Engineering of Energy Levels for Fully Conjugated D-A Block Copolymers via Tuning the Ratios of Donor P3HT and Acceptor PNDIT

Fully conjugated donor-acceptor (D-A) block copolymers, P3HT-b-PNDIT, containing p-type poly(3-hexylthiophene) (P3HT) and n-type poly(naphthalene bismide) (PNDIT) segments are synthesized in a one-pot reaction via Stille coupling polycondensation. Various D-A block copolymers with low polydispersities (1.42-1.56) are obtained through further separation via preparative GPC. The structural and molecular features of block copolymers are verified by ¹H NMR, FTIR spectra, UV-Vis absorption, differential scanning calorimetry (DSC) and cyclic voltammetry (CV). It is found that optical and electrochemical properties of D-A block copolymers are strongly dependent on the combination ratio of the donor P3HT and acceptor PNDIT segment. By reducing the acceptor block lengths, the highest occupied molecular orbital (HOMO) energy levels of D-A block copolymers sequentially rise, leading to the sequential decrease of energy gaps. To the best of our knowledge, this is the first report on engineering the energy levels of fully conjugated D-A block copolymers by tuning donor and acceptor chain lengths. More?over, compared to D/A polymer blends, the all-conjugated D-A block copolymer films show significant fine structures and much smoother film morphologies.