Additive Perturbed Molecular Assembly in Two- Dimensional Crystals: Differentiating Kinetic and Thermodynamic Pathways Seokhoon Ahn and Adam J. Matzger* Department of Chemistry and the Macromolecular Science and Engineering Program University of Michigan, Ann Arbor, Michigan 48109-1055 matzger@umich.edu Supporting Information (1) Synthesis and characterization of molecules investigated (2) Experimental details (3) 2D crystals dependent on 18-amide: additive molar ratio (4) 2D crystal of 17-triester. (5) Ostwald ripening of a mixture of 18-amide and 17-triester (6) Phase transformation from phase III to II at 25 µm 18-amide solution. (7) Determination of the difference of the activation energy ( E a ) from phase III to II to verify an additive effect. S1
(1) Synthesis and characterization of molecules investigated 4-dodecyloxybenzamide (12-amide), 4-octadecyloxybenzamide (18-amide) and diheptadecyl isophthalate (17-m-diester) were synthesized as previously reported. 1-2 Materials: 1,3,5-benzenetricarbonyltrichloride was purchased from Aldrich. 1-heptadecanol and pyridine were purchased from Acros Organics and all solvents were purchased from Fisher Scientific. All reagents were used as received. Synthesis of triheptadecyl benezene-1,3,5-tricarboxlate (17-triester): To a mixture of 1-heptadecanol (2.90 g, 11.30 mmol) and pyridine (15.1 mmol) in CH 2 Cl 2 (50 ml) was added 1,3,5-benzenetricarbonyl trichloride (0.50 g, 1.88 mmol). The mixture was heated to reflux for 5 days. The organic layer was washed with H 2 O and brine and dried over anhydrous MgSO 4. The solvent was removed under reduced pressure. Pure product was obtained by column chromatography on silica gel with 15% ethyl acetate in hexanes as eluent. Yield: 1.10 g, 63.2%. mp: 69.0-70.0 C. 1 H NMR (300 MHz, CDCl 3, δ): 0.88 (t, J = 6.6 Hz, 9H), 1.20-1.57 (m, 84H), 1.81 (quint, J = 7.0 Hz, 6H), 4.38 (t, J = 6.6 Hz, 6H), 8.85 (s, 3H). 13 C NMR (100 MHz, CDCl 3, δ): 14.32, 22.90, 26.20, 28.88, 29.58, 29.77 (broad), 32.14, 66.06, 131.71, 134.62, 165.33. Anal. Calcd for C 60 H 108 O 6 : C 77.87, H 11.76; Found: C 78.02, H 11.77. HRMS (EI) calcd. for C 60 H 108 O 6 (m/z): 924.8146, found: 924.8120. (1) Ahn, S.; Morrison, C. N.; Matzger, A. J. J. Am. Chem. Soc. 2009, 131, 7946-7947. (2) Plass, K. E.; Kim, K.; Matzger, A. J. J. Am. Chem. Soc. 2004, 126, 9042-9053. S2
(2) Experimental details Scanning tunneling microscopy: A Nanoscope E STM (Digital Instruments) was used for all imaging. Highly oriented pyrolytic graphite (HOPG) (SPI-1 grade, Structure Probe Inc.) was used as a substrate for monolayer formation. A 1-phenyloctane solution of the desired molecule or mixture was made and placed on freshly cleaved HOPG to obtain a self-assembled monolayer. The tips were made from Pt/Ir wire (20% Ir, 0.010 inch diameter, California Fine Wire) by mechanical cutting. STM imaging was performed using a quasi-constant height mode under ambient conditions and typical STM settings include 300 pa of current and 700-900 mv of bias voltage (sample positive). All images are unfiltered. Computational modeling: The packing structures apparent from the metrics and symmetry of the STM images were modeled using Cerius 2 version 4.2 (Accelrys Inc.). Energy minimization was performed using a COMPASS forcefield. This method has been shown to yield reasonable energies for the relative stabilization of three dimensional polymorphic packing in molecular crystals (Mitchell- Koch, K; Matzger, A. J. J. Pharm. Sci. 2008, 97, 2121-2129.). Non-periodic assemblies from these models were overlaid on a fixed graphite slab and energy minimized to get the optimized packing structure on HOPG. General preparation of solutions: The mixtures with additives were prepared using 100 µm of 18- amide and 100 µm of an additive. For the verification of the concentration effect, 1000 µm of 17-mdiester was also used to prepare mixture solutions. The molar ratio was controlled by using different volume of each solution. For example, 0.1 µl of 100 µm of 18-amide and 0.9 µl of 100 µm of an additive were used to make a mixture with 1:9 molar ratio. S3
(3) 2D crystals dependent on 18-amide : additive molar ratio Figure S1. 2D crystals from the mixture of 18-amide and 17-m-diester. Figure S2. 2D crystals from the mixture of 18-amide and 17-triester. Figure S3. 2D crystals from the mixture of 18-amide and 12-amide. S4
(4) 2D crystal of 17-triester Figure S4. High resolution STM image (20 20 nm 2 ) of 2D crystal of 17-triester. One alkyl chain for every four molecules in the unit cell is not imaged suggesting that it may be desorbed into the solution. The missing alkyl chain is represented by the green rectangular. S5
(5) Ostwald ripening of a mixture of 18-amide and 17-triester Figure S5. STM images (50 50 nm 2 ) showing Ostwald ripening observed from the mixture of 18- amide and 17-triester (2:1). The disordered assembly of 18-amide transforms to a more ordered assembly (phase I). S6
(6) Phase transformation from phase III to II at 25 µm 18-amide solution. Figure S6. STM images (top: 100 100 nm 2, bottom: 50 50 nm 2 ) showing the phase transformation to the rhombic nanoporous network (phase II) in 25 µm 18-amide solution where the honeycomb network (phase III) is observed as an intermediate form. S7
(7) Determination of the difference of the activation energy ( E a ) from phase III to II to verify an additive effect. The rate of phase transformation can be expressed as dn/dt = - ν N exp(-e a /RT) at temperature T, where E a is the activation energy, R is gas constant, and ν is a preexponential factor. Thus, the difference of the activation energy ( E a ) can be obtained by E a = E a2 - E a1 = - RT (ln (d(lnn)/dt)2 - ln (d(lnn)/dt) 1 ) where d(ln N )/dt can be obtained by counting the number of molecules associated with the phase transformation. The average values of d(ln N )/dt were -0.031±0.007 sec -1 for the homogeneous solution of 25 µm of 18-amide and -0.0034±0.0012 sec -1 for the mixture. Therefore, the E a was obtained as 1.33 ± 0.36 kcal/mol. Figure S7. The reaction coordination diagram describing the phase transformation from phase I to II where III is an intermediate form: (left) the homogeneous solution of 18-amide and (right) the mixture with 12-amide. S8