Conformation-Insensitive Ambipolar Charge Transport in a Diketopyrrolopyrrole-Based Co-polymer Containing Acetylene Linkages

A new donor acceptor organic semiconducting co-polymer (PDPP-TAT) containing acetylene linkages based on dithienyl-diketopyrrolopyrrole (tDPP) has been synthesized and compared with a tDPP-based co-polymer (PDPP-TVT) containing vinylene linkages. The sp-hybridized carbons in the acetylene linkages result in favorable overlap of the electron wave functions of the tDPP units along the main chain. Further, the pi-conjugation of PDPP-TAT was found to be highly insensitive to the chain conformation, in contrast to that of PDPP-TVT. As a result, PDPP-TAT provides favorable charge transport for electrons as well as holes, and enables facile charge transport in amorphous and tie-molecular regions connecting its crystalline domains. PDPP-TAT exhibits ambipolar characteristics with a high electron/hole mobility ratio (mu(e)/mu(h)) of similar to 0.3 in field-effect transistors, whereas PDPP-TVT exhibits unipolar characteristics with a mu(e)/mu(h) value that is a factor of 30 lower. Our results demonstrate that the conformation sensitivity of charge transport is a vital factor in the electrical performances of actual organic transistor devices.