Photo-oxidative doping in π-conjugated zig-zag chain of carbon atoms with sulfur-functional group

Abstract

Photo-oxidative doping processes were studied for the trans-polyacetylene backbone with the –SCH3 side group as a chemically representative of the precisely controlled S-functionalized zig-zag graphene nanoribbon edge. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy indicates that photochemical reaction of S–CH3 with atmospheric O2 forms selectively oxidized products such as –S(O)CH3 and –SO3– bound to the polyacetylene (PA) backbone. Using the correlation between the oxidation states of sulfur and the XANES peak positions, the partial charge distribution of CH3Sδ+–PAδ– has been estimated. Such positively charged sulfur atoms can attract higher electronegative oxygen atoms and expect to enhance the photooxidization capabilities. The formation of the –SO3– side group is evidently responsible for hole doping into the PA backbone. The results can provide some strategy for area-selective and controllable doping processes of atomic-scale molecular systems with the assistance of UV light.