Close Columnar Packing of Triangulenium Ions in Langmuir Films

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Langmuir 2009, 25, 3584-3592

Close Columnar Packing of Triangulenium Ions in Langmuir Films Jens B. Simonsen,†,| Kristian Kjær,‡ Paul Howes,§ Kasper Nørgaard,† Thomas Bjørnholm,† Niels Harrit,† and Bo W. Laursen*,† Nano-Science Center & Department of Chemistry, UniVersity of Copenhagen, UniVersitetsparken 5, DK-2100 Copenhagen, Denmark, Risø National Laboratory, FrederiksborgVej 399, DK-4000 Roskilde, Denmark, and Department of Physics, UniVersity of Leicester, UniVersity Road, Leicester, LE1 7RH, England ReceiVed NoVember 10, 2008. ReVised Manuscript ReceiVed December 29, 2008 Three new tris(dialkylamino)trioxatriangulenium (ATOTA+) salts rendered amphiphilic by attachment of two (5a · PF6 and 5b · PF6) or four (5c · PF6) n-decyl chains have been synthesized, and their Langmuir films have been studied by grazing incidence X-ray diffraction (GIXD). Compounds 5a · PF6 and 5b · PF6 both self-assemble into 2D-crystalline Langmuir monolayers, in which the planar triangular shaped carbenium ions form columnar aggregates segregated from the PF6- ions. The column width is found to be close to the width of the triangulenium moiety itself (∼17 Å), while the repeat distance along the columnar aggregates is only 3.45 Å, implicating a near cofacial columnar structure with only a small tilt of the planar carbenium ions relative to the columnar axis. A detailed Bragg rod analysis confirmed an 8-9° tilt and inferred a large anisotropy in the smearing/thermal displacement along the π-π stacking and lamellar packing directions. Specular X-ray reflectivity (SXR) was used to confirm the model derived from the GIXD data and elucidate the average position of the disordered PF6- ions, showing that the majority of the anions are accommodated in the ATOTA+ layer rather than in the water subphase.

Introduction Well-ordered thin films of conjugated organic molecules which form columnar structures by stacking of their π-systems continue to be investigated for application in optical and electronic devices.1,2 A large number of molecules forming such columnar stacks have been prepared by attaching various patterns of flexible alkyl chains to the periphery of the π-systems, favoring π-π stacking3 and nanoscale phase separation. The majority of these compounds are based on neutral aromatic and heteroaromatic π-systems,1,4,5 while only few systems based on heteroaromatic cations have been reported.6-9 On the other hand, it is wellknown that some of the most efficient dyes and fluorophores are based on stabilized carbenium ions, such as cyanines, acridiniums, and rhodamines.10,11 The 2,6,10-tris(dialkylamino)trioxatrian* To whom all correspondence should be addressed. Telephone: (+45) 3532 1881. Fax: (+45) 3532 0406. E-mail: [email protected]. † University of Copenhagen. ‡ Risø National Laboratory. § University of Leicester. | Present address: Department of Basic Sciences and Environment, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark. (1) Sergeyev, S.; Pisula, W.; Geerts, Y. H. Chem. Soc. ReV. 2007, 36, 1902– 1929. (2) Wu, J.; Pisula, W.; Mu¨llen, K. Chem. ReV. 2007, 107, 718–747. (3) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112, 5525–5534. (4) Cammidge, A. N.; Bushby, R. J. Synthesis and structural features of discotic liquid crystals, Handbook of Liquid Crystals 2B; Demus, D., Ed.; Wiley-VCH: Weinheim, Germany, 1998; pp 693-748. (5) Laschat, S.; Baro, A.; Steinke, N.; Giesselmann, F.; Haegele, C.; Scalia, G.; Judele, R.; Kapatsina, E.; Sauer, S.; Schreivogel, A.; Tosoni, M. Angew. Chem., Int. Ed. 2007, 46, 4832–4887. (6) Binnemans, K. Chem. ReV. 2005, 105, 4148–4204. (7) Davidson, P.; Jallabert, C.; Levelut, A. M.; Strzelecka, H.; Veber, M. Liq. Cryst. 1988, 3, 133–137. (8) Veber, M.; Berruyer, G. Liq. Cryst. 2000, 27(5), 671–676. (9) Wu, D.; Zhi, L.; Bodwell, G. J.; Cui, G.; Tsao, N.; Mu¨llen, K. Angew. Chem., Int. Ed. 2007, 46, 5417–5420. (10) Lakowicz, J. R. Principles of Fluorescence Spectroscopy, 2nd ed.; Kluwer Academic/Plenum Publisher: New York, 1999. (11) Haugland, R. P. Handbook of Fluorescent Probes and Research Chemicals, 9th ed.; Molecular Probes: Eugene, Oregon, 2002.

Figure 1. General structure of the 2,6,10-tris(dialkylamino)trioxatriangulenium ion (ATOTA+).

gulenium (ATOTA+) system12 (Figure 1) shares important photophysical properties with the rhodamine chromophore, that is, a high oscillator strength for the lowest electronic transition and a high fluorescence quantum yield.13 However, contrary to the rhodamines, the ATOTA+ system is symmetric and planar and forms a very closely packed columnar stack in the crystalline state with an interplanar distance of only 3.32 Å between neighboring π-surfaces.12 The combination of attractive photophysical properties,13 the cationic nature and the ability to form columnar structures,12 makes the ATOTA+ system interesting for both optical and electronic organic devices, such as highly sensitive fluorescent sensors based on an amplifying antenna effect14 and n-doped organic wires. The versatile procedure for synthesis of the ATOTA+ system easily allows attachment of various patterns of flexible alkyl chains at the nitrogen atoms.12 In view of these properties, we decided to explore whether this highly stabilized carbenium dye could be tailored to self-assemble into a new cationic columnar material. By attaching long hydrophobic alkyl chains to only one or two of the nitrogen atoms at the periphery of the ATOTA+ system, we expected to obtain amphiphilic ATOTA+ salts that might be (12) Laursen, B. W.; Krebs, F. C.; Nielsen, M. F.; Bechgaard, K.; Christensen, J. B.; Harrit, N. J. Am. Chem. Soc. 1998, 120, 12255–12263. (13) Laursen, B. W.; Reynisson, J.; Mikkelsen, K. V.; Bechgaard, K.; Harrit, N. Photochem. Photobiol. Sci. 2005, 4, 568–576. (14) Thomas, S. W.; Joly, G. D.; Swager, T. M. Chem. ReV. 2007, 107, 1339– 1386.

10.1021/la803733s CCC: $40.75  2009 American Chemical Society Published on Web 02/20/2009

Close Columnar Packing of Triangulenium Ions

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Figure 2. Structures of the ATOTA+ systems (5a-5c) and outline of their amphiphilic motives. Scheme 1. Synthesis of 4a+, 5a+ (R1 ) R2 ) n-Decyl, R3-R6 ) Me), 4b+, 5b+ (R1 ) R3 ) n-Decyl, R2 ) R4-R6 ) Me), and 4c+, 5c+ (R1-R4 ) n-Decyl, R5 ) R6 ) Me)

able to self-assemble into the desired columnar structure in Langmuir monolayers at the air-water interface, which in turn may lead to well-defined Langmuir-Blodgett (LB) multilayer films. The LB technique is well suited both for organizing films of amphiphilic electroactive columnar materials15-18 and for inducing uniaxial alignment of the columnar aggregates in the LB films leading to anisotropic optoelectronic properties.19,20 The latter feature of the LB films is caused by the so-called flow effect.21-23

In this study, we report the synthesis of three new amphiphilic ATOTA+PF6- salts 5a · PF6, 5b · PF6, and 5c · PF6 (Figure 2) with different patterns of lipophilic n-decyl chains and detailed structural studies of their Langmuir monolayers at the air-water interface. The structural studies are mainly based on grazing incidence X-ray diffraction (GIXD) studies including a detailed Bragg rod analysis. Surface pressure (Π)-area (A) isotherms and specular X-ray reflectivity (SXR) have also been employed to elucidate the structures of the different monolayers.

(15) Reitzel, N.; Hassenkam, T.; Balashev, K.; Jensen, T. R.; Howes, P. B.; Kjaer, K.; Fechtenko¨tter, A.; Tchebotareva, N.; Ito, S.; Mu¨llen, K.; Bjørnholm, T. Chem.sEur. J. 2001, 7, 4894–4901. (16) Nuckolls, C.; Katz, T. J.; Verbiest, T.; Van Elshocht, S.; Kuball, H. G.; Kiesewalter, S.; Lovinger, A. J.; Persoons, A. J. Am. Chem. Soc. 1998, 120, 8656–8660. (17) Bjørnholm, T.; Hassenkam, T.; Reitzel, N. J. Mater. Chem. 1999, 9, 1975–1990. (18) Norgaard, K.; Bjørnholm, T. Chem. Commun. 2005, 14, 1812–1823. (19) Piris, J.; Debije, M. G.; Stutzmann, N.; Laursen, B. W.; Pisula, W.; Watson, M. D.; Bjørnholm, T.; Mu¨llen, K.; Warman, J. M. AdV. Funct. Mater. 2004, 14(11), 1053–1061. (20) Smolenyak, P.; Peterson, R.; Nebesny, K.; Torker, M.; O’Brien, D. F.; Armstrong, N. R. J. Am. Chem. Soc. 1999, 121, 8628–8636. (21) Laursen, B. W.; Norgaard, K.; Reitzel, N.; Simonsen, J. B.; Nielsen, C. B.; Als-Nielsen, J.; Bjornholm, T.; Sølling, T. I.; Nielsen, M. M.; Bunk, O.; Kjaer, K.; Tchebotareva, N.; Watson, M. D.; Mullen, K.; Piris, J. Langmuir 2004, 20, 4139–4146. (22) Tabe, Y.; Ikegami, K.; Sugi, M. J. Appl. Phys. 1993, 73, 905–913. (23) Schwiegk, S.; Vahlenkamp, T.; Xu, Y.; Wegner, G. Macromolecules 1992, 25, 2513–2525.

Results and Discussion Synthesis. The asymmetrically substituted ATOTA+ salts 5a · PF6, 5b · PF6, and 5c · PF6 shown in Figure 2 were synthesized from the symmetric and readily available tris(trimethoxyphenyl)carbenium ion 1+ 12 (Scheme 1) through stepwise substitution of the three para-methoxy groups by dialkyl amines to give the amino substituted triarylmethanes 4a+-4c+. Subsequent ring closure gave the target molecules. The significant decrease in reactivity following each substitution step allows for formation of asymmetrically substituted products provided that the least reactive amines are introduced first.12 Hence, compound 4a · PF6 was obtained in a one-pot procedure by reacting 1 · BF4 with a slight excess of didecylamine at room temperature for 1 day, followed by addition of a large excess of dimethylamine, giving the desired product in 65% yield after column purification.

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Figure 3. Compression isotherms obtained with a barrier speed of 5 mm/min.

Compounds 4b · PF6 and 4c · PF6 were both prepared in two-step procedures by first introducing two long-chain amines (Nmethyldecylamine in the case of 4b+ and didecylamine in the case of 4c+). After workup, this step was followed by substitution of the last para-methoxy group by excess of the more reactive dimethylamine. Ring closure of compounds 4a · PF6-4c · PF6 to give 5a · PF6-5c · PF6 was achieved under mild ether cleaving conditions by heating with LiI in N-methylpyrrolidinone (NMP). Compounds 5a · PF6-5c · PF6 were isolated by column chromatography. Detailed descriptions of the synthesis and the characterization of all new compounds are given in the Experimental Section. Π-A Isotherms. Compounds 5a · PF6 and 5b · PF6 form stable monolayers at the air-water interface, with quite similar compress isotherms and a collapse pressure around 50 mN/m (Figure 3). The extrapolated mean molecular areas (MMA’s) of 5a · PF6 and 5b · PF6 are 58 and 61 Å2, respectively. The monolayer of the more highly substituted compound 5c · PF6 exhibits a significantly higher compressibility and lower collapse pressure. The two additional alkyl chains in 5c+ gave rise to phase transitions at MMA values of approximately 105, 85, and 75 Å2 (where the monolayer collapses or forms a bilayer) corresponding to average areas per alkyl chain of 26, 21, and 19 Å2, respectively. These values are very similar to the areas at which Langmuir layers of simple fatty acids display phase transitions and collapse.24,25 Thus, we conclude that the compression isotherm of 5c · PF6, contrary to those of 5a · PF6 and 5b · PF6, is dominated by the space requirements of the four dodecyl chains rather than packing of the aromatic ATOTA+ ions, for which a molecular area close to 60 Å2 can be deduced from the isotherms for 5a · PF6 and 5b · PF6. Grazing Incidence X-ray Diffraction. GIXD of the Langmuir films using synchrotron radiation was used to obtain more precise information about the structure of the ATOTA films at the air-water interface.26 The diffraction data for 5a · PF6 (at Π ) 20 mN/m, MMA ) 55 Å2, see Figure 3) in Figure 4a show two major peaks at Qxy ) 0.373 and 1.82 Å-1 corresponding to d-spacings (d ) 2π/Qxy) of 16.85 and 3.46 Å, respectively. The peak at 3.46 Å is assigned to the repeat distance along a columnar π-stack of the ATOTA+ (24) Roberts, G. Langmuir-Blodgett films; Plenum Press: New York, 1990. (25) Ulman, A. An Introduction to Ultrathin Organic Films; Academic Press: London, 1991. (26) Als-Nielsen, J.; Jacquemain, D.; Kjaer, K.; Leveiller, F.; Lahav, M.; Leiserowitz, L. Phys. Rep. 1994, 246, 252–313.

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cores, while the peak corresponding to 16.85 Å is assigned to the width of the columns. The latter assignment is in excellent agreement with the dimensions of the ATOTA+ system obtained from density functional theory (DFT) structure calculations and single crystal X-ray structure determination, which predict the width of the dimethylamino substituted ATOTA+ system to be 16.2 Å (including vdW radius).27 Furthermore, these distances provide a molecular area of 16.85 Å × 3.46 Å ≈ 58 Å2, which is similar to the MMA value obtained from the compression isotherm (∼55 Å2). The diffractogram of the Langmuir film of 5b · PF6 at II ) 20 mN/m is very similar to that of 5a · PF6; only the intensities of the Bragg peaks differ from each other. The MMA value for 5b · PF6 (58 Å2 at II ) 20 mN/m) is close to that of 5a · PF6 and similar to the molecular area calculated from the diffraction peak values (60 Å2). X-ray data collected at several different surface pressures (Π ) 5, 20, and 40 mN/m) are summarized in Table 1. At II ) 5 mN/m, a more qualitative dissimilarity appears between the Langmuir films of 5a · PF6 and 5b · PF6. Thus, while the 5a · PF6 Langmuir film displays a well-defined π-π stacking peak, 5b · PF6 exhibits no peak. The different behaviors could be due to the more flanked alkyl groups in the 5b · PF6 system, which may hinder coherent π-π stacking at low pressures. The higher compressibility of 5b · PF6 (less steep Π-A isotherm) compared to 5a · PF6 in the range of 0-20 mN/m (Figure 3) also points in this direction. An increase in surface pressure decreases the lamellar spacing, which converges toward the width of the ATOTA+ core (16.2 Å). Variations of the surface pressure also result in changes in domain size, which are reflected in the observed coherence lengths (see Table 1). The coherence lengths (L) were estimated from full-width at half-maximum (fwhm) of the peaks by the use of Scherrer’s formula (L ) 2π × 0.9/ fwhm(Qxy)).28 However, no clear trend of the coherence length as a function of the surface pressure is observed. At Π ) 20 mN/m, the Langmuir films of 5a · PF6 and 5b · PF6 form crystallites with coherence lengths along the π-stacks of 87 and 77 Å, respectively, corresponding to 25 and 22 coherently aligned ATOTA+ units (see Table 1). Coherence lengths of 598 and 531 Å were found in the lamellar direction for 5a · PF6 and 5b · PF6, which are equivalent to approximately 35 and 31 columns, respectively. The similar d-spacings (∼3.5 and ∼17 Å) and similar dimensions of the scattering crystallites of the 5a · PF6 and 5b · PF6 Langmuir films illustrate the high similarity of the 5a · PF6 and 5b · PF6 Langmuir films, despite the different molecular substitution pattern. The diffractogram of 5c · PF6 (Figure 4) confirms the conclusion based on the compression isotherm of 5c · PF6. The bulk of the four alkyl chains requires an MMA larger than what is ideal for coherent π-π stacking of the ATOTA+ cores. Hence, 5c · PF6 does not form well-defined 2D crystalline Langmuir films, and only one small and broad peak appears at Qxy ) 0.261 Å-1 (d ) 24.1 Å). Although no Bragg peak corresponding to a π-π stacking spacing of d ∼ 3.5 Å (Qxy ∼1.8 Å-1) is observed, an average distance around 3.5 Å could still exist in the Langmuir film as suggested by the measured MMA value of 84 Å2 (Figure 3) which exactly matches a 2D unit cell of 24 Å × 3.5 Å. All three ATOTA+ amphiphiles give rise to a broad lowintensity peak around 1.32 Å-1 (d ≈ 4.8 Å) in the GIXD (27) The width of the dimethylamino substituted ATOTA+ core present in 5a was calculated by DFT on the B3LYP/6-31G* level to be 16.2 Å (including vdW radius), in good agreement with the distances found in the single crystal data of 2,6,10-tris(N-pyrrolidinyl)trioxatriangulenium hexafluorophosphate; see ref 12. (28) Guinier, A. X-ray Diffraction; Freeman: San Francisco, 1968; p 121.

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Figure 4. (a) GIXD intensity (integrated over 0 < Qz < 0.8 Å-1 and corrected for the Lorentz, polarization, and sample area factors) at Π ) 20 mN/m for 5a · PF6 and 5b · PF6 and Π ) 15 mN/m for 5c · PF6. The individual profiles have been displaced vertically for clarity. The background signal from a bare water surface is shown for comparison. (b) Deconvolution of the reflections at high Q for 5a · PF6 and 5b · PF6, assigned as {02} (blue line) and {12} (red line) reflections (see The Unit Cell section below). Table 1. GIXD Data: Characteristic X-ray Peaks/Distances for the Langmuir Films of 5a · PF6, 5b · PF6, and 5c · PF6 compd

Π (mN/m)

Q10 (Å-1)/d{10} (Å)b

L (Å)c

Q02 (Å-1)/d{02} (Å)b

L (Å)b

2D unit cell area (Å2)

MMA (Å2)

5a · PF6 5a · PF6a 5b · PF6 5b · PF6a 5b · PF6 5c · PF6a

5 20 5 20 40 15

0.338/18.58 0.373/16.85 0.345/18.19 0.364/17.24 0.380/16.54 0.261/24.09

159 (9) 598 (35) 344 (20) 531 (31) 428 (26) 107 (4)

1.822/3.45 1.816/3.46

87 (25) 92 (26)

64.1 58.3

d

d

57.9 55.0 62.4 57.5 53.0

1.808/3.48 1.819/3.45

77 (22) 87 (25)

d

d

60.0 57.1

a Data extracted from graphs in Figure 4. b See text further below for the assignments {10} and{02}. c Coherence length (L) followed by the number of units corresponding to the repetition length in paranthesis. d No peak identified.

measurements (see Figure 4), which we assign to amorphous scattering from the disordered alkyl chains.29 The Unit Cell. In the single crystal of 2,6,10-tris(Npyrrolidinyl)trioxatriangulenium hexafluorophosphate, the ATOTA+ ions were found to pack in a 37° tilted columnar structure with an interplanar π-π stacking distance of only 3.32 Å.12 This distance is assumed to be the minimum π-π stacking distance between ATOTA+ ions. Based on the observed d-spacing of 3.46 Å, we can therefore deduce a maximum tilt (in any direction) of arccos(3.32 Å/3.46 Å) ) 16° for the ATOTA+ cores of 5a · PF6 in the Langmuir film. Hence, the ATOTA+ cores of 5a · PF6 in the Langmuir film are almost perpendicular to the π-π stacking direction. Such a nearly nontilted columnar stacking of identically oriented ATOTA+ ions implies an eclipsed packing along the stacking direction (as illustrated in Figure 5a). However, this is not compatible with the space filling requirements of the first methylene groups bound to the nitrogen atoms. Therefore, we propose a unit cell expanded by a dimer in which each of the two ATOTA+ cores is rotated, in opposite directions, around the π-π stacking direction, away from the eclipsed conformation (as in Figure 5b and c). The eclipsed conformation and dimers with only little rotation can be ruled out based on steric interaction between neighboring alkyl chains within the column. Semiempirical structure calculations for methyl substituted dimers suggest that this steric interaction between the first methylene units raises the energy of the eclipsed conformation by ∼50 kJ/mol relative to the lowest energy which was found for +30°/-30° conformation (Figure 5c). However, the intermediate +15°/-15° conformation (Figure 5b) is only ∼10 kJ/mol higher in energy. While (29) Reitzel, N.; Greve, D. R.; Kjaer, K.; Howes, P. B.; Jararaman, M.; Savoy, S.; McCullough, R. D.; McDewitt, J. T.; Bjornholm, T. J. Am. Chem. Soc. 2002, 122, 5788–5800.

these calculations nicely illustrate the steric effects that rule out the eclipsed conformation, they do not take into account interactions with neighboring columns or the water surface. Thus, while lowest in steric energy within the column, the highly rotated dimer conformations such as +30°/-30° (Figure 5c) are unlikely due to mixing of alkyl chains and π-systems as well as the resulting broadening of the columns. The extension of the unit cell is still in agreement with the GIXD data, if the two molecules in the unit cell give rise to identical/similar variation in electron density along the π-π stacking direction. In this situation, the odd {0k} combinations with respect to k will cancel/be reduced.29,30 Thus, we assign the observed peak at ∼1.82 Å-1 (3.46 Å) to the {02} reflection from the π-π stacking direction while the {01} reflection is not observed. The reflection along the lamellar packing direction is assigned as the {10} reflection. The intensities of additional combination reflections within the measured Qxy range were calculated. Only two combination reflections were predicted to give rise to intensities above 15% of the theoretical intensity of the {10} reflection, namely, the {21} and {12} reflections. The {21} reflection (Qxy ≈ 1.2 Å-1) is not present in our GIXD data (Figure 4a). The reason for this could be due to a high reduction of the intensity caused by a large smearing along the lamellar packing (details about anisotropic smearing will be discussed in the Bragg Rod Analysis section). On the contrary, the {12} reflection (Qxy ) 1.85 Å-1 in the case of 5a · PF6 and Qxy ) 1.84 Å-1 for 5b · PF6) could be extracted from the GIXD data by fitting two Voigt functions in Figure 4b representing the {02} and {12} reflections. Taking the Q-values and the assignment of the {10}, {12}, and {02} peaks into account, the unit cell has (30) Breiby, D. W.; Bunk, O.; Pisula, W.; Solling, T. I.; Tracz, A.; Pakula, T.; Mu¨llen, K.; Nielsen, M. M. J. Am. Chem. Soc. 2005, 127, 11288–11293.

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Figure 5. Dimer models of rotational isomers of the columnar π-π stacking, with the hindmost molecule shown as a space filling model, while the ATOTA+ unit in front is shown as a tube structure: (a) eclipsed, 0° conformation; (b) +15°/-15° conformation; (c) +30°/-30° conformation.

to be rectangular, meaning that the angle (gamma) between the two a and b lattice distances in the unit cell is 90°. Bragg Rod Analysis. In order to obtain further information about the orientation of the ATOTA+ cores of 5a · PF6 and 5b · PF6, analyses of the Bragg rods were carried out.26,31,32 The diffractograms in Figure 4a were obtained (cf. the Experimental Section) by integrating the position sensitive detector over that Qz-range, which showed intensities higher than the background. Profiles obtained by plotting the intensity of the Bragg peaks {10}33 and {02} as a function of Qz are called Bragg rods. They are related to the three-dimensional electron distribution of the scattering ATOTA+ core units. Hence, additional structure information such as tilt angle within the columnar stack and/or rotation around the π-π stacking direction of the ATOTA+ core may be obtained by comparing the experimental Bragg rods to simulated rods generated from structure models. Three dimer (31) Kjaer, K. Phys. B 1994, 198, 100–109. (32) Jensen, T. R.; Kjaer, K. In NoVel methods to study interfacial layers; Mo¨bius, D., Miller, R., Eds.; Elsevier: Amsterdam, 2001; Vol. 11, p 205. (33) The measured Bragg rod of {02} also includes the {12} rod due to the overlap between the peaks (see Figure 4 right). However, since the theoretical {12} Bragg rod profile is similar to the shape of the theoretical {02} Bragg rod and the {12} peak only integrates a small part relative to the {02} peak, we decided to call the Bragg rod based on the reflections in the 1.7 Å-1 < Qxy < 2.0 Å-1 range the {02} Bragg rod.

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conformations where considered for each of the compounds 5a · PF6 and 5b · PF6 with different rotation around the columnar axis: (1) 0° rotation (eclipsed), (2) +15°/-15° away from the surface normal, and 3) +30°/-30° away from the surface normal (Figure 5). DFT optimized structures of bis-dimethylamino(diethylamino) and bis-ethylmethylamino-(dimethylamino) ATOTA+ systems were used as components in the dimer conformations of 5a · PF6 and 5b · PF6, respectively. The anions and the remaining part of the alkyl chains were neglected because they were assumed to be incoherent.30 For all six cases (three rotational isomers for each compound), Bragg rods were calculated for orientations where both of the two ATOTA+ cores were tilted 0°-20° from the surface normal toward the surface. The out-of-plane rootmean-square displacement (also known as rms smearing) values used in all Bragg rod calculations of 5a+ and 5b+ were 2.6 and 2.7 Å, respectively, which is similar to the rms roughness of the surface of pure water.34 For 5a+ and 5b+, the best agreement between the simulated Bragg rods and the data obtained at 20 mN/m was achieved with a tilt of 8° (5a+) and 9° (5b+) along the columnar π-π stacking direction with respect to the surface normal. However, the Bragg rod analysis did not show any significant difference between the rotational isomers (0°, +15°/ -15°, and +30°/-30°). Even though the experimental techniques are unable to distinguish such rotational isomers, we can exclude the eclipsed (0°) and highly rotated (+30°/-30°) structures based on steric and volume arguments as discussed above. Thus, we have assumed a +15°/-15° rotation conformation for both 5a · PF6 and 5b · PF6 as illustrated in Figure 7. Figure 6displays normalized intensities of the Bragg rod data of 5a · PF6 and 5b · PF6 and the corresponding model based Bragg rods at {10} and {02}. The proposed structural model of the unit cell is shown in Figure 7. The different substitution patterns on the ATOTA+ cores in + 5a and 5b+ were designed in order to promote different orientations of the core with respect to the water phase (as indicated in Figure 2). At first sight, the identical Bragg rods of 5a · PF6 and 5b · PF6 shown in Figure 6 could lead to the conclusion that the two systems have their cores oriented in the same way on the water surface, in conflict with the amphiphilic design. However, the identical Bragg rods are a consequence of Friedel’s rule, which states that scattering from units, which only differ by an inversion symmetry operation, exhibits identical Bragg rods.35 It was not possible to get good agreement between the measured Bragg rod intensity ratios I{02}/I{10} at Qz ) 0 and those calculated from the models. Thus, I{02}/I{10} was found to be ∼4 for 5a · PF6 and ∼16 for 5b · PF6, while the ratios calculated from the models were ∼1 in both cases (when ignoring the in-plane Debye-Waller factor). Of course, the introduction of an isotropic in-plane rms displacement (smearing) in the model gave rise to a calculated ratio lower than 1.36 The discrepancies are most likely due to an anisotropic in-plane rms displacement (34) Braslau, A.; Deutsch, M.; Pershan, P. S.; Weiss, A. H.; Als-Nielsen, J.; Bohr, J. Phys. ReV. Lett. 1985, 54, 114–117. (35) The mathematical expression of Friedel′s rule is |F(h,k,l)| ) |F(-h,-k,-l)|, where F is the structure factor. (36) (a) The Debye-Waller factor (DWF) describes the attenuation of X-ray scattering caused by thermal displacements of the molecules/atoms within a crystal. The intensity of the diffracted X-rays from a crystal is proportional to the DWF. The general mathematical expression of the DWF as a function of the rootmean-square displacements away from the equilibrium position of the atoms along each of the Cartesian coordinates (σx,σy and σz) in a crystal is DWF ) exp(-σx2Qx2) exp(-σy2Qy2) exp(-σz2Qz2). In the case of the 5a · PF6 and 5b · PF6 Langmuir films, the out-of-plane σz-values are 2.6 and 2.7 Å-1, respectively. Theses values without applying in-plane smearing result in I{02}/I{10} ratios around one for both systems at Qz ) 0. By introducing a single in-plane smearing (σxy ) σx (σ[02]) ) σy (σ[10])), the I{02}/I{10} ratios are less than one, since Q[02] (1.83 Å-1) > Q[10] (0.38 Å-1) w DWF(0,1.83,0) ) exp(-σxy2 (1.83 Å-1)2) > DWF(0.38,0,0) ) exp(-σxy2 (0.38 Å-1)2). Therefore, to obtain a ratio greater than one in agreement with the experimental results, an in-plane anisotropic smearing has to be introduced such that σ[10] > σ[02].

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Figure 6. Normalized Bragg rod profiles (open circles) of the {10} (a and c) and {02} (b and d) peaks for both 5a · PF6 and 5a · PF6. Black solid lines represent Bragg rod fits calculated for the structures sketched in Figure 7 (8° and 9° tilt). The red and blue dashed lines are the {02} Bragg rods calculated for 0° and 15° tilt, respectively.

Figure 7. Proposed models of the unit cells of 5a · PF6 and 5b · PF6 Langmuir films depicted both along the π-π stacking direction {01} which shows two unit cells next to each other along the lamellar packing direction (a and b) and along the lamellar packing direction {10} showing two unit cells along the π-π stacking direction {01} (c).

(smearing) within the scattering crystallites.36 However, it was not possible to test this hypothesis in the software used to calculate Bragg rods. While in-plane smearing does not significantly change the profile of the Bragg rods, the relative intensity of the Bragg rods is very sensitive to in-plane smearing.36 The origin of such an anisotropic smearing could be due to a relatively larger smearing along the lamellar direction {10} because the lamellar packing is based on weak dispersion forces, compared to a small smearing caused by the rather strong π-π packing in the {02} direction. The variation of the interactions along the {10} and {02} packing directions can be inferred from the different compressibilities along the two packing directions. For example, the lamellar spacing of 5a · PF6 is reduced ∼9% from 18.60 Å at Π ) 5 mN/m to 16.85 Å at Π ) 20 mN/m, while the π-π

stacking distance is changed by less than 1% as a result of the same compression (see Table 1). The same trend is observed for 5b · PF6 (see Table 1). From the Bragg rod analysis, it was also possible to show that the degree of smearing along the lamellar packing direction versus the π-π stacking direction is dependent on the surface pressure. Thus, the {02} Bragg rod profile and absolute scattering intensity of 5b · PF6 is identical at Π ) 20 mN/m and Π ) 40 mN/m. On the other hand, the intensity of the {10} Bragg rod at Π ) 40 mN/m is increased by a factor of 2 compared to the Bragg rod obtained at Π ) 20 mN/m, due to the lower smearing along the lamellar packing direction at higher surface pressures. The lower intensity of the {10} Bragg peak of 5b · PF6 at Π ) 20 mN/m compared to 5a · PF6 (see Figure 4) could be due to the flanking alkyl groups in the 5b · PF6

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Simonsen et al.

Figure 8. SXR measurements of 5a · PF6 and 5b · PF6 Langmuir films at Π ) 20 mN/m. The top row shows the experimental data (white circles) as a function of the scattering vector Qz. The black thick solid line is a two-box fit to the data as shown in the bottom row. In the bottom row, height above the water surface is plotted as a function of the box electron density (dashed lines). The boxes have been smeared with a thermal displacement factor, giving the smooth black line. The atomic contents of the two boxes are shown schematically by using a black color for the alkyl chain and red color for the ATOTA+ unit. The blue N(CH3)2 moiety is placed in the “bulk” water. For clarity, only one of the two molecules in the proposed unit cell is shown; that is, the +15° rotational conformer of 5a · PF6 and the -15° rotational conformer of 5b · PF6 are shown. The green PF6- anion is sketched at several different positions to indicate the distribution of the anions.

system which may introduce a larger rms smearing along the alkyl-alkyl lamellar packing compared to 5b · PF6. These results support the hyphothesis that the Bragg rod intensity discrepancies are due to an anisotropic in-plane smearing within the scattering crystallites. X-ray Reflectivity from Langmuir Monolayers. The Langmuir monolayers of compounds 5a · PF6 and 5b · PF6 were further investigated by specular X-ray reflectivity (SXR) measured at the same surface pressure as the GIXD measurements (20 mN/ m). SXR measurements provide a quantitative measure of the, laterally averaged, electron density profile normal to the water surface of the Langmuir film and thus complement the GIXD scattering data by including information of the disordered components or moieties in the Langmuir film (which do not give raise to Bragg scattering).26,31,32 In case of the ATOTA+ Langmuir films, we are particularly interested in the positions of the PF6- counterions and to which extent water molecules are included in the monolayer. Figure 8a and b displays the reflectivity data of 5a · PF6 and 5b · PF6 Langmuir films (circles) and the best least-square fits to the data (thick lines). The fits are based on a two-box Parratt model in which the height and electron density for each of the boxes and (37) The Parratt32 software is available at http://www.hmi.de/bensc/ instrumentation/instrumente/v6/refl/parratt_en.htm. The software is based on Parratt’s dynamic approach described in Parratt, L. G. Phys. ReV. 1954, 95, 359– 369. And the roughness description is taken from Nevot, L.; Croce, P. ReV. Phys. Appl. 1980, 15, 761–779.

smearing factors for each of the interfaces are fitting parameters.37 The deduced electron-density profiles are shown in Figure 8c and d including schematic figures illustrating how the different boxes were defined with respect to the structure of the molecules. One box represents the hydrophobic alkyl chains, while the other box represents the aromatic ATOTA+ unit. The height of the ATOTA+ boxes were “fixed” to the DFT calculated values of the distances shown in Figure 8c and d. The best-fit values for the fitting parameters are listed in Table 2. Smearing values of 2.6 and 2.7 Å were used for both the bulk water and the ATOTA+ layer (Table 2). These values are comparable with the roughness of a water surface34 and are identical to the out-of-plane smearing used in the Bragg rod analysis. The smearing of the alkyl ATOTA+ interface was 2.7-3.1 Å. This value is higher, probably due to the more disordered alkyl chains. The alkyl box integrates to exactly the expected number of electrons, and hence, no water is included in the hydrophobic top layer. For the ATOTA+ boxes, an excess of 60 and 42 electrons were found for 5a · PF6 and 5a · PF6, respectively. As a single PF6- anion accounts for 70 electrons, this result suggests that at least 1/5 to 2/5 of the anions are located below the ATOTA+ layer (corresponding to fractions calculated for a water-free ATOTA+ layer in 5a · PF6 and 5a · PF6, respectively). However, we find it unlikely that much larger fractions of the anions are solvated in the water phase, since no sign of significant variations in the electron density is found for this region, and since this would lead to large dipole

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Table 2. List of the Different Values Obtained in the Two-Box Parratt32-Fits37 compd

box

H (Å)

F (e/Å3)

σ (Å)a

N (e) fitb

N (e) modelc

∆N (e)d

5a · PF6

alkyl ATOTA+ water

8.5 8.5 bulk

0.31 0.49 0.33

2.7 2.6 2.6

154 244

154 184

0 60

5b · PF6

alkyl ATOTA+ water

7.9 8.0 bulk

0.31 0.49 0.33

3.1 2.7 2.7

146 234

146 192

0 42

a Thermal displacement smearing (rms value). b Number of electrons based on the fitted density, box-height (H), and the GIXD-based MMA value. c Number of electrons based only on the contribution from the molecular parts shown in Figure 8c and d. d Excess electrons in the generated electron density profile compared to the molecular components.

moments and electrostatic repulsion in the Langmuir films. Hence, based on the SXR results, we suggest that the main part of the anions in the Langmuir films of 5a · PF6 and 5b · PF6 pack disorderly between the ordered cationic columns. Together with the structure models based on the GIXD measurements and Bragg rod analyses, the SXR analysis provides a final confirmation of the amphiphilic behavior of the molecules (Figure 2). In our ongoing work with transfer of the Langmuir films to solid substrates, we have observed that a low concentration of additional PF6- anions (1 mM KPF6) in the water subphase is required in order for the Langmuir film to be able to detach from the water surface. This observation also indicates that a part of the PF6ions are strongly bound in the water subphase. Well-defined LB multilayer films of both 5a · PF6 and 5b · PF6 can be prepared in this way, and they will be investigated for their exciton and charge transport properties.

Conclusions We have synthesized three new tris(dialkylamino)trioxatriangulenium (ATOTA+) salts, carrying two (5a · PF6 and 5b · PF6) or four (5c · PF6) n-decyl chains. The amphiphilic ATOTA+ ions self-assemble into columnar aggregates, with the cations standing upright with respect to the water surface. 5a · PF6 and 5b · PF6, both carrying only two long alkyl chains, form well-ordered 2D crystalline monolayers with a repeat distance along the columnar aggregates of only ∼3.45 Å. For both compounds, a small tilt of 8°-9° for the planar carbenium ions relative to the columnar axis is deduced from Bragg rod analysis. A qualitative discussion based on the Bragg rods infers an anisotropic smearing within the crystallites. The strong π-π stacking exhibits a smaller smearing or thermal displacement than the weak and highly compressible alkyl-alkyl packing along the lamellar packing direction. SXR measurements confirm the orientation of the ATOTA+ cores and the alkyl chains to be in agreement with the amphiphilic design, and SXR analysis also suggests that the anions are mainly located in the ATOTA+ layer.

Experimental Section Preparation of the Monolayers. Monolayers of the amphiphilic salts 5a · PF6, 5a · PF6, and 5a · PF6 were spread from chloroform solution (1 mg/mL) onto a Milli-Q purified water subphase (18.2 MΩ cm) in the LB trough at room temperature (rt). Compression was conducted after 20-30 min using a barrier speed of 5 mm/min. X-ray Measurements on Langmuir Films. Surface X-ray diffraction measurements on the Langmuir films were performed at the X-ray undulator beamline BW1 at the synchrotron facility HASYLAB at DESY in Hamburg, Germany. The X-ray wavelength was λ ) 1.304 Å. The sample was kept in a helium atmosphere. Two different X-ray techniques were used: grazing incidence X-ray diffraction (GIXD) and specular X-ray reflectivity (SXR). For GIXD, the grazing angle of incidence (R) was slightly below the critical angle (Rc) for total reflection (R ) 0.85 Rc) of water, thus increasing the surface sensitivity by minimizing the penetration depth of the

incident X-rays into the water subphase. The horizontal scattering angle (2θxy) was resolved by scanning a Soller collimator, while the vertical exit angle Rf was resolved by a position-sensitive detector. Under the circumstances, the vertical scattering vector component is Qz ≈ (2π/λ) sin Rf while the horizontal component is Qxy ≡ (Qx2 + Qy2)1/2 ≈ (2π/λ)[1 + cos2(Rf) - 2cos(Rf) cos(2θxy)]1/2. The GIXD intensities were corrected for the variation of the Lorentz and polarization factors and of the sample area contributing to the detected intensity. The SXR experiments probe the vertical electron density profile across the interface by varying the incident angle (Ri) and the exit angle Rf simultaneously (Ri ) Rf ≡ R) and recording the intensity pattern resulting from interference between rays reflected at different depths. The experimental data are shown as a function of the purely vertical scattering vector Qz ) (2π/λ)[sin(Ri) + sin(Rf)] ) (4π/λ) sin(R), as the measured reflectivity (R(Qz)). By model fitting, the data were inverted to yield the electron density profile normal to the water surface, F(z). Calculations. Molecular dimensions of the ATOTA+ system and input structures for the Bragg rod simulations was derived from DFT geometry optimizations using B3LYP-6-31* in Gaussian 03.38 Calculation of the energy of the three rotational conformations shown in Figure 5 was done using semiempirical AM1 geometry optimizations in the program packed Spartan ’06.39 These geometry optimizations were performed on a trimer where the central ATOTA+ ion was rotated relative to the two outer ATOTA+ ions. The structures and positions of two outer ATOTA+ ions were frozen at a mutual distance of 6.9 Å, to provide a symmetric steric environment for the central ATOTA+ unit. All three central carbon atoms were locked to the stacking axis at 3.45 Å separations. Synthesis. Compounds 5a · PF6, 5b · PF6, and 5c · PF6 were synthesized and identified by 1H NMR and 13C NMR, FAB MS measurements, and elemental analysis. Tris(2,4,6-trimethoxyphenyl)carbenium tetrafluoroborate (1 · BF4) was synthesized according to the reported procedure.12 4-Didecylamino-2,6-dimethoxyphenyl-bis(4-dimethylamino-2,6trimethoxyphenyl)-carbenium Hexafluorophosphate (4a · PF6). Compound 1 · BF4 (0.50 g, 0.84 mmol) was dissolved in dry N-methylpyrrolidinone (NMP) (7 mL). Didecylamine (0.27 g, 0.92 mmol) and 1 drop of diisopropylethylamine were added. The mixture was stirred for 20 h. Subsequently, dimethylamine (2 mL, 40% in THF) solution was added and the mixture was stirred for another 120 h. CH2Cl2 (DCM) was added and the mixture was washed with KPF6(aq) (2 × 50 mL, 0.2 M). The organic phase was concentrated, and the product was purified by column chromatography (silica gel, (38) Frisch, M. J.; et al. Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004. (39) Spartan ’06; Wavefunction, Inc.: Irvine, CA. Shao, Y. Molnar, L. F.; Jung, Y.; Kussmann, J.; Ochsenfeld, C.; Brown, S. T.; Gilbert, A. T. B.; Slipchenko, L. V.; Levchenko, S. V.; O’Neill, D. P.; DiStasio, R. A., Jr.; Lochan, R. C.; Wang, T.; Beran, G. J. O.; Besley, N. A.; Herbert, J. M.; Lin, C. Y.; Van Voorhis, T.; Chien, S. H.; Sodt, A.; Steele, R. P.; Rassolov, V. A.; Maslen, P. E.; Korambath, P. P.; Adamson, R. D.; Austin, B.; Baker, J.; Byrd, E. F. C.; Dachsel, H.; Doerksen, R. J.; Dreuw, A.; Dunietz, B. D.; Dutoi, A. D.; Furlani, T. R.; Gwaltney, S. R.; Heyden, A.; Hirata, S.; Hsu, C.-P.; Kedziora, G.; Khalliulin, R. Z.; Klunzinger, P.; Lee, A. M.; Lee, M. S.; Liang, W. Z.; Lotan, I.; Nair, N.; Peters, B.; Proynov, E. I.; Pieniazek, P. A.; Rhee, Y. M.; Ritchie, J.; Rosta, E.; Sherrill, C. D.; Simmonett, A. C.; Subotnik, J. E.; Woodcock, H. L., III; Zhang, W.; Bell, A. T.; Chakraborty, A. K.; Chipman, D. M.; Keil, F. J.; Warshel, A.; Hehre, W. J.; Schaefer, H. F.; Kong, J.; Krylov, A. I.; Gill, P. M. W.; Head-Gordon, M. Phys. Chem. Chem. Phys. 2006, 8, 3172.

3592 Langmuir, Vol. 25, No. 6, 2009 diethylether/DCM 1:1). Yield: 0.51 g (65%) of blue solid compound. 1 H NMR (400 MHz, CH3CN): δ 5.81 (s, 4H), 5.77 (s, 2H), 3.48 (s, 12H), 3.46 (s, 6H), 3.44 (t, J ) 6.6, 4H), 3.11 (s 12H), 1.65 (m, 4H), 1.28 (m, 28H), 0.88 (t, J ) 5.8, 6H). 13C NMR (250 MHz, CDCl3): δ 163.33, 162.81, 155.75, 154.55, 115.32, 115.05, 88.66, 88.55, 55.89, 51.24, 40.26, 31.73, 29.45, 29.40, 29.30, 29.15, 27.63, 26.91, 22.52, 13.97. MS (FAB+): m/z 804.5. 2-Didecylamino-6,10-bis(dimethylamino)-4,8,12-trioxatriangulenium Hexafluorophosphate (5a · PF6). Synthesized as 5b · PF6 (see below). Yield: 54%. 1H NMR (250 MHz, CDCl3): δ 6.41 (s, 4H), 6.36 (s, 2H), 3.37 (t, J ) 7.3, 4H), 3.16 (s, 12H), 1.61 (m, 4H), 1.22 (m, 28H), 0.81 (t, J ) 6.8, 6H). 13C NMR (250 MHz, CDCl3): δ 157.49, 156.03, 153.80, 153.44, 131.21, 94.46, 94. 33, 94.21, 52.17, 40.92, 31.78, 29.50, 29.45, 29.34, 29.21, 27.06, 26.87, 22.57, 14.01. MS (FAB+): m/z 666.7. Anal. Calcd for C43H60N3O3PF6: C, 63.61; H, 7.45; N, 5.18. Found: C, 63.43; H, 7.46; N, 5.14. Bis(4-decylmethylamino-2,6-dimethoxyphenyl)-4-dimethylamino2,6-trimethoxyphenyl-carbenium Hexafluorophosphate (4b · PF6). Compound 1 · BF4 (1.00 g, 1.67 mmol) was dissolved in dry tetrahydrofuran (THF) (10 mL). Decylmethylamine (1.04 g, 6.08 mmol) and diisopropylethylamine (2 drops) were added. The mixture was stirred at reflux for 14 h. The reaction mixture was absorbed on silica gel and washed with petrolether to remove excess amine. By washing the silica gel with DCM, an oily blue liquid was recovered (1.38 g) after evaporation of the solvent. Column chromatography (silica gel, DCM with increasing fraction of ethyl acetate) followed by anion exchange (DCM solution was washed with 2 × 50 mL 0.2 M KPF6(aq)) yielded 0.40 g of a dark blue solid. This intermediate product (3) was dissolved in acetonitrile (10 mL), and dimethylamine (2 mL, 40% in THF) was added. After 4 days at rt, solvent and excess dimethylamine were removed, yielding 0.40 g (25%) of a blue solid material. 1H NMR (250 MHz, CDCl3): δ 5.64 (s, 6H), 3.46 (s, 6H), 3.39 (s, 12H), 3.08 (t, J ) 7.5, 4H), 3.08 (s, 6H), 3.05 (s, 6H), 1.57 (m, 4H), 1.19 (m, 28H), 0.81 (t, J ) 6.9, 6H). 13C NMR (250 MHz, CDCl3): δ 163.29, 163.00, 155.93, 155.43, 115.43, 88.78, 56.10, 52.84, 40.47, 38.87, 31.94, 29.66, 29.61, 29.54, 29.36, 27.47, 27.06, 22.74, 14.18. MS (FAB+): m/z 804.8. Anal. Calcd for C49H78N3O3PF6: C, 61.94; H, 8.27; N, 4.42. Found: C, 61.53; H, 8.20; N, 4.32. 2,6-Bis(decylmethylamino)-10-dimethylamino-4,8,12-trioxatriangulenium Hexafluorophosphate (5b · PF6). LiI (1.00 g, 7.5 mmol) was added to 4b · PF6 (0.37 g, 0.39 mmol) dissolved in Nmethylpyrrolidinone (NMP) (25 mL). The mixture was stirred under reflux in 2.5 h at 200 °C. During the reaction, the color changed from light blue to dark yellow (orange). The mixture was cooled to rt and poured into KPF6(aq) (100 mL, 0.2 M), from which the product was extracted with DCM (2 × 50 mL). The DCM phase was washed with KPF6(aq) (3 × 100 mL, 0.2 M) and evaporated to yield a strongly colored messy liquid. Column chromatography (silica gel, diethylether with an increasing fraction of DCM) yielded TLC-pure

Simonsen et al. fractions which were combined and reprecipitated in diethylether/ petroelether. Yield: 0.16 g (51%) yellow/orange powder. 1H NMR (250 MHz, CDCl3): δ 6.27 (s, 2H), 6.26 (s, 2H), 6.24 (s, 2H), 3.39 (t, J ) 7.3, 4H), 3.10 (s, 8H), 3.08 (s, 4H), 1.58 (m, 4H), 1.20 (m, 28H), 0.80 (t, J ) 6.8, 6H). 13C NMR (250 MHz, CDCl3): δ 157.38, 156.71, 153.48, 153.26, 130.80, 94.30, 94.02, 53.41, 40.88, 39.54, 31.76, 29.48, 28.45, 29.38, 29.20, 26.83, 22.56, 13.99. MS (FAB+): m/z 666.3. Anal. Calcd for C43H60N3O3PF6: C, 63.61; H, 7.45; N, 5.18. Found: C, 63.39; H, 7.46; N, 5.10. Bis(4-didecylamino-2,6-dimethoxyphenyl)-4-dimethylamino-2,6dimethoxyphenyl-carbenium Hexafluorophosphate (4c · PF6). Compound 1 · BF4 (1.00 g, 1.68 mmol) was dissolved in CH3CN (2 mL). Didecylamine (4.0 g, 13.6 mmol) dissolved in hot benzene (10 mL) was added. The mixture was stirred under reflux for 72 h. The reaction mixture was absorbed on silica gel and washed with heptane to remove excess amine. The adsorbed product was washed out by DCM. The DCM solution was washed with KPF6(aq) (150 mL, 0,2 M) to exchange the anion. The raw product was purified by column chromatography (silica gel, diethylether/CH2Cl2 1:1), yielding 0.55 g of solid material (3). The product was dissolved in CH3CN (10 mL), and dimethylamine (1 mL, 40% in THF) was added. After 2 days at rt, solvent and excess dimethylamine were removed and the product precipitated from DCM/heptane solution by slow evaporation. Yield: 0.45 g (22%) blue solid. MS (FAB+): m/z 1056.7. 2,6-Bis(didecylamino)-10-dimethylamino-4,8,12-trioxatriangulenium Hexafluorophosphate (5c · PF6). LiI (1.00 g, 7.5 mmol) was added to 4c · PF6 (0.13 g, 0.11 mmol) dissolved in NMP (25 mL). The mixture was stirred under reflux for 3 h at 200 °C and allowed to stand overnight at rt (16 h). DCM was added to the reaction mixture, and the organic phase was washed with aqueous KPF6 solution (2 × 100 mL, 0.2 M). Evaporation of the organic phase yielded a oily product. Purification was conducted on two columns (silica gel, (1) gradient using petrolether with increasing fractions of DCM and (2) gradient using diethyl ether with increasing fractions of DCM). The pure fractions were mixed, evaporated, and recrystallized from DCM/heptane solution by slow evaporation, yielding 0.030 g (30%) of a yellow solid. 1H NMR (400 MHz, CDCl3): δ 6.53 (s, 2H), 6.45 (d, J ) 5.3 4H), 3.43 (t, J ) 7.6, 8H), 3.24 (s, 6H), 1.69 (m, 8H), 1.28 (m, 56H), 0.89 (t, J ) 6.8, 12H). 13C NMR (400 MHz, CDCl3): δ 157.71, 156.04, 154.03, 153.98, 153.68, 131.50, 94.71, 94.55, 94.44, 94.36, 52.15, 40.98, 31.79, 29.50, 29.44, 29.34, 29.21, 27.01, 26.90, 22.58, 14.06. MS (FAB+): m/z 918.4. Anal. Calcd for C61H96N3O3PF6: C, 68.83; H, 9.09; N, 3.95. Found C, 68.73; H, 9.10; N, 3.93.

Acknowledgment. This work was supported by the Danish Natural Science Research Council (FNU, Grant No. 272-060102) and the DANSYNC program. LA803733S