Spreading Films of Anthracene-Containing Gelator Molecules at the

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Interface-Rich Materials and Assemblies

Spreading Films of Anthracene-Containing Gelator Molecules at the Air/Water Interface: Nanorod and Circularly Polarized Luminescence Chenchen Yang, Penglei Chen, Yan Meng, and Minghua Liu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b03478 • Publication Date (Web): 25 Jan 2019 Downloaded from http://pubs.acs.org on January 26, 2019

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Spreading Films of Anthracene-Containing Gelator Molecules at the Air/Water Interface: Nanorod and Circularly Polarized Luminescence Chenchen Yang,1, 2 Penglei Chen, 1, 2 Yan Meng,3 and Minghua Liu* 1,2, 3, 1

Beijing National Laboratory for Molecular Science, CAS Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, No.2 ZhongGuanCun BeiYiJie, 100190, Beijing P. R. China. 2

3 CAS

University of Chinese Academy of Sciences, Beijing 100049, P. R. China

Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience

and Technology (NCNST) No.11 ZhongGuanCun BeiYiTiao, 100190 Beijing, P.R. China

ACS Paragon Plus Environment

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ABSTRACT

Two enantiomeric gelator molecules containing anthracene moiety were assembled at the air/water interface and several new insights into the films of the gelator molecules were revealed. When these molecules were spread at the air/water interface, they formed the nanorod structured monolayers and could be subsequently transferred to the solid substrate. The formed LB films showed both optical activity and circularly polarized luminescence (CPL) due to the chirality transfer upon assembling. The dissymmetric factors of the CPL in the LB films were enhanced nearly five times than those in gel systems. Through the formation of the organized nanofilms, the arrangement of the molecules become compact and the film showed enantioselectivity to chiral species, while the molecular solution could not.

Keywords: Langmuir−Blodgett film; Chirality; Circularly Polarized Luminescence; Gelator; Enantioselectivity; Nanorod; Anthracene


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INTRODUCTION Langmuir monolayer and related Langmuir−Blodgett (LB) as well as Langmuir–Schaefer (LS) films have received broad attention for a long time as a technique for the construction of molecular films.1-3 The technique offers an excellent way to control the molecular orientation and packing in a twodimensional mode at the air/water interface. Consequently, numerous amphiphiles have been designed and uniformly organized molecular films have been fabricated by the LB techniques at air/water interface. With the development of nanotechnology, the LB technique is further deemed as a useful platform to construct nanostructure via the bottom-up approach.3-6 At the same time, the techniques were proposed to provide two-dimensional nanostructures.7-9 Except for the classical amphiphiles, nonclassical building blocks could be spread at the air/water interface, such as polymers,9−11 nanoparticles,12−14 nanowires,15,16 nanotubes,17,18 nanosheets,19,20 etc.21 and varieties of nanostructures and their alignment were formed. Instead of the uniform molecular films, these nanostructured films could also be regulated and show potential applications in sensors,22,23 electronic memory,24 and field effect transistors.25 Besides these classical or non-classical amphiphiles or nanomaterials, recently, gelator molecules have been attracting great interest.26-29 The gelators refer to those molecules that can form supramolecular gels in certain solvents. Many of the gelators are amphiphiles and can self-assemble into various nanostructures during their gelation in solution.26-29 Since the solution provides a three dimensional environment, it is interesting to see how will the gelator molecules behave in a two-dimensional air/water interface. In this paper, we selected two enantiomeric gelator molecules: N,N’-bis(octadecyl)-L(D)-(anthracene-9-carboxamido)-glutamic diamide (abbreviated as LGAn/DGAn) and investigated their molecular films through the air/water interface, as illustrated in Figure 1. Several new insights into the LB films of the gelator molecules were revealed. Firstly, the gelator molecules self-assembled into nanofibers in solution30, it is interesting to find that when these molecules were spread at the air/water interface, they formed the nanorod structured films. It seems that the self-assembly habit of the molecules play an important role in their


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self-assembly either in gel or in 2D air/water interface. Secondly, since these molecules contain chiral center and fluorophore, the formed LB film showed both optical activity and circularly polarized luminescence (CPL).31 CPL refers to the excited-stated chirality of the system and has potential applications in 3D display32, asymmetric catalysis33 and chiral sensing.34 Considering the future application, it is important to make it into films. In this sense, the CPL properties of the LB films will provide a new platform for the investigation, which has so far scarcely reported. Thirdly, because of the formation of the films, the arrangement of the molecules become compact and a new function of enantioselectivity was observed, which could not be achieved by simple molecules or in dilute solution.

Figure 1. Schematic illustration of the formation of LGAn or DGAn nanorods films at the air/water interface. The formed films display circularly polarized luminescence (CPL) depending on the handedness of the formed nanorods. In addition, the LB films show enantioselectivity to chiral species, while the solution did not.

RESULTS and DISCUSSION Air/Water Interfacial Assembly of LGAn and DGAn. The used compounds are N,N’-bis(octadecyl)L(D)-(anthracene-9-carboxamido)-glutamic diamide, abbreviated as LGAn or DGAn, respectively, which were synthesized by the covalent conjugation of anthracene acids with the dialkyl glutamide.30 These compounds are enantiomers with just opposite molecular chirality. Both LGAn and DGAn are excellent gelators.30 When the molecules dissolved in chloroform were spread at the air/water interface, they formed stable Langmuir monolayers, which can be characterized through the surface pressure-area (−A) isotherms. ACS Paragon Plus Environment

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Figure 2. The Surface pressure−molecular area isotherms of DGAn and LGAn on a pure water subphase at 25 ℃.

Figure 2 shows the surface pressure−molecular area (−A) isotherms of the LGAn (DGAn) spreading on water subphase at 25 °C. Both of the spreading films show the onset of surface pressure at ca. 0.71 nm2 per molecule. Upon compression, the surface pressure shows a gradual and then a linear increase, reaching the inflection point at around 45 mN·m−1. After that the surface pressure showed still a slow increase. By extrapolating the linear part of the isotherm to zero surface pressure, the limiting molecular area of LGAn and DGAn on the surface of pure water was calculated to be 0.66 nm2/molecule.


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Figure 3. AFM images of one-layer LB films of LGAn deposited onto a freshly cleaved mica surface from the water subphase at different surface pressures: (a, b) 15, (c) 30, (d) 45 mN·m−1. The room temperature is 25 ℃.

The monolayers were transferred onto the freshly cleaved mica surface and their atomic force microscopy (AFM) was measured. A vertical lifting method with an uptake speed of 1 mm/min−1 was applied for the films deposited at various surface pressures. For the LGAn LB films at 15 mN/m, nanorods with a height of 2.9-4.3 nm were observed (Figure 3a and 3b), wherein many packed nanorods formed. When the surface pressure was increased to 30 mN/m, the nanorods were packed closer than the LB films deposited at 15 mN/m (Figure 3c). In addition, by further compressing the spreading film to the inflection point of 45 mN/m−1, the nanorods packed more densely (Figure 3d). However, the nanorod structures remained. It is the same for the DGAn LB films (Figure S1).


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The monolayer was further transferred to other solid substrates for characterizations. In this case, LS technique was applied to get more layers since the vertical transfer method could only afford a few layers, while the LS can provided multilayer transfer, which is enough for the film characterizations. Figure 4 shows the UV-Vis spectra of the LS films in comparison with those in chloroform solution. The UV−Vis spectrum of the LGAn (DGAn) in chloroform solution exhibits an intense absorption at 258 nm, which is attributed to the 1Bb absorption (Figure 4a).35 As shown in Figure 4b, a typical anthracene absorption in the region 330-400 nm, displaying four weak peaks at 347, 364, 384 and 396 nm, which can be attributed to the 1La band as well as the S0–S1 transition with different vibronic peaks,30,36 is also observed. In the transferred LS film, the 1Bb bands of the LS films of the LGAn (DGAn) show distinct hypsochromic shifted which maximum absorption at 250 nm, suggesting an Haggreation of the anthracene moiety in the films. On the other hand, the four weak absorption bands in the range of 330-400 nm show clear blue shift at 336, 352, 369 and 389 nm, respectively. The results indicate that the anthracene chromophores of the LGAn (DGAn) are arranged in H-aggregates at the air/water interface.35

Figure 4. CD spectra (top) and UV−Vis spectra (bottom) of DGAn (black line) and LGAn (red line) 40-layer LB films at 30 mN/m as well as LGAn in chloroform (dotted line).

Fourier transform infrared (FTIR) spectra were used to obtain insight into the driving force for the nanorods formation at the air/water interface. As indicated by the FTIR (Figure 5), the N-H stretching vibration at 3283 cm-1 for LGAn LS film was observed, which indicated the formation of hydrogen


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bond. In addition, the amide I band and II band appeared at 1639 cm-1 and 1551 cm-1 respectively, which indicated that both C=O and N-H were in the hydrogen bonding form.30,37-40 Furthermore, the NH stretching vibration, amide I band and amide Ⅱ band display the split bands, which suggested that there were more than one hydrogen bonds existing.39,40 In addition, two evident vibrations were observed at 2918 and 2847 cm-1, which attributed to the asymmetric and symmetric stretching vibrations of CH2, respectively.40,41 This result shows that the alkyl chains packed in an all-trans zigzag conformation.40,41 Accompany with the UV-Vis, the results indicate that synergistic effect of the hydrogen bonding interactions, the hydrophobic interactions of the long alkyl chains and strong π−π interactions are the main driving force for the formation of the LGAn (DGAn) LB film.

Figure 5. FT-IR spectra of 70-layer LS films of DGAn and LGAn at 30 mN/m-1.

Optical Activity and Circular Dichroism. Since the gelator molecules contain the chiral center, we further characterized the chiroptical activity of the transferred LS films with CD spectra, as shown in Figure 4. All of the CD measurements were carried out with rotation to eliminate the influence of linear dichromism (LD).51-53 DGAn LS films obtained from the water subphase show a positive Cotton effect (CE) at ca. 241 nm (Figure 4a), which is assigned to the 1Bb absorption of DGAn.31 In addition, the


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films display a negative Cotton effect at range of 300-410 nm (Figure 4b), which is ascribed to the 1La band of the anthracene. The results indicate that DGAn could form chiral supramolecular assemblies at the air/water interface. Moreover, the CD spectra of the LGAn LS films exhibit a mirror-imaged CE compared to the DGAn LS films (Figure 4). Fluorescence and CPL Properties of DGAn and LGAn LS Films. CPL used to evaluate the chirality of excited-state of assemblies is a unique property with regard to the chiral systems.30,42-44 As previously reported, the supramolecular gels formed by LGAn and DGAn possess two interesting properties, fluorescence and CPL.30 Herein, we further investigate the fluorescence and CPL of the LS films fabricated at air/water interface. As shown in Figure 6a, when it was excited at 370 nm, LGAn and DGAn LS films displayed relatively strong fluorescence. On the other hand, as shown in Figure 6b, different handedness CPL signals could be observed, wherein the emission maximum is at 460 nm and the excitation wavelength is set to 330 nm according to the 1La band of the anthracene.35 The relevance of the CD and CPL signals was investigated for comprehending the relationship between the groundstate supramolecular chirality and excited-state supramolecular chirality of the LS films. The results display that the LS films formed by DGAn show right-handed CPL (Figure 6b), as well as at range of 300-410 nm which is ascribed to the 1La band of the anthrancene,35 the CD spectra display negative Cotton effect (Figure 4b). While the LGAn LS films show left-handed CPL (Figure 6b), and the CD spectrum exhibits a positive Cotton effect at range of 300-410 nm (Figure 4b). The luminescence dissymmetry factor (glum) was used for evaluated the magnitude of CPL, and the glum is defined as glum = 2×(IL-IR)/(IL+IR), wherein IL and IR refer to the intensity of left hand righthanded CPL, respectively.45-47 An ideal left CPL is defined that the maximum glum value ranges from +2, while an ideal right CPL is defined the maximum glum value ranges from -2. However, when glum=0 indicate no circular polarization of the luminescence.30,47 Moreover, the glum (the maximum emission at 460 nm ) of the CPL signal is about -6.0×10-3 and 5.5×10-3 for DGAn and LGAn LS films, respectively,


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which is nearly 5 times larger than those in the gel system.30 It seems that the organized system will show more strong dissymmetry factors.47,48

Figure 6. (a) Fluorescene of DGAn and LGAn LS films; (b) CPL spectra of DGAn and LGAn LS films.

Enantioselective Recognition of DGAn and LGAn LS Films From the above sections, it can be seen that LGAn and DGAn LS films display relatively strong fluorescence when it was excited at 370 nm. It is well to be reminded that the fluorescence of LGAn and DGAn LS films remains unchanged, even though the LS films were immersed in water for 4 h (Figure S2). Moreover, because of the fixed handedness of the DGAn or LGAn chiral assemblies, the application of these systems for chiral recognition was studied. The devised strategy depends on the changes in fluorescence of DGAn or LGAn assemblies by dint of interaction with other small chiral molecules.

Figure 7. Changes in the fluorescence (460 nm emission) of LGAn and DGAn LS films upon dipping in aqueous solutions of D-(-)-tartaric acid and L-(+)-tartaric acid, respectively. (a) LGAn LS films recognize enantiomeric tartaric acid; (b) DGAn LS films recognize enantiomeric tartaric acid. Black curves stand for the LS films interacted with D-(-)-tartaric acid and red curves stand for the LS films interacted with L-(+)-tartaric acid.


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From the point of view of the molecular structure, each LGAn (DGAn) molecule contains three amide bands, which is expected to have subtle hydrogen bonding interactions with chiral acids. Therefore, the enantiotopic tartaric acids were selected as objects of chiral recognition. Experimentally, 40-layer LGAn or DGAn LS films were dipped into the aqueous solutions of L-(+)-tartaric acid and D-(-)-tartaric acid, respectively, and the corresponding fluorescence intensity changed dramatically depending on the molecular chirality of the tartaric acid (Figures 7). As shown in Figure 7a, when LGAn LS films were immersed into the aqueous solutions of L-(+)-tartaric acid and D-(-)-tartaric acid, respectively, the fluorescence of the LS films displays different degrees of enhancement. When LGAn LS films were dipped into L-(+)-tartaric acid, the rate of rise of the fluorescence intensity is evidently lower than the growth rate of the fluorescence intensity, wherein the LGAn LS films were immersed into D-(-)-tartaric acid. In addition, when the LS films were immersed for a certain period of time into the aqueous solution of tartaric acid, the fluorescence intensity was saturated. This observation indicates the occurrence of enantioselective discrimination between our LGAn LS films and the enantiomeric tartaric acid. At the same time, this could be validated by the fact that when DGAn LS films were dipped into the aqueous solutions of L-(+)-tartaric acid and D-(-)-tartaric acid, respectively, the growth rate of the fluorescence intensity of DGAn LS films soaking in L-(+)-tartaric acid is significantly higher the rate of rise of the fluorescence intensity of the LS films dipped into D-(-)-tartaric acid (Figure 7b). Such mutually interchangeable chiroptical responses of our LGAn and DGAn LS films towards the enantiomeric tartaric acid strongly confirm that our LS films could work as efficient stereoselective receptors. Moreover, all the changed fluorescene were shown in Figure S3. It should be noted that such phenomenon was also found for the other enantimeric molecules like L and D-tyrosine ( Figure S4) When the LS films interact with enantiomeric tartaric acids which show different molecular chirality, the changes in their fluorescence spectra could be different. And chiral recognition might be achieved. The interactions between the tartaric acid and LS films could change the molecular packing slightly, which causes the enhancement in fluorescence due to slight separation of anthracene.9 For the LGAn


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LS films, owing to the different molecular structure of the LGAn and D-(-)-tartaric acid, the molecular packing mode of the LGAn LS films is relatively loose, therefore, when the LGAn LS films interact with D-(-)-tartaric acid, the growth rate of the fluorescence intensity dramatically rise. However, when the LGAn LS films interact with L-(+)-tartaric acid, because of the similar molecular chirality of LGAn and L-(+)-tartaric acid, the molecular packing mode of the LGAn LS films is closer than the films interacted with D-(-)-tartaric acid. Hence, the increasing rate of the fluorescence intensity is lower than the films interacted with D-(-)-tartaric acid as shown in Figure 8c. Moreover, the UV-Vis spectra of the LS films upon interaction with enantiomers of tartaric acid are measured (Figure S5). As shown in Figure S5a, the red shifts at the 1La band of anthracene were also detected from the UV−Vis spectra of LGAn LS films interacting with tartaric acid. In addition, D-(-)-tartaric acid molecules, which induce the higher fluorescence enhancement, cause the largest red shift of the UV−Vis spectra of LGAn LS films. The similar results could be obtained in DGAn LS films system (Figure S5b). These results indicate that the interactions between LS films and the enantiomers of tartaric acid bring out influence in varying degrees on the molecular packing mode of the LS films, rendering successful chiral recognition towards tartaric acid. Since the LS films fluorescence intensity could be enhanced by tartaric acid, we further investigated the CPL of the LS films upon interaction with enantiomers of tartaric acid. Interestingly, the dissymmetry factors (glum) display amplification with increasing fluorescence as shown in Figure 8. Wherein, when LGAn LS film interacted with D-(-)-tartaric acid, the glum is higher than the glum of the film interacted with L-(+)-tartaric acid (Figure 8a), which is corresponding to the above results of the changes of the fluorescence. Similar phenomenon happened to DGAn LS filmswith L- and D-tartaric acid (Figure 8b).


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Figure 8. (a, b) Changes in the glum of LGAn and DGAn LS films upon dipping in aqueous solutions of D-(-)-tartaric acid and L-(+)-tartaric acid. All the glum values increased (c) Schematic illustration showing the possible reason of the chiral recognition of LGAn LS films for the enantiomeric tartaric acid. The insertion of the tartaric acid into the films could loosen the packing of anthracene, while the loosened extent was different depending on the molecular chirality of the tartaric acid. LGAn/ D-(-)-tartaric acid pair loosened the anthracene units more.

It is worth mentioning that the excellent chiral recognition properties of LS films maybe depend on the subtle molecular packing mode and the synergistic effect of different noncovalent interactions. The interactions between LGAn (DGAn) LS films and tartaric acid tend to help loosening the packing of anthracene units and thus enhanced the fluoresecene and CPL. However, the extent of the loosening is different depending on the molecular chirality of the tartaric acid.

CONCLUSION The gelator molecules LGAn (DGAn) containing an anthracene unit and dioctadecyl gluamide were found to form stable monolayer at the air/water interface. In spreading film, the molecuels organized to form a nanorod structure, in which the anthracene packed in an H-aggregates by means of π−π stacking. The fabricated LGAn (DGAn) LS films showed optical activity due to the chiral transfer from the chiral center localized at glutamic acid moiety to the whole assembly. Remarkably, the LB films showed CPL ACS Paragon Plus Environment

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with larger dissymmetry factors, which is nearly 5 times larger than those in gel systems. Furthermore, the fabricated LS films showed enantioselectivity to the chiral tartaric acid. With the enantioselective recognition, the dissymmetry factor of the CPL was further doubled. The results offer an excellent opportunity to further investigate the behaviors of the gelator molecules in a two-dimensional air/water interface as well as pave an important strategy for enantioselective recognition via LS films constructed by single component.

EXPERIMENTAL SECTION Materials. The synthesis and characterizations of the gelator molecules (L/DGAn) were published elsewhere.30 Chloroform was used as the spreading solvent for L/DGAn. Chloroform was purchased from Beijing Chemical Works. D-(−)-Tartaric acid and L-(+)-Tartaric acid were purchased from SigmaAldrich. D-Tyrosine and L-Tyrosine were purchased from Sigma-Aldrich. Ultrapure Milli-Q water (18 MΩ cm) was used in all cases. Procedures. All measurements were taken at 25 ℃ to avoid the surrounding interference. A chloroform solution of the L/DGAn (1× 10-4 M) was spread onto the surface of aqueous subphase (18.2 MΩ cm, 25 °C) to form the air/water interfacial assemblies. After allowing the solvent to evaporate for 20 min, the surfaces pressure-molecular area (−A) isotherms were recorded by compressing the floating film at a rate of 5 cm2·min−1 at 25 °C. The spreading films were transferred onto freshly cleaved mica using a vertical lifting method for AFM measurements with an upstroke of 1 mm·min−1 at different surface pressures. By the horizontal lifting method, 40-layer LS films were transferred onto quartz substrates for UV−Vis, and circular dichroism (CD) spectral measurements at 30 mN/m. 80-layer LS films were transferred onto quartz substrates for Circularly Polarized Luminescence (CPL) spectral measurements. And 70-layer LS films were transferred onto CaF2 optical windows and subject to the FT-IR measurements. The chiral recognition of the enantiomeric tartaric acid is dependent on the changes in fluorescence of L/DGAn assemblies. For this study, 40-layer L/DGAn LS films were


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transferred from the water subphase onto quartz substrates at a surface pressure of 30 mN/m. These 40layer L/DGAn LS films were subjected to fluorescence spectral measurements. When the LS films were dipped in an aqueous solution of enantiomeric tartaric acid and tyrosine (1 × 10−3 M), the changes of the fluorescence of L/DGAn assemblies were further analyzed. For the fluorescence measurements, the holder for membrane samples was used. 370 nm was set as the excitation wavelength; 5 nm was set as excitation and emission slits, and 1200 nm/min was set as the scan speed. The photomultiplier voltage was set to 700 V. All of the fluorescence spectral measurements were measured at a room temperature of 25 °C. Apparatus and Measurements. The surface pressure−area (−A) isotherm was recorded on a computer-controlled KSV-minitrough system with a surface area of 273 cm2 (L364 mm and W75 mm) (KSV Instruments, Helsinki, Finland). CD spectra were obtained using JASCO J-815 spectrometers. For the experiments, to eliminate the polarization-dependent reflections and avoid the possible angle dependence of the CD signal, the sample was immobilized perpendicular to the light path and at the meantime was rotated continuously using a custom build rotator.51-53 The method is possible to eliminate the artifacts from linear birefringence and LD effects, wherein we can obtain the linear birefringence- and LD-free CD spectra. The UV−Vis spectra were detected using a Hitachi UV-3900. FT-IR spectra were recorded on a JASCO FT/IR-660 Plus spectrophotometer with a wavenumber resolution of 4 cm−1 at 25℃. Fluorescence spectra were recorded on a Hitachi F-4600 fluorescence spectrophotometer. CPL measurements were performed with a JASCO CPL-200 spectrometer. AFM images were recorded on a Digital Instrument Nanoscope IIIa Multimode system (Bruker) with a silicon cantilever in the tapping mode (Silicon cantilevers of 30 μm in length with typical resonant frequencies of 400 kHz and with a spring constant of 4 N/m). All AFM images are shown in height mode without any image processing except flatting.


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ASSOCIATED CONTENT Supporting Information. AUTHOR INFORMATION Corresponding Author [email protected] Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB12020200), National Natural Science Foundation of China (21890734 and 51673050). REFERENCES (1) Ulman, A. An Introduction to Ultrathin Organic Films: From Langmuir−Blodgett to Self-Assembly; Academic Press, 1991; Vol. 354, p 120. (2) Giner-Casares, J. J.; Brezesinski, G.; Möhwald, H. Langmuir monolayers as unique physical models. Curr. Opin. Colloid Interface Sci. 2014, 19, 176-182. (3) Nie, H.-L.; Dou, X.; Tang, Z.; Jang, H. D.; Huang, J. High-Yield Spreading of Water−Miscible Solvents on Water for Langmuir−Blodgett Assembly. J. Am. Chem. Soc. 2015, 137, 10683-10688. (4) Rehman, J.; Araghi, H. Y.; He, A.; Paige, M. F. Morphology and Composition of Structured, PhaseSeparated Behenic Acid−Perfluorotetradecanoic Acid Monolayer Films. Langmuir 2016, 32, 5341-5349. (5) Gao, P.; Liu, M. Compression Induced Helical Nanotubes in a Spreading Film of a Bolaamphiphile at the Air/Water Interface. Langmuir 2006, 22, 6727-6729. (6) Liu, X.; Wang, T.; Liu, M. Porphyrin nanofiber patterning by air/water interfacial assembly: Effect of molecular structure, surface pressure, and ionic liquid doped subphase. J. Colloid Interface Sci. 2012, 369, 267-273.


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Table of Content

A Figure for Table of Contents Use: An anthracene-containing gelator molecules formed monolayers with nanorod structure and the subsequent transferred LS films exhibited welldefined CPL. In addition, depending on the changes of the fluorescence intensity, the chiral recognition of enantiomers of tartaric acid could be achieved.


Spreading Films of Anthracene-Containing Gelator Molecules at the

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