Liquid crystalline coronene derivatives with extraordinary fluorescence properties

Full text of DOI:10.1002/(SICI)1521-3773(19980605)37:10<1434::AID-ANIE1434>3.0.CO;2-P

COMMUNICATIONS
terminal alkynes and subsequent catalytic hydrogenation of
the triple bonds.[4] It appeared logical to apply this aryl ±
ethynyl coupling to the functionalization of the N,N'-dialkyl-
1,7-dibromo-3,4:9,10-bis(dicarboximide)s 6. However, a very
surprising reaction sequence was observed which led to the
novel compounds 8 (Scheme 1). The derivatives 6a and 6b
Liquid Crystalline Coronene Derivatives with
Extraordinary Fluorescence Properties**
Ulrike Rohr, Peter Schlichting, Arno Böhm,
Markus Gross, Klaus Meerholz, Christoph Bräuchle,
and Klaus Müllen*
Dedicated to Professor Emanuel Vogel
on the occasion of his 70th birthday
Perylene (1) and perylene-3,4:9,10-bis(dicarboximide)s 2
are among the most intensively investigated chromophores in
dye chemistry.[1] Coronene (3), which is similar to perylene,
constitutes a classical aromatic hydrocarbon; however, owing
to its limited preparative accessibility, there have been only
few attempts to modify it chemically.[2] We present here the
coronene-3,4:9,10-bis(dicarboximide)s 8, which as a combi-
nation of 2 and 3 represent a novel type of dye.
The photostable yellow title compounds 8
*
are obtained by a surprisingly simple procedure from
readily available derivatives of 2, and provide access to
additional chromophores.
*
are active in an interesting wavelength range between that
of 1 and 2 in both absorption and emission spectra,
form, when they contain suitable alkyl substitutents R1 and
*
Scheme 1. Synthesis of 8: a) Br2,
100% H2SO4, 408C, 12 h, 90 ±
95%; b) R1NH2, CH3COOH,
NMP, 858C, 8 h, 88 ± 95%;
R2, discotic mesophases and combine the properties of
both dyes and liquid crystals,[3] and
*
form aggregates in a solid matrix whose photolumines-
2
ꢀ
c) R C CH, 8 mol% [Pd(PPh3)4],
cence wavelength varies depending on the respective
tempering process. Therefore, 8 is a promising compound
for the preparation of multicolored displays on the basis of
organic luminescent diodes.
10 mol% CuI, THF/Et3N (1/1),
808C, 14 h, 85 ± 95%; d) DBU,
toluene, 1008C, 12 h, 95 ± 100%.
NMP ˆ N-methylpyrrolidone.
The functionalization and alkylation of perylene (1) was
achieved by coupling 3,9(10)-dibromoperylene with various
required in the first step of the alkyne coupling can be
obtained in a two-step synthesis. The commercially available
perylene-3,4;9,10-tetracarboxylic dianhydride (4) is subjected
to a twofold bromination with elemental bromine in 100%
sulfuric acid to provide 5 (90 ± 95%), which is then converted
into 6a and 6b (88 ± 95%) with cyclohexylamine or n-
octylamine, respectively.[5] The palladium(0)-catalyzed[4] reac-
tions of 6 with 1-alkynes in the presence of bases such as
triethylamine afforded the expected bis(alkynyl)-substituted
perylene-3,4:9,10-bis(dicarboximide)s 7a ± e in high yields
(85 ± 95%). Treatment of 7 with strong, nonnucleophilic bases
such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) triggers a
cyclization reaction of unknown mechanism to yield almost
[*] Prof. Dr. K. Müllen, Dipl.-Chem. U. Rohr, Dipl.-Chem. P. Schlichting
Max-Planck-Institut für Polymerforschung
Ackermannweg 10, D-55128 Mainz (Germany)
Fax: (‡49)6131-379-350
E-mail: muellen@mpip-mainz.mpg.de
Dr. A. Böhm
BASF AG, Farbenlaboratorium, Ludwigshafen (Germany)
Dipl.-Chem. M. Gross, Dr. K. Meerholz, Prof. Dr. C. Bräuchle
Institut für Physikalische Chemie
der Universität München (Germany)
[**] This work was supported by BASF AG, the Bundesministerium für
Bildung und Forschung, and the Fonds der Chemischen Industrie. We
thank Dipl.-Chem. C. Kayser for measuring the X-ray diffractograms.
1434
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3710-1434 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1998, 37, No. 10

COMMUNICATIONS
Table 2. Melting points of 8.
quantitatively the yellow title compounds 8 with various
substituents at the resulting phenyl rings.[6] The structures of
R2
R1 ˆ C6H11
R1 ˆ C8H17
1
8
Tm [8C]
8
Tm [8C]
the coronenebis(dicarboximide)s 8 could be verified by H
and 13C NMR spectroscopy, UV/Vis spectroscopy, and FD
mass spectrometry (Table 1). Saponification of the imide
functionalities in 8b under standard conditions (KOH in tert-
C6H13
C10H21
C13H27
CH(CH3)C3H7
a
b
d
f
> 300
245[a]
266[a]
> 300
±
c
e
±
±
192[a]
177[a]
±
[a] These derivatives form a mesophase at T> Tm.
Table 1. Spectroscopic data of 8b.
M.p. (DSC): Tm ˆ 2458C (Colho); 1H NMR (500 MHz, CDCl3): d ˆ 9.31 (s,
2H; ArH), 9.06 (s, 2H; ArH), 8.13 (s, 2H; ArH), 5.37 ± 5.31 (m, 2H; NCH),
3
coronene skeleton. However, hexyl substituents at the
aromatic moiety do not suffice to form a mesophase (Table 2:
derivative 8a; R1 ˆ C6H11, R2 ˆ C6H13). X-ray diffractometry
investigations suggest the presence of a columnar discotic
mesophase with a hexagonal superstructure (Colho) at temper-
atures above the melting point.[11] For the use of the coronene
derivatives 8 as photoconductors, the order in the mesophase
is important for a high charge-carrier mobility;[12] however,
lower transition temperatures are required for application
purposes.
ꢀ
3.46 ± 3.42 (t, 4H, J ˆ 7.8 Hz; CH2C C), 2.91 ± 2.85 (m, 4H; cHex), 2.18 ±
2.12 (m, 8H; cHex and CH2), 2.01 ± 1.90 (m, 6H; cHex), 1.74 ± 1.23 (m,
34H; cHex and CH2), 0.89 ± 0.86 (t, 6H, 3J ˆ 7 Hz; CH3); 13C NMR
ˆ
(125 MHz, CDCl3, spin-echo experiment): d ˆ 164.86 (q; C O), 164.6 (q;
ˆ
C O), 140.72 (q; arom. C), 128.97 (arom. CH), 128.43 (q; arom. C), 127.79
(q; arom. C), 127.12 (arom. CH), 125.00 (arom. CH), 121.84 (q; arom. C),
121.35 (q; arom. C), 121.27 (q; arom. C), 121.08 (q; arom. C), 120.59 (q;
arom. C), 119.19 (q; arom. C), 54.58 (CHN), 33.70 (CH2), 31.78 (CH2),
31.37 (CH2), 31.22 (CH2), 29.64 (CH2), 29.53 (CH2), 26.85 (CH2), 25.71
(CH2), 22.74 (CH2), 14.10 (CH3); UV/Vis (CH2Cl2): lmax (e) ˆ 477 (9400),
511 (19700), 428 (62100), 404 (30500), 382 (7900), 338 (73200), 334 nm
‡
(72800); FD-MS (8 kV, FD ˆ field desorption): m/z ˆ 882.5 (100%) [M ]
The formation of columnar mesophases with stacks of
disclike chromophores leads to the question of whether
aggregates are formed in solution, in amorphous films of the
pure substance, or in mixtures with host polymers, and
furthermore to what extent the absorption and emission
behavior can be controlled by the type of aggregate forma-
tion. UV/Vis spectra of solutions of 8b in chloroform are
butyl alcohol/water) afforded the dianhydride 9 in high yields
(85 ± 90%, Scheme 2).[7] Reaction of the latter with diamines
can be used to build up coronene-based polyimides, analogous
to the well-known polyperylenebis(dicarboximide)s.[8] Com-
pound 9 can be decarboxylated with Cu/Cu2O[9] to the
previously unknown dialkylcoronene 10.
The absorption bands of 8 show a hypsochromic shift with
respect to those of 2 and a bathochromic shift with respect to
those of 3. Coronenebis(dicarboximide)s 8 fluoresce with an
intensive green-yellow color with the maxima at 517 nm (in
CHCl3).[10] With suitable substituents R1 and R2, compounds 8
form mesophases with transition temperatures between 177
and 2668C; this could be proven by differential scanning
calorimetry (DSC) as well as by polarization microscopy and
X-ray diffractometry (for the transition temperatures see
Table 2; isotropization could not be observed, and decom-
position occurred at approximately 4508C). A comparison of
the transition temperatures for the derivatives prepared to
date does not allow a correlation between the melting points
and the type of alkyl side chains at the imide groups and the
7
concentration-independent in a range from 4 Â 10 to 1 Â
1 [14]
10 3 molL .
1
At the same concentration (10 3 molL
ꢁ
0.1 mass%) of 8b in a polystyrene (PS) matrix the absorption
spectrum of the film matches that of dissolved 8b, except for
the strong broadening of the band. Only at concentrations
above 1 ± 2 mass% does a new absorption band develop in the
long-wave range which suggests the formation of an aggregate
(Figure 1). PS films doped with 1 ± 40 mass% of 8b and
amorphous layers of the pure compound fluoresce orange,
and the spectra exhibit only a slight concentration depend-
ence (Figure 2a).
Entirely different spectra are obtained (Figure 2) when
these PS films and the film consisting of pure 8b are tempered
under an atmosphere of inert gas for 5 min at 2808C (i.e.,
above the melting point of 2458C in the mesophase): The
broad fluorescence band (590 nm) of films
containing small amounts of 8b (1 ±
2 mass%) is shifted towards blue, whereas
the band at 510 nm becomes more intense.
The emission spectrum of the tempered
film containing 1% of 8b exactly matches
that of the solution, which suggests the
existence of isolated coronenebis(dicar-
boximide) molecules. Whereas tempering
films with intermediate concentrations of
8b (5 ± 10 mass%) has a negligible effect
on the fluorescence spectrum, a shift
towards red can be observed after temper-
ing films containing more than 20 mass%
of 8b. The transition from PS films con-
taining 40 mass% of 8b to a film of the
pure compound is abrupt, with the band
Scheme 2. Synthesis of 10: a) KOH, H2O, tBuOH, 1008C, 4 h, 90%; b) decarboxylation with Cu and
Cu2O in quinoline at 2208C.
Angew. Chem. Int. Ed. 1998, 37, No. 10
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3710-1435 $ 17.50+.50/0
1435

COMMUNICATIONS
(several hours at 1208C). In contrast, pure 8b
has to be tempered at temperatures above the
transition point in order to obtain a color
change. Time-dependent experiments show
that the process occurring during tempering
at 1758C advances in a few seconds to such a
degree that could be utilized for the fabrica-
tion of multicolor pixelated displays. Partic-
ularly noteworthy in this context is that, in
contrast to other known fluorophores that
tend to form aggregates (e.g. quinacridone[15]),
no complete quenching of fluorescence takes
place for our compounds; instead, the light
output reaches a maximum for the films with
40% 8b. However, the fluorescence quantum
efficiency decreases with increasing concen-
tration (factor of 4 upon going from films with
1% to 4% of 8b).
Figure 1. Absorption spectra of 8b in solution (solid line) and in a PS matrix (10 mass%,
dotted line). e ˆ extinction coefficient, a ˆ absorption coefficient.
For the color shift caused by the tempering process we offer
the following interpretation: Spin-coating leads to inhomoge-
neous polymer films with microdomains in which aggregates
of various size (stacks) have formed due to the discotic shape
of 8b. These microdomains cause the broad excimer fluo-
rescence at approximately 590 nm (overlap of various tran-
sitions!). Assuming a linear relationship between the energy
of the fluorescence transition and 1/N,[16] N (the number of
molecules in an aggregate) can be estimated from the
fluorescence spectrum of the films (details are given in the
inset of Figure 2b). Accordingly, the untempered films consist
mainly of tetramers. Upon tempering of films with low
concentratins (1 ± 2 mass%), the material is better homogen-
ized by additional dissolving of the 8b molecules in the PS
matrix; the number of the aggregates decreases in favor of
isolated molecules, and their size also decreases (monomers to
trimers are present). In contrast, for higher concentrations
larger stacks are formed between the discotic molecules,
which emit light of longer wavelengths. The overall largest
bathochromic shift occurs upon tempering of the pure
coronenebis(dicarboximide) layers, as they are capable of
forming very long stacks.
Since the photo- and electroluminescence properties of the
title compounds match qualitativelyÐthis will be discussed in
detail in a separate publicationÐ the emissions of these
aggregates could be utilized for a variety of applications:
Selective heating allows the emission color to be controlled
locally, so that large areas can easily be colored dot by dot. To
create multicolored displays, current investigations focus on
the long-term stability of aggregate formation as well as how
the choice of substituents R1 and R2 can possibly lead to large
color changes upon aggregate formation, resulting in a drastic
increase in the slope of the Emax ± 1/N curve.
Figure 2. Normalized fluorescence intensities of PS films doped with
various concentrations of 8b [1 % (±), 2 % (± ± ± ), 5 % (- - - -), 10 %
(±- ± -), 20 % (±-- ± --), 40 % (------), 100 % ( ´´´´´ )]: a) freshly prepared
films, b) films tempered at 2808C. Inset: plot of Efl versus 1N (N ˆ number
of coronenebis(dicarboximide) mesogens in an aggregate). For N ˆ 1, the
energy of the fluorescence band of shortest wavelength of the smallest
concentration (0 ± 0 vibrational transition; 510 nm ꢀ 2.43 eV) was used, and
for N ˆ1 , the transition energy of the pure 8b films (620 nm ꢀ 2.00 eV)
was assumed. The following values were calculated from the linear
transformation: N ˆ 2: 560 nm; N ˆ 3: 578 nm; N ˆ 4: 588 nm; N ˆ 5:
594 nm.
Experimental Section
7b: In a carefully dried and argon-purged 500-mL Schlenk flask, 6a
(500 mg, 0.7 mmol) was dissolved in a 1:1 mixture (300 mL) of anhydrous
THF and anhydrous Et3N. To this solution was added 4 mol% [Pd(PPh3)4]
(32 mg, 26 mmol) and 5 mol% CuI (6.5 mg, 34 mmol). After two additional
cycles of evacuation and purging with argon, 1-dodecyne (466 mg,
2.80 mmol) was added with a syringe through a septum. This mixture was
being shifted 25 nm towards red (Figure 2b). The film of pure
8b fluoresces red.
In the case of the films doped with small concentrations of
8b, similar observations were also made at lower temper-
atures; however, much longer tempering times are required
1436
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3710-1436 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1998, 37, No. 10

COMMUNICATIONS
stirred for 10 ± 14 h at 808C. After the starting material had been consumed
(TLC), the mixture was added to an ice/HCl mixture (3/1, three times the
reaction volume). The mixture was then extraced several times with
CH2Cl2. The combined CH2Cl2 fractions were dried over MgSO4, and the
solvent was removed by distillation. The residue was purified by
chromatography on silica gel with CH2Cl2 to yield red 7b (555 mg, 91%).
[13] a) L. Dähne, J. Am. Chem. Soc. 1995, 117, 12855 ± 12860; b) L. Dähne,
A. Horvath, G. Weiser, G. Reck, Adv. Mater. 1996, 8, 486 ± 490.
[14] In contrast, other perylene mesogens show additional bands at higher
wavelengths, which suggest the existence of aggregates in solution:
a) ref.[3]; b) D. Pressner, C. Göltner, H. W. Spiess, K. Müllen, Ber.
Bunsen-Ges. Phys. Chem. 1993, 97, 1362 ± 1365; c) M. A. Biasutti, S.
De Feyter, S. De Backer, G. B. Dutt, F. C. De Schryver, M. Ameloot,
P. Schlichting, K. Müllen, Chem. Phys. Lett. 1996, 248, 13 ± 19.
[15] U. Keller, K. Müllen, S. De Feyter, F. C. De Schryver, Adv. Mater.
1996, 8, 490 ± 493.
[16] The assumption of a linear relationship between the optical transition
energy Emax and 1/N results from the model of a particle in a box. The
relationship also holds true, for example, for p-conjugated oligom-
ers.[17]
[17] a) J. Grimme, M. Kreyenschmidt, F. Uckert, K. Müllen, U. Scherf,
Adv. Mater. 1995, 7, 292 ± 295; b) P. Bäuerle, ibid. 1992, 4, 102.
8b: Bis(dicarboximide) 7b (500 mg) was dissolved in 250 mL of toluene.
The mixture was heated to 1008C and 0.5 mL of DBU added with a syringe
through a septum. The reaction mixture was stirred for 8 ± 12 h at 1008C.
For the workup, the mixture was added to ice-cooled, dilute HCl and
extracted with CHCl3. The organic layer was dried over MgSO4, and the
product precipitated from CH3OH to afford orange 8b in quantitative yield
(500 mg).
Spectroscopic investigations: For the film experiments defined amounts of
8b along with PS (Aldrich, Mw ˆ 280000, Tg ˆ 1008C) were dissolved in
CHCl3 and films prepared from these by spin-coating.
For the fluorescence experiments the samples were excited at 413 nm (ca.
10 mW on an irradiation area of 2 mm in diameter) with a krypton-ion
laser. The fluorescence spectra were recorded with a computer-integrated
spectrometer card (Ocean Optics, model PC1000) under an angle of 308. A
cut-off filter was used to suppress any scattered light of the excitation laser.
Received: October 28, 1997 [Z11092IE]
German version: Angew. Chem. 1998, 110, 1463 ± 1467
The Thioesterase of the Erythromycin-
Producing Polyketide Synthase:
Influence of Acyl Chain Structure on the
Mode of Release of Substrate Analogues
from the Acyl Enzyme Intermediates**
Keywords: chromophores ´ imides ´ liquid crystals ´ photo-
luminescence ´ polycycles
Kira J. Weissman, Cameron J. Smith, Ulf Hanefeld,
Ranjana Aggarwal, Matthew Bycroft,
James Staunton,* and Peter F. Leadlay
[1] a) H. Zollinger, Color Chemistry, 2nd ed., VCH, Weinheim, 1991;
b) W. Herbst, K. Hunger, Industrial Organic Pigments, VCH,
Weinheim, 1993.
[2] F. Vögtle, Reizvolle Moleküle der Organischen Chemie, Teubner,
Stuttgart, 1989, p. 161.
[3] For liquid crystalline dyes, see for example C. Göltner, D. Pressner, K.
Müllen, H. W. Spiess, Angew. Chem. 1993, 105, 1722 ± 1724; Angew.
Chem. Int. Ed. Engl. 1993, 32, 1660 ± 1662.
[4] P. Schlichting, U. Rohr, K. Müllen, Liebigs Ann. 1997, 395 ± 407.
[5] A. Böhm, H. Arms, G. Henning, P. Blaschka (BASF), patent
application DE19547210.
[6] For analogous reactions of arylethynylarenes, see for example M. B.
Goldfinger, K. B. Crawford, T. M. Swager, J. Am. Chem. Soc. 1997,
119, 4578 ± 4598.
[7] The direct transformation of 5 with alkynes is also possible; however,
the subsequent reaction with DBU does not lead to compounds 9. This
is why the detour via 6 was necessary.
[8] a) D. Dotcheva, M. Klapper, K. Müllen, Macromol. Chem. Phys. 1994,
195, 1905 ± 1911; b) G. Karayannidis, D. Stamelos, D. Bikiaris,
Makromol. Chem. 1993, 194, 2789 ± 2796; c) H. Gassemi, A. S. Hay,
Macromolecules 1994, 27, 4410 ± 4412.
[9] a)W. Neugierar (I. G. Farbe) D.R.P.486491, 1926 [Chem. Abstr. 1930,
24, 1870]; b) V. I. Rogovik, Zh. Org. Khim. 1974, 10, 1072 ± 1075.
[10] Coronenebis(dicarboximide)s 8 are very photostable. Irradiation of
8 Â 10 5 m solutions of 8b in toluene (quartz cuvettes; UV lamp with
lmax ˆ 366 nm), for instance, did not result in a significant decrease in
extinction, even after several weeks.
[11] In the X-ray diffractogram of 8c, for instance, the alkyl chains cause a
reflection at 2q ˆ 17.68 (halo reflex). The (001) reflex occurs at 2q ˆ
25.08, and its d value corresponds to the intracolumnar distance
(3.6 Š). The very intense (100) reflex at 2q ˆ 4.48 corresponds to an
intercolumnar distance of approximately 20.0 Š ((200) reflex at 2q ˆ
8.98). The hexagonal superstructure is verified by the weak (110)
The polyketide core of the antibiotic erythromycin A is
assembled by a polyketide synthase (PKS) from seven C3
units.[1] The units are condensed to form a putative enzyme-
bound heptaketide product 1, which is then released through
cyclization to the macrolactone, 6-deoxyerythronolide B (2)
(Scheme 1). The PKS contains a separate catalytic domain for
each step in the formation of 2, housed in three gigantic
multifunctional proteins, DEBS 1 ± 3. The ordering of the
domains can be analyzed in terms of six chain-extension
modules, fronted by a loading domain for the starter acyl
group, and terminated by an off-loading thioesterase (TE)
responsible for release of the completed product.[2]
A pivotal step in this biosynthetic scheme is the thioester-
ase-catalyzed cyclization of the heptaketide 1 to form the
macrolide ring 2. Early in vitro studies with simple substrate
[*] Dr. J. Staunton, K. J. Weissman, C. J. Smith, U. Hanefeld,
R. Aggarwal, M. Bycroft
Department of Chemistry, University of Cambridge
Lensfield Road, Cambridge CB2 1EW (UK)
Fax: (‡44)1223-226913
E-mail: js24@cus.cam.ac.uk
Dr. P. F. Leadlay
Department of Biochemistry, University of Cambridge
Tennis Court Road, Cambridge CB2 1QW (UK)
Fax: (‡44)1223-336656
reflex at 2q ˆ 7.78. The lattice constant a is given by a ˆ 1.1547  d100
ˆ
23.15 Š.
E-mail: pfl10@mole.bio.cam.ac.uk
[12] a) D. Adam, F. Closs, T. Frey, D. Funhoff, D. Haarer, H. Ringsdorf, P.
Schuhmacher, K. Siemensmeyer, Phys. Rev. Lett. 1993, 70, 457 ± 460;
b) D. Adam, P. Schuhmacher, J. Simmerer, L. Häusling, K. Siemen-
smeyer, K. H. Etzbach, H. Ringsdorf, D. Haarer, Nature 1994, 371,
141 ± 143.
[**] This work was supported by fellowships to K.J.W. from the Winston
Churchill Foundation of the United States and the Howard Hughes
Medical Institute, to C.J.S. from the Cambridge Commonwealth Trust,
and to U.H., m.B., and R.A. from the Biotechnology and Biological
Sciences Research Council (BBSRC) and GlaxoWellcome PLC.
Angew. Chem. Int. Ed. 1998, 37, No. 10
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
1433-7851/98/3710-1437 $ 17.50+.50/0
1437