Direct observation of alkyl chain interdigitation in conjugated polyquarterthiophene self-organized on graphite surfaces

A solution processible polymer -poly(3,3‴-didodecylquaterthiophene) (PQT-12) is investigated at the liquid/solid interface using the scanning tunneling microscopy (STM). Two-dimensional ordered films made up of self-assembled domains, with dimensions of 100 nm × 50 nm adsorbed on highly oriented pyrolytic graphite (HOPG) were formed. These domains consist of parallel lamellar polymer chains, with the alkyl chains forming interdigitated structures, along with U-shaped and closed ring segments of the polymer chains. A polymer chain packing model is proposed herein, which attempts to propose a correlation between the packing of long chains and charge mobilities. These STM results could help in understanding the relationship between the extended conjugation and molecular organization of the PQT-12 chains.