Effect of branching architecture on the optical properties of polyazomethines

The architecture of conjugated polymers has an important influence on their optical and electrical properties. In this study, the effect of branching architecture on the optical properties of polyazomethines (PAs) was investigated. Linear and branched PAs with degree of branching (DB) ranging from 0 to 0.52 were successfully synthesized through homogeneous condensation by changing the feeding ratios of diamine, tetramine and dialdehyde. All PAs showed good thermal stability, and their decomposition temperature was over 380 °C. Both UV-Vis absorption and fluorescence emission demonstrated that the optical properties of PAs were closely related to the DB. With the increase of DB, an obvious redshift was found in UV-Vis absorption spectra, and the fluorescence maximum emission intensity (FMEI) and relative fluorescence quantum efficiency (RFQE) initially increased to a maximum and then gradually diminished to almost zero. These phenomena could be attributed to the antagonistic effect between the auxochromic effect of amino groups and the intra- and inter-molecular interactions. To confirm this mechanism, the intra- and inter-molecular interactions were purposely broken by adding trifluoroacetic acid (TFA) and SnCl2, which resulted in an increase in FMEI. Therefore, the optical properties of conjugated polymers can be readily adjusted by changing the DB of polymers.