Phenanthracene Nanotubes for Template-designed Organic Electronics

Abstract

The overall increasing energy consumption worldwide demands for new fundamental research that can contribute to mitigate its negative ecological effects. One such valuable field of research is the area of organic electronics. Materials used in organic electronics offer a variety of advantages over established inorganic materials, such as easy solution processability, but also low power-consumption and flexibility of the resulting devices. However, to this date the efficiency of such devices is also lower than that of their inorganic counterparts. One prominent approach to overcome this challenge is to use supramolecular self-assembly of the active materials on a template to generate ordered structures, mimicking those in crystalline silicon-based devices, e.g. solar cells, to increase the efficiency of the resulting devices while retaining the intrinsic advantages of organic materials. <br> This work in particular focuses on the synthesis and fundamental investigation of materials relevant for such applications. A new class of materials, i.e. the phenanthracene nanotubes (short: PNTs) are presented and it is demonstrated how a reliable bottom-up approach towards these molecules was realised. For this the established synthetic approaches towards shape-persistent macrocycles and the synthesis of H-shaped molecules for ladder-polymers were combined. The modularity of this method was then used to obtain PNTs of different shapes (cylindrical, pyramidal and bowl-shape). After the successful synthesis of these compounds, they were investigated regarding the formation of self-assembled monolayers on a carbon-based substrate (highly oriented pyrolytic graphite) using scanning tunnelling microscopy. Together with quantum chemical models it was shown that the cylindrical PNTs are less rigid than their molecular formulae suggest and can collapse into a more compressed form. The flexibility in shape of the cylindrical PNTs was then utilized to demonstrate the potential of PNTs in the field of template-designed organic electronics by manufacturing a single-walled carbon nanotube chemiresistor (i.e. a sensing device). This sensor performed well for explosive detection (i.e. 2-nitrotoluene as marker for 2,4,6-trinitrotoluene) in terms of selectivity, stability, and humidity tolerance. In this way a low-power consumption device that is portable and can also be used for large area monitoring was made, displaying the advantages of organic electronics compared to the here usually used stationary and energy-intensive gas chromatographs. Moreover, regarding its sensitivity the limit of detection lies at 11 ppb, which is among the best results for single-walled carbon nanotube chemiresistors obtained to this date.