A novel class of light harvesting conjugated block copolymers, with electron-donating conjugated blocks (D) connected to electron-accepting conjugated blocks (A) via non conjugated and flexible bridge chains (B), has been designed, synthesized, and characterized. Specifically, D is a decyloxy-substituted polyphenylenevinylene (C10−PPV). A 1 and A 2 are PPVs with sulfone (SO2) acceptor moieties substituted on every other phenylene unit. A 1 carries two decyloxy groups on every phenylene unit, while in A 2 , half of the phenylene units are unsubstituted. The optical energy gaps are 2.24 eV for the donor block (D), 2.33 and 2.45 eV for A 1 and A 2 acceptor blocks. LUMO level offsets are 0.24 and 0.16 eV for D/A 1 and D/A 2 pairs, respectively. Comparing the photoluminescence from both films and solutions, very large red shifts (71 and 74 nm for A 1 and A 2 respectively) were observed in the two acceptor polymers. These red shifts in the emission spectra were more than twice as much as that observed for D (31 nm). The (DBA 1 B) n and (DBA 2 B) n block copolymer films exhibited improved processability and optoelectronic properties when compared with the corresponding films composed of donor/acceptor blends. Atomic force microscopic (AFM) studies of D, A 1 , and A 2 films were also undertaken to observe the degree of aggregation in the films. The results indicate the tendency of intermolecular aggregation increases as A 2 > D > A 1 . AFM topological images revealed that large aggregates of several hundreds of nanometers formed in donor/acceptor blend films, while in block copolymer films, domain sizes were similar to individual block sizes which are 1 order of magnitude smaller than in the blend.

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It has been predicted that nano-phase separated block copolymer systems containing electron rich donor blocks and electron deficient acceptor blocks may facilitate the charge carrier separation and migration in organic photovoltaic devices due to improved morphology in comparison to polymer blend system. This paper presents preliminary data describing the design and synthesis of a novel Donor-Bridge-Acceptor (D-B-A) block copolymer system for potential high efficient organic optoelectronic applications. Specifically, the donor block contains an electron donating alkyloxy derivatized polyphenylenevinylene (PPV), the acceptor block contains an electron withdrawing alkyl-sulfone derivatized polyphenylenevinylene (PPV), and the bridge block contains an electronically neutral non-conjugated aliphatic hydrocarbon chain. The key synthetic strategy includes the synthesis of each individual block first, then couple the blocks together. While the donor block stabilizes and facilitates the transport of the holes, the acceptor block stabilizes and facilitates the transport of the electrons, the bridge block is designed to hinder the probability of electron-hole recombination.Thus, improved charge separation and stability are expected with this system. In addition, charge migration toward electrodes may also be facilitated due to the potential nano-phase separated and highly ordered block copolymer ultra-structure.

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