Two new luminophore polymorphs of 4-bromo-7-(4nonylphenyl)benzo [c][1,2,5]thiadiazole (1α and 1β) exhibiting different color emissions, which switch into each other in response to shear force and solvent vapors, are presented and their X-ray structure is determined. Supramolecular organic framework topology (SOFT) studies on the two polymorphic structures led us to conclude that the mechanochromic phase transformation can be explained on the basis of modifications in their respective topological nets: mab and pcu for 1α and 1β, respectively, as a result of the breaking and restoration of a number of weak supramolecular interactions. The color changes accompanying this transformation have been rationalized with the help of time-dependent density functional theory. We firmly believe that our findings will inspire future research on the design of novel stimuli-responsive organic materials with switchable properties based on their supramolecular interactions by establishing clear SOFT-property relationships.

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 π-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.

A new rod-shaped benzothiadiazole fluorophore, namely, 4,7-di-(4-nonylphenyl)­benzo­[c]­[1,2,5]­thiadiazole, which strongly emits fluorescence both in solution and in solid state has been synthesized, and its photophysical properties were rationalized with the help of density functional theory calculations. This molecule crystallizes in two distinct light-emitting crystalline phases, which can be interconverted in response to pressure, temperature, and solvent vapors. Powder X-ray diffraction indicates that in both polymorph, molecules adopt a lamellar packing, the different interlayer spacing being the main difference between the two structures. Single-crystal analysis of one of the polymorphs allows us to identify weak interaction planes, which presumably facilitates the polymorphic transformation through mechanically or thermally induced sliding processes. The polymorphic transformation and the origin of the switchable fluorescence have been rationalized through a spectroscopic and theoretical study. This study suggests that the different colors observed are due to different intermolecular aromatic interactions owing to the displacement of the molecules with respect to the layer normal. Interestingly, blending this molecule with a biodegradable polymer such as poly­(vinyl alcohol) gives rise to a thermally activated reversible switchable fluorescent system, which entitles this material as an attractive candidate for technological applications, such as thermal sensors, security inks, or rewritable paper.

In the present work, we investigate at the density functional theory (DFT) level, two-dimensional (2D) conjugated polymers based on C3-symmetric truxene-based cores. In total, 27 different 2D polymers have been...