Zeolite-like liquid crystals

Zeolites represent inorganic solid-state materials with porous structures of fascinating complexity. Recently, significant progress was made by reticular synthesis of related organic solid-state materials, such as metal-organic or covalent organic frameworks. Herein we go a step further and report the first example of a fluid honeycomb mimicking a zeolitic framework. In this unique self-assembled liquid crystalline structure, transverse-lying π-conjugated rod-like molecules form pentagonal channels, encircling larger octagonal channels, a structural motif also found in some zeolites. Additional bundles of coaxial molecules penetrate the centres of the larger channels, unreachable by chains attached to the honeycomb framework. This creates a unique fluid hybrid structure combining positive and negative anisotropies, providing the potential for tuning the directionality of anisotropic optical, electrical and magnetic properties. This work also demonstrates a new approach to complex soft-matter self-assembly, by using frustration between space filling and the entropic penalty of chain extension.


Supplementary Figures
Supplementary Figure 1 Supplementary Table  3); electron density color code: purple/blue = high, red/yellow = low, green = medium. Based on the electron density maps, the negative birefringence of this phase and the molecular dimensions, only the hexagonal honeycomb structures (white line) is possible for the Col hex 1 phase.

a b
S6 πππ ππ0 π0π 0ππ Supplementary Figure 9 │ Reconstructed electron density maps of the Col hex 2 /p6mm phase of compound 14/6. Different structure factor combinations based on the three strongest reflections (11), (21) and (30) were used (see Supplementary Table 4); electron density color code: purple/blue = high, red/yellow = low, green = medium; the selected phase combination is framed; see Supplementary Note 1 for selection of phase combination.

Supplementary Notes
Supplementary Note 1 │ Selection of the phase combination for the Col hex 2 phase of compound 14/6. Based on the electron density maps (Supplementary Fig. 9) in principle two different structures are possible for the Col hex 2 phase with negative birefringence (having the aromatic cores organize in the plane of the 2D lattice), one with giant cylinders formed by two molecules along each of the walls of the hexagons (12-hexagons, see 0); the other one is the hexagon/pentagon tiling as shown in Fig. 4b-d in the main text. The former is discarded as the side length of the 12-hexagons would be 5.7 nm, which is significantly more than twice the molecular length (2 x 2.45 = 4.9 nm). In comparison, the length of one of the longer walls of the 9-hexagons in the pentagon/hexagon structure is 4.85 nm, which is rather close to the required 2 x 2.45 = 4.9 nm. Also the honeycomb walls of the small 6-hexagons of the pentagon/hexagon tiling have a length of 2.4 nm, in very good agreement with L mol . If the giant hexagonal structure was assumed, then the electron density map 0 indicates the presence of an additional high electron density cylinder (purple) in the centre of each 12hexagon. In principle these cylinders could be formed by coaxial rod-bundles, as it is the case of the Col rec /c2mm phase (the rod-bundle ribbons would in this case form a hollow cylinder, filled with the alkyl chains of the inner molecules). However, this would lead to a significant reduction of the birefringence or could even lead to positive birefringence, which is in conflict with the negative birefringence of the Col hex 2 phase, being very similar to the birefringence of the Col hex 1 phase (see Fig. 5c and Supplementary Figs. 2b and 3). Therefore, the  phase combination, best reflecting the molecular dimensions and being in agreement with the distribution of electron rich (aromatics, glycerols; blue/purple) and electron poor (alkyl chains; red/yellow/green) building blocks, was selected.
Supplementary Note 2 │ Selection of the phase combination for the Col rec /c2mm phase of compound 10/10. Even though 7 diffraction peaks have been used for the reconstruction of the c2mm electron density maps, two of them, (11) and (02), are very weak and do not make much qualitative difference to the maps reconstructed ( Supplementary Fig. 7b and Supplementary Table 5). Certain phase combinations show essentially the same map, with only the origin of the unit cell shifted to four different positions due to the c2mm symmetry. The number of essentially different maps obtained is in fact eight, and they are shown in the Supplementary Fig. 10. To determine the best phase combination, the first criterion used is that the map should have distinctive high density and low density regions, which can be attributed to the rigid aromatic backbone and flexible side chains respectively. On this basis maps (a), (b) and (h) can be eliminated, as there are large medium density (green, light-blue) regions which cannot be explained by a packing of 10/10 molecules. Next, map (f) can also be dismissed as the relative volume of the high density regions (blue to purple) is too high to be attributed to aromatic backbones, although if it was selected it would have given the same molecular arrangement as the chosen map (d). For the remaining four maps, maps (c) and (g) are all full of isolated high-density dots and it is difficult to see any honeycomb network. In addition, in (c) the aromatic backbone form a nearly circular cell which is rather unreasonable. Both (c) and (e) suggest models where the side length of the honeycombs is much longer than that of the molecular backbone. Between maps (d) and (e), (d) is better in that the high and low density regions are more uniform. Also the structure based on map (e) would have to have structural elements significantly longer than the length of the molecular core. While such electron density maps have their limitations due to the finite number of Fourier terms, map (d) is chosen in the end as on its basis an almost continuous honeycomb framework can be constructed, with wall lengths matching the molecular lengths, and because of its general agreement with other physical data, such as the molecular core length, the two orientations of the 2D lattice observed by GISAXS (see Fig. 6), and the reduced absolute value of birefringence, as discussed in the main text. Supplementary Fig. 11 there is a overcrowding of the pentagonal channels whereas sufficient space is available for the alkyl chains in the hexagonal channels. Supplementary Fig. 12 shows the calculation of the side-length ratio of the pentagons in the Col hex 2 phase.  Table 6. Assuming the proposed tiling pattern the number of cylinder side walls (n sides ) per unit cell is calculated, leading to n sides = 3 for the Col hex 1 phase, n sides = 18 for the Col hex 2 phase and n sides = 18 for the Col rec /c2mm phase, respectively. The number of molecules arranged back-to-back across the cylinder walls (n wall ) is calculated according to n cell /n sides , leading to n wall = 1.9…2.0 for the Col hex 1 phases and n wall = 1.7 for the Col hex 2 phase. n wall is not necessarily an integer number, as the considered systems are fluid and there are no fixed positions of the molecules. Hence, it is an average number considering the dynamics of the system and involving some defects and staggering of the molecules. The slightly reduced number of n wall = 1.7 for the Col hex 2 phase might be due to the three less defined walls in each 9-hexagon. For the Col rec /c2mm phase the presence of the axial rod-bundles must be considered. The number of molecules in the cross-section of these additional bundles can be estimated by assuming that n wall of the honeycomb framework is the same as in Col hex 1 (n wall = 1.9). Thus the 18 cylinder walls per unit cell require 18 x 1.9 = 34.2 molecules, leaving ~2.8 and ~4.4 molecules per unit cell for these coaxial bundles (n cell -34.2) in the c2mm phases of 12/8 and 10/10, respectively. As the coaxial molecules contribute to more than just one unit cell, their contribution to each unit cell can be calculated by dividing the height of the unit cell (h) by the molecular length (L mol = 2.45 nm), leading to about 0.2. This means that these coaxial molecules contribute with 20% to each of 5 adjacent unit cells. Thus, there are 14 and 22 molecules contributing to the rod-bundles in each unit cell of 12/8 and 10/10, respectively. Because there are two coaxial bundles per unit cell the number of molecules arranged side by side in the bundles (n bundle ) is half this number, i.e. n bundle = 7 and 11, respectively (see Supplementary Table 6). This number is very similar to that found in the cross section of the S13 axial bundles (~ 10 molecules) in the hexagonal axial bundle phases without additional honeycomb framework. (7)

Supplementary Methods
Synthesis of the compounds was performed according to Fig. 8 using the following procedures. Unless otherwise noted, all starting materials were purchased from commercial sources and were used without further purification. Column chromatography was performed with silica gel 60 (63-200 µm, Fluka). Determination of structures and purity of intermediates and products was obtained by NMR spectroscopy (VARIAN Gemini 2000 and Unity Inova 500, all spectra were recorded at 27 °C). Microanalyses were performed using a CARLO Erba-CHNO 1102 elemental analyzer and a micrOTOF HR-ESI mass spectrometer (Bruker). The purity of all products was checked with thin layer chromatography (silicagel 60 F 254 , Merck). CHCl 3 /EtOAc mixtures and CHCl 3 /MeOH mixtures were used as eluents and the spots were detected by UV radiation. All branched compounds with unequal chain length represent racemic mixtures; C m H 2m+1 and C n H 2n+1 represent linear chains. Bromoalkanes (2a-e). 1-Bromo-n-docosane (2a) was obtained from commercial sources and was used as received. The branched alkyl bromides 2b-e were synthesized as described in more detail below by alkylation of dialkyl malonates (methyl, ethyl) 3b-e, followed by dealkoxycarbonylation, yielding methyl or ethyl 2-alkylalkanoates 4b-e; reduction of 4b-e to the 2-alkylalkanols 5b-e with LiAlH 4 and transformation into the 2-alkyl-1-bromo-alkanes 2b-e with aqu. HBr/conc. H 2 SO 4 . Dialkylated malonates 3b-e (6,7). Diethyl 2-butyl malonate was obtained from Sigma Aldrich and was used as obtained. The others were synthesized according to the following procedures.

Procedure A:
The reaction was carried out under an argon atmosphere. Sodium hydride (1.5 eq / 60% in mineral oil) was slowly suspended in DMF (abs., 100 mL) and the mixture was cooled to 0 °C. Dialkyl malonate (1 eq.) and the appropriate 1-bromoalkane (0.8eq for monoalkylation) in DMF (50 mL) was added one after another and the mixture was stirred at room temperature for 3 h. After reaction water (250 mL) was added and the mixture was extracted with diethyl ether (3 x 100 mL). The combined organic layers were washed with sat. S14 aqu. LiCl, water and brine. After drying over anhydrous Na 2 SO 4 the solvent was removed under reduced pressure. The residue was purified by column chromatography (1. n-hexane, 2. CHCl 3 ).

Procedure B:
The reaction was carried out under an argon atmosphere. Sodium (3 eq) was dissolved slowly in MeOH (abs., 50 mL / g sodium); dialkyl malonate (1eq) and 1bromoalkane (1.1 eq for monoalkylation, 2.2 eq for dialkylation) were added one after another. The reaction was stirred at room temperature for 8 h. The mixture was concentrated under reduced pressure and poured into ice water to dissolve the precipitate. After extraction with diethyl ether (3 x 100 mL) the combined organic layers were washed with water and brine. After drying over anhydrous Na 2 SO 4 the solvent was removed under reduced pressure. The residue was purified by column chromatography (1. n-hexane, 2. CHCl 3 ).  General procedure for the synthesis of the branched carboxylates 4b-e (9). A mixture of the alkyl substituted malonate (1 eq), LiCl (2 eq), and water (1 eq) in DMSO (150 mL) was stirred at reflux for 24 h. After cooling to room temperature water (150 mL) was added. The mixture was extracted with Diethylether (3 x 50 mL) and the combined organic layers washed with water (3 x 50 mL) After drying over anhydrous Na 2 SO 4 the solvent was removed under reduced pressure. The residue was purified by column chromatography (CHCl 3 / n-hexane, 1 / 4 v/v). Procedure for the synthesis of the 2-alkylalkane-1-ols 5a-d (10). The reaction was carried out under a argon atmosphere. LiAlH 4 (3 eq / ester group) was slowly suspended in dry diethyl ether (100 mL). The dialkylated malonate was dissolved in dry diethyl ether (100 mL) and added dropwise to this suspension. The mixture was heated to reflux for 6 h. After reaction water was added dropwise until the excess of LiAlH 4 was destroyed. The precipitate was dissolved by adding H 2 SO 4 (10%, 50 mL) dropwise. The mixture was extracted with diethyl ether (3 x 50 mL) and the combined organic layers was washed with sat. aqu. Na 2 S 2 O 3 , water and brine. After drying over anhydrous Na 2 SO 4 the solvent was removed under reduced pressure and the residue purified by column chromatography (CHCl 3 ). Procedure for the synthesis of the 2-alkyl-1-bromo-alkanes 2b-e (11). The appropriate alcohol 5 (1 eq), Bu 4 NHSO 4 (5 mg) and conc. H 2 SO 4 (2 mL) was suspended in HBr (48%, 50 mL) and heated to reflux for 24 h. After cooling to room temperature the mixture was extracted with diethyl ether (3 x 50 mL). The combined organic layers were washed with water and brine and dried over anhydrous Na 2 SO 4 . After removal of the solvent the residue was purified by column chromatography (n-hexane). Synthesis of the acetonides Am/n. A mixture of 1 and 2a-e, K 2 CO 3 (250 mg, 1.8 mmol) and Bu 4 NI (5 mg) in anhydrous DMF (50 mL) was stirred at 80 °C for 12 h. After cooling to room temperature, the reaction was poured into water (50 mL) and the aqueous layer was extracted with Et 2 O (3x50 mL). The combined organic layers were washed with saturated aqu. LiCl, water and brine. After drying over anhydrous Na 2 SO 4 , filtration and evaporation of the solvent, the crude product was purified by column chromatography (silica gel, CHCl 3 /EtOAc, 4/1 v/v).