| Description |
Perylene tetracarboxylic diimide (PTCDI) derivatives, typical n-type organic semiconductors with high thermal- and photostability, have been extensively investigated for one-dimensional (1D) self-assembly and their applications in electronic and opto-electronic devices. Unfortunately, the intrinsically low electrical conductivity of PTCDI-based materials hinders further development of functions and applications. To solve this problem, covalently linked electron donor-acceptor (D-A) PTCDI molecules were designed, synthesized, and assembled into nanofibers in this work. Their electrical properties and the thermal- and photo-effects have been systematically studied. In addition to providing an improved understanding of the basic properties of the materials, these studies also open new and potential applications of the D-A PTCDI nanofibers. We designed a PTCDI molecule with 1-methylpiperidine (MP) substituted as electron donor to construct self-doped semiconductors, through one-dimensional (1D) self-assembly of the molecules into a nanofiber structure. The resultant nanofibers exhibit much higher conductivity than the other reported PTCDI molecules. The mechanism studies demonstrate that the MP moieties reduce the adjacent PTCDI core into an anionic radical, which acts as the n-type dopant in the PTCDI lattice. Such highly conductive nanofiber materials can be used as chemiresistive sensor for vapor detection of hydrogen peroxide. Our further study on the MP-PTCDI nanofibers reveals a persistent photoconductivity (PPC) effect, which is sustained conductivity after light illumination is terminated. Systematic study demonstrates the PPC effect is predominantly caused by the D-A structure of PTCDI. This study helps understand the PPC mechanism, and guide the design of new material structures for sustained charge separation to further enhance the photovoltaic and photocatalytic efficiency of organic semiconductor materials. Thermoactivated conductivity was studied in the nanofiber materials assembled from other two D-A PTCDI molecules both in the dark and under visible light illumination. A symmetric n-dodecyl side chain substituted PTCDI nanofiber was used as a control for the comparative study. The charge transport properties are strongly dependent on the PTCDI molecular structure and packing states within the nanofibers. The comprehensive understanding of the thermoactivated conductivity in PTCDI nanofibers can assist in designing new D-A molecules that can be fabricated into nanofibers to be used as temperature sensor with increased sensitivity. |
