Influence of polar substituents on the epitaxy of oligothiophenes on graphite: A systematic STM investigation

Abstract

Fig. 5. Schematic representation of electrochemical annealing. Differently oriented domains are represented by differently oriented line patterns, and the dashed line refers to the boundary of the original domain.(1) Upon application of a cathodic potential, -E, monolayer dissolution begins at the domain boundary. (Z), (3) If the cathodic potential is applied for an amount of time sufficient for complete domain dissolution, subsequent application of an anodic potential leads to growth of the surrounding monolayer with no new nucleation occurring where the original domain existed, thus affording a nominally defect-free film. (4) If a small island remains after domain dissolution, upon potential reversai monolayer growth occurs at the edges of the island and the surrounding terrace. In this case, the newly formed domain boundary has a smaller perimeter than before dissolution. (5) Continued potential cycling results in eventual disappearance of the smaller domain. ExperimentalAtomic force microscopy experiments were performed using a Digital Instruments, Inc. Nanoscope 111 scanning probe microscope and Si3N4 cantilevers (quoted spring constant of 0.06 N m-'). A piezoelectric scanner with a maximum lateral scanning range of 15 pm x 15 pm was used for imaging. All images shown were obtained in lateral force mode, at tip scan rates ranging from 2 to 10 Hz. Data were collected using Digital Instruments Nanoscope 111 version 4.1 software and were low-pass filtered once. Image analysis was performed with the Nanoscope I11 and with NIH Image version 1.59b2 (available by anonymous FTP at zippy.nimh.nih.gov) software.Electrodeposition of the monolayers was performed in acetonitrile solutions containing 0.5 mM ET (Aldrich) and 2 mM tetrabutylammonium triiodide (n-Bu4N'13e). The n-Bu4N'13e was prepared by addition of 5 g (0.01354 mol) n-Bu4N'Ie (Aldrich) to 120 ml of 1.7 M KI (Aldrich), followed by addition of 3.44 g of 12. The resulting dark brown solution and deep purple oil layer was stirred at 70 "C for approximately 10 min and allowed to cool to room temperature, resulting in the formation of dark black solids which were filtered, collected and rinsed with distilled water. Recrystallization from hot methanol and drying in vacuo afforded black plate-like crystals of TBAI3.Electrodeposition was performed in an AFM fluid cell (Digital Instruments) equipped with ports for fluid entry and exit. Freshly cleaved, highly oriented pyrolytic graphite (HOPG) was used as the substrate and working electrode, and platinum counter and quasi-reference electrodes were inserted through the outlet port of the fluid cell. Potential cycling was performed by applying a square wave with a homemade function generator. Potential limits were chosen based on the potential at which monolayer deposition and dissolution was observed in the scanning region. Typically, deposition first occurred at approximately 650 mV vs. AglAgCI, with the monolayer remaining stable at 620 mV. The potential was cycled at approximately 620 f 75 mV, with the anodic poten...

Anthryloligothienylporphyrins: Energy Transfer and Light-Harvesting Systems

“…[18] Lithiation of 3 with nBuLi in diethyl ether at room temperature and subsequent reaction with anthrone 8 at À 78 8C gave the desired 9-anthryl-substituted dipentylquinquethiophene 4 a after acid treatment in 51 % yield. The dianthryl compound 4 b, formed as a by-product in 6 % yield, could be separated by MPLC on silica gel with n-hexane/ dichloromethane (15:1) as eluent.…”

“…In analogy to the preparation of 5-formyldipentylquinquethiophene 9 by Vilsmeier ± Haack formylation (Scheme 1), [18] the corresponding 9-anthryl-substituted aldehyde 10 was synthesized. The formylation agent was generated from DMF and phosphoryl chloride in dichloromethane and added in about 4.5-fold excess at 40 8C to a solution of 4 a in dichloromethane to give compound 10.…”

“…The reactions were carried out under argon atmosphere in dried glassware. The following compounds were prepared according to known procedures: 2-bromo-3-pentylthiophene (6) and 5,5''-dibromo-2,2':5',2''-terthiophene (7), [18,32] 3,3''' '-dipentyl-2,2':5',2'':5'',2''':5''',2''''-quinquethiophene (3) and 5-formyl-3,3''''-dipentyl-2,2':5',2'': 5'',2''':5''',2''''-quinquethiophene (9). [18] Optical measurements: Optical spectra were measured in the indicated solvents at concentrations of 10 À5 to 10 À6 mol L À1 in order to maintain low optical densities and to exclude intermolecular interactions.…”

“…To remove unreacted 8 the residue was chromatographed on silica gel with CH 2 Cl 2 as eluent followed by n-hexane/CH 2 Cl 2 (5:1). 1.33 ± 1.50 (m, 8 H, H-c,d), 1.80 (tt, J 7.5 Hz, 4 H, H-b), 2.94 (t, J 7.7 Hz, 4 H, H-a), 7.03 (s, 2 H, H4,4''''), 7.14 (d, J 4.1 Hz, 2 H, H3',4'''), 7.15 (s, 2 H, H3'',4''), 7.18 (d,J 3.8 Hz,2 H,H4',3'''),7.43 ± 7.53 (m,8 H,anthracene H2,3,6,7),8.02 ± 8.06 (m,8 H,anthracene H1,4,5,8) 5''''-(9-Anthryl)-5-formyl-3,3''''-dipentyl-2,2':5',2'':5'',2''':5''',2''''-quinquethiophene (10): A solution of 4 a (0.55 g, 0.76 mmol) in CH 2 Cl 2 (6 mL) was heated to reflux and a solution of the Vilsmeier reagent (2.5 mL, 1 mL % 0.8 mmol) [prepared by addition of phosphoryl chloride (3.29 g, 21.46 mmol) to DMF (1.7 g, 23.26 mmol) in dry CH 2 Cl 2 (25 mL) at room temperature and stirring for 2 h [18] ] was added, followed by another 1.5 mL after 3 h. After stirring for a further 3.5 h, a solution of sodium hydrogencarbonate (1m) was added, and the reaction mixture stirred for 2 h. After dilution with water, the organic phase was separated and the aqueous phase extracted several times with CH 2 Cl 2 . The combined extracts were washed with water, dried (Na 2 SO 4 ) and concentrated.…”

Perspectives on Thin Molecular Organic Films

“…[20,22,23] The same principle should apply to other molecules as it does, for instance, to C 60 and oligothiophenes. [24] A variety of applications are foreseen for MO materials, especially in the form of thin films with effective areas larger than those achieved for the rather small single crystals. Artificial structures such as heterostructures and multilayers can be prepared at moderate temperatures (typically less than 200 C) with low-cost deposition techniques, and can be integrated in microfabricated circuits.…”