur. J. 1998, 4, 927Ϫ934.
It is assumed that despite back-folding processes, probes posi-
tioned at certain generations are at an increasingly large dis-
tance from the core the higher the generation at which they
are attached.
20.926(3), b ϭ 12.369(2), c ϭ 41.031(6) A, β ϭ 93.113(2)°, V ϭ
3
˚
10604(3) A , Z ϭ 8, 2θmax ϭ 27.51°; 11920 unique reflections. The
asymmetric unit contains three molecules of dichloromethane per
formula unit. The structure was solved by direct methods and full-
matrix least-squares refinement against F2; non-H atoms aniso-
tropic.[78] R1 (all data) ϭ 0.0674, wR2 ϭ 0.1530; R1 ϭ 0.0589,
wR2 ϭ 0.1480 for 11920 reflections with F Ն 2σF.
[24]
For generation-dependent solvatochromism of a probe at-
tached to the focal point of a homologous series of dendrons,
´
see: C. J. Hawker, K. L. Wooley, J. M. J. Frechet, J. Am. Chem.
Soc. 1993, 115, 4375Ϫ4376.
[25]
[26]
D. K. Smith, L. Müller, Chem. Commun. 1999, 1915Ϫ1916.
S. Koenig, L. Müller, D. K. Smith, Chem. Eur. J. 2001, 7,
979Ϫ986.
C. M. Cardona, J. Alvarez, A. E. Kaifer, T. D. McCarley, S.
Pandey, G. A. Baker, N. J. Bonzagni, F. V. Bright, J. Am. Chem.
Soc. 2000, 122, 6139Ϫ6144.
C. M. Cardona, A. E. Kaifer, J. Am. Chem. Soc. 1998, 120,
4023Ϫ4024.
For methods of synthesizing dendrimers with generation-spe-
cific anchor groups, see: Z. Bo, A. Schäfer, P. Franke, A. D.
Schlüter, Org. Lett. 2000, 2, 1645Ϫ1648.
A. W. Freeman, L. A. J. Christoffels, J. M. J. Frechet, J. Org.
Chem. 2000, 65, 7612Ϫ7617.
In this approach, the formation of pyrene excimers from the
dummies has to be avoided. This is achieved by selectively ex-
citing only the fluorescence probes, which is possible by virtue
Acknowledgments
[27]
Financial support by the Deutsche Forschungsgemeinschaft (DFG,
Sonderforschungsbereich 448, TP A1 and B3) and the Fonds der
Chemischen Industrie is gratefully acknowledged. We thank Lars
Hoffmann and Alexander Jagst for their skillful help with some of
the experiments, Dr. A. Schäfer for recording the 2D NMR spectra,
T. Kohlrep for carrying out the HPLC separations, and A. Rothe
for recording the UV absorption and fluorescence spectra.
[28]
[29]
[30]
[31]
´
[1]
For general information about dendrimers see, for example: G.
R. Newkome, C. N. Moorefield, F. Vögtle, Dendritic Molecules
Ϫ Concepts, Syntheses, Perspectives, VCH, Weinheim, 1996.
F. Zeng, S. C. Zimmerman, Chem. Rev. 1997, 97, 1681Ϫ1712.
[2]
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Eur. J. Org. Chem. 2001, 3819Ϫ3829

Arene-Substituted Pyrene Derivatives as Model Compounds for Fluorescent Polarity Probes
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Received May 31, 2001
[O01261]
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