Synthesis And Characterization Of Different Structures Of Nitro And Imino Polyphenylene Vinylene

In order to reduce polymer’s band gap, we usually introducing electron-donating or electron-withdrawing group may cause induction effect or mesomeric effect, and disrupt the molecular orbital. In this paper, we base on the skeleton of polyphenylene vinylene (PPV), introduce the nitro, imino, alkoxy or fluorene fragment, synthesize and characterize these polymers (A, B, C and D), and they hold a narrow band gap, and a high charge carrier mobility for charge transport. Details are as follows:1. Polymer A containing nitro, imino group is synthesized by Gilch reaction. Nitro-group can get a suitable lowest unoccupied molecular orbital (LUMO) energy level to provide enough offset for charge separation. Imino-group can get a suitable highest occupied molecular orbital (HOMO) energy level to produce a large open-circuit voltage (Voc). HOMO level of A is-5.45 eV, LUMO level is-2.96 eV, and the energy gap is 2.49 eV,which is 0.61 eV lower than PPV.2. Copolymer B1 and B2 containing nitro, imino, alkoxy group are synthesized by Gilch reaction. The ratio of alkoxy monomer and nitro, amino monomer are 1:3 and 1:6, respectively. Alkoxy group can improve the solubility of polymers, and broaden the absorption range without changing the conjugated skeleton. The maximum ultraviolet absorption wavelength of B1 and B2 in the solution is 478 and 417 nm, and this is an obvious red shift compared with A. HOMO level of B1 and B2 are -5.55 and -5.61 eV, LUMO energy level are -2.56 and -2.48 eV, and the energy gap are 3.01 and 3.02 eV, respectively. The solubility of copolymer B1 and B2 is better than that of A.3. Hyperbranched conjugated polymer C1 and C2 are synthesized by Gilch reaction. The ratio of tri-functional monomer and double group monomer are 1:3 and 1:6, respectively. Hyperbranched structure can cause an irreversible generated charge transfer, reduce the possibility of charge recombination, and improve the external quantum efficiency of non radiative decay process. HOMO level of C1 and C2 are -5.55 and -5.55 eV, LUMO energy level are -2.54 and -2.53 eV, and the energy gap are 3.01 and 3.02 eV, respectively. Compared with Ci, C2 gets a better solubility.4. Copolymer D1 and D2 containing nitro, imino group and fluorene fragment are synthesized by Gilch reaction. The ratio of fluorene monomer and nitro, amino monomer are 1:3 and 1:6, respectively. Due to a rigid plane, Di and D2 have a good thermal stability. Especially, fluorene is easy to introduce alkyl substituted, which greatly improved the solubility of polymers. HOMO level of polymer D1, D2 are -5.59 and -5.58 eV, LUMO energy level are -2.56 and -2.69 eV, and the energy gap are 3.03 and 2.98 eV, respectively.