Amorphous highly conjugated chemical-vapor-deposited polymer thin films

Using the parylene polymer platform, benzylic brominated poly (trifluoroacetyl-p-xylylene) thin films are deposited at room temperature from a novel synthesized precursor, 2-trifluoroacetyl-a,a,a′ tribromo-p-xylene using CVD. The as-deposited benzylic brominated parylene-type polymer is nearly transparent. However, upon subsequent post-deposition anneals dehydrohalogenation can take place, yielding vinyl and ethynyl moieties and a highly conjugated absorbing polymer. Previous attempts with the deposition and annealing of the analogous non-functionalized phenyl group polymer did not yield the desired structure, due to polymer crystallization that 'locked up' the structure preventing any further chemical reactions from occurring. The as-deposited films contain much hydroxyl bonding; however, after post-deposition annealing, the films dehydrate and hydrogen bromide eliminates at 200, 300, and 380°C. During HBr removal the films become much thinner, more absorbing in the visible region, and denser. After the 300°C anneal the films stay amorphous, as seen from X-ray diffraction (XRD) measurements, and some bromine still resides in the structure. 0.4 bromine atoms per repeat unit are left compared with 1.8 bromine atoms per repeat unit in the as-deposited condition.