ELECTROLUMINESCENCE IN LIGHT EMITTING POLYMERS FEATURING DEAGGREGATED POLYMERS

Abstract: In general terms, the present invention includes a light emitting polymeric material, the light emitting polymeric material capable of producing electroluminescence upon being provided with a flow of electrons, the light emitting polymeric material comprising a plurality of polymeric chains comprising polymeric chains each having substituent moieties of sufficient number and size and extending from the polymeric chain and about a substantial portion of the circumference about the polymer chain so as to maintain the polymeric chains in a sufficiently deaggregated state (referred to herein as a "strapped" polymer), so as to substantially prevent the redshifting of the electroluminescence and the lowering of light emission efficiency of the electroluminescence.

Description: ELECTROLUMINESCENCE IN LIGHT EMITTING POLYMERS FEATURING DEAGGREGATED POLYMERS This application claims the benefit of U.S. Provisional Application Serial No. 60/023,071 filed August 2, 1996. Technical Field The present invention is in the field of light-emitting polymers and light emitting devices produced therefrom. Background. Conjugated polymer based light-emitting devices have become an extensive area of academic and industrial research since the report of electroluminescence (EL) in poly(phenylene vinyleπe) (PPV) in 1990 [1]. A great number of different conjugated polymers have been found to exhibit EL including PPVs [1-3], poly(phenylphenylene vinylene) [4], polyphenylenes [5-7], polythiophenes [8-9], polyquinolines [10], polypyridines [1 1-12], poly(pyridyl vinylencs) [12-14] and many copolymcrs of these materials. i addition to many different materials, numerous configurations have been used to change and improve device performance. For instance, the use of additional layers to improve device efficiency has been known for some time [2,15]. Inserting a hole-transport (electron blocking) layer between the anode and emitting polymer or an electron-transport (hole-blocking) layer between the cathode and emitting polymer can greatly improve efficiency by confining the majority carrier to the emitting layer. A well known hole-transport (electron blocking) layer is poly(vinyl carbazole) (PVK) which has a large band gap (3.5 eV) and is itself luminescent [16-18]. Despite these advances there remains a need for improvements in the electroluminescence performance of light emitting polymers. Particularly, there remains a need to improve the performance of exiplex-forming bilayer devices so as to reduce or eliminate the redshifting believed to be associated with the aggregation of polymeric chains within the emitting polymer. It is a goal of the present invention to produce light emitting polymer and light emitting polymer devices made which give light emissions having reduced redshifting. In view of the present disclosure or through practice of the present invention, other advantages may become apparent. Summary of the Invention In general terms, the present invention includes a light emitting polymeric material the light emitting polymeric material capable of producing electroluminescence upon being provided with a flow of electrons, the light emitting polymeric material comprising a plurality of polymeric chains comprising polymeric chains each having substituent moieties of sufficient number and size and extending from the polymeric chain and about a substantial portion of the circumference about the polymer chain so as to maintain the polymeric chains in a sufficiently deaggregated state (referred to herein as a "strapped" polymer), so as to substantially prevent the redshifting of the elecli'υluiniπcscence and the lowering of light emission efficiency of the electroluminescence. It is preferred that the polymer of the presenl invention comprises polymeric chains selected from the group consisting of alternating and random copolymcrs, having comprising the structure: wherein m is the degree of polymerization; Y is selected from the group consisting of -CH 2 , 0, S, CO and NR 2 wherein R is an alkyl group containing 1 to 16 carbon atoms; A is selected from the group consisting of (CH 2 ) n . (CH 2 CH 2 O) n , (CH, CH 2 O) n NR wherein R is an alkyl group containing 1 to 16 carbon atoms, and aryl groups having 6 to 14 carbon atoms; B is selected from the group consisting of (CH 2 ) M) aryl groups having 6 to 14 carbon atoms, and calixarenc having 18 to 200 carbon atoms; wherein u may be of a value independently selected from the group 1 to 6, inclusive; wherein w may be of a value independently selected from the group 1 to 6, inclusive; wherein n may be of a value independently selected from the group 0 to 6, inclusive; and wherein Z may be a structure selected from the group consisting o : wherein R is an alkyl group containing 1 to 16 carbon atoms, wherein Y is selected from the group consisting of -CH,, 0, S, CO and NR 2 wherein R is an alkyl group containing 1 to 16 carbon atoms; B is selected from the group consisting of (CH 2 ) n , aryl groups having 6 to 14 carbon atoms, and calixarene having 18 to 200 carbon atoms; wherein u may be ofa value independently selected from the group 1 to 6, inclusive; and wherein w may be of a value independently selected from the group 1 to 6, inclusive. The electron transporting polymer may include polymeric chains selected from copolymers having the structure: Some specif i c examples of polymers used in the present invention include: The light emitting polymeric material may also be used in single layer, bilayer or other multiple layer devices, using the polymeric material of the present invention. In the case ofa single polymeric layer device, the polymeric material of the present invention may be used as the electron transporting/electron blocking layer. In the case ofa bilayer or muiti-layer devices, the polymeric material of the present invention may be used as the electron transporting layer in conjunction with an electron blocking layer of another appropriate polymer, such as might be selected from the group consisting of poly(vinyicarbazole). The present invention also includes a light emitting device comprising a light emitting polymeric material according to the present invention in all of its embodiments, and a source of electrical current so as to supply the light emitting deivce with a flow of electrons capable of producing electroluminescence from the device. Other examples of synthetic methods are described in reference 27 below. These devices may be constructed in accordance with deposition and assembly techniques known in the art. The present invention may be used in the creation ofa wide variety of lighting and lighted displays, giving the many advantages associated with polymeric materials. In accordance with the present invention, results are presented for bilayer devices using PVK. as a hole-transport layer and a family of copolymers of PPV and poly(pyridyl vinylene) PPyV with various side groups as the emitting layers. The absorption, photoluminesccnce and electroluminescence spectra indicate that the PL and EL are attributed to the formation of an exciplex at the PVK/copolymer interface for all the copolymer systems studied. An cxciplex, like an cxcimer, is an excited state complex, except that an exciplex is formed between two different molecules (polymers in this case) rather than identical ones for an cxcimer [1 ], Contrary to expectations, earlier reported devices do not exhibit exciplex formation. For example, Greenham et al reported a bilayer device with CN-PPV and PPV, but the EL matches the PL and EL ofa single CN-PPV film [3]. Results for other bilayer configurations also do not support exciplex formation [2]. Osaheni and Jenekhe [20] have observed exciplex formation in biiayers of PBO and TTA, but only for PL, although they do suggest that exciplexes may be important processes in organic light- emitting devices [20-21]. PL and EL due to exciplex formation has been reported in blends of PVK and a multiblock copolymer by Karasz and coworkers [17], but devices with separate layers were not investigated. Brief Description of the Drawings Figure 1 depicts three chemical structures relevant to the present invention: (a) a copolymer of PPyV and PPV with side groups R=C, 2 H 25 or COOC 12 H 25 , (b) a copolymer with side group R 1 =OC 16 H 33 and strap R =C l0 H 2O , and (c) a hole-transport layer poly(vinyl carbazoie). Figure 2 depicts plots showing absorbance ofa single layer of PVK, a single layer of copolymer, and a bilayer of PVK/copolymer: (a) PPyVP(COOC, 2 H 25 ) 2 V, (b) PPyVP(C 12 H 2S ) 2 V and (c) "strapped" copolymer. Figure 3 shows photoluminescence of (a) PPyVP(C, 2 H, 3 ) 2 V film (dashed line), PVK/PPyVP(C,,H 25 ),V bilayer film (solid line), PVK film (O) (b) PPyVP(COOC 12 H 25 ),V film (dashed line), PVK/ PPyVP(COOC 12 H 25 ) 2 V bilayer film (solid line), PVK film (O), and (c) strapped copolymer film (dashed line), PVK strapped copolymer bilayer film (solid line), PVK film (O). Figure 4 shows electroluminescence (solid lines) for . (a) 1TO/PVK/ PPyVP(COOC„H„) 2 V/A, device and . (b) ITO/PVK/strapped copolymcr/A, device, and photo.ummescence (dashed lines) for bilayer Huns of PVK and (a) PPyVP(COOC, Λi ) 2 V and (b) strapped copolymer. Figure 5 shows current density-voltage characteristics (O, and brightness-voltage characteristics * ofa,, device. ,« hows a comparison between a single layer, !TO/ PPyVP(COOC u H 2s > 2 V/A>, device (□) and the bilayer device (O). The bi.ayer device is .0 times brighter a. ,0 times lower current density irrrplying a 100 times improvement in efficiency. P tailed P y rintion of the Pr^ mfl Frn imr t In accordance with the foregoing summary of the invention, the foliowing presents a detailed description of the preferred embodiment of the vention which ,s presently considered to be its best mode. The synthesis of the PPyVPV eopolymers is described elsewhere [22]. Figure 1(a) shows the molecular structure of P ol y(p yridyl vinylene phenylene vinylene) (PPyVPV). We report results for copolymers with side groups R=COOC 12 H 25 and C 12 H 25 . Figure 1(b) shows the same copolymer with a "strap" across the phenyl ring in alternate PPV segments. For the second copolymer the side groups are ,-OC l 6 H 3 , with a strap R 2 =C 10 H 22 . The copolymers are soluble in common organic solvents such as tetrahydrofuran (THF), xylene, and chloroform. The PVK (Fig. 1(c)) was purchased from Aldrich Chemical Co. The PL and EL measurements were made using a PTI Q 1 luminescence spectrometer . The absorption measurements were made using a Perkin Elmer Lambda 19 UV/Vis/NIR spectrometer. The current-voltage characteristics were measured using two Keύhley 195A multimeters. The voltage was applied using a I IP 6218 A de power supply. Quantum efficiency measurements were made using a calibrated QTH lamp and a United Detector Technologies Silicon Photodiode (UV- 100). The samples for PL and absorption measurements were spin cast on quartz. PVK was spin cast (-3000 rpms) from a 10 mg/mi solution in THF. The copolymers were all spin cast (-1000 rpms) from xylene (~ 10 mg/ml) so the underlying PVK layer was not dissolved. For devices the polymers were spin cast on indium tin-oxide (ITO) substrates, which had previously been cleaned. The PVK layer in the bilayer configurations was dried for ~ 30 seconds in a laminar flow hood before the copolymer layer was spin cast. All fabrication steps for the devices were conducted in an ambient atmosphere in a Class 100 cleanroom. Aluminum electrodes were thermally evaporated onto the copolymer surface at low pressures (< 10 "6 torr). The active area of the devices was 7 mm . Results and Discussion Figure 2 shows the absorbance for single and bilayer systems. Each of the plots shows the absorbance of single layer of PVK, a single layer of copolymer, and a bilayer configuration of PVK and the corresponding copolymer. The onset of PVK absorption is at 3.5 eV and shows two spectral features at 3.6 and 3.75 eV similar to previous reports [6,7]. In each of the three cases (a), (b) and (c) of Fig. 2 the absorbance of the bilayer configuration is the sum of the absorbance of each of the individual layers. No new ground to excited state transitions are present. Photoluminescence excitation (PLE) results (not shown) for each of the systems confirm these results. The photoluminescence for the single layer and bilayer configurations are shown in Fig. 3. The PL (excited at 3.6 eV) ofa PVK film is shown in Fig. 3a, 3b and 3c by the open circles (O) and peaks at 3.05 eV similar to previous reports [6,7]. The dashed line is the PL o a single layer film of each copolymer, (a) PPyVP(C l2 H, 5 ),V, (b) PPyVPfCOOC » . 5 . ^ u yv i { LOOC l2 H 25 ) 2 V and (c) the strapped copolymer. The spectra arc similar with each of the peaks i t 7 i „v -n , ♦ . peaks at ~ 2.1 eV with the exception of the strapped copolymer which also has a significant shouider at 2,5 eV. The PL of the copolymer films, which peak near 2.6 eV [23,, are significantly redshifted from that of the soiution PL (no. shown). The PL 5 redshift from solution to film is due to aggregation i. the copolymer films (23J. The solid lines in Fig. 3 are the PL spectra for the bilayer configurations of PVK and each of the copolymers. ,n each case the bilayer films were exctted a, 3.6 eV an energy tha, is greater than the b nd gap of PVK. m each case, more prominent in Figs . 3b „ d 3c , mere is PL emis$i∞ „ ^ same energy as the PVK PL emission n l ,v \ u i - em t ss i on ( j .l eV). However, the main feature in the PL of the bilayer ■ 0 -films is located a, 2 . 5 eV for (a) PPyVP(C, 2 H 2i ) 2 V and (b) PPvVP(COOC, 2 H 2i): V and a, 2.4 eV for the (c) strapped copolymer. Emission at these energies is no, observed for individual fi.ms of either PVK or the copolymers indicatmg that the emission is due to a completeiy different species, the excip.ex. When the excitation energy is towered be.ow 3.4 eV (band gap of PVK) the emission due to the excipiex is drastically reduced. ,„ addition, varying the concentration or thickness of the J copolymer or PVK fi.ms in the bϋayer configuration wii, change the relative strengths of the exciplex peak and PVK peak. PPyVP(C, 2 H 25 ) 2 V and PPyVP(COOC l 2 H 25 ) 2 V have nearly identical PL results, which is expected since the side chains tend to perform the same function in both copolymers. The single layer PL results for the strapped copolymer in Fig. 3c show a completely new feature, a high energy shoulder. The high energy shoulder is closer to the solution PL and is attributed to unaggregated sites in the film. The C 10 H M strap around every other phenyl ring tends to disturb the aggregation lha l occurs in the other copolymers of this family, The same shoulder (now on the low energy side) also appears in the bilayer film, indicating the PL has contributions from exciplex sites and from utiaggregatcd regions of the strapped copolymer. The bilayer devices have turn-on voltages - 12-16 volts with current densities between 0.1 and 0.5 mA/mm . The devices can easily be seen in a brightly lit room and have internal quantum 5 efficiencies ~ 0.1-0.5%. Figure 5 shows the current-voltage (O) and voltage-brightness (solid line) characteristics for a typical ITO/PVK/PPyVP(COOC, 2 H 2j ) 2 V/Al bilayer device. The inset of Fig. 5 shows a comparison between a single layer device (ITO/PPyVP(COOC 12 H 25 ) 2 V/Al) and the bilayer device shown in the main plot. The bilayer device is ten times brighter at an order of magnitude lower current density which means the bilayer device is ~ 100 times more efficient than the single 10 layer device. In the devices the electrons are injected from the Al electrode into the conduction band of the copolymer, but they are confined at the PVK/copolymer interface due to a large barrier. The holes injected from the ITO also may be confined at the interface by a somewhat smaller barrier. The increased number of electrons and holes in the interface region increase the probability of !5 recombination via exciplex emission. In addition the buried interface severely reduces the non- radiative recombination that otherwise will occur near the electrodes. Conclusion In summary, the present invention demonstrates the presence of exciplex emission in hetcrojunctions of PVK and PPyVP(R),V. The addition of a C, 0 H o strap on every other phenyl 20 ring in the copolymer reduces the aggregation in the films. Emission from the strapped copolymer bilaycrs is a combination of light from exciplex and unaggrcgatcd sites. The exciplex is the primary method of electroluminescence in the bilayer devices. The bilayer devices we have fabricated show „,„„„, WO 98/05693 a 100 ti 3 increase in efficiency compared to single layer devices due to charge confinement and exciplex emission at the interface. The following references are hereby incorporated herein by reference: References [1] J.H.Buiτoughes, D.D.C. Bradley, A.R. Brown, R.N. Marks, K. Mackay, R.H. Friend, P.L. Burns, & A.B. Holmes, Nature, 347 (1990) 539. [2] A.R. Brown, D.D.C. Bradley, J.H. Burroughes, R.H. Friend, N.C. Greenham, P.L. Bum, A.B. Holmes, and A. Kraft, Appl. Phys. Lett. 61 (1992) 2793. [3] N.C. Greenham, S.C. Moratti, D.D.C. Bradley, R.H. Friend, and A.B. Holmes, Nature, 365 (1993) 628. [4] H. Vestweber ,A. Greiner, U. Lemmer, R.F. Mahrt, R. Richert, W. Heitz, and H. Bassler, Adv. Mater. 4 (1992) 661. [5] G.Grem, G. Leditzky, B. Ulrich, and G. Leising, Adv. Mater. 4 (1992) 36. [6] J. Gruner, P.J. Hamer, R.H. Friend, H-J. Huber, U. Scherf, and A.B. Holmes, Adv. Mater. 6 (1994) 748. [7] Y.Yang, Q. Pei, and A.J. Heeger. J. Appl. Phys. 79 (1996) 934. [8] Y. Ohmori, M. Uchida, K. Muro, and K. Yoshino, Sol. St. Comm. 80 (1991) 605. [9] Y. Ohmori, C. Morishima, M. Uchida, K. Yoshino, Jpn. J. Appl. Phys. 31 (1992) L568. [10] I.D. Parker, Q. Pei and M. Marrocco, Appl. Phys. Lett. 65 (1994) 1272. [11] D.D. Gebler, Y.Z. Wang, J.W. Blatchford, S.W. Jessen, L-B. Lin, T.L. Gustafson, H.L. Wang, T.M. Swager, A.G. MacDiarmid, and A.J. Epstein, J. Appl. Phys. 78 (1995) 4264. [12] Y.Z. Wang, D.D. Gebler, L.B. Lin, J.W. Blatchford, S.W. Jessen, H.L. Wang, A.J. Epstein, Appl. Phys. Lett. 68 (1996) 894. [13] J. Tian, C-C. Wu, M.E. Thompson, J.C. Sturm, R.A. Register, Chem. Mater. 7 (1995) 2190. [14] M. Onoda, J. Appl. Phys. 78 (1995) 1327. [15] C.W. Tang and S.A. VanSlyke, Appl. Phys. Lett. 51 (1987) 913. [16] R.H. Partridge, Polyme.24 (1983) 733-782. [17] B. Hu, Z. Yang, and F.E. Karasz, J. Appl. Phys. 76 (1994) 2419. [18] C. Zhang, H. von Seggern, K. Pakbaz, B. Kraabel, H-W. Scmidt and A.J. Heeger, Synth. Met. 62 (1994) 35. [19] M. Pope and C.E. Swenberg, Electronic processes in organic crystals. (Oxford University Press, New York, 1982), 739. [20] J.A. Osaheni and S.A. Jenekhe, Macromol. 27 (1994) 739. [21] S.A. Jenekhe and J.A. Osaheni, Science, 265 (1994) 765. [22] D-K. Fu and T.M. Swager, Poly(Pyridyl Vinylene Phenylene Vinylene)s: Synthesis and Solid State Organizations, to be published; copy enclosed. [23] J.W. Blatchford, S.W. Jessen, T.M. Swager, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. D, (1 96) in press. [24 J Y.Z. Wang, D.D. Gebler, T.M. Swager, D-K. Fu, A.G. MacDiarmid, A.J. Epstein. The contents of U.S. Provisional Patent Application Serial Number 60/023,071 are hereby incorporated herein by reference. In view of the present disclosure or through practice of the present invention, it will be within the ability of one of ordinary skill to make modifications to the present invention, such as through the use of equivalent arrangements and compositions, in order to practice the invention without departing from the spirit of the invention as reflected in the appended claims. Poly( yridylVinylenePhenyleneVinyleπ s: '*- ^^-- Synthesis and Solid State Organizations Dian-Kui Fu, Bing Xu and Timothy M. Swager* Department of Chemistry, Massachus tts Institute of Technology, Cambridge, MA 02139 Abstract: Por (pyndyl vinylene phenylene viπyJenes) wen: synthesized by Heck coupling proccduics. These mnirr*^ 1 * display large red shifts in their optical absorption which proioπation or ai ylation of ι he pyridyl nitrogen. Some of the polymers were found to be liquid crystalline. The protonaied or alkykvαi v rsion, exhibit highly organized structures due to charge-transfer interactions between polymer chains. INTRODUCTION Conjugated polymers have attracted much attention due to their electrical conductivity , 1 interesting optical, 2 nonlinear optical, 1 and more recently electroluminescent properties. 4 Since their disco very in 1990. polymer-based light-emitting diodes (PLED) have been investigated intensively for potential applications in flat panel displays. PT.FJD generally have the following advantages: 1) long term stability. 2) ease of fabrication, 3) wide spectral range. Poly(phenylene vinylene)s (PPV) are among the most studied PLED polymers and are most often prepared by elimination reactions on precursor polymers. Particularly interesting PPV derivatives are those with electron-poor cyano-substituted vinyl groups. These materials showed higher efficiencies in bilayer structures. 41 ' Inspired in part by this later work, we recently reported the svnthesis of all of the regioisomers of poly(methyl pyridinium vinylene (PMPyV), a very electron poor isoelectronic analog of PPV.* It has been demonstrated that PMPyV, its parent polymer poly(pyridyl vinylene) (PP V), and other analogs are promising materials for the construction of LED devices. 4,7 In those devices, environmentally stabic metals such as Λl, Cu and Ag were used as electron injection electrodes. As a continuation of our investigations of new PPV analogs, we report herein the synthesis and properties of copolymcrs comprised of alternating units of poly(pyridyl-2,5-vinylenes) and poly(2,S-disubstituted phenylene vinylene) which we abbreviate as PPyV-PDPV. In this paper we describe the synthesis of those copolymers under Heck coupling conditions. 10 Our interest in PPyV-PDPVs was further stimulated by their structural similarities to known liquid crystalline rigid polyesters. 1 The preparation of such self-organizing structures is of interest for the study of the factors which control the conducting and electroluminescent properties of these materials. e also anticipated that some of the PPyV-PDPVs may exhibit novel electronic and self-assembling properties associated with their alternating strongly electron-rich and electron-poor structures. Recent ohotophysical studies' have shown that the photoluminescent properties of conjugated polymers are highly dependent on their solid state organizations. In most cases conjugated polymers show greatly reduced photoluminescent (PL) quantum efficiencies in solid state relative to those obtained in dilute solution. This reduced efficiency is believed due to the strong interchain interactions which provide rapid nonradiative decay mechanisms. To reduce interchain interactions we have prepared the macrocycle containing copolymers PPy V- PDPV. RESULTS AND DISCUSSION Pd(PPh 3 ) 4 in the later part of our studies. While the reaction requires prolonged heating (55°C, <> days) and an excess of vinyltributyltin (4 eq.), it offers a simplified purification procedure and an improved yu.-ld of 80% ( a 43% overall yield was obtained for the two step procedure). Purification of 3 requires first a dk'illation under reduced pressure, to give a mixture of vinyltributyltin, 3, and a trace amount of 2. Further pun fication of the resulting mixture by flash column chromatography gave 3 as dear liquid in high purity (>99.5% by NMR) Monomer 3 was polymerized with the diiodide monomers under Heck reaction conditions immediately after purification in order to avoid free radical polymerization of the vinyl group. Dilute CH 2 C! 2 solutions of 3 could be stored for a period of one month in the dark at 0°C and were chromatographed before use. The 1,4- (oxydecanoxy)-2,5-diiodobezene macrocyclic monomer (S) was easily prepared by a Williamson ether synthesis. In this case, a 1 1 mixture of2,5-diiodo-l,4-dihydroquinone(4) and the commercially available 1,10- dibromodecane ere slowly added to a suspension of K 2 COj and KI in acetone via a syringe pump over a period of three days. The high dilution conditions were designed to maximize the formation of 5, however, a substantial amount (15%) of the undesired adduct, 6, was also produced. Since S and 6 were simiiar in physical properties, their separation was only possible through tedious gravity column chromatography (CHϊClj/hexanc (5:95), SiOj). Compound 5, was the first fraction and isolated in 25% yield. The structures ot 5 and 6 were confirmed by H and C NMR. in conjunction with mass spectrometry. Scheme 1 O 98/05693 As shown in Scheme 2, we have employed Heck coupling reactions for the copolymer svntheses. 10 For the purpose of fine-tuning the band structures of die non-macrocycle containing polymers, we synthesized polymers containing disubstituted phenylene units with different electron donating (or withdrawing) abilities. Monomers 7a, 7b and 7c were readily synthesized via standard organic transformations. The polymerizations to form polymers 8a, 8b, and 8c were conducted in toluene at 110°C using Pd(PPh 3 )jClj as a catalyst. In all cases, the precipitation of E sNT was observed during the polymerization. The precipitation of polymers 8b and 8c was also apparent after 24 hours. To circumvent these problems and improve the efficiency of uncoupling reactions, we used modified conditions for the preparation of polymer 9a and 9b. These conditions included a mixed solvent system consisting of DMF and xyleπe (1:1), for improved solubility, and Pd(P(o- tolyl))jCl 2 which appeared to be a more active catalyst. Scheme 2 related polymer 8b. Purification of the polymers involved precipitation from acetone and Soxhlct extraction with methaπol. Polymers 8a, 9b, 9c are highly soluble in various organic solvents such as CH7CI 1 , THF, anci toluene whereas polymers 8b and 8c are less soluble. All of the polymers are highly colored .ind fluorescc strongly in solution. Table 1: Results of Polymerization Polymer Isolated yield MB Color Properties The pyridine units of the copolymers are readily protonated with aqueous HC1 This transformatioi. i. accompanied by a dramatic color change (e.g. red to dark purple for polymer 8a) which is due to the donoi- acceptor nature of the polymer's electronic structure. Hence it appears that optical transitions involve a charge transfer from the donating dialkoxy phenyi moieties to the pyridine residue which is stabilized by protonation Treatment of polymer 9a with an excess of methyl triflate in CH 2 C1 2 gives polymer 11 which also displayed similar color changes. Table 2 lists the absorption maxima for all the neutral and canonic polymers. All of the catioαic polymers display strong red shifts relative to their neutral forms. Consistent with our characterization of these transitions as having a charge transfer nature, the magnitude of the shifts are consistent with the electron donating (or withdrawing) abilities of the side chains. Consequently, the largest shifts are observed for the dialkoxy groups (8a and 9a) and the diester (8b) displayed the smallest effects. The UV-Vis spectra of polymers 8a after protonation and methylation (11) are shown in Figure I. The neutral polymer (8a) displays a λ ^u , at 466 run which is totally absent in the protonated and methylated forms which have respective λ„„ values of 537 nm and 532 run. Scheme 3 8b 408 450 42 8c 426 452 26 9a 465 532 67 9b 443 502 59 Figure 1. UV-Vis spectra of polymer 8a (a), the protonated form (8a:H*) (b). and polymer 11 (c). DSC analysis of the polymers showed no detectable phase transitions up to 350°C. However, variable temperature x-ray diffraction studies (Figure 2) indicate that polymers 8a and 11 display liquid crystalline phases at elevated temperatures. The mesophases are of the lamellar Sanidic (∑) variety 12 in which the polymer chains exhibit a "board-like" biaxial organization in the layers. Based upon the lack of wide angle peaks, we conclude that 8a has very weak interpolymer correlations. We therefore label polymer Sa's mesophase as a disordered Sanidic (Σ_) Mcthylatioπ of 8a produces a greatly enhanced (100) diffraction and creates a new reflection at 3.47 A which indicates a stronger interaction between the polymer chains. We believe that this additional order originates from interpolymer charge-transfer interactions (Scheme 4). Due to the additional wide angle peak at 3.47 A in polymer 11, we assign this material as an ordered sanidic phase (Σ o). This two dimensional organization is novel since it creates a precise registry between polymer chains Other PPV derivatives generally only have nematic order between the polymer chains. The incorporation of macrocycles in the monomers diminishes co-facial chain-chain interactions. XRD studies of polymers 9a and 9b show only weak diffraction characteristics ofa very low degree of organization. Scheme 4 Figure 2. X-ray diffraction at 200°C of polymer 8a (top) and polymer 11 (TfO" salt) (bottom). CONCLUSION Polymers 8a, 8b, and 8c have been shown to be promising materials for the fabrication of LED devices. However, the electcoiuniinescent quantum efficiencies of these materials are still low. As mentioned earlier, this it i n part the result of the interchain interactions. However, the high degree of charge transfei interaction between polymer chains in ll's Σ. phase is novel and should result in other interesting electronic properties. The macrocycle containing polymers 9a and 9b, were designed to overcome the problem of interchain φie β cmng. Indeed, the initial photoluminescent studies on these polymers show improved efficicnciesand the deta i led photophyaical studies are currently under way. EXPERIMENTAL All experiments were carried out under argon atmosphere. THF was distilled from sodium benzophenone. DMF were dried over alumina and degassed before use. Vinyltributyltin, 13 and 4.". 7a and 7b" were prepared according to literature procedures. Monomer 7c M was easily prepared for a previously reported intermediate. 2,5-dibromopyridine (Aldrich), Pd(PPh 3 ) (Stre ), P(o-tolyl j (Aldrich) and PdCl, were used as received. NMR spectra were recorded with a Bruker AC-250 (250 MHz) spectrometer ITV-vis spectra were obtained using Hewlett Packard 8453 spectrometer. GPC was performed on a Rainin HPXL solvent delivery system with a RI-1 refractive index detector and a Shodex GPC K -80M column Molecular weights are reported relative to polystyrene standards. 2.5-Divinyl Pyridine (3): A THF (100 mL) solution of tetrakis(triphenylphosphanc) palladium (100 mg, 865 10 "2 m ol), 2,5-dibromopyndinc (3 50 g. 14.8 mmoi) and vinyltributyltin (18.0 g, 56.8 mmol) was heated at reflux for 5 days. After removal of THF by rotary evaporator, the resulting residue was subjected ; distillation under reduced pressure to remove a mixture of 5-bromo-2-vinyl pyridine and vinyltributyltin The resulting material was further purified by flash column chromatography (SiOj, EtOAc hexanc, 1 ' 0) to give 3 as aclear liquid (1.55 g, 80%). Η NMR (CDCl 3 ) 5 8.43 (s, 1H), 7 52 (δ, 1H), 7.12 (d, IK), 6 64-6.72 (m, 2H). 605 (d, IK), 5.64 (d, 1H), 532 (d, 1H). 5.18 (d, 1H); ,3 C δ 154.6, 147.7. 136.3, 132 9, 1326 131 5, 1206. 117.7, 115 4; MS 132 (M+1). 1.4-<Oxydecanoxy)-2,5-Diiodobczene (5): A mixture of 2,5-diiodo-l,4-dihydroquinone (724 g, 20.0 mmol), 1,10-dibromodecane (6.00 g, 20.0 mmol) and acetone (30 mL) was added to a 500 mL RB flask containing potassium carbonate (30.0 g.21.7 mmol), potassium iodide (0.50 g.3.0 mmol) and acetone (300 mL) via a syringe pump over a period of three days while maintainingthe reaction at reflux. After another three days, the acetone was removed with a rotary evaporator. The solid residue was then neutralized with dilute HC1, and extracted with CHjC! 2 (3 x 100 mL). Removal of CHjClj followed by flash column chromatography (SiO,, CH 2 C1 3 (hexaπe, 5.95) gave the desired product as a white solid (2.0 g, 20%). Η NMR (CDCI 3 ) δ 7.27 (s, 1H), 4.16-4.34 (m, 4H). 1.56-1.66 (b, 4H), 1.06-1.24 (m, 6H), 0.90-094 (b, 2H), 070 (b, AH), li C δ 152.6, 126.9. 89.1, 70.6, 27.6.27.4, 23.7; MS 518 (M^NH,) Polymer 8a: A mixture of divinylpyridiπe (0.493 g, 3.76 mmol), l,4-dihexadecanoxy-2,->-diiodobezene (3.05 g. 3.76 mmol), triethylamiπe (2.0 mL), bis(triphenylphosphene) palladium dichloride (30 mg, 0043 mmol) and toluene (10 m was heateα at 1 lO'C for 24 hours. The reaction was then diluted with 20 mL of toluene and poured into 600 mL of acetone to give a red precipitate. The resulting precipitate was collected by suction filtration. Further purification by Soxhiet extraction with methanol for 24 hours afforded polymer 8a as dark red solid (2.45 g, 95%) Η NMR (CDCl 3 ) δ 8 67, 7.82, 749. 7.46. 7.17, 7.12, 4.04, 1 88, 1 ' 2, 1.23, 0.84, "C δ 155.1, 151.4, 151.0, 148.7, 132.7, 131.8, 1288, 127.6, 126.8, 125.2, 124 8, 1 11.2, 1 104, 69.4. 69.3. 31.9, 29.7, 29.5, 29.4, 29.2, 26.2, 22.7, 14 1, Anal. Calcd: C, 82.28; H, 11.02; N, 2.04 Found C, 79.09; H, 10.67; N, 1.88. Polymer 8b- Monomers 3 and 7b were reacted under the same conditions as 8a to give polymer 8b in 88% yield. Η NMR (CDCI3) 58.76, 789-7.98, 745-7.55, 7.08-7.21, 2.65-2.80, 1 57-1.62, 1.26, 0.88. Polymer 8c: Monomers 3 and 7c were reacted under the same condition for the synthesis of polymer 8a to give polymer 8c in 90% yield 'H NMR (CDC1 3 ) δ 8.76, 8.36, 8.29, 7.91-8.08, 752, 708-7 13, 441, 1.84, 1 25.0.86. Polymer 9a: A mixture of 3 (581.4 mg, 4.43 mmol), 5 (1.108 g.2.215 mmol), 7a (1.797 g, 2.215 mmol), tricthylamine (3.0 mL), bis(triphenylphosphene)palladium dichloride (30 mg. 0.043 mmol). xylcne (70 L) and DMF (7.0 mL) was heated at 135°C. After 24 hours the reaction mixture was diluted wiui 10 mL of xylene and poured into a flask containing 600 mL of acetone. The resulting orange solid was collected by suction filtration and washed with methanol. Removal of the residue methanol gave polymer 9a as bright orange solid in 97% yield. Η NMR (CDClj) δ 8 69, 7.82-7.87, 7.49-7.56, 7.25, 7.11-7 16, 4 4", 4.24, 4 04. 1 87, 1 53. 1.23, 1 00, 0.84, 0.82, 0.73 Po'vmer 9b: A mixtur " 3 (121.6 mg, 0.927 mmoiχ 5 (231.8 mg, 0A mmol), 7b (307.1 ;mg,i | 0.463 mmoiχ triethylamine (0.5 mL), palladium dichloride (5.4 mg, 0.0304 mmol), tri(o-tolyl)phosphene (18.6 mg, 0.0304 mmol xylene (1.5 ' mL) and DMF (1.5 mL) was heated at 135°C. After 3 hours, the formation of yellow precipitate was observed. The reaction mixture was then diluted with 3 mL of xylene anil poured into a flask containing 500 mL of acetone. The resulting yellow solid was collected by suction filtration and washed with methanol. Removal of the residue methanol gave polymer 9b as bright yellow solid in 98% yield. Η NMR (CDCl,) 68.73, 7.84-7.90, 7.41-7.51, 7.26, 7.05-7.14, .48, 4.26, 2.80, 1.77, 1.62, 1.24, 0 82-0.85, 0.74. ACKNOWLEDGMENTS Funding from the Office of Naval Research is greatly appreciated. REFERENCES AND NOTES 1 Handbook of Conducting Polymers, Skotheira, T. A., Ed.; Dekker. New York, 1 86. 2. Patil, A. O.; Heeger, A. J.; Wudl, F. Chem. Rev. 1988, 88, 183-200. 3. Marder, S. R.; Sohn, J. E. laMatenals/or Nonlinear Optics: Chemical Perspectives, Stucl y, G. D., Ed.; ACS Symposium Series 455; American Chemical Society: Washington, DC, 1991. 4 Burroughes. J. H.; Bradley, D; D.; Brown, A. R.; Marks, R. N.; Mackay, .; Friend, R. H.. Bums.; P. L.. Holmes, A. B. Nature 1990, 347, 539. (b) Bum, P. L.; Holmes, A. B.; Kraft, A.; Bradley, D. D C .. Brown, A. R.; Friend, R. H.; Gymer, R. W. Nature 1992, 356, 47. (c) Greenham, N. C , oratti, S. C. Bradley. D. D. C; Friend, R. R; Holmes, A. B. Nature 1993, 365, 628 5. (a) Marsella, M. J.; Swager, T. M. Polymer Preprints (Proa Am. Chem. Soc.) 1992, 33 (1), 1196. (b) Marsella, M. J.; Fu, D.-K.; Swager, T. M Adv. Mater. 1995, 7, 145. 6. (a) Tian, J.; Wu, C-C; Thompson, M. E.; Sturm, J. C; Register, R. A.; Marsella, M. J ; Swager, T. M. Polymer Preprints, (Proc. Am. Chem. Soc.) 1994, 35 (iχ 275. (b) Tian, J.; Wu, C-C; Thompson, M. E.; Sturm, J. C; Register, R. A.; Marsella, M J.; Swager, . M. Adv. Mater. 1995, 7, 395. (c) Tian, J.; Wu, C-C; Thompson, M. E.; Sturm, J. C; Register, Chem. Mater. 1995, 7, 2190. 7. (a) Gebler, D. D.; Wang, Y. Z.; Blatchford, J. W.; Jessen, S. W.; Lin, L. B.; Gustufsoπ, T L.; Wang, H L.; Swager, T. M.; MacDiarmid, A. G. and Epstein, A. J. J. AppL Phys. 1995, 78, 4264. (b) Epstein, A. J.; Blatchford, J. W.; Wang. R L.; Gebler, D. D.; Jessen, S. W.; Lin, L. B.; Gusrufson, T. L.; Fu, D.-K., Wang, R L.; Swager. T. M.; MacDiarmid, A. G. Synth. Met 1996, 78, 253. (c) Wang, H L ; Park, J. W ; Fu, D.-K.; Marsella, M. J.; Swager, T. M.; MacDiarmid. A. G.; Wang. Y. Z.; Gebler, D D and Epstein, A J. Polymer Preprints, 1995, 36, 45. 8. (a) Rodriquez-Parada, J. M.; Duran, R.; Wegner.G. Macromolecules, 1989, 22, 2507 (b) Other liquid crystalline PPV derivatives have also been reported. Bao, Z.; Chen, Y.; Cai, R., Yu, L. Macromolecules, 1993, 26, 5281. 9. (a) Blatchford, J. W.; Jessen, S. W.; Lin, L. B.; Gustufson, T. L.; Fu, D.-K.; Wang, H. L ; S ager, T. M.; MacDiarmid, A. G. and Epstein, A. J. Phys. Rev. B 1996, 54, 9180. (b) Blatchford, J. W.; Gustufson, T. L., Epstein, A. J.; VandenBout, D. A.; Kerimo,B. J.; Higgins.D. A.; Barbara, P. F.; Fu, D.-K.; Swager, T. M. and MacDiarmid, A. G. Phys. Rev, B 1996, 54, 3683. 10 Heck, R. F. Palladium Reagents in Organic Synthesis, Academic Press, 198S. I I. (a) Louie, J.; Hartwig, J. F. Tetrahedron Lett. 1995, 36, 3609. (b) Hartwig, J. F ; Paul, F J. Am.Chem. Soc. 1995, 117, 5373. 12 Erert, M.; Herrmann-Schonherr. O.; Wendorff, J.H.; Ringsdorf, H.; Tschirner, P. Liq. Cryst. 1990, 7, 63. 13. Corey, E. J.; Wollengerg, J. Am. Chem. Soc. 1974, 96, 5581. 14. Zhou, Q.; Swager, T. M. J. Am. Chem. Soc. 1995, 117, 12593-12602. 15. Goldfinger, M. B.; Swager, T. M. J. Am. Chan. Soc. 1994, 116, 7895-6 16. Monomer 7c was readily synthesized from the diacid chloride derivative reported in ref. 1

Claims: In The Claims: 1. A light emitting polymeric material said light emitting polymeric material capable of producing electroluminescence upon being provided with a flow of electrons, said light emitting polymeric material comprising: 5 a plurality of polymeric chains comprising polymeric chains each having substituent moieties of sufficient number and size and extending from said polymeric chain and about a substantial portion of the circumference about said polymer chain so as to maintain said polymeric chains in a sufficiently deaggregated state, so as to substantially prevent the redshifting of said !0 electroluminescence and the lovvering of light emission efficiency of said electroluminescence. 2. A light emitting polymeric material according to claim 1 comprising polymeric chains selected from the group consisting of alternating and random copolymers, having the structure: 15 wherein m is the degree of polymerization; Y is selected from the group consisting of- CH 2 , O, S, CO and NR 2 wherein R is an alkyl group containing 1 to 16 carbon atoms; A is selected from the group consisting of (CH 2 ) „, (CH 2 CH 2 O) n , (CH 2 CH 2 O)„NR; wherein R is an alkyl group containing 1 to 16 carbon atoms, and aryl groups having 6 to 14 carbon atoms; B is selected from the group consisting of (CH 2 ) π , aryl groups having 6 to 14 carbon atoms, and calixarene having 18 to 200 carbon atoms; wherein u may be of a value independently selected from the group 1 to 6, inclusive; wherein w may be of a value independently selected from the group 1 to 6, inclusive; wherein n may be of a value independently selected from the group 0 to 6, inclusive; and wherein Z may be a structure selected from the group consisting of : wherein R is an alkyl group containing 1 to 16 carbon atoms; wherein Y is selected from the group consisting of - CH 2 , O, S, CO and NR 2 wherein R is an alkyl group containing I to 16 carbon atoms; B is selected from the group consis t ! o nf rru \ fe P cons i st i ng of (CH 2 ) n , aryl groups having 6 to 14 carbon atoms, and calixarcnc having 18 to 200 carbon atoms; wherein may be „ f . value indepen(taly ^ ^ ^ ^ ] ^ ^ ^^ ^ erein „ may be of value independent selected from ,ne group , , 0 6 , inclusive . 3. A Ugh. emitting poly meric materia| accordωg (o ^ [ ^^ ^ ^^ ^ polymeric chains seiected from the group consisting of copolymers, having the structure: wherein R, is OC ) 6 H 33 and R 2 is C ) ι 0 oH n 2 o- 4. A light emitting polymeric material according to claim 1 wherein said polymeric material is further provided with a layer of an electron blocking polymer . 5- A light emitting polymeric material according to claim 4 wherein sai electron blocking polymer s selected from the group consisting of poly(vinylcarbazole). 6. A light emitting polymeric material said light emitting polymeric material capable of producing electroluminescence upon being provided with a flow of electrons, said light emitting polymeric material comprising: a plurality of polymeric chains comprising polymeric chains each being provided with rotaxenes of sufficient number and size and extending from said polymeric chain and about a substantial portion of the circumference about said polymer chain so as to maintain said polymeric chains in a sufficiently deaggregated state, so as to substantially prevent the redshifting of said electroluminescence and the lowering of light emission efficiency of said electroluminescence. 7. A light emitting polymeric material according to claim 6 wherein said polymeric material is further provided with a layer of an electron blocking polymer. 8. A light emitting polymeric material according to claim 7 wherein said electron blocking polymer is selected from the group consisting of poly(vinylcarbazole). 9. A light emitting device, said device comprising a light emitting polymeric material according to claim 1 , and a source of electrical current so as to supply said electron transporting polymer with a How of electrons. ■0. A light emitting device, said device comprising a ,ight emitting polymeric material according .o Cam, 2 , and a source of e.ectrica, current so as to supp,y said electron transporting po , ymer with a How ol electrons. M. A light emitting device, said device comprising a light emitting polymeric material according <o claim 3, and a source of e.ectrica, current so as to supply said electron transporting polymer with a flow of electrons. 12. A light em.tting device, said device comprtsmg a light emitting polymeric materia, according . 0 Cairn 4, and a source of e.ectrica, current so as to supply said e.ectron transportmg po.ymer w,,h a flow of electrons. 13. A light emitting device, said device comprising a light emitting p„, ym eric materia. according to claim 5, and a source of electrical current so as to supply said e.ectron transporting polymer with a flow of electrons. ' 4- A light emitting device, sa t d device comprising a light emitting polymeric material according . 0 Cairn 6, and a source of electrical current so as ,„ supp.y said electron transporting polymer with a flow of electrons. 15. A light emitting device, said device comprising a light emitting polymeric material according to claim 7, and a source of electrical current so as to supply said electron transporting polymer with a flow of electrons. 16. A light emitting device, said device comprising a light emitting polymeric material according to claim 8, and a source of electrical current so as to supply said electron transporting polymer with a flow of electrons. 17 . A light emitting device, said device comprising a light emitting polymeric material according to claim 1 , and a source of electrical current so as to supply said electron transporting polymer with a flow of electrons, said device selected from the group consisting of single layer, bilayer and multi- layer light emitting devices. 18. A light emitting device, said device comprising a light emitting polymeric material according to claim 6, and a source of electrical current so as to supply said electron transporting polymer with a flow of electrons, said device selected from the group consisting of single layer, bilayer and multi- layer light emitting devices.

Inventors: EPSTEIN ARTHUR J, GEBLER DARREN D, SWAGER TIMOTHY M, WANG YUNZHANG, EPSTEIN, ARTHUR, J., GEBLER, DARREN, D., SWAGER, TIMOTHY, M., WANG, YUNZHANG
Applicants: UNIV OHIO, THE OHIO STATE UNIVERSITY
Application year: 1997
Main classification: C08F26
IPC codes: C08G61, C09K11, H01B1, H01L51, H05B33