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Crystallization of Supramolecular Materials Perhydrotriphenylene (PHTP) Inclusion Compounds with Nonlinear Optical Properties.

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Crystallization of Supramolecular Materials:
Perhydrotriphenylene (PHTP) Inclusion
Compounds with Nonlinear Optical Properties**
Ralf Hoss, Olaf Konig, Vera Kramer-Hoss,
Urs Berger, Peter Rogin, and J u r g Hulliger"
A prerequisite for the design and synthesis of materials with
nonlinear optical (NLO) properties is a molecular building
block that can be incorporated into a solid in an appropriately
functionalized and oriented manner. To obtain new, single-crystal materials that exhibit electrooptical (EO) effects more pronounced than those of the currently known organic NLO crystals,[' -41 stable molecules showing hyperpolarizabilities B, of up
to 10000 x
m 4 V 1 and. having dipole moments that can
be aligned in a parallel manner within the solid are required.
While a large number of target compounds can be envisioned
based on these known criteria,I3. '1 the probability is low that
during the crystallization of pure NLO compounds a crystal
structure with a parallel arrangement of the b, axes is realized
(about 25% for an acentric space group, less than 5 % for
a nearly parallel
Hence, the question of alternatives for the formation of crystalline and structurally optimized EO materials arises. In this study it is shown that perhydrophenylene (PHTP)I6] forms inclusion compounds with
electronically optimized NLO species, in which the guest molecules can attain a parallel arrangement; materials with polar
properties on a macroscopic level are formed about 90% of the
Approaches to incorporating NLO molecules in a parallel
fashion into supramolecular host - guest systems have been tried
more than ten years ago.[71Starting with fi-cyclodextrin,['' a
number of known clathrate-forming compound^[^^ l o ] such as
urea and thiourea, tri-o-thymotide, cyclophosphazene, deoxycholic acid, and PHTPr6I were examined with respect to the
formation of inclusion compounds with small organic as well as
organometallic species. These host and guest molecules provided a high proportion of poIar structures for the inclusion compounds (63-85%) as well.[''] Zeolites have been loaded with
NLO compounds with the same goal in mind.['2.131The successful incorporation of two strongly hyperpolarizable species
(5, 8; see Table 1 ) into racemic ( k ) - P H T P was reported only
recently.[I4l This led to the assumption, that relative to urea.
thiourea, and tri-o-thymotide, PHTP is particularly well suited
to incorporate NLO target molecules of various compositions.
The equatoriai protons of layered, disk-shaped PHTP molecules
form continuous, apolar channels in which the guest molecules
are arranged in a parallel fashion (Fig. 1). The formation of
inclusion compounds was first studied with the oblong, unbranched, conjugated species I-VI, which exhibit different patterns of donor (D) and acceptor (A) substituents. These molecular frameworks have already been used to create NLO
molecules with large [j, values.[51In this group, the thiovinyl
moiety 1V was of particular interest due to its strong delocalization of n electrons. Table 1 summarizes the compounds dis-
Prof. Dr. J. Hulliger, Dr. R Hoss. 0. Konig. Dr. V. Kramer-Hoss. U. Berger.
P. Rogin
lnstitut fur anorganische. analytische und physikalische Chemie
Freiestrirsse 3. CH-3011 Bernc (Switzerland)
Fax. Int. code +(31)631-3993
e-inail: hulliger(u lac
This work was supported by the Swiss Nationalfonds (projects 2100037166.93 1. 20-43116.95). We thank H. P. Pfmder (University of Bernc) and
Hoffrnann-La-Roche A C for providing 20 g of crocetin dialdehyde, Bayer AG
for the hydration to yield PHTP. and C. Bossard (ETH Zurich) as well as K.
Krimer (University of Brriie) for the use of the lasers
Fig 1. Van der Waals surface of a PHTP channel (without guest molecules) according to it recent structure elucidation [20];the van der Waals radii are shown reduced
by 30"L~;carbon grey. hydrogen yellow; computer program employed. ATOMS
(Shape Software).
cussed below and some details regarding the synthesis and the
detection of polar PHTP-guest materials.
crystals of PHTP-guest comAccording to the
plexes can be obtained from solutions as well as from melts.
While during crystallizations from solutions the co-inclusion of
solvent must be avoided, the formation ofcrystals from melts is
limited to a few, thermally stable NLO guest components. 2-Butanone, in which PHTP is just soluble enough, has been reported
as suitable in this context.[" However, a 'H N M R spectroscopic
analysis of the inclusion compounds studied showed co-inclusion of 2-butanone in about ten cases. For a homogeneously
colored single crystal of PHTP-16 that showed no macroscopically visible inclusions, the ratio of 16 to 2-butanone was 1 : 15.
The crystallization of PHTP-16 and other systems from paraldehyde. on the other hand, yielded solvent-free inclusion complexes. Paraldehyde, with a van der Waals diameter of about 8 A, is
too big to fit into the PHTP channels, which have an inner
diameter of about 5 A. The inclusion compounds could also be
prepared, independent of solvents, by solid state reactions and
by crystallizations from the gas phase. PHTP-5, for example, is
formed already during mixing of the powdered starting materials.
Tdble I . Summark of D-. A-disubstituted NLO compounds, indicating the SHG effects ( clearly positive. -below the detection limit) after excitation at 1064 (1-6) or 1300nm ( 7 - 2 0 ) . as well as the
crystallization conditions (BU. from 2-butanone. PA. from paraldehyde. FR, from solid state reactions:
GP. from the gas phase).
PHTP inclusion
complex. SHG
+ FR. + BU
- BU:
+ PA
- BU;
+ PA
+ FR: + BU, + G P
- BU: - P A
+ BU
+ FR: + BU
+ FR: + BU
FR: - BU
+ BU
- FR:
+ FR: + BU: + PA
+ FR: + BU
+ FR: + BU: + PA
+ FR; + BU; + P A
+ FR: + BU: + PA
+ F R . + BU: + PA
+ FR: + PA
+ BU; + PA
+ BU: + PA
+ BU: + PA
X-ray oscillation photographs of single crystals exhibited, apart from Bragg reflections
stemming primarily from the PHTP host lattice, diffuse X-ray scattering phenomena that
are caused by, among other things, a onedimensional periodic arrangement of the guest
molecules.['41 In the cases studied (2-9, 12,
15- 18), the translational periods agree well
with the calculated lengths of the corresponding
in some cases. the formation
of hydrogen bonds is observed. The guest species that absorb visible light were all observed
to exhibit a strong dichroism (x >> x I). clearly
indicating parallel charge-transfer axes.[161A
"closest packing" of guest molecules is important for two reasons: 1) the dilution of dipoles,
caused by the host-guest lattice, is not further
enhanced ; 2) the observed intermolecular interactions along the D-7c-A.. . D-71-A chains
support the assumption that photoconduction
might be possible upon a judicious choice of
the D and A substituents. A new pathway for
the formation of organic photorefractive crystals could be opened in this way.". ''I
The number of the obtained PHTP-guest
systems exhibiting macroscopic polar properties was also determined. Frequency doubling
experiments on polycrystahe samples" or
small single crystals showed that 18 of the 20
systems studied exhibit a second-order NLO
effect, while only four crystalline samples of the
pure guest species were SHG active (SHG =
second harmonic generation). A contribution
to the S H G effect by crystallites of pure NLO
species can be excluded for all samples obtained by solid-state reactions. as only crystal
modifications that are S H G inactive were used.
With respect to the high proportion of SHGactive PHTP-guest systems it remains to be examined how much the theoretically maximum
NLO or electrooptic effect is reduced by orientational disorder or by domain formation (regions showing antiparallel orientations of the
p, axes). The EO characterizations of PHTP-5
performed so far allow the exclusion of domains that are substantially larger than the
wavelength of visible light. For the PHTPguest complexes with 5. 8, 9, 13, 14, as well as
16-20, the 2 0 response was sufficiently intense
relative to that of pure 4-dimethylamino-Nmethyl-stilbenazolium-p-tosylate[']
to assume
a primarily parallel arrangement of dipoles. In
terms of potential crystallization mechanisms it
is surprising that even solid-state reactions between PHTP and apolar crystalline samples of
the guest species lead to polar PHTP-guest
materials, as does the co-inclusion of 2-butanone.
With a representative sample of compounds
we could show that racemic PHTP forms stable
channel-inclusion lattices with many electronically interesting guest molecules. Through the
supramolecular approach, the use of D-x-A
guest molecules yields crystals exhibiting
macroscopic polar properties in about 90% of
the cases studied. For now, the question why the formation of
a polar arrangement for PHTP inclusion complexes is so strongly preferred over a pure NLO species remains unanswered.
Oscillating Crystallization of (+) and (-)
Enantiomers during Resolution by Entrainment
of 2-Azabicyclo[2.2.1 ]heptd-en-3-one**
E.xperimental Procedure
Gerard A. Potter, Chantal Garcia, Raymond McCague,
Brian Adger, and Andre Collet*
The guest species were purified by chromatography before cocrystallization and
characterized with the usual analytical techniques. Of the large number of NLO
compounds [I -41 only the 20 D-x-A systems described herein were available to us.
The crystallizations by controlled isothermal evaporation of2-butanone or paraldehyde were performed as described [14,19]. When solid starting materials were employed, the first step was grinding with a mortar and pestle. followed by isothermal
annealing at 80- 100 C. Crystallization from the gas phase can he perforined (e.8..
for PHTP-5) according to reference I191 (evaporation from Knudsen cells) or in
sealed ainpules with AT'< 1 K. T = 60-120 C. depending on the vapor pressure o f
the guest species.
The PHTP -guest systems were detected and characterized by %IS chromatography
and ' H N M R spectroscopy in solution, as well as by single crystal X-ray structure
analysis. The melting points of these systems were above that of pure PHTP
(125.2 'C). Oscillation photographs show a system of diffuse layer lines perpendicular to the channel axis [14]. From this data. the translatioiial periods of the guest
molecules were calculated. In all studied cases this period corresponded well to the
calcukited length of the molecule (e.g.. IS,,,, '15,,,, = 22.9(3)'22.8(5)A. 16,,,
= 18.0(4) 19.2(6) A)."SIThelatticeconstant
16,,,, = 27 l(5) '28.8(7) A. 18eb.!18c8,L
c of the host lattice was also determined from oscillation photographs and was
always found to he4 75(5) A. Precession photographs indicated a host unit cell with
either orthorhombic C e n t e r e d (5, 8. 15) or monoclinic symmetry (16. 17. 18).
As summarized in Table I . polycrystalline samples and small single crystals of the
PHTP-guest complexes were examined for S H G at 1064 or 1300 nni (for 1 .. 6 and
7-20. respectively). To eliminate potential effects of trapped solvents. measurements involving guest species that d o not show S H G effects as pure solids were
performed on samples from solid-state reactions.
Received: November 6. 1995
Revised version. February 12. I996 [Z8527IEl
German version: A n p i . Climi. 1996. I O X . 1774- 1776
. inclusion
Keywords: electrooptical properties
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[2] Mofecirlrrr Norilrrieor. Opiics (Ed: J. Zyss). Academic Press. New York. 1994.
[3] Nonli17eorOptical Properria of Or.?m7i( Mnli~czi1e.sonrl Cry\/u/.\,Pi)/. I ,2 (Eds.
D. S. Chemla. J. Zyss), Academic Press. New York. 1987.
[4] "Materials for Nonlinear Optics", ACS Svnp Srr. 1991. 455.
[5] N. J. Long, Aiigeii.. Clieni. 1995, 107, 37-56, Aiigeii.. CIiiv7i. In!. Ed. G i g / . 1995.
34, 6-20.
[6] M Farina. Inelmion Compd. 1984. 69-95: G Allegra. M. Farina. A Immirzi.
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M. Farina, G. di Silvestro, P Sozzani. Conip. Siiprcrmol. Clrw7.. l4l. 6 , S o l d
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C i ~ s t o Enginreriiig
(Eds.: D. D MacNicol.
F. Toda. R. Bishop). Pergamon. in press.
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[XI S Tomaru. S. Zembutsu. M. Kawachi. M. Kobayashi. J Clinii. S i r . Cherii.
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US-4818898, 1989 [Clir~nAhs. 1991. 115. 24351411
[lo] E. Weber in Top. Curr. Cli~ni 1987. 140. 3-20; J. E. D. Davies. W. Kemula.
H. M. Powell. N. 0.
Smith. J Iriclir.sion Plrmom. Mol Recogiiii Cliiwi. 1983. 1.
3 -44.
11 11 D. F. Eaton. A. G . Anderson, W. Tam, Y. Wang, J Am. Clietri Soc. 1987. IUY.
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[12] S. D. Cox, T. E. Gier. G . D. Stucky. 1. D. Bierlein. J. A m Clrcwi Soc. 1988. 110.
2986 - 2987.
[13] I. Girnus. M.-M. Pohl. J. Richter-Mendau. M Schneider. M. Noack. D Venzke, 3. Caro, Arfi.. Marrr. 1995, 7, 711 -714
[14] J. Hulliger, 0 Konig. R. Hoss. Ad? Muter.. 1995, 7. 719- 721.
[15] We calculated the lengths of the molecules using the program Botchmni from
the program package MnkroMorld 4.5. Columbia University, Cleveland. OH.
[I61 S. K. Lee.Q. Y. Shang, B. Hudson. Mol C r y / .Liy. 1992, 211. 147-156.
[I71 K. Sutter, J. Hulliger. P. Gunter. Solid S t i r t ~Coniiiii/n. 1990. 74, 867--870:
J Hulliger, K . Sutter. Y. Schumacher. B Bierrina. V. A. Ivanshin, J Cry.s;r.
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[19] J. Hulliger, A n g i w Cliem 1994. 106. 151 171; Angeic. Clicwi. lnr Ed. Eiigl.
1994.33. 143-163.
[20] 0. Konig, H. B. Burgi, T. Armbruster, J. Hulliger, Z . Kri.\td/ogr. Sidppl. I 1
1996. 106.
,c' VCH Verlu~.~,
tnhH. D-6Y4jl W?inheim,1996
The ( - ) enantiomer of the bicyclic lactam 1 is a key synthon
for the preparation of enantiopure carbocyclic nucleosides['. '1
used as chemotherapic agents for the treatment of viral infections (HIV, herpes) and as
coronary v a s ~ d i l a t a t o r s ' ~ ~
in certain cardiac dise a s e ~ . ' ~At
, ~ ]present the
manufacture of this im0
portant compound is ef(+)-I
fected by biocatalytic resolution of the racemate with suitable microbial strains.[61 We
recently discovered that ( k ) - lis a conglomerate (a feature that
had not been reported before).['] and this finding led us to focus
on the possibility of resolving this compound by the preferential
crystallization (or entrainment) method,[*- which is well suited to large scale applications. In this communication we report
an amazing observation made during the development of a practical entrainment process for 1;we found that the crystallization
of supersaturated solutions of this lactam proceeds by a series of
oscillations of their enantiomeric composition (the optical rotation value varies from ( - ) to (+) and back), until the final
racemic composition corresponding to the solubility equilibrium is attained. This unprecedented physical phenomenon provides a new insight into some of the factors that determine the
kinetics of crystallization of enantiomeric mixtures remote from
their solubility equilibrium.
We first examined the crystallization and solubility properties
of lactam 1 in various solvents. This compound crystallizes well
from diisopropyl ether, in which it is sparingly soluble at 20 'C
(racemate: S, = 3.56 wt YO, enantiomer: S, = 1.1 wtYo).['21
In this apolar solvent, however, the solubility ratio r = S,/S,
has an anomalously high value ( r = 3.24), indicating that
each enantiomer of 1 enhances the solubility of its mirror image
beyond what is usually observed. The same solubility properties
were observed in other ethereal solvents such as tert-butyl
methyl ether (TBME, I = 3.4). In most conglomerates there
is not normally such mutual solubility enhancement, and the
racemate is usually about twice as soluble as the individual
enantiomers (that is, I is close to 2).[13]The amide structure of
1 lends itself to the formation of strong intermolecular hydrogen bonds, and the enhancement of the racemate solubility
is possibly due to the existence of preferential heterochiral
H-bonding in solution. This is substantiated by the observation that addition of an alcoholic solvent to diisopropyl
ether. which can disrupt the intermolecular H-bonding, increases the solubility of 1 and significantly decreases 3 . Since a high
value of I is not favorable for the method of enantiomeric
resolution by preferential crystalli~ation,"~~
we attempted carrying out the entrainment experiments in a 90: I0 (w/w) mixture
aH H'D
[*] Prof. A Collet. Dr. C Garcia
Ecole normale superieure de Lyon
Stereochiniie et Interactions Moleculaires ( U M R CNRS 117)
46. Allee d'ltalie. 69364 Lyon cedex 07 (France)
Fax- Int code +(33)72 72 84 83
e-mail' andre.collet(ii
Dr. G . A Potter. Dr R . McCague. Dr. B Adger
Chiroscience. Cambridge ( U K )
[**I This work was supported by sabbatical funding from Chiroscience (to
G. A. P.)
$ IS.OO+ .25/0
Angei~'.Cliem. Int.
Ed. Engl. 1996, 35. NO. 15
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nonlinear, properties, perhydrotriphenylene, phtp, compounds, optical, supramolecular, inclusion, material, crystallization
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