Effect of the Linkage Position on the Conjugation Length of Truxene-Based Porous Polymers: Implications for Their Sensing Performance of Nitroaromatics

Four highly porous truxene-based organic polymers have been synthesized via C-C cross coupling methodologies (under Yamamoto and Suzuki-Miyaura conditions) starting from two different brominated hexamethyltruxene isomers (2,7,12- and 3,8,13-tribromohexamethyltruxene). We have found that the linkage position in these polymers has a strong influence not only on the porosity but also on the absorption and light emitting properties of the final materials. We have performed a joint theoretical and experimental investigation to shed light on the role of the positional isomeric effect of the monomers on the degree of pi-conjugation of the final materials. Our study indicates that the 2,7,12 linkage significantly enhances the electronic communication between the covalently linked building units, thus strongly influencing the conjugation length and the position of the energy levels of the final materials. The result of this work provides us with a new design tool to fine-tune the electronic properties of conjugated porous polymers with important implications for their potential applications, as demonstrated by their sensing performance for the detection of nitroaromatic compounds.