Donor-acceptor alternating π-conjugated polymers containing Di(thiophen-2-yl)pyrene and 2,5-Bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H, 5H)-dione for organic thin-film transistors

New diketopyrrolopyrrole (DPP)-containing conjugated polymers such as poly(2,5-bis(2-octyldodecyl)-3-(5-(pyren-1-yl)thiophen-2-yl)-6-(thiophen-2-yl) pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (P(DTDPP-alt-(1,6)PY)) and poly(2,5-bis(2-octyldodecyl)-3-(5-(pyren-2-yl)thiophen-2-yl)-6-(thiophen-2-yl) pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (P(DTDPP-alt-(2,7)PY)) were successfully synthesized via Suzuki coupling reactions under Pd(0)-catalyzed conditions. P(DTDPP-alt-(2,7)PY), incorporating 2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2- yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DTDPP) at the 2,7-position of a pyrene ring showed a lower band-gap energy (E gopt. = 1.65 eV) than the 1,6-substituted analog, P(DTDPP-alt-(1,6)PY) (E gopt = 1.71 eV). The energies of the molecular frontier orbitals of the substituted polymers were successfully tuned by changing the anchoring position of DTDPP from the 1,6- to the 2,7-position of the pyrene ring. An organic thin-film transistor fabricated using the newly synthesized P(DTDPP-alt-(2,7)PY), as a semiconductor material exhibited a maximum mobility of up to 0.23 cm² V^-1 s ^-1 (I_on/off ∼ 10⁶), which was much larger than that obtained using P(DTDPP-alt-(1,6)PY). This distinction is attributed to morphological differences in the solid state arising from differences between the geometrical configurations of DTDPP and the pyrene ring. In addition, the organic phototransistor devices made of P(DTDPP-alt-(2,7)PY) showed interesting photoinduced enhancement of drain current when irradiating the excitation light whose intensity is very small. Based on the photoinduced effect on I _DS, photocontrolled memory could be realized under the variation of gate voltages.