Supramolecular Order of 2,5-Bis(dodecanoxy)phenyleneethynylene

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SUPRAMOLECULAR ORDER OF 2,5-BIS(DODECANOXY) PHENYLENEETHYNYLENE-BUTADIYNE OLIGOMERS IN THE SOLID STATE Edgar Vergara, Eduardo Arias, Ivana Moggio, Carlos Gallardo-Vega, Ronald F. Ziolo, Rosa M. Jiménez-Barrera, Damaso Navarro, Oliverio Rodríguez, Salvador fernández, and Manuel Herrera Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.5b01318 • Publication Date (Web): 29 May 2015 Downloaded from http://pubs.acs.org on June 4, 2015

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SUPRAMOLECULAR ORDER OF 2,5-BIS(DODECANOXY) PHENYLENEETHYNYLENE-BUTADIYNE OLIGOMERS IN THE SOLID STATE †

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†

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Edgar Vergara , Eduardo Arias* , Ivana Moggio , Carlos Gallardo-Vega , Ronald F. †

†

†

†

Ziolo , Rosa M. Jiménez-Barrera , Damaso Navarro , Oliverio Rodríguez , Salvador †

Fernández and Manuel Herrera§ †

Centro de Investigación en Química Aplicada (CIQA), Blvd. Enrique Reyna 140, 25294,

Saltillo,

México.

Tel:

00528444389830,

Fax:

00528444389839,

e-mail:

[email protected] §

Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de México, Ensenada, 22800 Baja California. México

Abstract The supramolecular order of a 2,5-bis(dodecanoxy) phenyleneethynylene-butadiyne series of rod-like oligomers with 2, 4, 6 and 8 phenyleneethynylene moieties was studied in the solid state by differential scanning calorimetry (DSC), temperature dependent small and wide angle X-ray diffraction (SWAXS), selected area electron diffraction (SAED), polarized optical microscopy (POM), high resolution transmission microscopy (HRTEM) and scanning tunneling microscopy (STM). It was found that all of the oligomers selfassemble in blocks of molecules that resemble bricks that are randomly oriented. These oligomers are described as sanidic liquid crystals as a term to classify their mesomorphic behavior because of their brick or board-like structure. The strong π-π interaction that governs the package of conjugated backbones was evidenced by the reiterative distances of 0.36 ± 0.017 nm found by SWAXS and 0.32 ± 0.017 nm found by HRTEM. A STM study of a cast film of the tetramer deposited on highly oriented pyrolitic graphite (HOPG) allowed the visualization and determination of the conjugated backbone length of 2.48 nm and a phenyl-phenyl distance of 0.34 nm, suggesting that the molecules are stacked in lamellae perpendicularly aligned to the substrate.

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Introduction Phenyleneethynylene (PE) molecules and macromolecules (PPE) continue to emerge as scientifically and technologically important materials in one, two and three dimensions and in self-assembly scenarios, due to their high electronic delocalization and strong light emission properties. Areas of study include semiconducting molecular wires,1-5 optoelectronics,6 organic light emitting diodes (OLEDS), solar cell applications and in other areas where photoconductive and nonlinear optical properties play a key role. On the technological side, there are at least two features of PPE macromolecules that are of major importance and interest. The PPEs are liquid crystals where SmA, SmC or N are the more typically found mesophases,7,8 and they are highly fluorescent materials.9 OLED devices made of organic polymers, for example, can be found in the marketplace, but the challenge, since the discovery of the electroluminescent properties of poly(p-phenylenevinylene) (PPV) has always been to obtain, in the same molecule, the molecular orientation and light emission that could allow for the development of brighter and lower cost displays. This appears to be a worthy goal, since in principle, the illumination source and the polarizers that absorb light could be eliminated from the devices.10 PPE oligomers exhibit very particular assembly behaviors depending on their conjugation length and emission properties that can be tailored as a function of their length. These materials have a very high quantum yield derived from their high quinoid coplanarization in the excited state,11 low intersystem crossing, high singlet formation, and an oligomer with seven repetitive units, that almost attains the effective conjugation with respect to their homologue polymers.12 As liquid crystals, however, the PPE materials present very broad mesophases that are practically temperature or electrically unchanged and that are birefringent, but they do not exhibit known textures reported in the literature. It has been demonstrated that thin films of PPE macromolecules can be oriented by “rubbing” at room temperature or below their transition temperature13,14 and thus polarized emission has been obtained.15 But in most cases, absorbance and/or emission dichroic rates are low, and little, if any work has been done to understand the causes. In this respect, we have found that thin films of benzoateethynylene type macromolecules exhibit a low degree of dichroism after being rubbed, even those bearing cholesteryl as mesogen groups,16 which we have attributed to their spontaneous tendency to self-assemble in bilayers and to the strong π-π interaction 2 ACS Paragon Plus Environment

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that gives rise to molecules packaging into “bricks”, that are difficult to orient by mechanical forces. But in 2,5-bis(alcoxy) phenyleneethynylene type macromolecules, very little work can be found in the literature devoted to understanding their supramolecular behavior with the aim to obtain oriented films. Within this context, we present a supramolecular order study of a 2,5-bis(dodecanoxy) phenyleneethynylene-butadiyne series of oligomers in the solid state, Fig. 1, whose syntheses, spectroscopic and photophysical properties were reported elsewhere.17 These rod-like macromolecules by themselves resemble bricks, and low dichroic rates between 0.2 of 1.0 are obtained by rubbing thin films. We found that indeed the series exhibits wideranging mesophases, which are dependent on the oligomer’s length. In general, these 2,5bis(dodecanoxy) ethynylene oligomers exhibit a mesomorphic behavior similar to those of the (cholesteryl) benzoateethynylenes.16 Their stacking as brick-like moieties, which in turn are randomly oriented as determined by HRTEM, is responsible for the low dichroic values. The supramolecular order was determined by SWAXS, where the average alkyl chain distances within the lamellae could be determined and showed a tilt angle dependent on the oligomer’s length. The strong π-π interaction between conjugated chains was in particular evidenced by HRTEM, electron diffraction patterns and by determining their FFTs. The blocks of stacked conjugated molecules were clearly identified with a calculated periodicity of 0.33 nm. Unexpectedly, this reiterative value of 0.33 nm was also found by STM, suggesting that the molecules stand perpendicular to the graphite surface.

Experimental Section Equipment: DSC analyses were carried out on a DuPont 951 instrument under nitrogen at a heating rate of 10 °C/min and using 5-8 mg of sample. Optical textures were captured with an Olympus BX60 polarizing optical microscope coupled with a Mettler FP84HT hot stage. Small and wide angle X-ray scattering patterns were obtained with an Anton Paar SAXSess mc2 SWAXS instrument using CuKα radiation at a wavelength of 0.1542 nm. For electron microscopy studies, all of the materials were deposited by casting from CHCl3 (2 mg/mL) solutions on lacey carbon grids and were examined by SAED and HRTEM techniques in an FEI-TITAN-200 kV field emission gun microscope, which has a symmetrical condenserobjective lens type S-TWIN (with an spherical aberration Cs = 1.25 mm). Samples 3 ACS Paragon Plus Environment

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analyzed in cryogenic mode were placed into a holder that uses liquid nitrogen to maintain a negative temperature during the analysis in a Cryo-TEM (JEOL 2010, 200 kV) microscope and the images were acquired with a CCD camera. The tunneling conditions used are given in the corresponding figure captions and were taken at ambient conditions using a multimode scanning microscope from Digital Instruments and a Nanosurf Easyscan 2. Electrochemically etched tungsten wires were used as STM tips, which were washed with an NH4OH solution to remove residual tungsten oxide. Highly oriented pyrolytic graphite (HOPG) from SPI (grade SPI-2) was used as the semiconductor and orienting support for the conjugated molecules. The surface of the graphite was cleaned by the adhesive tape cleavage method.

Results and discussion Thermal behavior and solid state organization. The thermal behavior of the oligomers series, Fig. 1, was examined by differential scanning calorimetry (DSC), polarized-light optical microscopy (POM) and small and wide angle X-ray scattering (SWAXS). The thermograms of the series are shown in Fig. 2. As can be seen, 2DAc and 4DAc present well-defined melting peaks at 86 °C (∆Hm = 122 J/g) and 58 °C (∆Hm = 24 J/g) and crystallization peaks at 47 °C (∆Hc = -102 J/g) and 48 °C (∆Hc = -25 J/g), respectively. The fusion and crystallization enthalpies for 2DAc are almost five times higher than those of 4DAc due to its polycrystalline nature, Fig. 1S-a (electronic supplementary information); 4DAc develops very small crystals during the cooling process, which gives rise to spherulite-type growth, Fig. 2c. Upon heating, both 6DAc and 8DAc oligomers give a series of broad transitions between 61 to 105°C and 34 to 123°C, respectively. Melting and clearing points were clearly identified by POM and DSC. When both oligomers were cooled very slowly from the isotropic liquid, small needles for 6DAc (Fig. 1S-d) and filaments for 8DAc, Fig. 2g, were observed, giving rise later to birefringent textures, Fig 2h. However, at lower temperatures, ~71 °C for 6DAc and ~55 °C for 8DAc, homeotropic domains appeared, Fig. 2i, which later changed to an oily, streak-like texture observable only for 8DAc, Fig. 2j. The homeotropic phase is likely due to the perpendicular alignment of the molecules with respect to the substrate surface18 (according to their SAXs patterns, at 4 ACS Paragon Plus Environment

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these temperatures, the molecules are tilted almost 45°), while the oily streak texture could be related to a nematic phase. We observed that both oligomers present fluidity when pressed and/or heated between two glass plates and at room temperature are pasty birefringent materials, i.e., features of their liquid crystal behavior. Further information of the structure of the liquid-crystalline phases of the series was obtained from the X-ray diffraction patterns, Fig. 3. First, the polycrystalline nature of 2DAc was re-confirmed by the number of diffraction peaks exhibited in the diffraction pattern, while the diffractogram of 4DAc is totally different. A series of first order peaks centered at 2θ of 2.54, 5.14 and 7.26 with a ratio of ca. 1:2:3 are indicative of a lamellar system and representative of a smectic phase with a corresponding layer spacing d, of 3.48 nm. In this respect, the theoretical distance of its more extended conformation determined from the equilibrium geometries through Density Functional Theory, was of 3.68 ± 0.0086 nm,17 suggesting that the alkyl chains are tilted 19° with respect to the normal and is thus a signature of a tilted smectic phase, such as is illustrated in the model in Fig. 4 for 6DAc. It is worth noting that, at higher angles, two sets of broad bands coexist with the well-defined intense peaks. The first set at 2θ = 20.19, 20.75 and 21.13° with corresponding distances of 0.439, 0.428 and 0.420 nm are attributed to the distance between alkyl chains, Fig. 3. The second set of peaks centered at 2θ = 23.35 and 24.76° with corresponding distances of 0.381 and 0.356 nm are assigned to the distance between conjugated chains, and suggest a strong π-π interaction for 4DAc. In general 4DAc can be classified as an ordered crystal smectic material. The crystal smectics have no liquidity and possess a long range positional order, in this case, imparted by the flexible dodecanoxy side chains (0.43 nm), and smectic layer order of the rigid PPE chains (0.37 nm) in an orthogonal direction. The multiple peaks in the X-ray scattering wide angles, therefore are evidence of a possible columnar phase arrangement. In contrast, 6DAc shows only one sharp reflection peak at 2θ of 2.40°, d(001) of 3.681 nm and a broad peak at 2θ of 21.13° providing a signature of a smectic A phase in the lamellae. However, upon heating, the diffractograms revel that: i) the layer spacing decreases, because molecules tilt 15° at 50°C and 37° after 70°C, signifying a change to a tilted smectic phase; ii) a second order peak appears at 4.16°, d 2.12 nm; iii) and, in addition, sharper peaks also appear at the wide angle region coexisting with the diffuse band. The two former features are indicative of a type ordering of the molecules within the 5 ACS Paragon Plus Environment

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smectic layers. We have observed that PPE materials in general attain more order by heating below their transition temperature (a kind of annealing). Concerning 8DAc, the diffractogram at 30°C shows a distribution of sharp peaks at low angles, which average 2.75°, d 3.21 nm, and meaning that the molecules are tilted 29°. Since the limit between non-ordered smectic and nematic phases is very narrow, a possible “skewed cybotatic nematic”16,19 or “De Vries Smectics”20 phase could be considered for this material. However, after heating, the diffractograms revealed that the relatively diffuse peak at low angles for 8DAc becomes two well defined lamellar peaks with distances of 3.2 and 2.5 nm with tilting angles of 30° and 47°, whereas, at higher angles, sharper bands coexist with the diffuse band as observed for 6DAc, and, as well, indicative of partial ordering of the side chains of the molecules within the smectic layers. Actually, the homeotropic texture observed by POM, Fig. 2i, is consistent with this supramolecular order mesophase. In general, all of these PPEs have been considered as sanidic LC materials, as a term to classify their mesomorphic behavior,21 and because of their shape,7 which can be visualized as brick-like.18 The bricks are composed of packages of molecules with the coexistence of at least two supramolecular ordered domains driven by tilting of the alkyl chains. These bricks are oriented in all directions as is sketched in Fig. 4 III.

High Resolution Transmission Microscopy (HRTEM). All of the materials were analyzed by HRTEM. After many attempts to analyze 6DAc and 8DAc, we realized that, after some minutes of exposure to the TEM experimental conditions, the two materials became fluid and the observed periodicities disappeared giving rise to ordered domains embedded in isotropic phases, or, as well, the materials moved constantly making it difficult to acquire images. To overcome this behavior, we used the Cryo-TEM mode, which allowed the acquisition of good quality images as that of 6DAc shown in Fig. 5, as a representative example of the series (supplementary information). In general, all the images helped to confirm the sanidic character of all the materials. The images revealed that: i) in planar view, what is seen, corresponds to the phenyleneethynylene backbones with the alkyl chains protruding perpendicularly, Fig 4 II, ii) molecules are randomly oriented, Fig. 5 left, and are packaged in blocks as is also confirmed by their electron diffraction patterns (SAED), Fig. 6, where many diffraction spots can be seen and that can actually be 6 ACS Paragon Plus Environment

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visualized in the sketch of Fig. 4 III, iii) the calculated periodicity is of 0.33 ± 0.018 nm corresponding to distances between phenyleneethynylene chains, Fig. 5 right, confirming the strong π-π interaction that governs the package of conjugated skeletons.

Scanning Tunneling Microscopy (STM). In our interest to corroborate the structural parameters of the series obtained by SWAXS, we carried out STM of 4DAC, 6DAc and 8DAc on HPOG, by following the experimental conditions used in different articles on oligomers and polymers of the PPE type. In particular, we followed the work of G. Thomas22 on phenyleneethynylene-butadiyne oligomers. Our idea was to find both, the conjugated backbone lengths and the distance of extreme to extreme of the dodecanoxy side chains; we hypothesized that molecules should lie flat on the basal plane of the HPOG and proceeded to calculate their unit cell parameters. However, and after many attempts to obtain adequate images, we obtained the length of the 4DAc oligomer, but the distance between the conjugated chains did not coincide with that expected. Two concentrations were evaluated for the analysis; 10 mg/mL in phenyloctane and 0.02 mg/mL (~5 µmol) in THF:1,2,4-trichlorobenzene (1:9), using two configurations for samples in the STM systems: horizontally in the multimode scanning probe microscope and vertically in the Nanosurf microscope. The solutions were drop casted on the HOPG surface, either by drying the solvent or by partially wetting the surface before analysis; the obtained images were the same as that shown in Fig. 7 for 4DAc. The conjugated chains of 4DAc are seen as bright rods, due to their high electron density that generates a high tunneling current at the STM tip. The calculated molecular length is 2.48 nm (theoretical: 2.8 nm). From these images, it can be inferred that: i) molecules are aligned parallel with respect to the nearest neighbor with a separation distance of 0.34 nm, Fig. 7a,c and parallel to the HOPG substrate surface, but in a sideways, vertical standing position perpendicular to the HOPG surface through their side chains. ii) The molecules pack in blocks in a lamella type fashion, as observed in the high-resolution STM image (Fig. 7c), and that this packing is due to the π-π interaction between the conjugated chains, iii) the molecules, however, are intercalated between the lamellae, leading to the formation of a stepwise arrangement as described by Thomas22 for meta-carboxylic acids terminated oligomers, filling so the maximal volume, Fig. 7e, but also explaining the difference of 0.32 nm between the 7 ACS Paragon Plus Environment

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theoretical and experimental values. It is worth mentioning that in Fig. 7d, we observed that the so called lamellae are superposed each on the other in such a way that just half of the 4DAc molecule is exposed in a manner analogous to roof tiles on a house. This particular behavior was found in a region where the film thickness was high. In general, we believe that even when solutions are very dilute, the tendency of the conjugated backbones is to self-assemble forming blocks of molecules, a phenomenon that occurs during the deposition and that is promoted during the solvent evaporation. Unfortunately we could never get well defined images of 6DAc and 8DAc as aggregates were ever much evident, likely associated with a stronger π-π interaction in these two oligomers due to their longer length. From these results and from making a comparison with similar oligomers reported in the literature, we hypothesize, that in carboxylic acids terminated oligomers, the hydrogen bonding is more dominant than the π-π interaction (the carboxylic acids dimerize) driving the molecules to physically polymerize, and, if, in addition, they are composed of two, three or four carboxylic acids,22,23 the 2D net formed (with different patterns) forces, in turn, the molecules to lie flat on the HPOG, where now the π-π interaction plays its role. However, this hypothesis does not completely explain the fact that Thomas was able to obtain cell parameters from quality STM images for a phenyleneethynylene trimer24 (where the central phenylene is composed of 2,5-bis (hexyloxy) chains) and a symmetrical phenyleneethynylene-butadiyne tetramer22 (where the two central phenyl-butadiynes are composed of 2,5-bis (hexyloxy) chains). He found that their molecular organization resulted from different modes of the alkyl side chains with the ethynylene moieties CH· π interaction. This finding made us hypothesize further that, it is either the long alkyl chains, or the number of the alkyl chains on the phenyls (or both), that facilitates the occurrence of the π-π interaction between the conjugated backbones, and that this may explain the fact that Höger,25 could also obtain the unit cell parameters of a 2,5-bis(hexyl)benzene-butadiyne tetramer, where interdigitation of the alkyl side chains occurs. On the basis of these results, we are currently designing and synthesizing new oligomers, similar to that of 4DAc, but carboxylic acid terminated, and of the butadiyne type as the repetitive moiety that could help clarify the latter hypothesis. 8 ACS Paragon Plus Environment

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Conclusions Strong π-π interactions dominate between the conjugated chains in this series of rod-like oligomers with 2, 4, 6 and 8 phenyleneethynylene moieties. These interactions give rise to: i) molecules that self-assemble in blocks resembling bricks or board-like shapes that can be categorized as sanidic LC as a term to classify their mesomorphism; ii) bricks that are randomly oriented as observed by HRTEM and SAED, iii) molecules that are intercalated in a step-wise fashion between blocks or lamellae as seen by STM, and iv) molecules that aggregate spontaneously during the deposition or during solvent evaporation. As seen by microscopy, the conjugated molecules align parallel to each other with an average distance between the molecules of 0.32 ± 0.017 nm by HRTEM, 0.34 nm by STM and of 0.36 ± 0.017 nm by X-ray scattering. The X-ray scattering patterns suggest a crystal tilted smectic phase for the tetramer, while the hexamer presents a SmA order at room temperature that changes to tilted smectic at 50°C; the octamer presents a cybotactic nematic order. Almost all of the molecules in which the latter phase has been investigated have had bent rather than rod-like structures.8,19,26 These findings help to understand why rubbed films of PPEs exhibit low dichroism and it seems to be difficult to practically obtain higher values. A possible alternative, however, would be to use mesogens instead of the dodecanoxy side chains.

Associated content Supplementary Information. POM and HRTEM images of 2DAc, 4DAc and 8DAc are provided. This material is available free of charge via the internet at http://pubs.acs.org.

Acknowledgements This work was financially supported by CONACYT through the project 232753 Laboratorio Nacional de Materiales Grafénicos and the United States Air Force Office for Scientific Research (AFOSR) through the grant FA9550-11-1-0169. Authors also thank Gabriela Padrón, Guadalupe Mendez and Enrique Díaz for their technical assistance.


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(22) Zalake, P.; Thomas, K.G. Role of Hydrogen Bonding on the Self-Organization of Phenyleneethynylenes on Surfaces. Langmuir 2013, 29, 2242-2249. (23) Zhao, J.–F.; Li, Y.-B.; Lin, Z.-Q.; Xie, L.-H.; Shi, N.-E.; Wu, X.-K.; Wang, C.; Huang, W. Molecule Length Self-Assembly Behavior of Tetratopic Oligomeric Phneylene-Ethynylene End-Capped with Carboxylic Groups by Scanning Tunneling Microscopy. J. Phys. Chem. C 2010, 114, 9931-9937. (24) Yoosaf, K.; James, P.V.; Ramesh, A.R.; Suresh, C.H.; Thomas, K. G. SelfOrganization of Phnyleneethynylene into Wire-Like Molecular Materials on Surfaces. J. Phys. Chem. C. 2007, 111, 14933-14936. (25) Mössinger, D.; Jester, S.-S.; Sigmund, E.; Müller, U.; Höger, S. Defined Oligo(pphenylene-butadiynylene) Rods. Macromolecules 2009, 42, 7974-7978. (26) Lehmann, M.; Seltmann, J. low temperature Enantiotropic Nematic Phase from Vshaped, Shape-persistent Molecules. Beilstein J. Org. Chem. 2009, 5, 1-9.


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Langmuir

Captions to Tables and Figures

Table 1. Experimental calculated diffraction spacing d(100) at a given 2θ angle and as a function of the temperature for the 2,5-bis(dodecanoxy)ethynylene-butadiyne series. L is the theoretical molecular length on its more extended conformation from aliphatic to aliphatic chain and l corresponds to the conjugated backbone length. The molecular tilt angle was calculated from: cosϕ = d(100)/L.

Figure 1. Chemical structure of the 2,5-bis(dodecanoxy) phenyleneethynylene-butadiyne oligomers labeled as the dimer (2Ac), tetramer (4DAc), hexamer (6DAc) and octamer (8DAc) studied in this work.

Figure 2. DSC traces of the oligomer series; second heating and cooling cycle performed at scanning rates of 10 °C/min under nitrogen. Values correspond to the melting or crystallization enthalpies, while letters correspond to the POM images taken during the cooling cycle. Only the most relevant textures are shown in the figure, the rest are reported in the supplementary information; magnification: 20x.

Figure 3. X-ray diffractograms patterns of the oligomer series taken at different temperatures.

Figure 4. (I) 3D molecular conformation and (II) top view of 6DAc as an example of the molecular ordering determined by B3LYP/6-311G** level. The L,

l

and φ

molecular net parameters are summarized in Table 1, while a and b denote the average distances between alkyl chains (0.429 nm) and between phenyls (0.365 nm), respectively. (III) Sketching of the proposed supramolecular packaging of the oligomers.


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Figure 5. (Right) Low resolution TEM image of a film of 6DAc deposited on a Laceycarbon grid taken in cryogenic mode; lines indicate the package of molecules that are randomly oriented. (Left) High resolution TEM image with the determined periodicity of 0.33 nm corresponding to the phenyl-phenyl distance between molecules as is sketched in Figure 4 (II).

Figure 6. Selected area electron diffraction (SAED) patterns of cast films of the oligomer series on Lacey-carbon grids: 2DAc and 4DAc were taken under TEM experimental chamber conditions, while 6DAc and 8DAc were taken under cryogenic mode.

Figure 7. (a) 2D STM image of 4DAc on HOPG (pheyloctane): Vbias = -540 mV, It = 250 pA. The calculated distance of 0.34 nm matches the distance between conjugated chains as is intended to depict the superposed sketched molecular design, (b) the related 3D image. (c) Corresponds to the high resolution image: Vbias = -550 mV, It = 350 pA and (d) is its related 3D image. (e) Representation of the step-wise order of the oligomers from a top view.


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Langmuir

Table 1.

Oligomer 4DAc

6DAc

b

Τ [°C]

2θ [°]

d (100) [nm]

a L [nm]

[nm]

30 50 70

2.54 2.51 2.51

3.47 3.52 3.52

3.68 ± 0.0086

2.80± 0.022

30 50 70 90

2.40 2.48 3.01 2.99

3.68 3.56 2.93 2.95

3.68 ± 0.0086

4.19± 0.007

30 2.75 3.21 50 2.75 3.21 3.68 ± 0.0086 80 2.78, 3.52 3.17, 2.51 100 2.75, 3.46 3.21, 2.55 a Theoretical molecular length in its more extended conformation. b Theoretical length of the pheneyleneethynylene-butadiyne backbone.

l

8DAc


5.63± 0.0085

Tilt angle φ [°] 19 17 17 3 15 37 37 29 29 30, 47 29, 46

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Figure 1


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Figure 2 122 J/g

2DAc

Flow

102 J/g 24 J/g

a

4DAc

25 J/g

b

c

32 J/g

6DAc

Heat

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31 J/g

f

4 J/g

8DAc j

1 J/g

d e 3 J/g

0

10 J/g g

i h

-20

c

17 J/g

20 40 60 80 100 120 140 Temperature (°C) g

j

i


h

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Figure 3

8DAc/80°C

Intensity (a.u.)

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8DAc/30°C

6DAc/70°C 6DAc/30°C 4DAc/30°C

2DAc/30°C

5

10

15

20 2θ(°)

25


30

35

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Figure 4


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Figure 5


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Figure 6


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Figure 7


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TOC graphic


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Chemical structure of the 2,5-bis(dodecanoxy) phenyleneethynylene-butadiyne oligomers labeled as the dimer (2Ac), tetramer (4DAc), hexamer (6DAc) and octamer (8DAc) studied in this work. 146x92mm (300 x 300 DPI)

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Langmuir

DSC traces of the oligomer series; second heating and cooling cycle performed at scanning rates of 10 °C/min under nitrogen. Values correspond to the melting or crystallization enthalpies, while letters correspond to the POM images taken during the cooling cycle. Only the most relevant textures are shown in the figure, the rest are reported in the supplementary information; magnification: 20x. 196x167mm (96 x 96 DPI)


Langmuir

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X-ray diffractograms patterns of the oligomer series taken at different temperatures. 169x136mm (96 x 96 DPI)


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(I) 3D molecular conformation and (II) top view of 6DAc as an example of the molecular ordering determined by B3LYP/6-311G** level. The L, l and Φ molecular net parameters are summarized in Table 1, while a and b denote the average distances between alkyl chains (0.429 nm) and between phenyls (0.365 nm), respectively. (III) Sketching of the proposed supramolecular packaging of the oligomers. 270x317mm (96 x 96 DPI)


Langmuir

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(Right) Low resolution TEM image of a film of 6DAc deposited on a Lacey-carbon grid taken in cryogenic mode; lines indicate the package of molecules that are randomly oriented. (Left) High resolution TEM image with the determined periodicity of 0.33 nm corresponding to the phenyl-phenyl distance between molecules as is sketched in Figure 4 (II). 342x190mm (96 x 96 DPI)


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Selected area electron diffraction (SAED) patterns of cast films of the oligomer series on Lacey-carbon grids: 2DAc and 4DAc were taken under TEM experimental chamber conditions, while 6DAc and 8DAc were taken under cryogenic mode. 274x288mm (96 x 96 DPI)


Langmuir

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(a) 2D STM image of 4DAc on HOPG (pheyloctane): Vbias = -540 mV, It = 250 pA. The calculated distance of 0.34 nm matches the distance between conjugated chains as is intended to depict the superposed sketched molecular design, (b) the related 3D image. (c) Corresponds to the high resolution image: Vbias = -550 mV, It = 350 pA and (d) is its related 3D image. (e) Representation of the step-wise order of the oligomers from a top view. 335x374mm (96 x 96 DPI)


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Supramolecular Order of 2,5-Bis(dodecanoxy)phenyleneethynylene

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