Simultaneous Control over both Molecular Order and Long-Range Alignment in Films of the Donor-Acceptor Copolymer

Control over both molecular order and long-range alignment order in films of the donor–acceptor copolymer of 3,6-bis(thiophen-2-yl)-N,N′-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-c]pyrrole and thieno[3,2-b]thiophene (PDBT-TT) was demonstrated via off-center spin-coating (OCSC) from its blend solution with polystyrene (PS). It was found that the dichroic ratio (DR) of OCSC blend films was dependent on both the physical process of spin-coating and the effect of PS chains. The highest DR of 2.75 was obtained via OCSC from the blend solution in oDCB at 1500 rpm. Meanwhile, both the intrachain and interchain molecular order were improved in blend films compared with neat ones, which were indicated by the red-shift of the max absorption, enhanced J-aggregation absorption, and smaller π–π stacking distance (from 3.77 to 3.70 A). According to the results of the investigation into the macro anisotropy, micro morphology, solution rheology properties, and photophysics features of films, an overall mechanism of si...