Distinct bulk emission properties of the hexacatenar molecules by varying the polarity of peripheral chains

In this study, we explored the distinct emission properties of two hexacatenar molecules 1 and 2 with an identical intramolecular charge transfer (ICT) chromophore in the bulk state, influenced by the type of peripheral chain. Their chromophore comprises an electron acceptor (A) composed of naphthalene-conjugated 1,3,4-oxadiazoles, and an electron donor (D) composed of 3,4,5-alkoxybenzene. The nonpolar decyl and polar tri(ethylene oxide) (TEO) chains are the peripheral chains for 1 and 2 , respectively. 1 exhibits a crystalline (Cry) to a liquid crystalline (LC), and then to a liquid (Liq) state as the temperature increases, but 2 exists in a Liq state at room temperature (RT). The morphological analysis of 1 in the LC phase suggests a hexagonal columnar structure where the stacking distance between chromophores is 3.4 Å. In the solution state, 1 and 2 strongly reveal ICT emission properties with increasing solvent polarity, consistent with DFT simulations. Remarkably, the bulk samples of 1 and 2 display distinct emission colors at RT, which blue-shift with increasing temperature. The complex temperature-dependent emission properties of 1 and 2 are associated with their molecular dynamic motions, characterized by dielectric relaxation spectroscopy (DRS) studies. The emission differences between bulk 1 and 2 are attributed to the degree of stabilization of the ICT state, by varying the type of non-emissive peripheral chains. This study demonstrates that the emission properties of the same chromophore can be engineered by the polarity of the peripheral chains in the bulk state. The molecular engineering of chain polarity in hexacatenar molecules, which are composed of an identical D-A-D chromophore leads to distinct emission properties in the bulk state.