Photophysical Properties and Orbital Energy Calculation in Diketopyrrolopyrrole Based Conjugated Polyelectrolytes

Theoretical calculation study of two alternating conjugated polyelectrolytes, named SDPP-PPV and SDPP-PPE, constituted of 1,4-diketo-2,5-bis(4-sulfonylbutyl)-3,6-bis(4-bromophenyl) pyrrolo[3,4-c]pyrrole (SDPP) with 2,5-diethoxy-1,4-phenylenevinylene (DVB) or 2,5-diethoxy-1,4-phenyleneethynylene (DEB) were carried out with Gaussian 09 software. The absorption spectral study shows that SDPP-PPV and SDPP-PPE have broad coverage of visible spectra and considerable red shift compared with water-soluble poly(p-phenylenevinylene)s (PPVs) and poly(p-phenyleneethynylene)s (PPEs). The TD-DFT calculation results show that LUMO of the polymers can be significantly reduced and the HOMO-LUMO gap can be changed by introducing DPP into the backbone. Theoretical study indicates that introduction of electro-deficient unit DPP in the polymer main chain can optimize the band structure of traditional PPV and PPE. The improved optical properties and excellent water solubility of these two novel DPP-based conjugated polyelectrolytes allow them to be promising materials in optoelectronic applications.