Perfluorocyclobutyl-linked hexa-peri-hexabenzocoronene networks

Full text of DOI:10.1021/ja046855j

Published on Web 09/21/2004
Perfluorocyclobutyl-Linked Hexa-peri-hexabenzocoronene Networks
Bryan K. Spraul,† S. Suresh,† Sibylle Glaser,† Dvora Perahia,† John Ballato,‡ and
Dennis W. Smith, Jr.*,†
Center for Optical Materials Science and Engineering Technologies (COMSET), Department of Chemistry and
School of Materials Science and Engineering, Clemson UniVersity, Clemson, South Carolina 29634
Received May 27, 2004; E-mail: dwsmith@clemson.edu
Scheme 1. General Cyclopolymerization to Perfluorocyclobutyl
(PFCB) Polymers
In the quest for improved materials for photonics, the design
and synthesis of polyaromatic systems are increasingly important
considerations.1 One such class of recent interest are hexa-peri-
hexabenzocoronene (HBC) derivatives, pioneered by Mu¨llen and
others.2-4 HBCs can exhibit liquid crystalline properties and hole
transport capabilities, and they can emit light over a broad range
of wavelengths.
Scheme 2. Synthesis of Compounds 1-4 and Poly3 and Poly4a
To date, substituents on HBC systems have been limited
primarily to long alkyl chains or phenyl groups due to solubility
and reactivity constraints. Although the synthesis of hexakisalkoxy-
substituted HBCs using a monolayer precursor on Cu 111 surfaces
has been reported,4 undesired side products result under standard
oxidation conditions, which has precluded their general preparation.
Here we report the first synthesis of a hexa-peri-hexabenzo-
coronene compound containing trifluorovinyl ether substituents able
to undergo thermal cyclopolymerzation and copolymerization to
perfluorocyclobutyl (PFCB) networks. Polymers containing the
PFCB linkage have been established for high-performance optical
applications.5,6 Vinyl ether or perfluorovinyl ether substitutions on
HBC structures were not known previously.
Trifluorovinyl ether-substituted arenes, in general, undergo
thermal cyclodimerization when heated above 150 °C to form
fluorinated cyclobutyl rings, as shown in Scheme 1. These unique
semi-fluorinated polymers have shown great promise as components
in optical devices due to their excellent processability and transpar-
ency at telecommunication wavelengths.5
The syntheses of hexaphenylbenzenes have traditionally been
accomplished by Diels-Alder reaction7 of tetraphenylcyclopenta-
dienones with a diphenylacetylene or, alternatively, cobalt-catalyzed
cyclotrimerization of diphenylacetylenes.8 Thermal sensitivity of
the aryl trifluorovinyl ether group restricted our approach to the
cobalt route, as shown in Scheme 2. Bromo aromatic 1 was
converted to the iodo analogue and subsequently to new bisaryl
acetylene 2 via Sonogashira chemistry. Hexakis intermediate 3 was
obtained in 40% yield, and its X-ray crystal structure is shown in
Figure 1, the morphology of which resembles that of other
hexaphenylbenzene compounds.9
Benzene derivative 3 underwent standard oxidative ring fusion10
with FeCl3 to give hexa-peri-hexabenzocoronene 4 and the first
hexakisalkoxy-substituted HBC by this route. Sparingly soluble
monomer 4 was characterized by MALDI-TOF-MS as similarly
reported for other insoluble benzocoronenes.11 The spectrum clearly
indicates the loss of 12 DA from 3. Solid-state FTIR (sOCFd
CF2, 1831 cm-1) and 19F NMR (sparingly soluble in pyridine-d5,
δ -122.5 (dd), -129.8 (dd), -138.4 (dd)) confirmed the presence
of trifluorovinyl ether substitution.12 Modulated differential scanning
calorimetry (MDSC) of 4 exhibited an exothermic peak with an
onset temperature of 190 °C and a peak at 215 °C, characteristic
a Reagents and conditions: (i) t-BuLi, I2; (ii) CuI, trimethylsilylacetylene,
Pd(II), NEt3; (iii) KOH, MeOH; (iv) CuI, 1, Pd(II), NEt3; (v) Co2(CO)8,
1,4 dioxane; (vi) CH2Cl2, MeNO2, FeCl3.
of trifluorovinyl ether cyclodimerization. Disappearance of the
fluoroolefin and formation of the PFCB linkage (960 cm-1) were
confirmed by FTIR of poly4. Alternatively, monomer 3 can be
polymerized upon melting at 162 °C with a similar DSC profile.
The wide-angle X-ray diffraction pattern of 4 powder is shown
in Figure 2. The first peak, centered at 16.7 Å, is attributed to the
† Department of Chemistry.
‡ School of Materials Science & Engineering.
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J. AM. CHEM. SOC. 2004, 126, 12772-12773
10.1021/ja046855j CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
Scheme 3. Copolymerization of 4 with 5
the presence of HBC absorption peaks as a function of elution
volume (see Supporting Information). The copolymer emission
spectrum revealed HBC luminescence in addition to the 360 nm
emission of the homopolymer poly5 (Figure 3b,c).
Figure 1. X-ray crystal structure of 3.
The first synthesis and polymerization of trifluorovinyl ether-
substituted hexa-peri-hexabenzocoronene to perfluorocyclobutyl
polymers and copolymers has been demonstrated. Unlike hydro-
carbon ethers, fluorovinyl ethers are stable under HBC oxidation
conditions. Discrete HBC units in PFCB polymers provide access
to potentially processable HBC optical materials.
Acknowledgment. We thank the Defense Advanced Research
Projects Agency (DARPA) and the National Science Foundation
CAREER Award (DMR 9985160 to D.W.S.) for funding. We also
thank Dr. D. Vanderveer (Clemson) for X-ray crystallography and
Dr. M. Watson (University of Kentucky) for valuable expertise.
D.W.S. is a Cottrell Scholar of Research Corporation.
Figure 2. WAXD of monomer 4 powder.
Supporting Information Available: Detailed synthetic procedures
for 1-4 and characterization data of 3 and 4 including, MALDI, DSC,
excitation, emission, WAXD, and GPC data (PDF). Crystallographic
data, including bond angles and distances (CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
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Figure 3. Emission and absorption spectra (inset): (a) 4, (b) poly4-co-5,
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Monomer 4 was further mixed, via sonication, with other
trifluorovinyl ether monomers such as monomer 5.5 Upon copo-
lymeriztion at 150 °C, monomer 4 adducts became soluble, resulting
in a new PFCB copolymer (Scheme 3). Cyclopolymerization to
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