<title>Design and synthesis of novel block copolymers for efficient optoelectronic applications</title>

Abstract

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.

Design, synthesis, and characterization of a novel c‐donor‐nc‐bridge‐c‐acceptor type block copolymer for optoelectronic applications

“…We have been working on the second approach and have earlier developed a ( DBAB ) n type block copolymer earlier (shown in Scheme , top), where D is a conjugated donor block, A is a conjugated acceptor block, and B is a nonconjugated and flexible bridge chain . However, as Scheme shows, the ( DBAB ) n type block copolymer could suffer from poor solid‐state phase separation when the sizes of the donor or acceptor blocks are not uniform.…”

“…There have been a number of efforts on the development of various block copolymer systems containing conjugated donor and acceptor blocks, since chemically different donor and acceptor blocks may undergo phase separation on the nanometer scale. 7,10,11,[16][17][18][19][20][21][22][23][24][25][26][27][28] When two different conjugated blocks are covalently connected directly, charge separated states appear not stable. 20,27,28 Two popular approaches include, for example, (1) block copolymers where a conjugated electrondonating block is covalently linked to a nonconjugated flexible block with an electron acceptor as side chains, 7,23,24 and (2) donor/acceptor block copolymers where D/A-conjugated blocks are separated by nonconjugated bridge units (B).…”

“…20,27,28 Two popular approaches include, for example, (1) block copolymers where a conjugated electrondonating block is covalently linked to a nonconjugated flexible block with an electron acceptor as side chains, 7,23,24 and (2) donor/acceptor block copolymers where D/A-conjugated blocks are separated by nonconjugated bridge units (B). 7,10,11,[16][17][18][19][20][21][22] We have been working on the second approach and have earlier developed a (DBAB) n type block copolymer earlier (shown in Scheme 1,top), where D is a conjugated donor block, A is a conjugated acceptor block, and B is a nonconjugated and flexible bridge chain. 7,10,11,[16][17][18][19][20][21][22] However, as Scheme 1 shows, the (DBAB) n type block copolymer could suffer from poor solid-state phase separation when the sizes of the donor or acceptor blocks are not uniform.…”

Design, Synthesis, and Characterization of a −Donor−Bridge−Acceptor−Bridge- Type Block Copolymer via Alkoxy- and Sulfone- Derivatized Poly(phenylenevinylenes)

“…The polymerization in the scheme and presented in this work is based on the Horner−Emmons coupling reaction for producing carbon−carbon double bond from a phosphonate and an aldehyde. This reaction appears ideal for constructing desired end-functionalized PPV blocks as it was used in our earlier synthesis of second-order nonlinear optical chromophores , and similar PPVs. − , Selection of the base (to produce the reactive anion from phosphonates) is critical since, as was shown previously, it was difficult to obtain a desired molecular weight when NaH was used due to the slow reaction rate and low polymer yields. − When t -BuOK was used in place of NaH, the polymerizations were completed in a few minutes instead of a few days, and high yields (95−99%) of polymers are obtained after the routine precipitation in methanol. Equation 1 can be used to predict molecular weight.…”

“…Over the past several years, we have been developing a light harvesting block copolymer focusing on a different and unique structural system. − Specifically, we have been developing a ( DBAB ) n -type block copolymer, where D is a conjugated donor block, A is a conjugated acceptor block, and B is a nonconjugated bridge connecting D and A . The lack of conjugation in the bridge is to separate the electronic states of the donor from the acceptor and to slow the intramolecular charge recombination.…”