Chromophore-labeled dendrons as light harvesting antennae

Article abstract of DOI:10.1021/ja954021i

A novel series of polyether dendrimer segments (dendrons) end-capped with pyrenyl, naphthyl, or methyl groups has been prepared by a convergent growth method. Steady-state fluorescence measurements indicate the absence of intramolecular naphthalene excimer in the naphthyl-capped dendrons. However, in the pyrenyl-capped dendrons, excimer emission predominates. Fluorescence from both the naphthyl monomer and pyrenyl excimer are quenched when a suitable electron donor (e.g., a 3-[dimethylamino]phenoxy group) is covalently attached at the dendron focal point. No sensitized emission from the dendron backbone is observed in the chromophore-labeled dendrons, although the control methyl-capped dendron fluoresces weakly at 310 nm when excited at 284 nm. Absorption and fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes for the chromophore-labeled dendrons axe reported.

Full text of DOI:10.1021/ja954021i

4354
J. Am. Chem. Soc. 1996, 118, 4354-4360
Chromophore-Labeled Dendrons as Light Harvesting Antennae
Gina M. Stewart and Marye Anne Fox*
Contribution from the Department of Chemistry and Biochemistry,
The UniVersity of Texas at Austin, Austin, Texas 78712
ReceiVed NoVember 29, 1995X
Abstract: A novel series of polyether dendrimer segments (dendrons) end-capped with pyrenyl, naphthyl, or methyl
groups has been prepared by a convergent growth method. Steady-state fluorescence measurements indicate the
absence of intramolecular naphthalene excimer in the naphthyl-capped dendrons. However, in the pyrenyl-capped
dendrons, excimer emission predominates. Fluorescence from both the naphthyl monomer and pyrenyl excimer are
quenched when a suitable electron donor (e.g., a 3-[dimethylamino]phenoxy group) is covalently attached at the
dendron focal point. No sensitized emission from the dendron backbone is observed in the chromophore-labeled
dendrons, although the control methyl-capped dendron fluoresces weakly at 310 nm when excited at 284 nm.
Absorption and fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes for the chromophore-
labeled dendrons are reported.
Introduction
synthetic scheme is of course advantageous in these early
generation dendrons.
In recent years, the study of directional energy transport and
electron transfer in chromophore-labeled polymers and su-
pramolecular arrays has been the focus of an ever-increasing
number of reports.1-5 Flexible random-coil polymers bearing
electron donor-acceptor pairs exhibit low net efficiency for
charge separation because of rapid back-electron transfer through
a contact ion pair.5 In contrast, block copolymers incorporating
linear, rigid backbones permit singlet energy migration to the
block interface, where exciplex formation takes place, thus
functioning as an energy trap.6 The unusual molecular archi-
tecture of dendritic polymers provides a suitable framework for
the support of redox-active functionalities since: (1) the
spherical shape of these highly branched polymers inhibits the
chain entanglement that occurs in many linear polymers;7,8 (2)
the solubilities of dendrimers in organic solvents far exceed
those of linear polymers of similar composition and molecular
weight;7 and (3) the synthetic methodology in which the dendron
is assembled, one layer or generation at a time,9 allows for
controlled placement of a series of two or more functional
groups to produce a thermodynamic driving force gradient for
sequential photoinduced electron transfers. A dendrimer ar-
chitecture also permits variation of the number and ratio of donor
and acceptor functionalities and allows for the insertion of a
defined number of spacer units between the redox-active
chromophores. Although the dendrons reported here are prob-
ably too small to adopt the spherical conformation for which
dendrimers are known, this study provides valuable information
about the suitability of the dendrimer backbone for electronic
communication of appended chromophores. The controlled
placement of chromophores made possible by the stepwise
A prototypical dendron for our study has aryl chromophores
(acting as electron acceptors C1) at the periphery and an
energetically suitable electron donor at the growth focal point.
Photoexcitation of the acceptor chromophores should lead to
electron transfer from the donor moiety C2 through the
dendrimer backbone to the outer array of acceptors, eq 1. The
separation between the benzyl-capped chain ends and an ester-
terminated focal point for a Fre´chet-type second generation
polybenzyl ether dendron as determined by a single-crystal
structure is about 14 Å.10 This measurement gives us an
approximation of the C1-C2 separation for the chromophore-
labeled second generation dendrons reported here. In the current
work, we sought to characterize the interactions between the
appended aryl chromophores and to determine whether their
excited states could be quenched by a covalently bound donor
present on the same dendrimer segment. To the best of our
knowledge, this work represents the first photophysical study
of electron donor-acceptor pairs covalently attached to a
dendritic architectural skeleton.
Results and Discussion
X Abstract published in AdVance ACS Abstracts, April 15, 1996.
(1) Fox, M. A. Acc. Chem. Res. 1992, 25, 569.
(2) Balzani, V. Tetrahedron 1992, 48, 10443.
(3) Fox, M. A.; Watkins, D. M.; Jones, W. E., Jr. Chem. Eng. News
1993, 38.
(4) Wasielewski, M. R. Chem. ReV. 1992, 92, 435.
(5) Webber, S. E. Chem. ReV. 1990, 90, 1469.
(6) (a) Watkins, D. M.; Fox, M. A. J. Am. Chem. Soc. 1994, 116,
6441. (b) Fox, H. H.; Fox, M. A. Macromolecules 1995, 28, 4570.
(7) Fre´chet, J. M. J. Science 1994, 263, 1710.
(8) Fre´chet, J. M. J.; Hawker, C. J.; Wooley, K. L. Pure Appl. Chem.
1994, A31, 1627.
Synthesis. First, second, and third generation polyether
dendrons bearing aryl functionalities such as substituted naph-
thalene or pyrene at the periphery have been synthesized. The
naphthyl-capped dendrons were produced by condensing 2-bro-
momethylnaphthalene with 3,5-dihydroxybenzyl alcohol in the
presence of potassium carbonate and 18-crown-6 ether in
refluxing acetone to give the bis(naphthylether) benzyl alcohol
1a. This alcohol was then converted to the corresponding
(10) Schlu¨ter, A.-D.; Claussen, W.; Amoulong-Kirstein, E.; Karakaya,
B. In American Chemican Society DiVision of Polymeric Materials: Science
and Engineering; Chicago, 1995; pp 226-227.
(9) Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1990, 112,
7638.
S0002-7863(95)04021-2 CCC: $12.00 © 1996 American Chemical Society

Chromophore-Labeled Dendrons
J. Am. Chem. Soc., Vol. 118, No. 18, 1996 4355
Table 1. Absorption and Emission Data for Naphthyl- and
Chart 1
Methoxy-Capped Dendrons Excited at 284 nma
ꢀ
compd
(cm-1 M-1
)
λ
em (nm)b
Φfb
0.17
Φfc
b
2-naphthalenemethanol
3000
9800
7600
335
0.069
0.021
0.059
0.028
1a
2a
3a
3d
3e
3g
4a
290, 335 0.014
292, 335 0.057
290, 335 0.020
19 000
290, 335 0.0064 0.025
310 0.0058 0.0099
312, 354 0.0056d 0.0067d
290, 335 0.064 0.063
5500
8200
12 000
a Measured as ∼10-7 M degassed solutions (except extinction
coefficient determinations). b In acetonitrile. c In dichloromethane. d In-
cludes fluorescence at 354 nm (attributed to [dimethylamino]phenoxy
group).
Table 2. Absorption and Emission Data for
Pyrenyl-Functionalized Dendrons Excited at 344 nma
ꢀ
Φfb
Φfc Φfd
b
compd
(cm-1 M-1
)
λ
em (nm)b
1-pyrenemethanol
38 000
375, 395,
0.011 0.17 0.22
415,e 435e
375, 395,
415,e 435e
2c
44 000
0.097 0.24 0.34
4c
4d
5a
5c
53 000
62 000
70 000d
92 000d
480
480
480
480
0.18
0.34 0.30
0.025 0.15 0.079
0.17f 0.38 0.23
0.047f 0.31 0.18
a Measured as ∼10-6 M degassed solutions (except extinction
coeffient determinations). b In acetonitrile. c In dichloromethane. d In
tetrahydrofuran. e Shoulder. f 5a and 5c are not very soluble in aceto-
nitrile. Therefore, these quantum yields are approximate.
reactions of the dendron-building sequence are unchanged for
the pyrenyl- and naphthyl-capped series.
The (dimethylamino)phenoxy-terminated dendron 3d was
produced as a clear glass by condensation of 3b with 3-di-
methylaminophenol in the presence of K2CO3 and 18-crown-6
ether in acetone. The (dimethylamino)phenoxy group was also
used to terminate the methoxy- and pyrenyl-capped dendrons
to give 3g, 4d, and 5c, which were all obtained as white or
pale yellow solids. Computer-generated models using Cache
software indicate a through-space separation of the pyrenyl
groups from the (dimethylamino)phenoxy groups of approxi-
mately 15 Å in 4d and approximately 22 Å in 5c. The
triethylamino quencher-labeled dendrons 1c and 3c were
prepared by functionalization at the dendrimer growth focal
point by treating diethylaminoethanol with sodium hydride
before adding the appropriate dendron 1b or 3b. The triethyl-
amino substituted dendrons 1c and 3c were obtained as oils and
were inseparable from minor residual impurities.
Photophysical Properties. All dendrons were studied either
as the alcohols (without a donor) or as the amino-terminated
species. Steady-state emission spectra of the naphthyl-capped
and methoxy-capped dendrons are summarized in Table 1, as
are steady-state emission spectra of the pyrenyl-capped dendrons
in Table 2. The methoxy-capped dendrons 3e and 3g were used
as probes for fluorescence of a polyether dendron lacking aryl
chromophores at the chain ends. The second-generation alcohol
3e fluoresces weakly with a very broad signal at 310 nm when
excited at 284 nm (Figure 1). No fluorescence quenching by
the covalently attached 3-(dimethylamino)phenoxy group in 3g
was observed. Instead, the 3-(dimethylamino)phenoxy group
(which absorbs 284-nm light) competitively absorbs the excita-
tion pulse and fluoresces at 355 nm.
bromide 1b by treatment with carbon tetrabromide and tri-
phenylphosphine in tetrahydrofuran (THF). Subsequent genera-
tions 3a and 3b were built by repetition of this two-step reaction
scheme. The methoxy-capped dendrons 3e and 3f, lacking
absorptive aryl groups at their periphery, serve as controls in
the photophysical experiments: they were similarly synthesized
from 3,5-dimethoxybenzyl alcohol.
Condensation of 2 equiv of 1-bromomethylpyrene with 3,5-
dihydroxybenzyl alcohol proceeded in extremely poor yield,
presumably because of steric hindrance. However, a condensa-
tion of 1 equiv of 1-bromomethylpyrene with 3-hydroxybenzyl
alcohol proceeded cleanly and in high yield to give 2c. The
corresponding series of naphthyl-functionalized dendrons 2a,
2b, and 4a were synthesized for comparison. The subsequent
In the naphthyl-capped series consisting of 1a, 3a, and 3d,
intermolecular excimer formation was observed only in solutions

4356 J. Am. Chem. Soc., Vol. 118, No. 18, 1996
Stewart and Fox
Figure 1. Steady-state fluorescence spectra of (a) 3e and (b) 3g in
degassed acetonitrile (<10-5 M); λex ) 284 nm.
Figure 3. Steady-state fluorescence spectra of (a) 2c, (b) 4b, (c) 4d,
and (d) 1-pyrenemethanol in degassed acetonitrile (<10-5 M); λex
344 nm.
)
Emission from 4b, a second generation dendron bearing two
pyrenyl groups, is dominated by intramolecular excimer fluo-
rescence (∼97%, Figure 3). The emission of 5a (not shown)
also shows predominant excimer fluorescence. Ground state
stacking of the pyrenyl groups is probably not responsible, as
the absorption spectra of 4b and 5a show no observable
differences from pyrene itself.
The driving force for intermolecular electron transfer from
dimethylaniline to the lowest singlet excited state pyrene is 480
mV,16 and about 250 mV for electron transfer to pyrene excimer,
which is stabilized by 4 kcal/mol (at room temperature)
compared to singlet pyrene.17 Stern-Volmer bimolecular
quenching of 4b by 3-dimethylaminophenol in acetonitrile
revealed a kq of 1 × 1010 M-1 s-1, indicating diffusion-
controlled quenching with no evident exciplex formation.
Stern-Volmer bimolecular quenching of 5a by 3-(dimethyl-
amino)phenol in THF resulted in a kq of 4 × 109 M-1 s-1. As
the integrated intensity of the excimer emission from 4b (from
420-580 nm) decreased with the addition of each aliquot of
the quencher solution, the relative emission intensity from singlet
pyrene (in the region 370-400 nm) increased. Thus, the
excimer is more efficiently quenched than is the singlet excited
state, most likely because a larger solvent reorganization is
required in the production of a charge-separated species from a
relatively nonpolar precursor (i.e., the singlet excited state) than
from a more polar precursor (i.e., the excimer). Pyrene excimer
has a dipole moment of 2.5 D.18 Pyrene excimer emission also
was preferentially quenched over pyrene singlet emission for
bimolecular quenching of 5a by 3-(dimethylamino)phenol in
THF.
Figure 2. Steady-state fluorescence spectra of (a) 3a and (b) 3c in
degassed acetonitrile (<10-5 M); λex ) 266 nm.
with concentrations greater than 10-6 M; dilution to concentra-
tions below 5 × 10-7 M eliminated the excimer signal. Steady-
state fluorescence spectra for naphthyl-capped dendrons 1a, 2a,
3a, and 4a (both mono- and disubstituted at the chain ends)
show strong typical naphthalene fluorescence centered at 335
nm (Figure 2), plus a minor (always <5%) fluorescence at 290
nm. The fluorescence quantum yields (referenced to naphtha-
lene in cyclohexane11 ) for the disubstituted naphthyl-capped
dendrons 1a and 3a are 1-7% in acetonitrile or dichlo-
romethane. The fluorescence yields for the monosubstituted
naphthalene dendrons 2a and 4a are several times greater than
the fluorescence yields of corresponding disubstituted dendrons
1a and 3a in acetonitrile, most likely due to self-quenching by
nonradiative pathways. Therefore, in order to maximize den-
drimer fluorescence yield it is desirable to use the less-
substituted dendrons. This decrease of fluorescence intensity
upon polymerization has been observed frequently.6
Stern-Volmer bimolecular quenching of 3a with diethylami-
noethanol in acetonitrile gave a quenching constant kq of 6 ×
Dilution studies of 4d and 5c revealed a linear relationship
between fluorescence intensity and concentration (from 10-7
to 10-6 M), which is consistent with intramolecular fluorescence
quenching. Further evidence for intramolecular quenching is
found by comparing the intensities of emission steady-state
fluorescence spectra of the quencher capped dendrons 4d and
5c with the spectra of the corresponding alcohol-terminated
dendrons 4b and 5a. In the most dramatic case, the strong
excimer fluorescence of 4b in acetonitrile is quenched by almost
108 M-1 s-1
. This kq is somewhat slower than a typical
diffusion-controlled quench (kq ) 1.9 × 1010 in acetonitrile),12
as has been previously reported for the quenching of naphthalene
by aliphatic amines.13 Intramolecular fluorescence quenching
in acetonitrile is observed for 1c compared to 1a and for 3c
compared to 3a. When the donor was changed to a 3-(di-
methylamino)phenoxy group in 3d, 70% intramolecular quench-
ing was observed in acetonitrile (Figure 2). The driving force
for photoinduced electron transfer from dimethylaniline to the
lowest singlet excited state of naphthalene is 940 mV.14
The first generation pyrenyl-capped dendron 2c exhibits
typical pyrene fluorescence (Figure 3) when excited at 344 nm.15
(14) The driving force was calculated using ∆G ) E(D•+/D) - E(A/
A•+) - E00(S), where E(D•+/D) ) 0.81 V for N,N-dimethylaniline (vs SCE
in CH3CN), E(A/A•+) ) -2.29 V for naphthalene (vs SCE in CH3CN),
and E00(S) ) 92 kcal/mol, or 3.99 V for naphthalene: Kavarnos, G. J.;
Turro, N. J. Chem. ReV. 1986, 86, 401.
(15) Fo¨rster, T.; Kasper, K. Z. Physik. Chem. N. F. 1954, 1, 275.
(16) Schoburg, M.; Staerk, M.; Weller, A. Chem. Phys. Lett. 1973,
22, 1.
(11) Eaton, D. F. Pure Appl. Chem. 1988, 60, 1107.
(12) Kavarnos, G. J. Fundamentals of Photoinduced Electron Transfer;
VCH Publishers: New York, 1993.
(13) Meeus, F.; Van der Auweraer, M.; De Schryver, F. C. J. Am. Chem.
Soc. 1980, 102, 4017.
(17) Birks, J. B. Photophysics of Aromatic Molecules; Wiley-Inter-
science: New York, 1970.
(18) Gosh, A. S.; Basu, S. J. Photochem. 1974, 3, 247.

Chromophore-Labeled Dendrons
J. Am. Chem. Soc., Vol. 118, No. 18, 1996 4357
Table 3. Excimer Quenching of Pyrenyl-Capped Dendrons as a
Function of Solvent
the excitation flash, which is comparable to intramolecular
pyrene excimer formation in simple model systems such as 1,3-
di(1-pyrenyl)propane.20 Intramolecular quenching of excimer
or locally excited pyrene is evident in the shortened decay
lifetime of 4d compared to that of 4b (in both acetonitrile and
THF) and of 5c compared to that of 5a. A transient absorption
experiment of 4d in acetonitrile shows evidence for the
appearance of a pyrenyl radical anion absorbance at 700 nm,21
as is consistent with electron transfer as a possible quenching
mode. Strong coupling throughout the dendron skeleton, both
through-bond and through-space, would be expected by virtue
of the small energy gap between the HOMOs of alkoxyaniline
and of dialkoxybenzene.
Φf (Q)/Φf (0)a
dendron
in CH2Cl2
in THF
in CH3CN
4d
5c
60
20
80
50
90
70d
a Ratio of excimer fluorescence yield in the donor-appended dendron
to that observed in the analogous dendron lacking the attached donor.
b 4d is compared with 4a. c 5c is compared with 5a. d 5a and 5c are
not very soluble in acetonitrile. Therefore, this percent quenching is
approximate.
Table 4. Fluorescence Lifetimes for Monomer and Excimer in
Pyrenyl-Substituted Dendronsa
τ (ns)
τ (ns)
τ(ns)
τ (ns)
Conclusions
τ (ns)
480 nm 480 nm 480 nm 480 nm
A methoxy-capped model of the dendrimer backbone 3e
fluoresces weakly at 310 nm when excited at 284 nm. No
quenching of dendrimer backbone fluorescence in the model
compound 3g by a covalently-attached (dimethylamino)phenoxy
electron donor group was observed. Sensitized backbone
fluorescence was not detected in the emission spectra of any
naphthyl- or pyrenyl-capped dendron in these studies.
Steady-state fluorescence spectra of naphthyl-capped dendrons
(both mono- and disubstituted at the chain ends) provide no
evidence of intramolecular naphthalene excimer in dilute
solution, although intermolecular excimer does form in more
concentrated solutions. Naphthyl-capped dendrons with skel-
etons 1 and 3 had lower fluorescence quantum yields than those
with skeletons 2 and 4, possibly because of competing nonra-
diative self-quenching. Intramolecular quenching of the fluo-
rescence of the peripheral naphthyl groups by a covalently
attached electron donor (such as a triethylamino or [dimethyl-
amino]phenoxy group) has been demonstrated as a highly
efficient process.
Pyrene excimer emission dominates the observed fluorescence
spectrum for all pyrenyl-capped dendrons of generation two or
greater. The pyrene excimer fluorescence is quenched more
effectively than the pyrene singlet fluorescence upon bimolecular
quenching with 3-(dimethylamino)phenol. Intramolecular quench-
ing in dendrons bearing covalently attached electron donor
functionalities has been demonstrated through steady-state and
time-resolved fluorescence measurements and is attributed to
intramolecular photoinduced electron transfer. The amount of
quenching observed is a function of dendrimer generation
number and of solvent polarity.
compd
380 nm growthb decayb growthc decayc
1-pyrenemethanol
325
298
4a
4d
5a
5c
2.8
1.3
59
23
17
4.7
9.3
4.9
62
41
60
48
a Dilute solutions (∼10-6 M) were bubble degassed with argon. λex
) 355 nm. b In acetonitrile. c In THF.
90% in 4d (Figure 3). Quenching was always less efficient in
the third generation dendron than in the second generation for
each set of conditions studied. The decreased ratio of donor to
acceptors (and hence the effective local quencher concentration)
and the increased separation of the donor and acceptors on
electron transfer are reflected in the diminished quenching in
the third generation.
Table 3 shows solvent effects on excimer quenching for 4b
compared to 4d and for 5a compared to 5c. The alcohol-
terminated dendrons were used as standards because their
fluorescence intensity varies with solvent. For both sets of
dendrons, the quenching efficiency increases with increasing
solvent polarity (CH2Cl2 < THF < CH3CN), as would be
anticipated if a polar, coordinating solvent were to help stabilize
the transition state leading to the charge-separated product, thus
enhancing the observed steady-state fluorescence quenching
efficiency.
Fluorescence lifetimes of monomer (380 nm) and excimer
(480 nm) components of 1-pyrenemethanol, 4b, 4d, 5a, and 5c
obtained with single photon counting techniques are listed in
Table 4. Singlet emission of both 1-pyrenemethanol and 4b in
acetonitrile can be described by a single exponential decay with
lifetimes of approximately 300 ns. In 4b, 4d, 5a, and 5c, the
excimer emission grows in and then decays, and is best
described by a biexponential equation19
Together, these results suggest substantial electronic coupling
between appended chromophores and quenchers across the
dendrimer framework, affirming the possibility that these
chromophore-labeled dendrons can be used as molecular light
harvesters. Experiments to study energy transfer in chro-
mophore-labeled dendrons are under way.
k1
98 B 98 C
k2
A
k1[A]0
Experimental Section
(e-k t - e-k t
)
1
2
[B] )
k2 - k1
All chemicals were purchased from Aldrich and were used as
received unless otherwise indicated. 1-Pyrenemethanol and 1-bro-
momethylpyrene were synthesized by literature methods.22,23 Acetone
when [B]0 ) 0; k1 ) 1/τ1; k2 ) 1/τ2
(20) For example, see: (a) Zachariasse, K. A.; Ku¨hnle, W.; Leinhos,
U.; Reynders, P.; Striker, G. J. Phys. Chem. 1991, 95, 5476. (b)
Goedeweeck, R.; Ruttens, F.; Lopez-Arbeloa, F.; De Schryver, F. C.
Biopolymers 1987, 26, 1833. (c) Collart, P.; Demeyer, K.; Toppet, S.; De
Schryver, F. C. Macromolecular 1983, 16, 1390. (d) Collart, P.; Toppet,
S.; Zhou, Q. F.; Boens, N.; De Schryver, F. C. Macromolecules 1985, 18,
1026.
where τ1 ) rise lifetime; τ2 ) decay lifetime
where A ) singlet pyrene, B ) pyrene excimer, and C ) ground
state pyrene (in the case of 4b) or the pyrene radical anion
attained by intramolecular electron transfer (in the case of 4d).
The excimer signal reaches its maximum intensity 5 ns after
(21) Shida, T. Electronic Absorption Spectra of Radical Ions; Elsevier:
New York, 1988.
(19) Steinfeld, J. I.; Francisco, J. S.; Hase, W. L. Chemical Kinetics and
Dynamics; Prentice Hall: Englewood Cliffs, NJ, 1989.
(22) Akiyama, S.; Nakasuji, K.; Nakagawa, M. Bull. Chem. Soc. Jpn.
1971, 44, 2231.

4358 J. Am. Chem. Soc., Vol. 118, No. 18, 1996
Stewart and Fox
was distilled from potassium carbonate. Dichloromethane was distilled
from calcium chloride. Tetrahydrofuran (THF) was freshly distilled
from benzophenone ketyl. Potassium carbonate was stored in a 130
°C oven. 3-(Dimethylamino)phenol was purified by column chroma-
tography, followed by recrystallization from dichloromethane/hexanes.
All column chromatography was performed on silica gel. All solutions
were studied at an OD of ∼0.03 to ∼0.10. Single photon counting
experiments were conducted at the Center for Fast Kinetics Research
in Austin and were analyzed using Kaleidograph software.
Fluorescence quantum yields of all pyrene-labeled dendrons and of
1-pyrenemethanol were determined by reference to 9,10-diphenylan-
thracene in cyclohexane (Table 2).11 Dendrons 5a and 5c were only
sparingly soluble in acetonitrile, so the fluorescence quantum yields
for these compounds in acetonitrile should only be taken as approxima-
tions.
Preparation of 3,5-Bis[3,5-bis-(2-naphthylmethyloxy)benzyloxy]-
benzyl Bromide [3b]. Carbon tetrabromide (130 mg, 0.40 mmol) was
added to a stirred solution of 3a (120 mg, 0.13 mmol) in dry THF (1
mL) under Ar. After 5 min stirring, triphenylphosphine (140 mg, 0.55
mmol) was added, and the resulting reaction mixture was stirred for 3
h. The reaction mixture was partitioned between water (3 mL) and
CH2Cl2 (10 mL). The organic layer was washed with another 10 mL
water, and the combined aqueous solutions were extracted with CH2-
Cl2 (2 × 10 mL). The combined dichloromethane portions were dried
over MgSO4, filtered through Celite, and concentrated in Vacuo. The
product was purified by flash column chromatography in 20% ethyl
acetate:80% hexanes increasing to 40% ethyl acetate:60% hexanes; the
eluent was then dissolved in a minimum amount of CH2Cl2 and added
dropwise to a mixture of equal parts ether and hexanes. The precipitated
white solid was collected on a glass frit to give the desired product in
50-80% yield, mp 120-124 °C. 1H NMR (CDCl3): δ 7.86-7.81 (m,
16 H), 7.52-7.46 (m, 12 H), 6.72 (d, J ) 1.6 Hz, 4 H), 6.66 (m, 2 H),
6.59 (d, J ) 1.9 Hz, 2 H), 6.51 (m, 1 H), 5.20 (s, 8 H), 4.96 (s, 4 H),
4.36 (s, 2 H). 13C NMR (CDCl3): δ 160.2, 159.9, 139.7, 139.2, 134.3,
133.3, 133.1, 128.4, 128.0, 127.7, 126.4, 126.2, 126.1, 125.3, 108.3,
106.5, 102.2, 101.9, 70.30, 70.05, 33.55. HRMS (m/z): calcd. for
C65H51O6Br, 1007.2947; found, 1007.2938.
Preparation of 3,5-Bis[3,5-bis-(2-naphthylmethyloxy)benzyloxy]-
benzyl (3-N,N-Dimethylaminophenyl) Ether [3d]. A suspension of
3-(dimethylamino)phenol (62 mg, 0.45 mmol), K2CO3 (87 mg, 0.63
mmol), and 18-crown-6 ether (24 mg, 0.090 mmol) in dry acetone (25
mL) was heated at reflux for 0.5 h before neat 3b (500 mg, 1.0 mmol)
was added. The mixture was heated at reflux for 2 h and then stirred
at room temperature for 16 h. Acetone was removed in Vacuo, and
the product was dissolved in CH2Cl2 (3 × 20 mL) before being washed
with water (2 × 75 mL) and then brine (100 mL). Solvent was removed
in Vacuo. The product, a clear glass, was isolated in 95% yield upon
column chromatography in CH2Cl2. 1H NMR (CDCl3): δ 7.86-7.79
(m, 16 H), 7.53-7.45 (m, 12 H), 7.16-7.11 (m, 1 H), 6.74-6.73 (m,
4 H), 6.68-6.65 (m, 4H), 6.55-6.54 (m, 1 H), 6.38-6.33 (m, 3 H),
5.20 (s, 8 H), 4.98 (s, 4 H), 4.96 (s, 2 H). 13C NMR (CDCl3): δ 160.2,
160.0, 159.9, 152.0, 139.9, 139.4, 134.3, 133.3, 133.1, 129.7, 128.4,
128.0, 127.7, 126.4, 126.2, 126.0, 125.3, 106.5, 106.5, 106.0, 102.3,
101.8, 101.5, 100.1, 70.28, 70.00, 69.84, 40.55. HRMS (m/z): calcd.
for C73H61NO7, 1063.4448; found, 1063.4424.
Preparation of 3,5-Dimethoxybenzyl Bromide [1e]. Carbon
tetrabromide (12 g, 37 mmol) and triphenylphosphine (9.8 g, 37 mmol)
were added to a solution of 3,5-dimethoxybenzyl alcohol (5.0 g, 30
mmol) in dry THF (50 mL) under Ar. After 1 h, the reaction was
quenched by the addition of water (100 mL). After having been stirred
for 10 min, the mixture was extracted with CH2Cl2 (3 × 50 mL). The
organic layer was washed with brine (100 mL) and was concentrated
in Vacuo. Isolation by column chromatography (20% ethyl acetate:
80% hexanes) gave an off-white powder, which was recrystallized from
CH2Cl2/hexane in 61% yield, mp 69-70 °C. 1H NMR (CDCl3): δ
6.54 (d, J ) 2.2 Hz, 2 H), 6.40-6.39 (m, 1 H), 4.42 (s, 2 H), 3.80 (s,
6 H). 13C NMR (CDCl3): δ 160.9, 139.7, 107.0, 100.6, 55.38, 33.56.
HRMS (m/z): calcd. for C9H12O2Br, 231.0021; found, 231.0022.
Preparation of 3,5-Bis[3,5-(dimethoxy)benzyloxy]benzyl Alcohol
[3e]. A suspension of 3,5-dimethoxybenzyl alcohol (1.0 g, 7.3 mmol),
K2CO3 (2.5 g, 18 mmol), and 18-crown-6 ether (390 mg, 1.5 mmol) in
dry acetone (180 mL) was heated at reflux under Ar for 0.5 h before
neat 1e (3.7 g, 16 mmol) was added. The mixture was heated at reflux
for 42 h before acetone was removed in Vacuo. The product was
dissolved in CH2Cl2 (3 × 75 mL) and washed with water (2 × 200
mL) and then with brine (250 mL). Removal of solvent in Vacuo gave
a white solid, isolated in 88% yield upon column chromatography in
CH2Cl2, mp 83-86 °C. 1H NMR (CDCl3): δ 6.62 (d, J ) 1.9 Hz, 2
H), 6.57 (d, J ) 1.9 Hz, 4 H), 6.54 (t, J ) 1.8 Hz, 1 H), 6.41 (t, J )
1.9 Hz, 2 H), 4.98 (s, 4 H), 4.63 (d, J ) 6.1 Hz, 2 H), 3.80 (s, 12 H),
1.61 (t, J ) 5.9 Hz, 1 H). 13C NMR (CDCl3): δ 161.0, 160.1, 143.4,
139.2, 105.8, 105.2, 101.4, 99.93, 70.03, 65.28, 55.35. HRMS (m/z):
calcd. for C25H28O7, 440.1835; found, 440.1819.
Preparation of 3,5-Bis-(2-naphthylmethyloxy)benzyl Alcohol [1a].
2-Bromomethylnaphthalene (2.2 g, 10 mmol), 3,5-dihydroxybenzyl
alcohol (640 mg, 4.5 mmol), anhydrous K2CO3 (1.6 g, 11 mmol), and
18-crown-6 ether (240 mg, 0.91 mmol) were placed in dry acetone
(40 mL) and heated at reflux under Ar for 56 h, before being stirred at
room temperature for another 12 h. Acetone was removed in Vacuo,
and the remaining solid was taken up in CH2Cl2 (3 × 50 mL) and then
washed with distilled water (3 × 50 mL). The aqueous layer was
extracted with CH2Cl2 (25 mL), and the combined organics were washed
with brine (50 mL), dried over MgSO4, filtered, and concentrated in
Vacuo. Recrystallization from hot toluene/hexanes gave a white
crystalline product in 69% yield, mp 94-95 °C. 1H NMR (CDCl3):
δ 7.83-7.97 (m, 8 H), 7.47-7.54 (m, 6 H), 6.68 (d, J ) 1.5 Hz, 2 H),
6.64 (d, J ) 1.5 Hz, 1 H), 5.22 (s, 4 H), 4.65 (s, 2 H), 2.36 (s, 1 H).
13C NMR (CDCl3): δ 160.2, 143.5, 134.3, 133.3, 133.1, 128.4, 128.0,
127.7, 126.3, 126.2, 126.1, 125.3, 105.9, 101.5, 70.3, 65.3. HRMS
(m/z): calcd. for C29H24O3, 420.1725; found, 420.1716.
Preparation of 3,5-Bis-(2-naphthylmethyloxy)benzyl Bromide
[1b]. Carbon tetrabromide (1.6 g, 4.9 mmol) was added to a stirred
solution of 1a (1.6 g, 3.9 mmol) in dry THF (5 mL) under Ar. After
5 min stirring, triphenylphosphine (1.4 g, 5.3 mmol) was added, and
the resulting reaction mixture was stirred for 1 h. The reaction mixture
was partitioned between water (50 mL) and CH2Cl2 (20 mL). The
organic layer was washed with water (3 × 100 mL), and the combined
aqueous solutions were extracted once with CH2Cl2. The combined
CH2Cl2 solutions were dried over MgSO4, filtered through Celite, and
concentrated in Vacuo. Recrystallized from a mixture of ether,
methanol, and hexanes gave a white solid in 23-48% yield, mp 108-
109 °C. 1H NMR (CDCl3): δ 7.88-7.83 (m, 8 H), 7.54-7.45 (m, 6
H), 6.70 (d, J ) 2.0 Hz, 2 H), 6.64 (d, J ) 2.0 Hz, 1 H), 5.20 (s, 4 H),
4.43 (s, 2 H). 13C NMR (CDCl3): δ 160.1, 139.8, 134.1, 133.3, 133.1,
128.4, 128.0, 127.7, 126.4, 126.3, 126.1, 125.3, 108.3, 102.3, 70.3,
33.5. HRMS (m/z): calcd. for C29H23O2Br, 482.0881; found, 482.0883.
Preparation of 3,5-Bis[3,5-bis-(2-naphthylmethyloxy)benzyloxy]-
benzyl Alcohol [3a]. A suspension of 1b (530 mg, 1.1 mmol), 3,5-
dihydroxybenzyl alcohol (70 mg, 0.5 mmol), anhydrous K2CO3 (170
mg, 1.3 mmol), and 18-crown-6 ether (26 mg, 0.10 mmol) in dry
acetone (10 mL) was heated at reflux under Ar for 45 h. Acetone was
removed in Vacuo, and the remaining solid was taken up in CH2Cl2 (2
× 20 mL) and then washed with distilled water (3 × 20 mL). The
organic layer was dried over MgSO4, filtered, and concentrated in
Vacuo. The product was purified by flash column chromatography in
CH2Cl2 to give a fluffy white solid in 62% yield, mp 65-70 °C. 1H
NMR in CDCl3: δ 7.93-7.80 (m, 16 H), 7.52-7.46 (m, 12 H), 6.72
(d, J ) 2.1 Hz, 4 H), 6.66 (m, 2 H), 6.51 (d, J ) 2.1 Hz, 2 H), 6.57
(m, 1 H), 5.20 (s, 8 H), 4.99 (s, 4 H), 4.57 (d, J ) 6.1 Hz, 2 H). 13C
NMR (CDCl3): δ 160.2, 160.1, 143.4, 139.4, 134.3, 133.3, 133.1, 128.4,
128.0, 127.7, 126.4, 126.2, 126.1, 125.3, 106.5, 105.8, 101.8, 101.4,
70.28, 69.97, 65.29. HRMS (m/z): calcd. for C65H52O7, 944.3713;
found, 944.3711.
(23) Okamoto, H.; Arai, T.; Sakuragi, H.; Tokumaru, K. Bull. Chem.
Soc. Jpn. 1990, 63, 2881.
(24) Reimann, E. Liebigs Ann. Chem. 1971, 750, 109.
(25) Pitt, C. G.; Seltzman, H. H.; Sayed, Y.; Twine, C. E., Jr.; Williams,
D. L. J. Org. Chem. 1979, 44, 677.
(26) Sargent, M. V.; Stanojevic, E. J. Chem. Soc., Perkin Trans. I 1984,
1919.
Preparation of 3,5-Bis[3,5-(dimethoxy)benzyloxy]benzyl Bromide
[3f]. Carbon tetrabromide (2.38 g, 7.18 mmol) and triphenylphosphine
(1.88 g, 7.18 mmol) were added to a solution of 3e (2.53 g, 5.74 mmol)
in dry THF (50 mL) under Ar. After 2 h, the reaction was quenched

Chromophore-Labeled Dendrons
J. Am. Chem. Soc., Vol. 118, No. 18, 1996 4359
by the addition of water (100 mL). After having been stirred for 30
min, the mixture was extracted with CH2Cl2 (2 × 100 mL). The organic
layer was washed with brine (200 mL) and was concentrated in Vacuo.
The product was isolated by column chromatography (50% CH2Cl2:
50% hexanes) as a white powder in 83% yield, mp 127-129 °C. 1H
NMR (CDCl3): δ 6.63 (d, J ) 2.2 Hz, 2 H), 6.57 (d, J ) 2.2 Hz, 4 H),
6.54 (t, J ) 2.2 Hz, 1 H), 6.42 (t, J ) 2.2 Hz, 2 H), 4.97 (s, 2 H), 4.41
(s, 2 H), 3.80 (s, 12 H). 13C NMR (CDCl3): δ 160.0, 160.0, 139.8,
139.0, 108.2, 105.6, 102.3, 100.0, 70.14, 55.36, 33.52. HRMS (m/z):
calcd. for C25H27O6Br, 502.0991; found, 502.0985.
Preparation of 3,5-Bis[3,5-(dimethoxy)benzyloxy]benzyl (3-N,N-
Dimethylaminophenyl) Ether [3g]. A suspension of 3-(dimethylami-
no)phenol (110 mg, 0.80 mmol), K2CO3 (170 mg, 1.3 mmol), and
18-crown-6 ether (42 mg, 0.16 mmol) in dry acetone (25 mL) was
heated at reflux under Ar for 1 h before neat 3f (500 mg, 1.0 mmol)
was added. The mixture was heated at reflux for 2 h and then stirred
at room temperature for 16 h before acetone was removed in
Vacuo. The product was dissolved in CH2Cl2 (100 mL) and then
washed with water (150 mL) and then brine (150 mL). Removal of
solvent in Vacuo a clear glass, isolated in 69% yield by column
chromatography in 50% CH2Cl2:50% hexanes increasing to 100% CH2-
Cl2. 1H NMR (CDCl3): δ 7.14 (t, J ) 7.8 Hz, 1 H), 6.70 (s, 2 H),
6.58-6.56 (m, 4 H), 6.42-6.33 (m, 6 H), 4.98 (s, 6 H), 3.80 (s, 12 H),
2.93 (s, 6 H). 13C NMR (CDCl3): δ 161.0, 160.1, 159.9, 152.0, 139.9,
139.2, 127.9, 106.5, 106.0, 105.3, 102.3, 101.6, 100.1, 100.0, 70.09,
69.86, 55.36, 40.57. HRMS (m/z): calcd. for C33H37NO7, 559.2570;
found, 559.2571.
Preparation of 3-(2-Naphthylmethyloxy)benzyl Alcohol [2a]. A
solution of 3-hydroxybenzyl alcohol (1.6 g, 13 mmol), anhydrous K2-
CO3 (2.1 g, 15 mmol), and 18-crown-6 ether (68 mg, 2.6 mmol) in dry
acetone (25 mL) was heated at reflux under Ar for 30 min, and then
neat 2-bromomethylnaphthalene (3.1 g, 14 mmol) was added. The
mixture was heated at reflux for 16 h before acetone was removed in
Vacuo. The product was dissolved in CH2Cl2 (300 mL) and washed
with water (2 × 200 mL) and then with brine (300 mL). Removal of
solvent in Vacuo followed by flash column chromatography in CH2Cl2
gave a white solid in 78% yield, mp 106-108 °C. 1H NMR (CDCl3):
δ 7.89-7.83 (m, 4 H), 7.55-7.46 (m, 3 H), 7.31-7.25 (m, 1 H), 7.07,
(s, 1 H), 6.97-6.94 (m, 2 H), 5.25 (s, 2 H), 4.68 (d, J ) 6.0 Hz, 2 H),
1.63 (t, J ) 6.0 Hz, 1 H). 13C NMR (CDCl3): δ 159.1, 142.6, 134.5,
133.3, 133.1, 129.7, 128.4, 127.9, 127.7, 126.3, 126.2, 126.1, 125.2,
119.4, 114.2, 113.4, 70.14, 65.28. HRMS (m/z): calcd. for C18H16O2,
264.1150; found, 264.1137.
Preparation of 3-(2-Naphthyloxy)benzyl Bromide [2b]. Carbon
tetrabromide (4.2 g, 13 mmol) and triphenylphosphine (3.3 g, 13 mmol)
were added to a solution of 2a (2.6 g, 10 mmol) in dry THF (20 mL)
under Ar. After 0.5 h, the reaction was quenched by the addition of
water (40 mL). After having been stirred for 10 min, the mixture was
extracted with CH2Cl2 (3 × 25 mL). The organic layer was washed
with brine (100 mL), concentrated in Vacuo, and purified by column
chromatography (30% CH2Cl2:70% hexanes to 50% CH2Cl2:50%
hexanes) to give a white powder in 86% yield, mp 105-106 °C. 1H
NMR (CDCl3): δ 7.89-7.84 (m, 4 H), 7.56-7.48 (m, 3H), 7.29-
7.24 (m, 1 H), 7.07 (s, 1 H), 7.02-6.94 (m, 2 H), 5.24 (s, 2 H), 4.47
(s, 2 H). 13C NMR (CDCl3): δ 159.0, 139.2, 134.2, 133.3, 133.1, 129.9,
128.4, 128.0, 127.7, 126.4, 126.3, 126.1, 125.2, 121.6, 115.6, 115.0,
70.23, 33.41. HRMS (m/z): calcd. for C18H15OBr, 326.0306; found,
326.0303.
126.2, 126.0, 125.2, 119.9, 114.4, 113.9, 105.7, 101.3, 69.87, 65.21.
HRMS (m/z): calcd. for C43H36O5, 633.2641; found, 633.2619.
Preparation of 3-(1-Pyrenylmethyloxy)benzyl Alcohol [2c].
A
suspension of 3-hydroxybenzyl alcohol (120 mg, 1.0 mmol), anhydrous
K2CO3 (260 mg, 1.2 mmol), 18-crown-6 ether (28 mg, 0.20 mmol),
and 1-bromomethylpyrene22,23 (350 mg, 1.2 mmol) in dry acetone (25
mL) was heated at reflux under Ar for 22 h before acetone was removed
in Vacuo. The remaining solid was dissolved in CH2Cl2 (2 × 20 mL),
and the resulting solution was extracted with distilled water (3 × 20
mL). The organic layer was washed with brine and concentrated in
Vacuo. Upon column chromatography in CH2Cl2 a pale yellow solid
was obtained in 96% yield, mp 117-119 °C. 1H NMR (CDCl3): δ
8.31-8.00 (m, 9.5 H), 7.35 (t, J ) 7.8 Hz, 1 H), 7.30 (s, 1 H), 7.16-
6.99 (m, 2 H), 5.75 (s, 2 H), 4.70 (d, J ) 5.8 Hz, 2 H), 1.73 (t, J ) 6.0
Hz, 1 H). 13C NMR (CDCl3): δ 159.2, 142.7, 131.6, 131.2, 130.7,
129.7, 129.3, 128.0, 127.6, 127.4, 126.8, 126.0, 125.4, 125.4, 124.9,
124.7, 124.6, 123.0, 119.5, 114.3, 114.3, 113.4, 68.76, 65.26. HRMS
(m/z): calcd. for C24H18O2, 338.1307; found, 338.1304.
Preparation of 3-(1-Pyrenylmethyloxy)benzyl Bromide [2d].
Carbon tetrabromide (1.9 g, 5.7 mmol) and triphenylphosphine (1.5 g,
5.7 mmol) were added to a solution of 2c (1.5 g, 4.5 mmol) in dry
THF (10 mL) under Ar. After 1 h, the reaction was quenched by the
addition of water (20 mL). After 30 min stirring, the mixture was
extracted with CH2Cl2 (3 × 50 mL). The organic layer was washed
with brine (50 mL) and concentrated in Vacuo. Column chromatog-
raphy (20% CH2Cl2:80% hexanes to 50% CH2Cl2:50% hexanes) yielded
a pale yellow solid in 96% yield, mp 110-112 °C. 1H NMR
(CDCl3): δ 8.30-8.00 (m, 9 H), 7.31 (t, J ) 8.0 Hz, 1 H), 7.16 (s, 1
H), 7.15 (d, J ) 7.9 Hz, 2 H), 5.73 (s, 2 H), 4.50 (s, 2 H). 13C NMR
(CDCl3): δ 159.1, 139.3, 131.6, 131.2, 130.7, 129.9, 129.5, 129.3,
128.1, 127.7, 127.4, 126.9, 126.0, 125.4, 125.4, 124.9, 124.6, 124.6,
123.0, 121.7, 115.6, 115.1, 68.83, 33.42. HRMS (m/z): calcd. for
C24H17OBr, 400.0463; found, 400.0472.
Preparation of 3,5-Bis[3-(1-pyrenylmethyloxy)benzyloxy]benzyl
Alcohol [4b]. A suspension of 3,5-dimethoxybenzyl alcohol (640 mg,
4.6 mmol), K2CO3 (1.6 g, 11 mmol), and 18-crown-6 ether (240 mg,
0.91 mmol) in acetone (180 mL) was heated at reflux under Ar for 30
min before neat 2d (4.0 g, 10 mmol) was added. The mixture was
heated at reflux for 96 h. Acetone was removed in Vacuo. The product
was dissolved in CH2Cl2 (2 × 75 mL), and the resulting solution was
extracted with distilled water (3 × 150 mL). The organic layer was
washed with brine (50 mL) and concentrated under reduced pressure
to give a pale yellow solid. Column chromatography in CH2Cl2 gave
a pale beige powder (55%), mp 77-79 °C, and 1.45 g of recovered
2d. 1H NMR (CDCl3): δ 8.31-7.98 (m, 18 H), 7.36 (t, J ) 7.8 Hz,
2 H), 7.19 (s, 2 H), 7.07-7.03 (m, 4 H), 6.60 (d, J ) 1.8 Hz, 2 H),
6.54 (d, J ) 2.0 Hz, 1 H), 5.75 (s, 4 H), 5.04 (s, 4 H), 4.59 (d, J ) 6.2
Hz, 2 H) (benzyl alcohol proton signal was obscured by water). 13C
NMR (CDCl3): δ 160.1, 159.2, 143.4, 138.6, 131.6, 131.2, 130.7, 129.8,
129.7, 129.3, 128.0, 127.6, 127.4, 126.9, 126.0, 125.4, 125.4, 124.9,
124.7, 124.6, 123.0, 120.0, 114.6, 113.9, 105.8, 101.4, 69.93, 68.81,
65.29. HRMS (m/z): calcd. for C55H40O5, 780.2876; found, 780.2817.
Preparation of 3,5-Bis[3-(1-pyrenylmethyloxy)benzyloxy]benzyl
Bromide [4c]. Carbon tetrabromide (988 mg, 2.98 mmol) and
triphenylphosphine (782 mg, 2.98 mmol) were added to a solution of
4b (1.86 g, 2.38 mmol) in dry THF (20 mL) under Ar. After 1.5 h,
the reaction was quenched by the addition of water (40 mL). After
being stirred for 30 min, the mixture was extracted with CH2Cl2 (2 ×
30 mL). The organic layer was washed with brine (30 mL) and was
concentrated in Vacuo to give a yellow foam. Column chromatography
(50% CH2Cl2:50% hexanes to 70% CH2Cl2:30% hexanes) gave a pale
yellow solid in 90% yield, mp 128-129 °C. 1H NMR (CDCl3): δ
8.31-7.98 (m, 18 H), 7.35-7.31 (t, J ) 8.1 Hz, 2 H), 7.19 (s, 2 H),
7.08-7.05 (m, 4 H), 6.62 (d, J ) 2.1 Hz, 2 H), 6.54 (d, J ) 2.0 Hz,
1 H), 5.75 (s, 4 H), 5.02 (s, 4 H), 4.37 (s, 2 H). 13C NMR (CDCl3):
δ 160.0, 159.2, 139.8, 138.4, 131.6, 131.2, 130.8, 129.8, 129.7, 129.3,
128.1, 127.6, 127.4, 126.9, 126.0, 125.4, 125.4, 124.9, 124.7, 124.7,
123.0, 120.1, 114.7, 114.0, 108.3, 102.2, 70.01, 68.84, 33.52. HRMS
(m/z): calcd. for C55H39O4Br, 842.2032; found, 842.2037.
Preparation of 3,5-Bis[3-(1-naphthyloxy)benzyloxy]benzyl Alco-
hol [4a]. A suspension of 3,5-dimethyoxybenzyl alcohol (486 mg, 3.47
mmol), K2CO3 (1.20 g, 8.68 mmol), and 18-crown-6 ether (180 mg,
0.69 mmol) in dry acetone (150 mL) was heated at reflux under Ar for
1 h, and then neat 2b (2.50 g, 7.64 mmol) was added. The mixture
was heated at reflux for 41 h. Acetone was removed in Vacuo. The
product was taken up in CH2Cl2 (2 × 100 mL) and then washed with
water (2 × 150 mL) and brine (250 mL). Removal of solvent in Vacuo
and column chromatography in CH2Cl2 gave a colorless glass in 75%
yield. 1H NMR (CDCl3): δ 7.89-7.84 (m, 8 H), 7.56-7.48 (m, 6 H),
7.32 (t, J ) 8.1 Hz, 2 H), 7.13 (s, 2 H), 7.04-6.97 (m, 4 H), 6.62 (d,
J ) 1.9 Hz, 2 H), 6.56 (d, J ) 2.1 Hz, 1 H), 5.23 (s, 4 H), 5.02 (s, 4
H), 4.60 (s, 2 H), 2.38 (s, 1 H). 13C NMR (CDCl3): δ 160.1, 159.1,
143.4, 138.5, 134.4, 133.3, 133.0, 129.7, 128.4, 127.9, 127.7, 126.3,
Preparation of 3,5-Bis[3-(1-pyrenylmethyloxy)benzyloxy]benzyl
(3-N,N-Dimethylaminophenyl) Ether [4d]. A suspension of 3-(dim-
ethylamino)phenol (66 mg, 0.048 mmol), K2CO3 (80 mg, 0.58 mmol),

4360 J. Am. Chem. Soc., Vol. 118, No. 18, 1996
Stewart and Fox
and 18-crown-6 ether (25 mg, 0.096 mmol) in acetone (30 mL) was
heated at reflux for 0.5 h before neat 4c (410 mg, 0.48 mmol) was
added. The mixture was heated at reflux for 17 h before acetone was
removed in Vacuo. The product was dissolved in CH2Cl2 (25 mL),
and the resulting solution was washed with distilled water (2 × 25
mL). The organic layer then was washed with brine (25 mL) and
concentrated under reduced pressure. The product, a very faint yellow
solid, was isolated in 45% yield by column chromatography (50% CH2-
Cl2:50% hexanes increasing to 100% CH2Cl2), mp 78 °C. 1H NMR
(CDCl3): δ 8.29-7.97 (m, 18 H), 7.33 (t, J ) 7.9 Hz, 2 H), 7.21 (s,
2 H), 7.20-7.03 (m, 1 H), 7.06-7.03 (m, 4 H), 6.71 (d, J ) 2.0 Hz,
2 H), 6.58 (m, 1 H), 6.36 (m, 2 H), 5.72 (s, 4 H), 5.04 (s, 4 H), 4.97
(s, 2 H). 13C NMR (CDCl3): δ 160.1, 159.9, 159.2, 152.0, 139.9, 138.6,
131.5, 131.2, 130.7, 129.7, 129.7, 129.7, 129.2, 128.0, 127.6, 127.4,
126.9, 126.0, 125.4, 125.4, 124.9, 124.7, 124.6, 123.0, 120.1, 114.6,
113.9, 106.5, 106.0, 102.2, 101.5, 100.1, 69.96, 69.82, 68.79, 40.53.
HRMS (m/z): calcd. for C63H49NO5, 899.3611; found, 899.3615.
Preparationof3,5-Bis{3,5-bis-[3-(1-pyrenylmethyloxy)benzyloxy]-
benzyloxy}benzyl Alcohol [5a]. A suspension of 3,5-dimethoxybenzyl
alcohol (140 mg, 1.0 mmol), K2CO3 (360 mg, 2.6 mmol), and 18-
crown-6 ether (50 mg, 0.2 mmol) in acetone (60 mL) was heated at
reflux under Ar for 1 h before neat 4c (1.8 g, 2.2 mmol) was added.
The mixture was heated at reflux for 48 h. Dry benzene (15 mL) was
added in an attempt to solubilize a yellow film coating the flask. After
a total reflux time of 72 h, solvent was removed in Vacuo. The product
was dissolved in CH2Cl2 (3 × 100 mL), and the resulting solution was
extracted with distilled water (2 × 200 mL). The organic layer was
washed with brine (250 mL) and concentrated under reduced pressure
to give a pale yellow solid. Column chromatography (50% CH2Cl2:
50% hexanes increasing polarity to 100% CH2Cl2 to 95% CH2Cl2:5%
methanol) gave a pale yellow solid in 95% yield, mp 113-115 °C. 1H
NMR (CDCl3): δ 8.21-7.93 (m, 36 H), 7.34-7.24 (m, 4 H), 7.14-
7.13 (m, 4 H), 7.03-6.97 (m, 12 H), 6.61 (d, J ) 2.2 Hz, 2 H), 6.52-
6.51 (m, 2 H), 6.46 (t, J ) 2.2 Hz, 1 H), 5.64 (s, 8 H), 4.97 (s, 8 H),
4.88 (s, 4 H), 4.51 (s, 2 H). 13C NMR (CDCl3): δ 160.0, 159.9, 159.1,
143.6, 139.3, 138.5, 131.4, 131.1, 130.6, 129.7, 129.5, 129.1, 127.9,
127.8, 127.5, 127.4, 127.2, 126.7, 125.9, 125.2, 124.7, 124.5, 122.8,
120.0, 114.5, 113.9, 106.4, 105.6, 101.5, 101.2, 69.85, 69.78, 68.58,
64.98. HRMS (m/z): calcd. for C117H84O11, 1664.6014; found,
1664.3024.
Preparationof3,5-Bis{3,5-bis-[3-(1-pyrenylmethyloxy)benzyloxy]-
benzyloxy}benzyl Bromide [5b]. Carbon tetrabromide (300 mg, 0.91
mmol) and triphenylphosphine (240 mg, 0.91 mmol) were added to a
solution of 5a (1.21 g, 0.727 mmol) in dry THF (30 mL) under Ar.
After 1 h, carbon tetrabromide (300 mg) and triphenylphosphine (240
mg) were added. After an additional hour, the reaction was quenched
by the addition of water (50 mL). After having been stirred for 15
min, the mixture was transferred to a separatory funnel, and water (50
mL) and dichloromethane (100 mL) were added. Layers were
separated, and the aqueous portion was extracted with CH2Cl2 (2 × 50
mL). The organic layer was washed with brine (100 mL) and was
concentrated in Vacuo. Column chromatography (75% CH2Cl2:25%
hexanes) yielded a pale beige solid (97%), mp 105-109 °C. 1H NMR
(CDCl3): δ 8.18-7.91 (m, 36 H), 7.26 (t, J ) 7.9 Hz, 4 H), 7.13 (s,
4 H), 6.99-6.97 (m, 8 H), 6.59 (d, J ) 2.1 Hz, 4 H), 6.55 (d, J ) 2.2
Hz, 2 H), 6.53 (t, J ) 2.2 Hz, 2 H), 6.46 (t, J ) 2.1 Hz, 1 H), 5.61 (s,
8 H), 4.96 (s, 8 H), 4.84 (s, 4 H), 4.31 (s, 2 H). 13C NMR (CDCl3):
δ 160.1, 159.2, 139.0, 138.5, 131.5, 131.2, 130.7, 129.7, 129.6, 129.2,
128.0, 127.9, 127.6, 127.5, 127.4, 127.3, 126.8, 125.9, 125.3, 124.9,
124.6, 124.5, 122.9, 120.0, 114.6, 113.9, 108.2, 106.4, 101.7, 69.9,
69.9, 68.7, 33.6. HRMS (m/z): calcd. for C117H84O10Br, 1727.5287;
found, 1727.5269.
Preparationof3,5-Bis{3,5-bis-[3-(1-pyrenylmethyloxy)benzyloxy]-
benzyloxy}benzyl (3-N,N-Dimethylaminophenyl) Ether [5c].
A
suspension of 3-(dimethylamino)phenol (32 mg, 0.23 mmol), K2CO3
(32 mg, 0.23 mmol), and 18-crown-6 ether (3.0 mg, 0.010 mmol) in
acetone (15 mL) was heated at reflux for 0.5 h before neat 5b (40 mg,
0.023 mmol) was added. The mixture was heated at reflux overnight
before acetone was removed. The burgundy-colored residue was
dissolved in CH2Cl2 (25 mL), and the resulting solution was washed
with distilled water (2 × 25 mL). The organic layer then was washed
with brine (25 mL) and concentrated in Vacuo. The product, a very
faint yellow film, was isolated in 83% yield by column chromatography
(50% CH2Cl2:50% hexanes increasing to 75% CH2Cl2:25% hexanes).
1H NMR (CDCl3): δ 8.20-7.80 (m, 36 H), 7.26 (t, J ) 8.0 Hz, 4 H),
7.14 (t, J ) 1.7 Hz, 4 H), 7.08-7.06 (m, 1 H), 6.99 (d, J ) 7.9 Hz, 4
H), 6.98 (d, J ) 7.9 Hz, 4 H), 6.64 (d, J ) 2.2 Hz, 2 H),6.61 (d, J )
2.3 Hz, 4 H), 6.52 (t, J ) 2.2 Hz, 2 H), 6.49 (t, J ) 2.2 Hz, 1 H),6.30-
6.29 (m, 3 H), 5.64 (s, 8 H), 4.97 (s, 8 H), 4.90 (s, 2 H), 4.89 (s, 4 H),
2.82 (s, 6 H). 13C NMR (CDCl3): δ 160.1, 160.0, 159.2, 139.9, 139.3,
138.6, 131.5, 131.2, 130.7, 129.8, 129.7, 129.7, 129.2, 128.0, 127.7,
127.6, 127.3, 126.8, 126.0, 125.3, 124.9, 124.6, 123.0, 120.0, 114.7,
113.9, 110.1, 106.5, 106.4, 106.4, 106.0, 102.2, 102.2, 101.6, 101.5,
100.1, 69.9, 69.9, 69.8, 68.7, 40.5. HRMS (m/z): calcd. for C125H94-
NO11, 1784.6827; found, 1784.6883.
Preparation of 3,5-Dihydroxybenzyl Alcohol [29654-55-5] by a
Modified Procedure.24-26 Excess 1 M solution of borane in tetrahy-
drofuran (260 mL) was added dropwise over an 80-min period to a 0
°C solution of 3,5-dihydroxybenzoic acid (Pfaltz and Bauer, 12.5 g) in
anhydrous THF (40 mL) under Ar. A white precipitate formed after
∼50 mL of borane solution was added. The resulting mixture was
allowed to warm to room temperature over a 2 h period, stirred
overnight at room temperature, and then heated at reflux for an
additional 2 h. Distilled water (80 mL) was added dropwise to the
cooled reaction mixture. The resulting clear solution was allowed to
stir for 45 min before being transferred to a separatory funnel. Brine
(∼50 mL) was added, and the layers were separated. Excess NaCl
was added to the aqueous layer, which was subsequently extracted with
diethyl ether (2 × 75 mL). The combined organics were washed with
brine (100 mL), dried over MgSO4, filtered, and concentrated in Vacuo
to give a pale yellow solid. The solid was recrystallized from acetone/
hexanes to give the product in 76-81% yield.
Acknowledgment. Financial support from the Office of
Basic Energy Sciences of the U.S. Department of Energy and
from the Texas Advanced Research Program is gratefully
acknowledged. G.S. wishes to thank Dr. D. V. O’Connor for
assistance with single photon counting experiments, T. A.
Rhodes for assistance with the transient absorption experiments,
and Dr. H. H. Fox for many helpful discussions.
JA954021I