Effect of selenophene in naphthalene-diimide-vinylene-based small molecules on n-type organic field-effect transistors

Abstract

Two naphthalene diimide (NDI)-based small molecules, one with a thiophene-vinylene-thiophene linker donor unit (N-TVT-N) and the other with a selenophene-vinylene-selenophene linker donor unit (N-SVS-N), were newly synthesized for the purpose of serving as the active materials of n-type organic field-effect transistors (OFETs). We investigated the various characteristics of the synthesized small molecules to study how the type of donor unit would affect the charge transport of the resulting thin film. The monomeric molecular structure of N-SVS-N, i.e., that with selenium (Se) substituted for sulfur, was found to be tilted about twice as much as that of N-TVT-N, and to display lower backbone planarity. Unexpectedly, the thin films of N-SVS-N each showed a smoother and more uniform surface morphology and predominantly edge-on orientation in comparison with those of N-TVT-N. As the result, the optimally annealed OFETs containing N-SVS-N and N-TVT-N exhibited electron mobilities of up to 0.016 cm(2) V-1 s(-1) and 6.6 x 10(-3) cm(2) V-1 s(-1), respectively. These results could be explained by the structural features of N-SVS-N facilitating interactions between the electron-rich selenophenes.