Supramolecular Dendriphores: Anionic Organometallic Phosphors

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Supramolecular Dendriphores: Anionic Organometallic Phosphors Embedded in Polycationic Dendritic Species Aidan R. McDonald,† Davide Mores,† Celso de Mello Donega´,§ Cornelis A. van Walree,† Robertus J. M. Klein Gebbink,† Martin Lutz,‡ Anthony L. Spek,‡ Andries Meijerink,§ Gerard P. M. van Klink,† and Gerard van Koten*,† Chemical Biology and Organic Chemistry, Faculty of Science, Utrecht UniVersity, Padualaan 8, 3584 CH Utrecht, The Netherlands, Crystal and Structural Chemistry, BijVoet Centre for Biomolecular Research, Utrecht UniVersity, Padualaan 8, 3584 CH Utrecht, The Netherlands, and Condensed Matter and Interfaces, Faculty of Science, Utrecht UniVersity, P.O. Box 80.000, 3508 TA Utrecht, The Netherlands ReceiVed March 11, 2008

Heteroleptic iridium(III) organometallic complexes have been functionalized with sulfate tethers. These systems have been thoroughly characterized spectroscopically. Subsequently these iridium(III) complexes were reacted with polyionic dendritic materials yielding iridium(III) organometallic phosphorescent emitters supramolecularly bound in dendritic materials. The synthesized supramolecular core-shell materials were characterized using a range of standard spectroscopic and spectrometric techniques. Furthermore, a thorough analysis of the photophysical properties (UV-vis absorption/emission, quantum yield, lifetime of emission) was carried out. The tethered sulfate complexes were found to have similar photophysical properties compared to their unfunctionalized analogues. It was found that immobilization of the iridium lumiphores within the core of the dendritic material resulted in quenching of the triplet emitting state. The quenching was found to be a consequence of intramolecular triplet-triplet annihilation resulting in quenching of the emissive state of the phosphorescent organometallics. It was shown by varying the dendrimer generation, and flexibility around the core, that we could alter the extent of triplet-triplet annihilation. It was also discovered that multiple phosphorescent sites existed in a single host-guest polyionic material. All host-guest materials demonstrated this property. Lifetime decay patterns were solved using biexponential statistics, suggesting more than one type of decay. The developed host-guest materials were applied as lumiphores in OLED devices, and showed that in the solid state the observed quenching is diminished. Introduction The development of efficient luminescent transition metal materials for uses in light emitting devices has received considerable attention in recent years.1 Since the application of cyclometallated platinum 2-phenylpyridine-type (ppy) complexes as lumiphores in highly efficient organic light emitting diodes (OLED’s) was demonstrated,2 tremendous effort has been put into developing similar organometallics with improved quantum efficiencies and applicability in OLED devices.3 Cyclometallated ppy iridium(III) complexes, discovered in the early 1980’s, showed quantum efficiencies as high as 0.44 and therefore have become the system of choice as lumiphores in OLED technologies. Present work in this field has been directed * Corresponding author. Fax: +31-30-252-3615. E-mail: g.vankoten@ uu.nl. † Chemical Biology and Organic Chemistry, Faculty of Science, Utrecht University. § Condensed Matter and Interfaces, Faculty of Science, Utrecht University. ‡ Crystal and Structural Chemistry, Bijvoet Centre for Biomolecular Research. (1) Kalyanasundaram, K.; Gra¨tzel, M. Coord. Chem. ReV. 1998, 77, 347– 414. (2) (a) Baldo, M. A.; Lamansky, S.; Burrows, P. E.; Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett. 1999, 75, 4–6. (b) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151–154. (3) Evans, R. C.; Douglas, P.; Winscom, C. J. Coord. Chem. ReV. 2006, 250, 2093–2126. (4) King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc. 1985, 107, 1431–1432.

toward augmenting ligand electronics so as to adjust the energy levels of cyclometallated iridium complexes and thus to further improve quantum efficiencies and to cover the full visible spectrum. This has resulted in a huge range of aromatic cyclometallating ligands being tested and used in homoligated complexes.5 Tris-cyclometallated iridium complexes [Ir(C,N)3] tend to show higher quantum yields (QY) and internal quantum efficiencies than their bis-cyclometallated analogues. However, bis-cyclometallated complexes show very valuable photophysical properties and thus a huge range of charged heteroleptic [Ir(C,N)2(L)][X] complexes have also been developed.6 Neutral heteroleptic tris-cyclometallated complexes [Ir(C,N)2(E,E′)] with the heteroligand being an acetylacetonoate (E, E′ ) O,O′) or picolinate (E, E′ ) N, O) have also been developed.7 The picolinate derivatives, in particular, have been thoroughly investigated and used in OLED devices.8 Separate reports have shown how the photophysical properties of heteroleptic-picoli(5) (a) Huo, S.; Deaton, J. C.; Rajeswaran, M.; Lenhart, W. C. Inorg. Chem. 2006, 45, 3155–3157. (b) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau, R.; Thompson, M. E.; Holmes, R. J.; Forrest, S. R. Inorg. Chem. 2005, 44, 7992–8003. (c) Jung, S.; Kang, Y.; Kim, H.-S.; Kim, Y.-H.; Lee, C.-L.; Kim, J.-J.; Lee, S.-K.; Kwon, S.-K. Eur. J. Inorg. Chem. 2004, 3415–3423. (d) Okada, S.; Okinaka, K.; Iwawaki, H.; Furugori, M.; Hashimoto, M.; Mukaide, T.; Kamatani, J.; Ogawa, S.; Tsuboyama, A.; Tagiguchi, T.; Ueno, K. Dalton Trans. 2005, 1583–1590. (e) Su, Y.-J.; Huang, H.-L.; Li, C.-L.; Chien, C.-H.; Tao, Y.-T.; Chou, P.-T.; Datta, S.; Liu, R.-S. AdV. Mater. 2003, 15, 884–888. (f) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.; Petrov, V. A.; Wang, Y. Chem. Commun. 2001, 1494–1495.

10.1021/om800226q CCC: $40.75  2009 American Chemical Society Publication on Web 01/23/2009

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Figure 1. Synthesis of core-immobilized organometallics.

nate complexes can be tuned by either varying the homoligands (C,N) or the heteroligands (E,E′; picolinates).9 In fact, by altering the heteroligand alone, emisson over the full visible spectrum has been achieved.10 OLED devices consist of a number of layers which all play a role in excitation, hole and electron transport, and emission. Ideally, good interaction between electrodes, lumiphore, hole transport (HTL) and electron transport layers (ETL) is desired. Several approaches have been followed to bridge the gap between layers (materials that make up anode, cathode, HTL, ETL, lumiphore), and improve efficiency in OLED devices. Attempts have been made at making a covalent linkage between the hole/electron transport layer materials and the organometallic emitter.11 [Pt(ppy)(acac)] derivatives have been tethered, via the acetylacetonoate (acac) ligand, to multifunctional polystyrene supports with copolymerised electron and hole transport moieties.12 Some interesting photophysical properties (increased quantum yield, less triplet-triplet annihilation), as a result of iridium (6) (a) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N. N.; Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem. 2005, 44, 1713–1727. (b) Nazeeruddin, M. K.; Humphry-Baker, R.; Berner, D.; Rivier, S.; Zuppiroli, L.; Graetzel, M. J. Am. Chem. Soc. 2003, 125, 8790–8797. (c) Ionkin, A. S.; Marshall, W. J.; Fish, B. M. Organometallics 2006, 25, 1461–1471. (d) Tamayo, A. B.; Garon, S.; Sajoto, T.; Djurovich, P. I.; Tsyba, I. M.; Bau, R.; Thompson, M. E. Inorg. Chem. 2005, 44, 8723– 8732. (e) Yang, C.-H.; Li, S.-W.; Chi, Y.; Cheng, Y.-M.; Yeh, Y.-S.; Chou, P.-T.; Lee, G.-H.; Wang, C.-H.; Shu, C.-F. Inorg. Chem. 2005, 44, 7770– 7780. (7) (a) Zhao, Q.; Jiang, C.-Y.; Shi, M.; Li, F.-Y.; Yi, T.; Cao, Y.; Huang, C.-H. Organometallics 2006, 25, 3631–3638. (b) Hsu, N.-M.; Li, W.-R. Angew. Chem., Int. Ed. 2006, 45, 4138–4142. (c) Lamansky, S.; Djuorvich, P.; Murphy, D.; Abdel-Razzaq, F.; Kwong, R.; Tsyba, I.; Bortz, M.; Mui, B.; Bau, R.; Thompson, M. E. Inorg. Chem. 2001, 40, 1704–1711. (8) D’Andrade, B. W.; Brooks, J.; Adamovich, V.; Thompson, M. E.; Forrest, S. R. AdV. Mater. 2002, 14, 1032–1036. (9) Kwon, T.-H.; Cho, H. S.; Kim, M. K.; Kim, J.-W.; Kim, J.-J.; Lee, K. H.; Park, S. J.; Shin, I.-S.; Kim, H.; Shin, D. M.; Chung, Y. K.; Hong, J.-I. Organometallics 2005, 24, 1578–1585. (10) You, Y.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438–12439. (11) Gong, X.; Robinson, M. R.; Ostrowski, J. C.; Moses, D.; Bazan, G. C.; Heeger, A. L. AdV. Mater. 2002, 14, 581–585.

site isolation, have been observed with [Ir(ppy)3]-type systems at the core of a highly conjugated aromatic dendritic system.13 Similarly conjugated polymers have been coupled with organometallic iridium triplet emitters to enable energy transfer from their own nonemissive triplet state to emissive states of the complex.14 The van Koten group has recently shown the supramolecular immobilization of palladium organometallics in polyionic core-shell dendritic materials.15 Anionic sulfate functionalized NCN-pincer palladium complexes were immobilized in octacationic core-shell dendrimers, which comprise eight quaternary ammonium sites in the core, and a shell of Fre´chet polybenzylaryl-ether wedges.16 Immobilization was mediated through an ion exchange reaction between the ammonium sulfate of the complex (guest) and the ammonium bromide of the core (host, Figure 1). These systems are easily purified by making use of nanofiltration techniques.17 We have set out to functionalize the phosphorescent complexes [Ir(ppy)2(E,E′)] with a sulfate tether and to subsequently study the immobilization of these complexes in the abovementioned polycationic materials (Figure 1). A study of this sort has potential to assemble varying numbers of iridium(III) lumiphores within ordered polymeric materials. In principle these materials could be tuned to facilitate high or low lumiphore (12) Furuta, P. T.; Deng, L.; Garon, S.; Thompson, M. E.; Fre´chet, J. M. J. J. Am. Chem. Soc. 2004, 126, 15388–15389. (13) Lo, S.-C.; Nambas, E. B.; Burn, P. L.; Samuel, I. D. W. Macromolecules 2003, 36, 9721–9730. (14) (a) Sandee, A. J.; Williams, C. K.; Evans, N. R.; Davies, J. E.; Boothby, C. E.; Ko¨hler, A.; Friend, R. H.; Holmes, A. B. J. Am. Chem. Soc. 2004, 126, 7041–7048. (b) Evans, N. R.; Devi, L. S.; Mak, C. S. K.; Watkins, S. E.; Pascu, S. I.; Ko¨hler, A.; Friend, R. H.; Williams, C. K.; Holmes, A. B. J. Am. Chem. Soc. 2006, 128, 6647–6656. (15) van de Coevering, R.; Alfers, A. P.; Meeldijk, J. D.; MartinezViviente, E.; Pregosin, P. S.; Klein Gebbink, R. J. M.; van Koten, G. J. Am. Chem. Soc. 2006, 128, 12700–12713. (16) Kleij, A. W.; van de Coevering, R.; Klein Gebbink, R. J. M.; Noordman, A.-M.; Spek, A. L.; van Koten, G. Chem. Eur. J. 2001, 7, 181– 192.

1084 Organometallics, Vol. 28, No. 4, 2009 Scheme 1. Synthesis of 4-(Hydroxymethyl)-2-pyridinecarboxylic Acid, 1

loading. On top of that, the dendritic material itself could be tuned so as to modify both the solubility and phobicity of the material. Likewise the dendritic support material could be applied as an HTL or ETL in an OLED. This would essentially mean a perfect contact between lumiphore (Ir(III)) and HTL or ETL. We hope to gain insights into how these organometallics interact with the polycationic host material. Similarly we hope to see the effect of site isolation of the luminescent organometallic as a result of entrapping the lumiphore in the polycationic dendritic core. Conversely we hope to see the effect of having multiple iridium sites held intramolecularly at close proximity to one another. This report presents a proof of principle to the above concept, with insights gained into the effects of both the dendritic support on the lumiphore and vice versa.

Results and Discussion Synthesis and Characterization of Functionalized [Ir(C,N)2(N,O)] Complexes. Synthesis of sulfate functionalized iridium(III) complexes has been achieved in a three-step procedure from a precursor iridium(III) monochloride and a functionalized 2-pyridinecarboxylic acid. Our previous work has focused on developing functionalized systems of the type [Ir(C,N)2(C′,N′)],18 however, this requires advanced synthetic methods, so we elected for a more simple manner to develop functionalized, and tethered cyclometallated iridium complexes. Scheme 1 depicts the synthesis of ligand 1 by a slight modification of the reported procedure for the synthesis of the analogous ester.19 Simultaneous deprotection and hydrolysis of TBDMS-protected 4-(hydroxymethyl)-2-pyridinecarbonitrile using aqueous hydrochloric acid yields 4-(hydroxymethyl)-2pyridinecarboxylic acid with an overall yield of 40%. The HCl salt of 1 was characterized using 1H and 13C NMR spectroscopy. Crystals of 1 suitable for X-ray diffraction were acquired and analyzed.20 The synthesis of the iridium complex 5 was carried out according to a literature procedure.14b Complex 6 was synthesized by adding 2 equiv of 2-pyridinecarboxylic acid to 5 in the presence of excess base (Na2CO3), as was reported for analogous complexes (Scheme 2).7c The reaction of the HCl salt of 4-(hydroxymethyl)-2-pyridinecarboxylic acid with 5 was carried out in a similar manner to the synthesis of 6. However, a larger excess of base was used to account for the fact that the hydrochloride salt of 1 was used. The new compounds 6 and 7 were characterized using 1H and 13C NMR spectroscopy, and MALDI-TOF mass spec-

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trometry. The data confirmed that the reactions yielded single products and a single isomer was obtained in each case. Single crystals of 7 · 2EtOH suitable for X-ray diffraction were acquired from slow evaporation of a 50:50 CH2Cl2/EtOH solution. The system is monoclinic with the space group P21/c. The bond lengths and angles are as expected for such heteroleptic [Ir(ppy)2(pic)] complexes (Figure 2). The ligands are bound in a distorted octahedral fashion around the iridium center. The ppy ligands are aligned such that the nitrogen atoms lie trans to each other and the σ-bound carbon atoms are trans to the pic-heteroligand. The complex is a homo-(N)-trans isomer, which is standard for bis-cyclometallated [Ir(ppy)2(E,E′)] complexes. The homo-(N)-trans configuration is preferred as a result of the configuration of starting material 5, which is a C2-(N)trans isomer.18 The crystal packing of 7 · 2EtOH is of particular interest. By hydrogen bonding the 2-pyridinecarboxylate ligands form a onedimensional polymer along the crystallographic a-axis (Figure 3). Thereby the hydroxyl group acts as a hydrogen bond donor and the coordinated carboxylate oxygen O11 as acceptor. Two crystallographically independent cocrystallized ethanol molecules also take part in the hydrogen bonding. Their OH groups act as hydrogen bond donors and the noncoordinated carboxylate oxygen and the hydroxyl group of the 2-pyridinecarboxylate ligand act as hydrogen bond acceptors. Complex 7 was further functionalized by reaction with pyridine sulfite complex yielding a pyridinium sulfate complex (see Scheme 3). This was converted, without workup, to n-butylammonium (nBu4N+) sulfate 8, by stirring 7 in a water/ CH2Cl2 biphasic system with excess nBu4NCl. Complex 7 was also reacted with 1,3,2-dioxathiolane-2,2-dioxide yielding a sulfated complex 9, which has a longer tether between the complex and the anchoring sulfate group. The sodium salt was likewise converted to the nBu4N+ salt. The nBu4N+ salts were synthesized because their halides show higher water solubility, which is important when anchoring the complex in a polycationic dendrimer (see following section). Both complexes 8 and 9 were characterized using 1H and 13C NMR spectroscopy, and ESI-mass spectrometry. 1H NMR shows a clear disappearance of hydroxymethyl OH signals, and a slight shift in the methylene CH2 signal confirming complete conversion of the alcohol to the sulfate/ethereal-sulfate. IR spectroscopy confirmed the presence of a sulfate group. Synthesis and Characterization of Host-Guest Polyionic Dendritic Materials. Anionic complexes 8 and 9 were immobilized within the core of polycationic core-shell supports (Scheme 3). This was done by carrying out a biphasic (CH2Cl2/ H2O) ion-exchange reaction between ammonium sulfates 8 and 9 and polyionic systems 3 and 4. Compound 8 was also reacted with compound 2. Equimolar amounts of ion-exchange components were added. Numerous washings of the organic phase with water were carried out to ensure removal of all halide contaminants. All host-guest materials (Figure 4, materials 10-14) were characterized using 1H and 13C NMR. A typical 1H spectrum, DMSO-d6, is depicted in Figure S7 (see Supporting Information for 1H of 12). In all cases no nBu4N+ resonances were observed,

Scheme 2. Synthesis of Complexes 6 and 7

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Figure 2. Displacement ellipsoid plot (50% probability level) of 7 · 2EtOH in the crystal. Ethanol molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg.): Ir1-N11 2.139(2), Ir1-N21 2.044(2), Ir1-N31 2.039(2), Ir1-C212 2.009(3), Ir1-C312 1.991(3), Ir1-O11 2.1883(19), C16-O11 1.284(3), C16-O12 1.234(4), N11-Ir1-O11 76.01(8), N21-Ir1-C212 80.72(11), N31-Ir1-C312 80.88(11), O11-C16-O12 124.7(3).

Figure 3. Hydrogen bonded one-dimensional polymer of 7 · 2EtOH in solid state. C-H hydrogen atoms are omitted for clarity. Symmetry operations: (i) x - 1, y, z; (ii) x + 1, y, z; (iii) 1 - x, 1 - y, -z.

suggesting all starting material 8 or 9 had reacted. Furthermore, the integration intensity of peaks belonging to the guest complexes compares favorably with the integration intensity of peaks of the core-shell dendritic support. The methyl group resonances of the dimethylammonium functionality (RN(CH3)2R resonances are at 2.84 ppm) integrate favorably with respect to the signals that belong to the bound complex (CHAr) (6.00 or 6.22 ppm) in a ratio of 6:1 (six dimethyl amino host protons for every one aromatic guest proton). This means that all sulfate functionalized iridium complexes are in a ratio of 1:1 with dimethylamino groups, and thus all bromides have been replaced by sulfate-guests. There are four separate peaks corresponding to methylene CH2’s of both host and guest. The peak at 4.86 ppm belongs to the sulfatomethyl CH2 of the picolinate ligand (guest). This is shifted with respect to the starting material 8 (4.89 ppm). The peaks at 4.54 and 4.47 ppm correspond to the (17) Dijkstra, H. P.; van Klink, G. P. M.; van Koten, G. Acc. Chem. Res. 2002, 35, 798–810. (18) McDonald, A. R.; Lutz, M.; von Chrzanowski, L. S.; van Klink, G. P. M.; Spek, A. L.; van Koten, G. Inorg. Chem. 2008, 47, 6681–6691.

separate CH2’s bound to the dimethylamino group of the host (Ar-CH2-NMe2-CH2-Ar′). These peaks are substantially shifted with respect to the starting bromide salt in DMSO-d6 (4.68 and 4.59 ppm in 4). The peak at 5.10 is the benzylic ethereal OCH2 of the Fre´chet wedge. The aromatic region is relatively uncomplicated, and host and guest signals can be relatively easily differentiated and assigned. A thorough NMR investigation into the characterization of similar host-guest complexes has been previously reported by our group.15 ESI-MS analysis was also used to characterize systems 10-14. Unfortunately, it was not possible to observe systems with more than one host-guest interaction. For example, the mass observed for material 10 is expected to be 3111.17 g/mol, but the observed value is 2379.01 g/mol. That mass corresponds to host plus only one guest, not the expected two. It appears (19) El Hadri, A.; Leclerc, G. J. Heterocycl. Chem. 1993, 30 (3), 631– 635. (20) von Chrzanowski, L. S.; Lutz, M.; Spek, A. L.; McDonald, A. R.; van Klink, G. P. M.; van Koten, G. Acta Crystallogr. 2007, E63, o1121o1122.

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Scheme 3. Synthesis of Short- and Long-Tailed Ammonium Sulfate Complexes 8 and 9 and Their Reaction with a Cationic Dendritic Core

that the only ions that fly in the mass spectrometer are by loss of a sulfate functionalized guest. ESI-MS only confirms that a host-gest species has formed, it cannot confirm that all docking sites are occupied by sulfate groups, the NMR information is necessary to prove this point. Compound 11 also gave results corresponding to host with one guest present. With the larger systems (12-14) it was not possible to observe any host-guest compounds using any of the mass techniques available to us. Electrochemistry. Cyclicvoltametry (CV) was performed on compounds 2, 4, 6-10, and 13 in MeCN (Table 1). Compounds 6 and 7 showed reversible oxidation at around 0.60 V and reversible reduction at around -2.40 V. Compounds 8-10 and 13 showed chemically irreversible oxidation and reduction with similar values. The observed irreversibility is believed to be as a result of having ammonium sulfates present which are deterring the reduction of oxidized complexes and vice versa. The overall outcome of the electrochemical results is that the Table 1. Electrochemical Data Pertaining to Compounds 2, 4, 6-10, 13a compound

oxidation (V)

reduction

Eg (eV)

2 4 6 7 8 9 10 13

0.90 and 1.20 0.90 and 1.20 0.57 0.57 0.57 0.59 0.60 0.60

-2.36 -2.41 -2.45 -2.41 -2.41 -2.41

2.93 2.98 3.02 3.02 3.01 3.01

All measurements carried out in MeCN. Fc/Fc+ used as internal standard (reference 0.51 V). a

functionalization and immobilization of the organometallic has little to no effect on the standard oxidation and reduction potentials of the lumiphore. Electronic Spectroscopy. Polyionic compounds 2-4 show π-π* absorptions at ∼230 and ∼280 nm, with the intensity highly dependent on the generation of the dendrimer (Table 2). There was no observed shift in wavelength upon docking of the lumiphores in the dendritic cores. The UV-vis absorption spectra of compounds 2-4 show no absorption above 300 nm. UV-vis absorption spectra of the nonfunctionalized complex 6 and functionalized complexes 7-14 are all similar. Spin allowed π-π* absorptions are observed at ∼265 nm, while lower energy spin forbidden MLCT transitions are observed above 320 nm. With host-guest compounds 10-14, absorptions at 230 and 280 nm, belonging to host systems, are clearly visible. Guest species show less prominent absorptions, due to the intensity of the host absorption. All guest components show similar extinction coefficients, when calculated on a per iridium site basis, compared to compounds 6–9. Immobilization of the complexes as guests at the core of host polycationic dendritic molecules shows little or no effect on the UV-vis absorption properties of the iridium organometallic. On the contrary, emission studies of compounds 6–14 yielded more contrasting results. In the solid state all compounds were highly emissive at room temperature when placed under a UV lamp. All compounds emitted at room temperature between 511 and 514 nm in both MeCN and 2-MeTHF solutions (Table 2). The polyionic materials 2–4 showed no emission at all in either solvent. There was little observable difference in the appearance

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Figure 4. Starting polycationic materials 2-4 and host-guest materials 10-14.

of the emission spectra of compounds 6–14. Slightly positive solvatochromism was observed, with a bathochromic shift in the maxima of the emission peaks when comparing 2-MeTHF with more polar MeCN. QY measurements were carried out at room temperature in 2-MeTHF. QY measurements showed significant differences depending on the functionality bound to the iridium complex or on the surroundings of the iridium complex. fac-[Ir(ppy)3] in 2-MeTHF was used as a reference (Φ ) 0.4). In quantum yield studies considerable functionalization and immobilization effects were observed. Nonfunctionalized 6 has a Φ ) 0.57, which upon functionalization, yielding compounds 7-9, increases to ∼ 0.70. This positive influence on the quantum efficiency is probably as a result of the higher electron donating ability of the methylene group resulting in a more efficient emission process.10 The functionalized complexes 7-9 show a faster emission lifetime than 6. The maximum quantum yield observed in the host-guest systems is 0.37 (11), a substantial decrease compared to the parent complex 6. Immobilization of emissive organometallic Ir(III) complexes in polycationic support materials quenches the emission of the iridium phosphor. The quantum yield is dependent on the generation of the dendrimer. Furthermore, it is also dependent on how tightly bound the complex is, that is how much flexibility there is in the polymeric material (see discussion). Complex 6 and functionalized complexes 7-9 have phosphorescent emission lifetimes in the 550-750 ns range (Figure 5, compound 8). Luminescence lifetime plots of compounds 6-9

show a monoexponential decay plot. All host-guest materials (10–14) show faster decay than complexes 6-9. All host-guest systems give decay emission lifetime spectra which are best fitted using biexponential statistics (Figure 5, compound 10). Fitting the decay curve shows that there is a process which generally has τ > 200 ns and a process which has τ ∼100 ns. This suggests more than one emission process is occurring in the host-guest materials (it is not necessarily only two, the biexponential just gives the best fit, there can be several phosphorescent sites present giving an average of the decay, which is best fitted by a biexponential). The emission spectra show only one observable emission maximum at room temperature. The ratio of the slower emission compared to the faster emission is both dendrimer generation, and core flexibility dependent. Concentration effects (amount of host-guest material in solution was varied over a large concentration range) on the lifetime and quantum yield were tested. There was no change in the acquired Φ over this large concentration range. Furthermore, the lifetime measurements were also not affected by variations in the solution concentration, nor was the ratio of slower:faster processes. The intensity of the laser was also varied to monitor the effect on the lifetimes measurements. Likewise no effect was observed on the ratio of slower:faster processes or how slow/fast each was. Discussion Relating to Photophysical Results. The questions that must be answered are the following: (a) how supramolecular immobilization in the dendrimer support is quenching the

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Table 2. Electronic Spectroscopy of Unfunctionalized, Dendritic, and Host Guest Materials compound f

2 (H) 3 (H) 4 (H) 6 7 8 (G) 9 (G) 10 (H-G) 11 (H-G) 12 (H-G) 13 (H-G) 14 (H-G)

abs. λ (nm) {ε, 103 L mol-1cm-1}a

emission (nm)b

Φc,d

τ (ns)c,e

229 (81.0), 279 (16.3), 284 (16.3) 230 (185.1), 278 (24.1), 286 (23.6) 230 (191.2), 279 (43.9), 283 (44.6) 263 (46.9), 325 (10.5), 363 (5.1), 396 (3.9), 431 (2.8) 264 (34.7), 324 (9.0), 350 (5.1), 397 (3.1), 429 (2.3) 265 (35.9), 325 (9.8), 350 (5.9), 397 (3.9), 429 (2.9) 264 (44.1), 324 (12.6), 351 (7.6), 397 (4.7), 432 (3.4) H-229 (107.8), G-265 (39.3), H-281 (65.3), G-325 (9.6), G-351 (5.8), G-396 (3.6), G-432 (2.8) H-229 (239.1), G-266 (43.9), H-277 (89.2), G-351 (5.6), G-395 (4.1), G-430 (2.8) H-232 (454.2), G-265 (46.2), H-282 (266.1), G-323 (14.4), G-343 (9.3), G-396 (5.7), G-432 (4.5) H-230 (687.9), G-269 (52.5), H-283 (388.1), G-326 (10.8), G-349 (7.0), G-396 (4.2), G-433 (3.2) H-229 (189), G-266 (35.0), H-277 (71.0), G-350 (5.5), G-396 (3.5), G-430 (2.3)

no em. no em. no em. 511 512 511 512 511

0.57 0.66 0.69 0.71 0.35

740 540 630 630 390 (76%), 130 (24%)

512

0.37

390 (74%), 140 (26%)

512

0.30

360 (62%), 90 (38%)

512

0.12

220 (58%), 90 (42%)

512

0.13

190 (40%), 90 (60%)

a Measured at room temperature in CH2Cl2, guest values measured per Ir site. b Carried out in MeCN and MeTHF at room temperature, with little difference in the spectra. c Measured at room temperature in 2-MeTHF. d Quantum Yield, Referenced to fac-[Ir(ppy)3], Φ ) 0.4, e Emission lifetime, f H-Host, G-Guest.

Compounds 13 and 14 show dissimilar results. They both have a relatively low Φ (0.12 and 0.13, respectively); however, the lifetime measurements are slightly different. Both systems have a slow lifetime component of ∼200 ns and a fast component of ∼90 ns. In 13, the slow component is 60% of the emission and the fast component 40%. In 14 these data are inverted with the slower component showing 40% and the faster component 60% of the emission, respectively.

Figure 5. Luminescence lifetime plots of compounds 8 and 10. Excitation at 406 nm (65 ps pulsed laser). Emission at 510 nm. Measured in 2-MeTHF at RT.

phosphorescence of the organometallic; (b) why do we observe multiple types of phosphorescence in these host-guest materials. In general quenching of similar systems is as a result of exposure to dioxygen, or by triplet-triplet annihilation. We have carried out all measurements in the absence of dioxygen, so quenching by dioxygen can therefore be excluded. The insensitivity of the materials to concentration and laser intensity variation shows that the quenching of the emission is not as a result of intermolecular triplet-triplet annihilation.21 Compounds 10and 11 show very similar results. This suggests that the length of the tether has little effect on how the guest interacts with the host 2. They both show Φ ) ∼ 0.35, which is approximately 50% of the unbound system’s value. They both have emission lifetime measurements which contain a 400 ns component and a 120 ns component. The slower process is responsible for approximately 75% of the total emission. Compound 12 is similar to 10 and 11 with a slightly decreased Φ (0.30). The lifetime shows a higher fraction of the faster emission component compared to compounds 10 and 11. (21) Varying the laser intensity should give an indication of triplettriplet annihilation, with higher laser intensities giving more excited molecules, and thus intermolecular triplet-triplet annihilation would be more probable. We see no difference in the quenching observed, whether we use very high or very low laser intensities. However, with iridium phosphors bound closely to one another, this experiment is not efficient, because the phosphors are tightly bound, and are not expected to move rapidly. Thus it would be necessary that neighbouring phosphors are excited to allow for triplet-triplet annihilation. This is highly unlikely unless extreme laser intensities were used.

To deduce why a biexponential resolution of the lifetime decay measurements is required we have focused on previous work in our group that has shown how the core-shell dendritic systems are aligned in the solid state.22 Figure 6 depicts the molecular structure of a compound analogous to compound 3 attained by single crystal X-ray diffraction measurements, however the dendritic wedge is of a lower generation. It can be seen that the two Br atoms are not isopositional. In fact, Br-1 sits directly “bound” between the arms of the quaternized amine/Fre´chet wedges, or in an entrapped manner, while Br-2 sits in open space, or in an open site, and is relatively unaffected by the dendritic wedge. If we refer this to the present study and presume that the “Ir-sulfates” bind in a similar manner, it then gives a possible confirmation for the observed biexponential lifetime measurements. If the sulfate-iridium guests behave in a similar fashion, some guests lie bound entrapped with high interactions with the Fre´chet wedge, however lower interaction with other iridium sites, thus low likelihood of triplet-triplet annihilation. The remaining sulfateiridium guests lie in open space, and thus have more possible interaction with other iridium phosphors sitting in “open” sites, and thus a higher likelihood of triplet-triplet annihilation. The entrapped iridium complexes, we propose, are the slower emitters due to site-isolation and hence no triplet-triplet annihilation, and the open space complexes the faster emitters due to higher interaction levels with other phosphors. Recent X-ray diffraction patterns of compounds similar to dendrimers 3 and 4 have further confirmed the entrapment/open space theorem.23 It was found that up to four cationic units were (22) van de Coevering, R.; Bruijnincx, P. C. A.; Lutz, M.; Spek, A. L.; van Koten, G.; Klein Gebbink, R. J. M.; New, J. Chem. 2007, 31, 1337– 1348. (23) Snelders, D.; van Koten, G.; Klein Gebbink, R. J. M.;unpublished work.

Supramolecular Dendriphores

Organometallics, Vol. 28, No. 4, 2009 1089

Figure 6. Molecular structure of compound 3 analogue in the crystalline state.22

surrounding an anion, giving an entrapped site. The remaining anions were in open space, theoretically allowed to interact with each other. The observed biexponential decay pattern confirms that some of the iridium phosphorescent sites are more easily quenched than others. Compounds 10 and 11 have two phosphors associated with the relatively flexible bis-ionic core. Two G2dendritic wedges are bound to this core. However, the likelihood of the two phosphors interacting with each other is relatively low. In compounds 10 and 11, we propose a system similar to that in Figure 6. One phosphor lies entrapped and one lies in open space. However, because no intermolecular triplet-triplet annihilation is observed, we presume that this is a relatively flexible system, and intramolecular (phosphor-phosphor24) interactions sometimes occur resulting in triplet-triplet annihilation, and sometimes do not. This results in a biexponential decay pattern, containing a mixture of entrapped emissions, and intramolecularly quenched emissions. Upon making the system less flexible, in 12, with eight proximal phosphors, we observe a higher proportion of the faster decay component. Eight G1-dendritic wedges are bound to the core. Material 12 has much less flexibility than 10 or 11, however it also has less polyaromatic groups. The likelihood of interactions between phosphor is higher in 12 than in 10 and 11. In material 12 we propose only two or three phosphors are lying in entrapped positions, and five or six phosphors lie in open space. These five or six can easily interact (intramolecular) with each other, and hence the higher proportion of the faster decay process compared to 10 and 11. Compounds 13 and 14 are octacationic cored species with eight iridium phosphors immobilized within the species. The core has eight bulky G3-dendritic wedges bound to it. The higher generation species 13 and 14 are probably less likely to have multiple entrapped sites, where slower emission processes can take place, because of the increased crowding around the core. With low flexibility and high content of polyaromaticity, substantial quenching is observed, and a high proportion of the emissions are of the faster component. This suggests that there are a minimum amount of phosphors lying in entrapped sites, and the rest are lying in open space with a high probability for (24) Intramolecular: phosphors bound to the same polycationic core quenching each others emission. Intermolecular: phosphors bound to different polycationic cores quenching each others emission.

interaction between phosphors associated with the one polycationic core, resulting in quenching of the emision, and fast emission. Summarizing, comparing compounds 10 and 11 with 12, 13, and 14, we propose that because of increased flexibility and decreased generation, iridium phosphors interact with each other less in the materials containing two lumiphores around the dicationic core (10/11) compared to the eight lumiphores around the sterically hindered cores (12/13/14). Comparing compound 12 with 13 and 14, the increased bulk of 13 and 14 results in more phosphor-phosphor interactions, presumably because of a lack of freedom of motion/space around the core. It is apparent to us that intramolecular triplet-triplet annihilation is resulting in quenching of the emission of the docked phosphors. This is proved by the fact that we observe increased quenching in systems with more phosphors. The essential point, though, is the formation of entrapped phosphorescent sites, which are not demonstrating triplet-triplet annihilation. We have found no experimental or literature proof that the polybenzylether wedge could quench the triplet emission of the iridium complex and we believe it unlikely that the dendrons, which display absolutely no emission, be it singlet or triplet, would be quenching the organometallic phosphorescence to the extent that we have observed. All of the experimental evidence shows that the excited states of the dendrons are too high in energy to quench the excited triplet state of the iridium phosphor. OLED Device Performance. Separate OLED devices were fabricated containing compounds 8, 10, and 13 as the emissive layer. The devices consist of multilayer configuration ITO/ PEDOT/PVK/PBD/CGF/LUMIPHORE (Ir)//Ba/Al as can be seen in Table 3. The emission layer was spin coated onto the anode from chlorobenzene. The electroluminescence results are presented in Table 3. The dendrimer immobilized species performed with 50% the efficiency of the functionalized species 8. There was little difference in the properties of materials 10 and 13. Interestingly, the quenching of the phosphorescence is not as severe in the solid state devices as it is in solution. As we have observed in solution state experiments, there is a marked difference in the quantum efficiency between the devices of functionalized species 8 and the host-guest materials 10 and 13. We propose this is, again, because of the higher likelihood of triplet-triplet intramolecular quenching in the host-guest materials 10 and 13 as a result of a higher probability of

1090 Organometallics, Vol. 28, No. 4, 2009

McDonald et al.

Table 3. OLED Devices Prepared Using Materials 8, 10, and 13a emission layer

anode

materials ratio %

PVK+PBD+TPD+CGF-8

ITO/PEDOT

PVK+PBD+CGF-8

ITO/PEDOT

PVK+ PBD+CGF-10

ITO/PEDOT

PVK+ PBD+CGF-13

ITO/PEDOT

47 PVK001 26 PBD001 22 TPD 5 CGF-C008253 63 PVK001 32 PBD001 5 CGF-C008253 63 PVK001 32 PBD001 5 CGF-C008255 63 PVK001 32 PBD001 5 CGF-C008254

a

cathode

max cd/A

max QY %

CIE1931 x

CIE1931 y

voltage at 100 cd/m2

Ba/Al

6.5

2.2

0.28

0.54

6.8

Ba/Al

2.6

0.82

0.32

0.56

9

Ba/Al

3.3

1

0.31

0.59

9.6

Devices were prepared by spin coating the emission layer from chlorobenzene. The cathode was placed by an evaporation process.

phosphor–phosphor interactions. In the devices, the host-guest materials are in the solid state, and thus there is even greater imposed rigidity on the dendritic supports, this may somewhat limit the likelihood of phosphor-phosphor interactions and hence the relative rate of quenching between 8, 10, and 13 is less compared to the solution state experiments.

Conclusions A range of heteroleptic [Ir(C,N)2(E,E′)] complexes have been developed for use in OLED devices. Organometallic phosphors with an anionic sulfate-tail have been synthesized. These anion functionalized complexes have been immobilized in poly cationic core-shell dendritic systems. All new materials were fully characterized using standard techniques. Furthermore, all new materials were characterized using photophysical techniques such as UV-vis absorption and emission spectroscopy, and quantum yield and lifetime measurements. Anion functionalized complexes showed electronic spectroscopic properties similar to their unfunctionalized analogues. Complexes immobilized within core shell polycationic dendritic systems showed diminished emission quantum yield compared to their unbound analogues. Furthermore, all host-guest species showed biexponential lifetime decay patterns, suggesting multiple phosphorescent sites within the host-guest materials. This is believed to be as a result of separate site phenomena, where some phosphors lie in entrapped sites with high interaction levels with polyaromatic dendritic wedges and thus lower interactions with other phosphors. Whereas other phosphors lie in sites where less interactions between the phosphor and the polyaromatic dendrimer occur and more phosphor-phosphor interactions occur. Triplet-triplet annihilation is a common source of phosphorescent emission quenching in cyclometallated iridium complexes. The site-isolation phenomenon results in low levels of phosphor-phosphor interactions, and thus it is unlikely triplet-triplet annihilation occurs at these sites. However, phosphors which lie in more open sites, are likely to interact with other phosphors, bound to the same polycationic core, which results in a higher probability of triplet-triplet annihilation with these phosphors. We have found that intramolecular triplet-triplet annihilation is the likely source of emission quenching, and we have shown that it is not as a result of intermolecular triplet-triplet annihilation. A proof of principle has been demonstrated; with relative synthetic ease organometallic phosphors can be functionalized so as to facilitate interaction between the organometallic and a polymeric support. The obtained host-guest materials have been shown to be efficient phosphors in OLED devices. Future work will be directed toward developing HTL and ETL functionalized polycationic materials, and immobilizing organometallic phosphors in them. Functionalization of polymeric supports with

fluorophilic or hydrophobic groups will also allow for application of the novel materials in fabricated OLED devices. This work also gives further insights into the molecular structure of polyionic host guest materials. Previous work has demonstrated how the anionic guests interact with cationic hosts using both solution NMR studies and solid-state X-ray diffraction studies. The present study demonstrates solution-state electronic spectroscopy on a site-specific basis. It was demonstrated here, in contradiction to NMR results where only an average is observed, that there are multiple types of host-guest interactions. Timescale is of importance in this discussion. NMR studies have been taken on a time scale which gives an average view how host-guest interactions.15 The present report demonstrates a snapshot view. What is really happening is probably occurring on a time scale between the two presented. However, all studies to date have shown that the anionic guests are tightly bound to a single poly cationic host, and that there is no interhost exchange of guests. Some guest are tightly bound, with one guest unit bound by multiple host units, while the remnant, charge-balancing guest units, sitting in open space, are less strongly interacting with the poly cationic core.

Experimental Section General Information. Standard Schlenk procedures under dinitrogen were utilized throughout. Reactions were carried out in the absence of light, unless otherwise stated. Reagents were used as supplied from Acros or Sigma-Aldrich. The synthesis of 5 was carried out as earlier reported.25 1H and 13C solution NMR was carried out on a Varian Inova 300 spectrometer or a Varian Oxford AS400. Elemental analyses were performed by Dornis and Kolbe, Mikroanalytisches Laboratorium, Mu¨llheim a. d. Ru¨hr, Germany. MS measurements were carried out on an Applied Biosystems Voyager DE-STR MALDI-TOF MS or on an LCT micromass ESI-MS. Photophysics. UV-vis absorption spectroscopy was performed on a Varian CARY 50 Scan UV-vis spectrophotometer in CH2Cl2. Emission measurements were carried out on a SPEX FLUOROLOG 1680 0.22 m spectrometer. fac-[Ir(ppy)3] in 2-MeTHF was used as a reference (Φ ) 0.4). The excitation wavelength was 360 nm. Emission lifetimes were obtained (in 2-MeTHF) using a DPL 800-B pulsed diode laser. The results were manipulated by exponentially fitting the emission decay curves. Electrochemistry. CV measurements were carried out on an EG&G Princeton Applied Research Potentiostat Model 263A. Experiments were carried out at room temperature (20 °C). A platinum disk working electrode was polished with alumina on felt before use. A platinum wire was used as counter electrode. A silver wire was used as a pseudo/quasi-reference electrode. Tetrabutylammonium hexafluorophosphate (0.1M) in MeCN was used as electrolyte. The scan rate was 0.1 V/s. The silver reference electrode was calibrated using ferrocene/ferrocenium (Fc/Fc+) redox couple as an internal standard. The oxidation potential of Fc/Fc+ was found to be 0.51V against the silver reference electrode.

Supramolecular Dendriphores PicMeOH, 1. 4-Hydroxymethyl-2-pyridinecarboxylic Acid Hydrochloride. 4-[{(tert-Butyldimethylsilyl)oxy}methyl]-2-pyridinecarbonitrile (1.71 g, 4.7 mmol) was added to a HCl solution (30 mL, 4M). This mixture was heated at reflux for 24 h, subsequently it was evaporated to dryness. The remaining solid was washed with acetone three times. A white crystalline material was acquired in almost quantitative yield. 1H NMR (300 MHz, D2O) δ ) 4.88 (s, 2H, CH2), 7.99 (d, 1H, CH), 8.26 (s, 1H, CH), 8.59 (d, 1H, CH). 13 C NMR (75 MHz, D2O) δ ) 62.1, 123.7, 125.7, 141.1, 143.7, 162.9, 164.5. Anal. Calcd for C7H8O3NCl: C, 44.34; H, 4.25; N, 7.39. Found: C, 44.31; H, 4.21; N, 7.35. Ir(ppy)2(pic), 6. Bis(2-phenylpyridinato-N,C2)-mono(2-pyridinecarboxylato-N,O)iridium(III). Bis(2-phenylpyridinato-N,C2)-iridium(III) chloride (0.53 g, 0.99 mmol) was mixed with 2-ethoxyethanol (20 mL), 2-pyridinecarboxylic acid (0.24 g, 2 mmol) and Na2CO3 (0.22 g, 2.1 mmol) and heated at reflux for 24 h. The resulting mixture was cooled to room temperature and the precipitate was filtered off as a bright yellow powder which was washed twice with deionized water, ethanol, and hexane respectively. 45% yield. 1H NMR (300 MHz, DMSO-d6) δ ) 6.04 (d, 1H, CH), 6.23 (d, 1H, CH) 6.67-6.89 (m, 4H, CH’s), 7.20 (t, 1H, CH), 7.36 (t, 1H, CH), 7.53 (d, 1H, CH), 7.59-7.63 (m, 2H, CH’s), 7.79 (t, 2H, CH’s), 7.88-7.93 (m, 2H, CH’s), 8.06-8.22 (m, 4H, CH’s), 8.49 (d, 1H, CH).13C NMR (75 MHz, CD2Cl2) δ ) 119.9, 120.0, 121.3, 121.7, 122.5, 122.6, 124.3, 12.6, 128.2, 129.6, 130.0, 132.6, 137.4, 137.5, 137.9, 144.4, 144.5, 144.6, 147.6, 148.4, 148.7, 148..9, 149.8, 152.5, 167.7, 168.9, 172.6. Anal. Calcd: C, 54.01; H, 3.24; N, 6.75. Found: C, 53.78; H, 3.37; N, 6.67. M/Z (MALDI-ToF) 624.03 (M + H+). Ir(ppy)2(picCH2OH), 7. Bis(2-phenylpyridinato-N,C2)-mono(4[hydroxymethyl]-2-pyridine carboxylato-N,O)iridium(III). Bis(2phenylpyridinato-N,C2)-iridium(III) chloride (0.50 g, 0.93 mmol) was added to a 2-ethoxyethanol (30 mL) solution containing Na2CO3 (0.44 g, 4 mmol, 4.4 equiv) and 4-hydroxymethyl-2pyridine carboxylic acid (0.46 g, 2.4 mmol, 2.6eq.). The resulting mixture was heated to reflux for 24 h and then cooled to room temperature. Filtration yielded a bright yellow solid which was washed with ethanol and then acetone. Yield 0.43 g (70%). 1H NMR (300 MHz, DMSO-d6) δ ) 4.59 (d, 2H, CH2), 5.58 (t, 1H, OH), 6.03 (d, 1H, CH), 6.22 (d, 1H, CH), 6.75 (m, 2H, CH’s), 6.87 (m, 2H, CH’s), 7.20 (t, 1H, CH), 7.35 (t, 1H, CH), 7.55 (m, 3H, CH’s), 7.78 (m, 2H, CH’s), 7.90 (m, 2H, CH’s) 8.06 (s, 1H, CH) 8.19 (m, 2H, CH’s), 8.49 (2, 1H, CH). 13C NMR (75 MHz, DMSO-d6) δ ) 61.9, 119.9, 120.0, 121.6, 121.8, 123.6. 123.9, 124.9, 125.2, 125.5, 126.5, 129.6, 130.3, 132.4, 132.7, 138.6, 138.7, 144.7, 145.3, 148.0, 148.2, 148.2, 148.9, 150.8, 151.5, 155.6, 167.6, 168.5, 172.6. Anal. Calcd: C 53.36; H 3.40, N 6.44. Found: C 53.45, H 3.36, N 6.33. M/Z (MALDI-ToF) 675.9 (M + Na+). Ir(ppy)2(picCH2OSO3NBu4), 8. Tetra-n-butylammonium Bis(2phenylpyridinato-N,C2)-mono([4-sulfatomethyl]-2-pyridinecarboxylato-N,O)iridium(III). Pyridine sulfur trioxide (0.5 g, 3.1 mmol) and pyridine (0.1 mL, 1.2 mmol) were added to a solution of bis(2phenylpyridinato-N,C2)-mono(4-[hydroxymethyl]-2-pyridinecarboxylato-N,O)iridium(III) (0.60 g, 0.93 mmol) in CH2Cl2 (15 mL) and stirred for 12 h at room temperature. The yellow mixture was then filtered and the filtrate was concentrated. The remaining solution was added slowly to Et2O resulting in a yellow precipitate. The pyridinium salt was disssolved in CH2Cl2 (10 mL) and added to a solution of nBu4NCl (1 g) in deionized water (50 mL). The biphasic system was stirred for 16 h. The organic layer was collected by phase separation and washed 8 times with water. The organic layer was dried over MgSO4 and concentrated and recrystallized (25) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc. 1984, 106, 6647–6653. (26) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; Garcia-Granda, S.; Gould, R. O.; Smits, J. M. M.; Smykalla, C. The DIRDIF99 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen; University of Nijmegen: Nijmegen, The Netherlands, 1999.

Organometallics, Vol. 28, No. 4, 2009 1091 from Et2O resulting in a bright yellow powder. Yield ) 0.52 g (57%). 1H NMR (300 MHz, DMSO-d6): δ ) 0.93 (t, 12H, NBu4), 1.30 (m, 8H, NBu4), 1.540 (m, 8H, NBu4), 3.16 (m, 8H, NBu4), 4.89 (s, 2H, CH2), 6.04 (d, 1H, CH), 6.24 (d, 1H, CH), 6.73 (m, 2H, CH’s), 6.88 (m, 2H, CH’s), 7.23 (t, 1H, CH), 7.36 (t, 1H, CH), 7.55 (m, 3H, CH’s), 7.79 (m, 2H, CH’s), 7.91 (m, 2H, CH’s), 8.08 (s, 1H, CH), 8.19 (m, 2H, CH’s), 8.50 (d, 1H, CH). 13C NMR (75 MHz, DMSO-d6): δ ) 14.1, 19.9, 23.7, 58.2, 66.1, 119.9, 121.6, 121.9, 123.6, 123.9, 124.8, 125.4, 125.8, 125.9, 127.2, 129.5, 129.7, 130.2, 130.4, 132.3, 132.6, 138.7, 144.7, 145.3, 147.9, 148.2, 149.0, 150.8, 151.3, 151.6, 167.6, 168.5, 172.4. Anal. Calcd: C, 55.48; H, 5.90; N, 5.75: Found: C, 54.88; H, 6.07; N, 5.68. M/Z (MALDI-ToF) 732.16 (M - counterion). Ir(ppy)2(picCH2OC2H4OSO3NBu4), 9. Tetra-n-butylammonium Bis(2-phenylpyridinato-N,C2)-mono([4-sulfatoethyloxymethyl]-2pyridinecarboxylato-N,O)iridium(III). A DMF (25 mL) solution of bis(2-phenylpyridinato-N,C2)-mono(4-[hydroxymethyl]-2-pyridinecarboxylato-N,O)iridium(III) (0.54 g, 0.83 mmol) was stirred at 0 °C for 30 min, after which NaH (0.022 g, 0.91 mmol) was added. The resulting black suspension was stirred at room temperature for 16 h. 1,3,2-Dioxathiolane 2,2-dioxide (0.123 g, 1 mmol) was subsequently added and the resulting orange solution was stirred for 12 h. This was concentrated to 2 mL by evaporation of the DMF. The resulting reddish mixture was slowly added to Et2O precipitating a yellow solid. This was dissolved in 20 mL DCM and added to a solution of nBu4NCl (0.664 g) in deionized water (40 mL), and stirred for 16 h. The organic layer was collected by phase separation and washed 8 times with water, dried over MgSO4 and concentrated. The remaining solution was added slowly to Et2O yielding a yellow powder. Yield: 0.40 g (80%). 1H NMR (300 MHz, DMSO-d6): δ ) 0.92 (m, 12H, NBu4), 1.28 (m, 8H, NBu4), 1.54 (m, 8H, NBu4), 3.14 (m, 8H, NBu4), 3.63 (t, 2H, CH2), 3.84 (t, 2H, CH2), 4.62 (s, 2H, CH2), 6.04 (d, 1H, CH), 6.22 (d, 1H, CH), 6.72 (m, 2H, CH’s), 6.86 (m, 2H, CH’s), 7.22 (t, 1H, CH), 7.35 (t, 1H, CH), 7.55 (m, 3H, CH’s), 7.78 (m, 2H, CH’s), 7.87 (t, 1H, CH), 7.92 (t, 1H, CH), 8.01 (s, 1H, CH), 8.18 (m, 2H, CH’s), 8.48 (d, 1H, CH). 13C NMR (75 MHz, DMSO-d6): δ ) 14.2, 19.9, 23.7, 31.4, 58.2, 65.5, 70.2, 119.9, 121.5, 121.8, 123.6, 124.1, 124.8, 125.5, 125.7, 126.6, 126.7, 128.0, 129.5, 130.3, 131.1, 132.5, 132.7, 138.8, 144.7, 145.3, 148.0, 148.3, 148.4, 149.2, 150.8, 151.7, 167.6, 168,4, 172.3. Anal. Calcd: C, 55.44; H, 6.04; N, 5.50. Found: C, 55.35; H, 6.12; N, 5.41. M/Z (ESI-) 773.95 (M - counterion). General Procedure for Ion Exchange Reaction between Tetran-butyl Ammonium Sulfato Complexes and Polycationic Halide Dendritic Species. Approximately 0.1 g of the required equivalency of ammonium sulfato complex in CH2Cl2 (10 mL) was added to a solution of the required equivalency of polyionic dendritic species in water (10 mL). The biphasic system was vigorously stirred at room temperature for 12 h. The organic layer was separated and washed 10 times with water (10 mL). The CH2Cl2 solution was dried over MgSO4, concentrated and recrystallized from Et2O. All products were bright yellow solids and yields were always over 85%, with the losses believed to be as a result of the high number of washing steps. Dialysis can also be used as a purification technique, but was not utilized in most cases. In NMR spectra host signals (H) and guest signals (G) are assigned where possible to differentiate. NCN{2G2}[Ir(ppy)2(picCH2OSO3)]2, 10. NCN{2G2}-Di[bis(2phenylpyridinato-N,C2)-mono([4-sulfatomethyl]-2-pyridinecarboxylato-N,O)iridium(III)]. 1H NMR (300 MHz, DMSO-d6): δ ) 2.86 (br s, 12H, NMe2), 4.49 (br d, 8H, CH2NMe2CH2), 4.88 (s, 4H, SO4CH2), 5.05 (br s, 24H, ArOCH2), 6.06 (d, 2H, CHg), 6.22 (d, 2H, CHg), 6.63-6.92 (m, 25H, mix ArCH’s), 7.15-7.44 (m, 49H, mix ArCH’s), 7.50-7.60 (m, 9H, mix ArCH’s), 7.67 (m, 5H, CHg), 7.80 (m, 4H, CHg), 7.91 (m, 6H, CHg), 8.08 (s, 2H, CHg), 8.19 (m, 4H, CHg), 8.50 (d, 2H, CHg). 13C NMR (75 MHz, CD2Cl2): δ ) 29.9, 30.8, 49.1, 66.6, 70.1, 101.6, 106.7, 112.4, 118.9, 119.3, 121.4,

1092 Organometallics, Vol. 28, No. 4, 2009 121.8, 122.6, 122.8, 124.3, 124.7, 126.1, 126.2, 127.8, 128.2, 128.7, 129.7, 129.8, 130.0, 132.4, 132.6, 137.1, 137.5, 137.8, 139.3, 144.3, 144.6, 146.7, 148.4, 149.8, 150.8, 151.6, 160.1, 160.3, 167.6, 168.7, 173.2. Anal. Calcd: C, 64.85; H, 4.78; N, 3.60. Found: C, 63.51; H, 4.86; N, 3.48. M/Z (ESI+) 2379.01 (one guest present). NCN{2G2}[Ir(ppy)2(picCH2OC2H4OSO3)]2, 11. NCN{2G2}-Di[bis(2-phenylpyridinato-N,C2)-mono([4-sulfatoethoxymethyl]-2-pyridinecarboxylato-N,O)iridium(III)]. 1H NMR (300 MHz, DMSOd6): δ ) 2.86 (s, 12H, NMe2) 3.63 (t, 4H, OCH2CH2O(g)), 3.86 (t, 4H, OCH2CH2Og), 4.53 (br s, 8H, CH2(h)), 4.59 (s, 4H, PicCH2O), 5.03 (s, 24H, CH2(h)), 6.03 (d, 2H, CHg), 6.22 (d, 2H, CHg), 6.60-7.00 (m, 23H, CHg and CHh), 7.16-7.50 (m, 46H, CHg and CHh) 7.50 -7.70 (m, 10H, CHg and CHh), 7.77 (t, 4H,CHg), 7.93-7.84 (m, 4H, CHg), 8.01 (s, 2H, CHg), 8.16 (t, 4H, CHg), 8.48 (d, 2H, CHg).13C NMR (75 MHz, DMSO-d6): δ ) 49.2, 65.7, 68.2, 70.0, 101.7 (H), 107.3 (H), 112.9 (H), 119.9, 121.5, 121.8, 123.6, 124.1, 124.8, 125.5, 125.7, 127.3, 127.9, 128.4 (H), 128.6 (H), 129.1 (H), 129.6, 130.4, 132.5, 132.7, 135.6, 137.532, 138.7 (H), 139.7 (H), 144.7, 145.3, 147.9, 148.3, 148.4, 149.2, 150.7, 151.6, 151.7, 160.1 (H), 160.3 (H), 167.6, 168.4, 172.4. M/Z (ESI+) 2422.96 (one guest present). Si[NCN{2G1}][Ir(ppy)2(picCH2OSO3)]2, 12. Si-[NCN{2G3}Di{bis(2-phenylpyridinato-N,C2)-mono([4-sulfatomethyl]-2-pyridinecarboxylato-N,O)iridium(III)}]4. 1H NMR (300 MHz, DMSOd6): δ )2.84 (s, 48H, NMe2) 4.47 (br s, 16, CH2(h)), 4.54 (br s, 16H, NCH2), 4.86 (s, 16H, PicCH2), 5.10 (s, 32H, CH2(h)), 6.03 (d, 8H, CHg), 6.22 (d, 8H, CHg), 6.66-6.90 (m, 60H, CHg and CHh), 7.16-7.45 (m, 88H, CHg and CHh), 7.50 -7.65 (m, 40H, CHg and CHh), 7.77 (t, 16H, CHg), 7.80-7.95 (m, 16H, CHg), 8.06 (s, 8H, CHg), 8.16 (t, 16H, CHg), 8.48 (d, 8H, CHg).13C NMR (75 MHz, DMSO-d6): δ ) 49.3, 66.0, 68.2, 70.3, 101.2 (H), 103.3 (H), 109.1 (H), 112.8 (H), 119.9, 121.3, 124.7, 130.3, 132.7, 135.4, 137.2 (H), 137.5, 138.8 (H), 144.2, 144.5, 145.5, 148.3, 149.0, 150.8, 151.1, 151.6, 160.3 (H), 167.6, 168.7, 172.7. Elem. anal. calcd. C, 59.16; H, 4.29; N, 4.97. Found: C, 57.50; H, 4.24; N, 4.77. Si[NCN{2G3}][Ir(ppy)2(picCH2OSO3)]2, 13. Si-[NCN{2G3}Di{bis(2-phenylpyridinato-N,C2)-mono([4-sulfatomethyl]-2-pyridinecarboxylato-N,O)iridium(III)}]4. 1H NMR (300 MHz, DMSOd6): δ ) 2.80 (br s, 48H, NMe2), 4.64-4.83 (br s, 272H, all ArCH2’s), 5.98 (d, 8H, CHg), 6.16 (d, 8H, CHg), 6.40-6.70 (br m, 104H,mix ArCH’s), 6.78 (br m, 32H, CHg), 6.97-7.37 (br m, 320H, ArCH’s), 7.43 (br m, 32H, mix ArCH’s), 7.69 (br m, 56H, mix ArCH’s),8.08 (br m, 24H,CHg), 3.41 (d, 8H, CHg). 13C NMR (75 MHz, CD2Cl2): (some host peaks overlap guest) δ ) 66.5, 70.1 (H), 101.4 (H), 106.6 (H), 118.7, 119.0, 121.4, 121.7, 122.7, 125.8, 126.0, 127.7 (H), 127.9 (H), 128.6 (H), 130.0, 130.1, 132.4, 137.0 (H), 137.5, 139.2 (H), 139.5, 144.1, 144.5, 147.0, 148.3, 149.7, 150.4, 158.1, 160.1 (H), 167.4, 168.4, 173.1. Anal. Calcd: C, 69.87; H, 5.22; N, 2.31. Found: C, 69.79; H, 5.24; N, 2.39. Si[NCN{2G3}][Ir(ppy)2(picCH2OC2H4OSO3)]2, 14. Si-[NCN{2G3}di{bis(2-phenylpyridinato, N, C2)-mono-([4-sulfatoethoxy-methyl]2-pyridine carboxylato-N, O)-iridium(III)}]4. 1H NMR (300 MHz, DMSO-d6): δ ) 2.86 (br s, 48H, NMe2), 3.54 (br s, 16H,

McDonald et al. OCH2CH2O), 3.85 (br s, 16H, OCH2CH2O), 4.44 (br s, 16H, NMe2CH2) 4.87 (br s, 256H, mix CH2’s), 6.01 (d, 8H, CHg), 6.18 (d, 8H, CHg), 6.40-6.60 (br m, 118H, mix ArCH’s), 6.82 (m, 24H, CHg), 7.21 (br s, 336H, mix ArCH’s), 7.49 (br s, 20H, mix CH’s), 7.73 (br m, 36H, CHg), 7.96 (s, 8H, CHg), 8.06 (m, 16H, CHg), 8.45 (d, 8H, CHg). 13C NMR (75 MHz, DMSO-d6): δ ) 50.0, 65.8, 69.3, 70.4, 101.6, 107.1, 112.8, 119.8, 121.5, 121.8, 123.4, 123.8, 124.8, 125.4, 125.5, 126.8, 127.8, 128.2, 128.4, 129.0, 129.6, 130.3, 132.4, 132.6, 137.4, 137.5, 138.6, 139.3, 139.7, 144.6, 145.2, 147.8, 148.2, 148.3, 148.9, 150.6, 151.4, 151.6, 160.2, 167.5, 168.4, 172.4. Elem. anal. calcd. C, 69.60; H, 5.29; N, 2.27. Found: C, 67.17; H, 6.87; N, 4.23. X-ray crystal structure determination of 7 · 2EtOH. C29H22IrN3O3 · 2C2H6O, Fw ) 744.83, colorless needle, 0.36 × 0.06 × 0.06 mm3, monoclinic, P21/c (no. 14), a ) 9.3151(2), b ) 9.48152(13), c ) 33.3339(3) Å, β ) 103.229(1)°, V ) 2865.97(8) Å3, Z ) 4, Dx ) 1.726 g/cm3, µ ) 4.707 mm-1. A total of 42910 reflections were measured on a Nonius Kappa CCD diffractometer with rotating anode (graphite monochromator, λ ) 0.71073 Å) up to a resolution of (sin θ/λ)max ) 0.65 Å-1 at a temperature of 150 K. An analytical absorption correction was applied (0.36-0.80 correction range). A total of 6585 reflections were unique (Rint ) 0.0478). The structure was solved with automated Patterson methods (DIRDIF-9926) and refined with SHELXL-9727 against F2 of all reflections. Non hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms were introduced in calculated positions and refined with a riding model. 315 Parameters were refined with no restraints. R1/wR2 [I > 2σ(I)]: 0.0222/0.0459. R1/wR2 [all reflections]: 0.0315/0.0494. S ) 1.075. Residual electron density was between -0.96 and +0.99 e/Å3. Geometry calculations and checking for higher symmetry was performed with the PLATON program.28

Acknowledgment. Ciba (Basel, CH) is thanked for the provision of [IrCl3 · 3H2O] and for financial assistance. In particular Dr. Roger Pretot, and Dr. Paul van der Schaaf are acknowledged for their assistance. Dr. R. van de Coevering is thanked for synthesis of core-shell halide compounds. This work was supported in part (M.L., A.L.S.) by the Council for the Chemical Sciences of The Netherlands Organization for Scientific Research (CW-NWO). Supporting Information Available: CIF files for X-ray crystal structure of 7 and figures showing all absorption and emission spectra of compounds 6-14, luminescent lifetime decay plots for compounds 6-14, and 1H NMR spectra of materials 6-14. This material is available free of charge via the Internet at http://pubs.acs.org. OM800226Q (27) Sheldrick, G. M. SHELXL-97. Program for crystal structure refinement. University of Go¨ttingen: Go¨ttingen, Germany, 1997. (28) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7–13.