New chemistry to the synthesis of quinoline oligomers and a CVD technique for high temperature conducting thin films

Abstract

We report a new concept of catalytic dehydrogenative polycondensation (CDHP) reaction for the synthesis of linear rigid rod-like polyaromatic heterocyclic oligomers. Specifically, we demonstrate this type of condensation leading to a new synthesis of nonsubstituted quinoline oligomers from 1,2,3,4-tetrahydroquinoline in an one-step reaction using transition metal sulfides as catalysts. The method offers a good insight to the synthesis of polyquinoline and some of its derivatives since monomers are readily available and the synthesis can be simplified. From the reaction mechanism a delicate balance between dehydrogenation and polymerization activity of catalyst is required to optimize the yield and the molecular weight of the product in the CDHP reaction. To prepare highly thermal oxidative stable conducting polymers, we developed a chemical vapor deposition (CVD) technique for processing organic oligomers. The technique enable us to fabricate the reproducible high temperature conducting polymer thin films (200 – 2000Å) from the polyquinoline based materials with an excellent adhesion to the substrate surface. These films exhibit a low resistivity without chemical doping and high stability at elevated temperatures. The conductivity of the CVD thin films prepared at 900°C were found to be 695, 700, 750 and 920S/cm at 30K, 150K, 300K and 950K, respectively. Interestingly, those samples treated at temperatures above 800°C, the resistivity was found to be very weakly temperature dependent. For example, the 900°C treated sample gives a resistance ratio of R30K/R950K equal to only 1.32, and a resistance maximum at 30K.