Naphthodithiophene-diketopyrrolopyrrole-based donor-acceptor alternating π-conjugated polymers for organic thin-film transistors

Novel naphtho[1,2-b:5,6-b′]dithiophene (NDT) and diketopyrrolopyrrole (DPP)-containing donor-acceptor conjugated polymers (PNDTDPPs) with different branched side chains were synthesized via Pd(0)-catalyzed Stille coupling reaction. Octyldodecyl (OD) and dodecylhexadecyl (DH) groups were tethered to the DPP units as the side chains. The soluble fraction of PNDTDPP-OD polymer in chloroform has much lower molecular weight than that of PNDTDPP-DH polymer. PNDTDPP-DH polymer bearing relatively longer DH side chains exhibited much better charge-transport behavior than PNDTDPP-OD polymer with shorter OD side chains. The thermally annealed PNDTDPP-DH polymer thin films exhibited an outstanding charge carrier mobility of ∼1.32 cm² V^-1 s^-1 (I_on/I_off ∼ 10⁸) measured under ambient conditions, which is almost six times higher than that of thermally annealed PNDTDPP-OD polymer thin films.