Control of liquid crystallinity of diazadibenzoperylene dyes by covalent and hydrogen-bonded attachment of mesogens

Article abstract of DOI:10.1002/1521-3773(20011203)40:23<4425::AID-ANIE4425>3.0.CO;2-Z

Fluorescent liquid crystals: Hydrogen bonding of benzoic acids to azaaromatic receptor groups of diazadibenzoperylene fluorophores induces columnar liquid crystalline mesophases which are highly fluorescent. The structure of a mesogenic supermolecule generated in this way is shown on a background of a polarizing micrograph of the resulting liquid crystalline phase.

Full text of DOI:10.1002/1521-3773(20011203)40:23<4425::AID-ANIE4425>3.0.CO;2-Z

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IR (KBr): nÄ ˆ 3360(br, s), 2945(m), 1622(s), 1553(s), 1513(s), 1412(s),
1365(w), 1328(w), 1278(m), 1244(m), 1228(m) 1186(w), 1120(w), 1103(w),
1068(w), 1030(w), 1016(w), 951(w), 918(w), 857(w), 835(w), 780(w),
[30] Crystal data for 2: C42H52N4O9Cd, orthorhombic, space group P212121,
a ˆ 13.7818(9), b ˆ 15.0617(10), c ˆ 19.355(13) ä, a ˆ b ˆ g ˆ 90.008,
Vˆ 4017.8(5) ä3, Z ˆ 4, Mr ˆ 869.28, 1calcd ˆ 1.437 MgmÀ3, R1 ˆ 0.0436,
718(w), 644(w), 605(w) cmÀ1
.
wR2 ˆ 0.1054, Tˆ 293 K, m ˆ 0.604 mmÀ1
,
S ˆ 0.744, Flack c ˆ
À0.02(2).
Received: July 16, 2001 [Z17516]
[31] Crystal data for 3: C43H54N4O9Cd, orthorhombic, space group P212121,
a ˆ 13.8756(8), b ˆ 15.1162(8), c ˆ 19.2999(10) ä, a ˆ b ˆ g ˆ 90.008,
Vˆ 4048.1(4) ä3, Z ˆ 4, Mr ˆ 883.30, 1calcd ˆ 1.449 MgmÀ3, R1 ˆ 0.0797,
wR2 ˆ 0.1684, Tˆ 293 K, m ˆ 0.601 mmÀ1
,
S ˆ 1.227, Flack c ˆ
À0.04(4). The structures were solved with Direct methods using the
program SHELXTL (Sheldrick, 1997).[32] All the non-hydrogen atoms
were located from the trial structure and then refined anisotropically
with SHELXTL using a full-matrix least-squares procedure. The
hydrogenatom positiosn were fixed geometrically at calculated
distances and allowed to ride on the parent carbon atoms. The final
difference Fourier map was found to be featureless. Crystallographic
data (excluding structure factors) for the structures reported in this
paper have beendeposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC-166932 166935.
Copies of the data canbe obtained free of charge onapplicationto
CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (‡44)1223-
336-033; e-mail: deposit@ccdc.cam.ac.uk).
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Control of Liquid Crystallinity of
Diazadibenzoperylene Dyes by Covalent and
Hydrogen-Bonded Attachment of Mesogens**
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Dedicated to Dr. G¸nther Seybold
on the occasion of his 60th birthday
Functional liquid crystals (LCs) with intrinsic luminescence
properties are of great interest in the development of new
organic materials, such as anisotropic light emitters, organic
lasers, photoconductors, and in LC display technology.[1 In
contrast to dissolving a fluorescent dye in a LC matrix,
fluorescent LCs are thought not only to overcome miscibility
and stability problems but also to exhibit novel enhanced
optoelectronic properties. To date, only a few examples have
beenreported such as tripheynleens,
hexacatenar compounds,[1a] and perylenes,[2] but the field is
3]
benzopyrenes,[3e]
[3a d]
[*] Priv.-Doz. Dr. F. W¸rthner, Dr. A. Sautter, Dr. C. Thalacker
Abteilung Organische Chemie II
Universit‰t Ulm
Albert-Einstein-Allee 11, 89081 Ulm (Germany)
Fax : (‡49)731-5022840
E-mail: frank.wuerthner@chemie.uni-ulm.de
[**] We thank P. Zell for his assistance in the practical work, Frau G.
Dˆrfner and Prof. U. Thewalt (Sektion Rˆntgenbeugung, Universit‰t
Ulm) and Dr. B. Heise (Abteilung Experimentelle Physik, Universit‰t
Ulm) for X-ray diffraction studies. Financial support from the
Deutsche Forschungsgemeinschaft (Habilitandenstipendium for
F.W.), the Fonds der Chemischen Industrie (Liebig-Stipendium for
F.W.), and the Dr. Otto Rˆhm Ged‰chtnisstiftung is gratefully
acknowledged.
[28] Crystal data for quitenine ¥ 4H2O: C19H30N2O8, orthorhombic, space
group P212121, a ˆ 9.5585(9), b ˆ 10.3410(9), c ˆ 20.8404(19) ä, a ˆ
b ˆ g ˆ 90.008, Vˆ 2060.0(3) ä3, Z ˆ 4, Mr ˆ 414.45, 1calcd
ˆ
1.336 MgmÀ3, R1 ˆ 0.0667, wR2 ˆ 0.1770, Tˆ 293 K, m ˆ 1.040 mmÀ1
,
S ˆ 1.265, Flack c ˆ 0.001(2).
[29] Crystal data for 1: C38H42N4O8Cd, orthorhombic, space group P212121,
a ˆ 13.8639(8), b ˆ 15.1012(8), c ˆ 19.4313(11) ä, a ˆ b ˆ g ˆ 90.008,
Vˆ 4068.0(2) ä3, Z ˆ 4, Mr ˆ 795.16, 1calcd ˆ 1.298 MgmÀ3
,
R1 ˆ
0.0646, wR2 ˆ 0.1358, Tˆ 293 K, m ˆ 0.588 mmÀ1, S ˆ 1.017, Flack c ˆ
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
0.01(3).
Angew. Chem. Int. Ed. 2001, 40, No. 23
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rapidly expanding. Here, we report a series of diazadibenzo-
perylenes 3a d that bear mesogenic dodecyloxybenzoyl
substituents and aza coordination sites suited for additional
control of dye packing by intermolecular interactions. All the
compounds 3a d exhibit strong luminescence in solution and
inthe pristine (i.e. solid) states , and 3a c form thermotropic
columnar liquid crystalline phases in the presence and/or
absence of benzoic acids 4a d.
Cleavage of all the methoxy ethers of the diazadibenzoper-
ylene 1[4, 5] with BBr3 indichloromethaen afforded tetra-
(p-hydroxyphenoxy)diazadibenzoperylene 2 in95% isolated
yield. Esterificationreactions of 2 with various dodecyloxy-
substituted benzoic acid chlorides in dichloromethane in the
presence of triethyl amine led to the title compounds 3a d in
42 54% isolated yields (Scheme 1) after purificationby
chromatography.[5]
All the diazadibenzoperylenes 3a d show identical ab-
sorption and fluorescence spectra in dichloromethane, with
absorption maxima at 495 nm and 464 nm, and a mirror-image
fluorescence emission with maxima at 512 nm and 545 nm
(Figure 1). The fluorescence quantum yields FF range be-
tween0.65 ( 3c) and 0.83 (3b).[6] Aggregationof the molecules
in nonpolar solvents, for example methylcyclohexane (MCH),
or in the solid state causes pronounced changes in the UV/Vis
and fluorescence spectra. For thin films a bathochromic shift
of about 10 nm and a pronounced line broadening of the UV/
Vis absorptionspectra is observed, which implies strong dye
dye interactions in the solid state (Figure 1). As a result of a
considerable bathochromic shift of about 100 nm in the
fluorescence spectra these films exhibit intense red emission
incotnrast to the greenemissioninsolutio.n A spectral
fine structure is only observed for 3a and b but not for 3c
which indicates a higher molecular ordering for 3a, b
(Figure 1).
Figure 1. UV/Vis absorption and fluorescence spectra of 3b indichloro-
methane (––) and as thin film (- - - -) on a quartz substrate and film
*
*
emissionspectrum of 3c (
).
The thermotropic properties of 3a d were investigated by
optical polarization microscopy (OPM) and differential scan-
ning calorimetry (DSC). Phase-transition temperatures and
associated enthalpy values for compounds 3a d are givenin
Table 1. 3d with only four dodecyloxy chains, melts at 2498C
Table 1. Phase transition temperatures T [8C] and transition enthalpies
c]
DHt [kJmolÀ1] (in parentheses) for diazadibenzoperylenes 3a d.[a
Compound
T [8C] (DHt [kJmolÀ1])
3a
3b
3c
3d
Col 174 (16.3) I
Col 177 (27.3) I
Cr 249 (36.5) I
[a] Col ˆ columnar mesophase; [b] I ˆ isotropic liquid; [c] Crˆ crystalline
solid.
and crystallizes upon cooling. No LC phase was found for this
compound. Compound 3c which bears (3,5-didodecyloxy)-
benzoyl substituents exhibits an unexpected thermotropic
behavior. The viscosity of a completely
amorphous film of 3c gradually decrease
when the compound is heated and neither
a melting point nor a glass transition was
observed by OPM and DSC. In contrast,
3b and 3a bearing four (3,4-didodecyl-
oxy)- and (3,4,5-tridodecyloxy)benzoyl
substituents, respectively, are liquid crys-
talline from room temperature to their
clearing points at 1778C (3b) and 1748C
(3a).[7] Onslow cooling from the isotropic
liquid state large spherulitic textures (ca.
100 mm) canbe observed at crossed
polarizers by OPM that are characteristic
for columnar LC phases (Figure 2a).[8]
The X-ray crystal structure of a closely
related N,N'-dibutylated diazadibenzo-
perylene revealed a twisting of the cen-
tral six-membered ring of the aromatic
diazadibenzoperylene backbone by 258,
because of the electrostatic repulsionof
the oxygenatoms of the phenoxy sub-
stituents.[4] This twisting leads to a pro-
peller-like arrangement of the phenoxy
Scheme 1. Synthesis of dodecyloxybenzoyl-substituted diazadibenzoperylenes 3a d.
substituents in contrast to most tradi-
4426
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The columnar nature of the mesophase of 3b was confirmed
by X-ray diffraction (XRD) and assigned to a columnar
rectangular disordered (Colrd) LC phase with four sharp
reflections in the small-angle region at 2Wˆ 2.048, 2.578, 4.088,
and 8.838, and a halo in the wide-angle region of the
diffractogram.[10] XRD also confirmed the crystalline state
of 3d (abundant sharp reflections) and the amorphous nature
of 3c (only a diffuse reflection at 2Wˆ 2.738 corresponding to
32.3 ä which is about the size of an individual molecule, and a
halo in the wide-angle region around 2Wˆ 208).
Compounds 3a d are distinguished from other mesogens
by a unique combination of functionality (optical and redox)[4]
and diaza receptor sites suitable for additional control of the
supramolecular organization through coordination to carbox-
ylic acid or Lewis-acidic binding partners (e.g. metal
13]
ions).[11
Here, we will concentrate on hydrogen-bonded
complexes between diazadibenzoperylenes 3a d and the
different dodecyloxy-substituted benzoic acids 4a
(Scheme 2).[12]
d
Scheme 2. Complex formationbetweensubstituted benzoic acids
4a
d
and a diazadibenzoperylene 3a d through hydrogen bonding by melting
both compounds together between glass slides or by evaporation of a 1:2
stoichiometric solutionof the two components.
Figure 2. Optical micrographs of the textures of a) the columnar meso-
phase of 3a obtained by cooling from the isotropic melt to room
temperature; b) the contact region of
a melting preparation of the
columnar mesogen 3a and the calamitic mesogen 4d (top right corner);
c) the contact region of a melting preparation of 3c and 4c, showing
amorphous 3c (A); a regionrich in 3c (B); complex [4c ¥ 3c ¥ 4c] (C), and a
region with a lower content of 3c (D). All micrographs were takenat
crossed polarizers.
For this purpose contact melting preparations were made
by melting first a diazadibenzoperylene 3a d and then a
benzoic acid 4a d betweenglass slides to give a contact
regionwith a gradient instoichiometry of the two compo-
nents. Investigation of the phase behavior of these prepara-
tions by repeated heating cooling cycles on a hot-stage OPM
at crossed polarizers revealed crystallinity for all complexes
between 3d and 4a d, and liquid crystallinity for all
complexes formed between 3a, b and 4a d. For all 1:2
complexes [4a d ¥ 3a, b ¥ 4a d] we observed a decrease in
the clearing points between 10 and 30 K with respect to the
pure compounds 3a, b. This indicates a destabilization of the
columnar mesophases by addition of the benzoic acids which
disturb the columnar organization of the mesogenic dyes
tional columnar mesogens[8] which exhibit disclike central
units. Nevertheless, a number of molecules were recently
reported that lack a flat core but that are capable of forming
columnar mesophases. Here, the main driving force is
ascribed to microsegregation,[9] which also plays the crucial
role in the formation of columnar mesophases of compounds
3a, b by segregation of the polar diazadibenzoperylene cores
from the nonpolar dodecyl chains.
Angew. Chem. Int. Ed. 2001, 40, No. 23
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and physical properties of compounds 3a d refer to the Supporting
Information.
[6] a) Determined by the optically dilute method with refractive-index
correction, maximum absorptions of the solutions ꢀ0.05. All fluo-
rescence spectra were corrected. Measurements relative to fluorescein
3a, b. When the calamitic mesogenic benzoic acid 4d is
applied especially beautiful transitions of the mesophases are
observed inthe cotnact regiosn with
3a, b (Figure 2b).
Remarkably, all the benzoic acids 4a d were able to induce
columnar LC phases upon coordination to the formerly
amorphous diaza ligand 3c giving rise to well-pronounced
textures in the boundary regions of the contact melting
preparations. An optical micrograph taken at crossed polar-
izers for complexationof 3c with 4c is depicted inFigure 2c.
The left bottom corner (A; the black area), shows amorphous
pure 3c, and the region (B) exhibits small textures which we
attribute to anintermediate phase between 3c and 4c, rich in
3c. In the middle region (C) well-pronounced and large
textures of complex [4c ¥ 3c ¥ 4c] with the correct 1:2 stoichi-
ometry canbe observed which exhibit a sharp clearign
transition at 1168C. Region(D) has a low 3c content and
the textures become smaller. The same textures as inthe
middle regions of these contact melting preparations are also
observed if complexes [4a d ¥ 3c ¥ 4a d] are prepared inan
exact 1:2 stoichiometry from stock solutions. According to
OPM all these mesophases have well-defined clearing points
at 1118C for [4a ¥ 3c ¥ 4a], 1008C for [4b ¥ 3c ¥ 4b], 1168C for
[4c ¥ 3c ¥ 4c], and 948C for [4d ¥ 3c ¥ 4d] and also here no
crystallizationis observed uponcooling these samples to room
temperature.[14]
In conclusion, we presented a new class of highly fluores-
cent mesogenic diazadibenzoperylenes 3a c, the morpho-
logical behavior of which could be controlled by hydrogen-
bond directed coordination to carboxylic acids. In future work
chiral hydrogen-bond donors and metal ions will be applied to
induce chiroptical properties by means of the inherently
atropisomeric backbone of 3a d and applications of these
supramolecular assemblies inoptoelectroincs will be ad-
dressed.[15]
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n
NaOH (Fref ˆ 0.9); H. G. O. Becker, Einf¸hrung in die
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[7] No crystallizationof the compounds could be observed at room
temperature over a period of six months.
[8] For a review on polycatenar and phasmidic mesogens see: H.-T.
√
Nguyen, C. Destrade, J. Malthete in Handbook of Liquid Crystals,
Vol. 2B: Low Molecular Weight Liquid Crystals II (Eds.: D. Demus, J.
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1998, pp. 865 885.
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[10] The reflections were indexed as the (100), (010), (200), and (230)
reflections of a columnar rectangular lattice with lattice constants of
a ˆ 43.2 and b ˆ 34.3 ä (for diffractogram refer to the Supporting
Information). The absence of an additional sharp reflection in the
wide-angle region suggests a disordered columnar mesophase with no
distinct intracolumnar repeat distance as expected for the rather
flexible twisted core of the molecules.
[11] Reviews on metallomesogens: a) A.-M. Giroud-Godquin, P. M.
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Liquid Crystals, Vol. 2B: Low Molecular Weight Liquid Crystals II
(Eds.: D. Demus, J. Goodby, G. M. Gray, H.-W. Spiess, V. Vill), Wiley-
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Received: July 2, 2001 [Z17402]
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[14] The lower clearing temperatures of these supramolecular LCs
compared to those of the mesogenic dyes 3a, b and the smaller size
of the domains indicate a lower stability of these mesophases. Based
on the textures a simple hexagonal or rectangular columnar ordering
seems unlikely but further XRD studies are required to reveal the
exact type of supramolecular organization.
[15] It is noteworthy that there is no quenching of the diazadibenzoper-
ylene fluorescence upon hydrogen bonding to benzoic acids according
to a fluorescence titration experiment in methylcyclohexane.
Wendorff, Chem. Unserer Zeit 2000, 34,
4 15; e) A. Beer, G.
Scherowsky, H. Owen, H. Coles, Liq. Cryst. 1995, 19, 565 572.
[4] a) F. W¸rthner, C. Thalacker, A. Sautter, Angew. Chem. 2000, 112,
1298 1301; Angew. Chem. Int. Ed. 2000, 39, 1243 1245; b) A.
Sautter, D. G. Schmid, G. Jung, F. W¸rthner, J. Am. Chem. Soc. 2001,
123, 5424 5430.
[5] The methoxyphenoxy-substituted diazadibenzoperylene 1 was ob-
tained as previously reported.[4] For synthetic details, characterization,
4428
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