Aggregation-Induced Emission in Tetraphenylthiophene-Derived Organic Molecules and Vinyl Polymer

In this study, organic molecules of tetraphenylthiophene (TP) and the derived model compound of TP-Qu and vinyl polymer of PS-Qu with the pendant group of TP-Qu were prepared and characterized to identify their photoluminescent (PL) responses toward the effect of aggregation-induced emission (AIE). During aggregate formation by adding the nonsolvent water to the THF solvent, the corresponding TP solutions greatly gained the emission intensity. In contrast, TP-Qu and PS-Qu in THF/water solution mixtures emitted strongly with nearly the same emission intensity despite the composition differences on the applied THF/water mixtures. Restricted intramolecular rotation (RIR) is the key factor deciding the AIE effect in different media. With four small phenyl rotors around the central thiophene stator, the RIR of the TP molecules in dilute solution is low but increases upon aggregate formations. In contrast, the bulky C-2 quinoline rotor of the TP-Qu molecule enhances the RIR effect and its PL emissions in the aggregate and in the solution states are essentially the same (irrespective of the aggregate formation by adding nonsolvent water). With the inherent TP-Qu pendant groups, the vinyl polymer PS-Qu behaves similarly to the TP-Qu molecule; that is, solutions of PS-Qu have similar emission spectra in different solution mixtures. Several methods including PL excitation (PLE), low-temperature PL emission study, and computer simulation were used in this study to estimate the relative extents of RIR and therefore, the resulting ATE effect in all the TP-derived materials.