1,10-Phenanthroline-based hexacatenar LCs with complex self-assembly, photophysical and binding selectivity behaviors

Abstract

A novel series of V-shaped phenanthroline-based hexacatenars containing a 1,10-phenanthroline which was substituted on 2,9- positions with two cyanovinyl units were synthesized using oxidation and Knoevenagel reactions. The self-assembly, photophysical properties and chemosensor behavior were investigated by POM, DSC, XRD, SEM, DFT calculation, UV–vis absorption and luminescence emission spectroscopies. The shorter homologues are non-mesogens, whereas the highest homologue could self-assemble into complex CubI/Pm3¯n mesophase in the bulk state. These compounds could form fluorescence organogels and the self-assembly morphologies could be tuned from disordered plate morphologies via winkled morphologies and nanofibers to nanosheets by changing the solvent polarity. The UV–vis absorption and fluorescence spectra demonstrated that these compounds showed obvious solvatochromism and strong fluorescence in both solution and aggregated states. The fluorescence intensity in the solution was much higher than that in the aggregated state due to the poor solubility and large conjugated planar of 1,10-phenathroline which was demonstrated by DFT calculation. These compounds could act as chemosensor for Ag+ among the different anions and cations with an extremely low detection limit of 50 nM, and the binding site and recognition mechanism were proved by FT-IR, 1H NMR and DFT calculation. Therefore, the design strategy of such luminescent LCs would offer a new perspective for constructing novel 3D self-assembly materials and expand their applications in chemosensor.