Stepwise Formation and Characterization of Covalently Linked Multiporphyrin−Imide Architectures on Si(100)

Abstract

A major challenge in molecular electronics and related fields entails the fabrication of elaborate molecular architectures on electroactive surfaces to yield hybrid molecular/semiconductor systems. A method has been developed for the stepwise synthesis of oligomers of porphyrins linked covalently via imide units. A triallyl-porphyrin bearing an amino group serves as the base unit on Si(100), and the alternating use of a dianhydride (3,3',4,4'-biphenyltetracarboxylic dianhydride) and a porphyrin-diamine for reaction enables the rapid and simple buildup of oligomers composed of 2-5 porphyrins. The properties of these porphyrin "multad" films on Si(100) were interrogated using a variety of techniques. The charge densities of the redox-active porphyrin oligomers were determined via electrochemical methods. The stepwise growth was evaluated in detail via Fourier transform infrared (FTIR) spectroscopy and by selected X-ray photoelectron spectroscopic (XPS) studies. The morphology was probed via AFM methods. Finally, the thickness was evaluated by using a combination of ellipsometry and AFM height profiling, accompanied by selected XPS studies. Collectively, these studies demonstrate that high charge density, ultrathin, multiporphyrin films of relatively well-controlled thickness can be grown in a stepwise fashion using the imide-forming reaction. The increased charge densities afforded by the porphyrin multads may prove important for the fabrication of molecular-based information-storage devices. This bottom-up process for construction of surface-tethered molecular architectures complements the top-down lithographic approach for construction of functional devices with nanoscale dimensions.

Syntheses and Characterization of Molybdenum/Zinc Porphyrin Dimers Bridged by Aromatic Linkers

“…Materials: Unless otherwise stated, all reagents, such as Zn(OAc) 2 · 2H 2 O, Mo(CO) 6 , benzene-1,4-dicarbaldehyde and benzene-1,3-dicarboxylic acid, were obtained commercially and used without further purification. N,N-Dimethylformamide (dmf) for electrochemical measurement was distilled from 4 Å molecular sieves under reduced pressure before use.…”

“…The second synthetic strategy consists of two steps: preparation of the mono-zinc bis(porphyrin) complexes 1a and 2a, and subsequent treatment of 1a, 2a with Mo(CO) 6 to give the Mo/Zn compounds. [35] This method produces fewer by-products, although the yield of compound 2 is low, presumably due to the cleavage of the imido linkage at higher temperatures.…”

“…[1][2][3] Among the many porphyrins and metalloporphyrin complexes, dimeric and oligomeric porphyrins with extensive electronic delocalization have attracted increasing interest due to their potential applications in molecular electronics and photonics, which range from light-emitting diodes, [4] nonlinear optical (NLO) materials, [5] information storage materials, [6] photovoltaic cells, [7][8][9] chemical sensors, [10] biomimetic systems, [11,12] photosensitizers in photodynamic therapy, [13,14] and so forth. Optional linkages connecting monomeric porphyrin rings would allow the spatial configuration of porphyrins to be adjusted, thereby altering the sizes and shapes of the porphyrinato cavities.…”

“…The first band, which eluted with CHCl 3 , was unreacted [{5-(p-NH 2 )-TPP}Zn]. The main purple band, which eluted with 2 % C 2 H 5 OH/ CHCl 3 (v:v), was collected and the solvents evaporated to dryness to obtain the desired product (164 mg, 35 % 6 (50 mg, 0.190 mmol) were added to 10 mL of 1,2,4-trichlorobenzene and the mixture was refluxed while stirring for 4 h under N 2 . The progress of the reaction was monitored by UV/Vis spectroscopy.…”

Construction of Various Self-assembled Films and Their Application as Lubricant Coatings

“…Generally speaking, there are two approaches to construct SAMFs with unique structures, viz, one-step assembling and multi-step assembling. As to the one-step process, the pre-designed target precursors are assembled onto the substrate (Tam-Chang et al, 1995; www.intechopen.com 1999; Song et al, 2006;Chambers et al, 2005); The multistep method involves common selfassembling and subsequent interface chemical reaction (Ren et al, 2003;Jiao et al, 2006). In most cases, the synthesis and the succedent purification for precursor molecules are too difficult to perform.…”