Use of side-chain incompatibility for tailoring long-range p/n heterojunctions: Photoconductive nanofibers formed by self-assembly of an amphiphilic donor-acceptor dyad consisting of oligothiophene and perylenediimide

To tailor organic p/n heterojunctions with molecular-level precision, a rational design strategy using side-chain incompatibility of a covalently connected donor-acceptor (D-A) dyad has been successfully carried out. An oligothiophene-perylenediimide dyad, when modified with triethylene glycol side chains at one terminus and dodecyl side chains at the other (_2Amphi), self-assembles into nanofibers with a long-range D/A heterojunction. In contrast, when the dyad is modified with dodecyl side chains at both termini (2_Lipo), ill-defined microfibers result. In steady-state measurements using microgap electrodes, a cast film of the nanofiber of 2_Amphi displays far better photoconducting properties than that of the microfiber of 2_Lipo. Flash-photolysis time-resolved microwave conductivity measurements, in conjunction with transient absorption spectroscopy, clearly indicate that the nanofiber of 2_Amphi intrinsically allows for better carrier generation and transport properties than the microfibrous assembly of 2_Lipo.