Donor-Acceptor Conjugated Polymers Based on Indacenodithiophene Derivative Bridged Diketopyrrolopyrroles: Synthesis and Semiconducting Properties

Two indacenodithiophene derivative bridged diketopyrrolopyrroles (DPP), i.e., 2,7-bis(2,5-bis(2-decyltetradecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-tetrahydro-pyrrolo [3,4-c] pyrrol-1-yl)-s-indaceno [1,2-b :5,6-b'] dithiophene4,9-dione (DDPP-PhCO) and 2,2'-(2,7-bis(2,5-bis(2-decyltetradecy1)-3,6-dioxo-4-(thiophen-2-y1)-2,3,5,6-tetrahydro-pyrrolo [3,4-c] pyrr ol-1-yl)-s-indaceno [1,2-b:5,6-b']dithiophene4,9-diylidene)dimalononitrile (DDPP-PhCN), were developed via intramolecular Friedel-Crafts acylation and Knoevenagel condensation. A series of donor-acceptor (D-A) conjugated polymers were synthesized by Stile or direct arylation polycondensation with these two novel units as acceptors and vinyl or thiophene derivatives as donors. The polymers with DDPP-PhCO as acceptor unit exhibited optical bandgaps (E-g(opt)) of ca. 1.2 eV and the highest occupied molecular orbital (HOMO) energy levels of similar to-5.3 eV with the difference less than 0.1 eV, and their lowest unoccupied molecular orbital (LUMO) levels were in the range of -3.73 to -3.91 eV. The polymer based on DDPP-PhCN showed similar HOMO level (-5.29 eV) but remarkably lower LUMO level (-4.21 eV). Top-gate/bottom-contact (TGBC) organic field-effect transistors (OFETs) of all the polymers exhibited ambipolar transport behavior with the highest hole mobility (/h) and electron mobility Vie) up to 1.09 and 0.44 cm(2) V-1 s(-1), respectively, in air. Owing to their favorable molecular orientation and frontier molecular orbital distribution, the polymers based on DDPP-PhCO displayed much higher hole and electron mobilities than that based on DDPP-PhCN.