Triflate Salts as Alternative Non-Chlorinated Oxidants for the Oxidative Chemical Vapor Deposition and Electronic Engineering of Conjugated Polymers

Oxidative chemical vapor deposition (oCVD) stands as an attractive approach for the synthesis, engineering, and integration of conjugated polymers for advanced electronic and optoelectronic applications. In oCVD, the oxidant significantly influences the conformational and optoelectronic properties of the resulting conjugated polymer thin films. In this work, triflate salts of iron(III) and copper(II) (Fe(OTf)₃ and Cu(OTf)₂, respectively) are investigated for the first time as suitable alternative oxidants to the widely used iron(III) chloride (FeCl₃) for the oCVD of conjugated polymers. Structural and compositional characterizations of the resulting thin films evidenced the successful polymerization of cobalt(II) 5,15-diphenyl porphyrin using either Fe(OTf)₃ or Cu(OTf)₂. Along with an intermolecular dehydrogenative C-C coupling reaction, the occurrence of side reactions, such as the inclusion of -CF₃ groups and demetalation and subsequent insertion of copper(II) in the porphyrin macrocycle when using Cu(OTf)₂, were evidenced. Interestingly, the inclusion of -CF₃ groups into the polymer backbone when using triflate salts results in a deepening of the frontier energy levels, while the insertion of copper(II) contributes to a reduction in the band gap energy. This work demonstrates that the careful selection of the oxidant agent in oCVD enables fine-tuning the optoelectronic properties of conjugated polymers to suit specific application requirements.